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- Title
- Single Mode Wavelength-Tunable Thulium Fiber.
- Creator
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Shin, Dong Jin, Richardson, Martin, Schulzgen, Axel, Amezcua Correa, Rodrigo, University of Central Florida
- Abstract / Description
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Thulium fiber lasers have the broadest emission wavelength bandwidth out of any rare-earth doped fiber lasers. The emission wavelength starts from 1.75(&)#181;m and ends at around 2.15(&)#181;m, covering a vast swath of the eye safe wavelength region and intersecting with a large portion of mid-infrared atmospheric transmission window. Also, thulium fiber lasers provide the highest average output power of any other rare-earth doped fiber lasers in these wavelength regimes, making them...
Show moreThulium fiber lasers have the broadest emission wavelength bandwidth out of any rare-earth doped fiber lasers. The emission wavelength starts from 1.75(&)#181;m and ends at around 2.15(&)#181;m, covering a vast swath of the eye safe wavelength region and intersecting with a large portion of mid-infrared atmospheric transmission window. Also, thulium fiber lasers provide the highest average output power of any other rare-earth doped fiber lasers in these wavelength regimes, making them uniquely suited for applications such as remote sensing. At the moment, high power beam propagation of continuous wave laser through the atmosphere in the mid-infrared range is yet to be investigated anywhere. In particular, the effects of atmospheric water vapors on the thulium fiber laser propagation are unknown and are of great research interest. This dissertation identifies the stringent requirements in constructing a high power, single frequency, wavelength tunable, continuous wave thulium fiber laser with the aim of using it to study various atmospheric transmission effects. A fine spectral control scheme using diffraction gratings is explored and improvements are made. Moreover, a fiber numerical simulation model is presented and is used for designing and implementing the thulium fiber laser system. The current limitations of the implemented system are discussed and an improved system is proposed. This will lay the foundation for the future high power atmospheric propagation studies.
Show less - Date Issued
- 2018
- Identifier
- CFE0007372, ucf:52084
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007372
- Title
- Computational imaging systems for high-speed, adaptive sensing applications.
- Creator
-
Sun, Yangyang, Pang, Sean, Li, Guifang, Schulzgen, Axel, Pensky, Marianna, University of Central Florida
- Abstract / Description
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Driven by the advances in signal processing and ubiquitous availability of high-speed low-cost computing resources over the past decade, computational imaging has seen the growing interest. Improvements on spatial, temporal, and spectral resolutions have been made with novel designs of imaging systems and optimization methods. However, there are two limitations in computational imaging. 1), Computational imaging requires full knowledge and representation of the imaging system called the...
Show moreDriven by the advances in signal processing and ubiquitous availability of high-speed low-cost computing resources over the past decade, computational imaging has seen the growing interest. Improvements on spatial, temporal, and spectral resolutions have been made with novel designs of imaging systems and optimization methods. However, there are two limitations in computational imaging. 1), Computational imaging requires full knowledge and representation of the imaging system called the forward model to reconstruct the object of interest. This limits the applications in the systems with a parameterized unknown forward model such as range imaging systems. 2), the regularization in the optimization process incorporates strong assumptions which may not accurately reflect the a priori distribution of the object. To overcome these limitations, we propose 1) novel optimization frameworks for applying computational imaging on active and passive range imaging systems and achieve 5-10 folds improvement on temporal resolution in various range imaging systems; 2) a data-driven method for estimating the distribution of high dimensional objects and a framework of adaptive sensing for maximum information gain. The adaptive strategy with our proposed method outperforms Gaussian process-based method consistently. The work would potentially benefit high-speed 3D imaging applications such as autonomous driving and adaptive sensing applications such as low-dose adaptive computed tomography(CT).
Show less - Date Issued
- 2019
- Identifier
- CFE0007867, ucf:52784
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007867
- Title
- Holographic optical elements for visible light applications in photo-thermo-refractive glass.
- Creator
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Kompan, Fedor, Glebov, Leonid, Schulzgen, Axel, Richardson, Kathleen, Rahman, Talat, University of Central Florida
- Abstract / Description
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This dissertation reports on design and fabrication of various optical elements in Photo-thermo-refractive (PTR) glass. An ability to produce complex holographic optical elements (HOEs) for the visible spectral region appears very beneficial for variety of applications, however, it is limited due to photosensitivity of the glass confined within the UV region. First two parts of this dissertation present two independent approaches to the problem of holographic recording using visible radiation...
Show moreThis dissertation reports on design and fabrication of various optical elements in Photo-thermo-refractive (PTR) glass. An ability to produce complex holographic optical elements (HOEs) for the visible spectral region appears very beneficial for variety of applications, however, it is limited due to photosensitivity of the glass confined within the UV region. First two parts of this dissertation present two independent approaches to the problem of holographic recording using visible radiation. The first method involves modification of the original PTR glass rendering it photosensitive to radiation in the visible spectral region and, thus, making possible the recording of holograms in PTR glass with visible radiation. The mechanism of photoionization in this case is based on an excited state absorption upconversion process in the glass when doped with Tb3+. By contrast, the second approach uses the original Ce3+ doped PTR glass and introduces a new modified technique for hologram formation that allows for holographic recording with visible light. Complex HOEs including holographic lenses and holographic curved mirrors were fabricated in PTR glass with visible light using both techniques. The third part of the dissertation takes a step in a different direction and discusses the development of the methods for fabrication of phase masks in PTR glass. A method for relatively straightforward and inexpensive fabrication of phase masks with the aid of a Digital Micromirror Device is presented. This method enabled to produce phase masks containing complex greyscale phase distributions for generation of vortex (helical) beams. A phase mask can be holographically encoded into a transmission Bragg grating where a holographic phase mask (HPM) is formed. HPM has an advantage over a regular phase mask of being capable of multi-wavelength operation. All optical elements recorded in PTR glass preserve the advantages peculiar to VBGs recorded in PTR glass such as stability to heating and illumination with high-power laser beams.
Show less - Date Issued
- 2019
- Identifier
- CFE0007665, ucf:52480
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007665
- Title
- Mode-locked Laser Based on Large Core Yb3+-Doped Fiber.
- Creator
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Jia, Fei, Amezcua Correa, Rodrigo, Schulzgen, Axel, Fathpour, Sasan, University of Central Florida
- Abstract / Description
-
The thesis reviews principle of laser cavity and gives a general introduction to mode-locked laser (MLL). By using Yb3+-doped fiber as gain medium, passive MLL cavity is developed in experiment, aiming to obtain femtosecond pulses with high pump power from 25W to 35W. The gain medium fiber with 65(&)#181;m core diameter is cleaved with one flat end and another angled. Pump laser with 976nm wavelength is coupled into Yb3+-doped fiber to excite signal from 1020nm to 1040nm in the core. 9W is...
Show moreThe thesis reviews principle of laser cavity and gives a general introduction to mode-locked laser (MLL). By using Yb3+-doped fiber as gain medium, passive MLL cavity is developed in experiment, aiming to obtain femtosecond pulses with high pump power from 25W to 35W. The gain medium fiber with 65(&)#181;m core diameter is cleaved with one flat end and another angled. Pump laser with 976nm wavelength is coupled into Yb3+-doped fiber to excite signal from 1020nm to 1040nm in the core. 9W is threshold for laser setup. After locking all modes, picosecond pulses are output from laser cavity and coupled into dispersion delay fiber. By compressing pulse width, pulses are in soliton mode and then femtosecond laser pulses are obtained pulses are obtained. To measure ultrafast pulse width effectively, an auto-correlator based on Mach(-)Zehnder interferometer is developed. In the receiver terminal, a photodiode with range 320 nm to 1000 nm is used to detect signal and two photon absorption (TPA) method is applied.
Show less - Date Issued
- 2018
- Identifier
- CFE0007199, ucf:52249
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007199
- Title
- Computationally Efficient Digital Backward Propagation for Fiber Nonlinearity Compensation.
- Creator
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Zhu, Likai, Li, Guifang, Schulzgen, Axel, Likamwa, Patrick, Wei, Lei, University of Central Florida
- Abstract / Description
-
The next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion...
Show moreThe next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion compensation and account for most of the computation per step. A method of designing a complementary filter pair is proposed. The individual errors in the frequency response of the two filters in a complementary filter pair cancel each other. As a result, larger individual filter error can be tolerated and the required filter length is significantly reduced.Unequal step size can be used in DBP to minimize the number of steps. For unrepeatered transmission with distributed Raman amplification, the Raman gain as a function of the distance and the effective fiber length of each DBP step need to be calculated by solving the differential equations of Raman amplification. The split-step DBP is performed only for transmission where the signal power is high.In comparison with solving the nonlinear Schrodinger equation (NLSE) for the total field of the WDM signal, solving the coupled NLSE requires a smaller step number and a lower sampling rate. In addition, the phase-locking between the local oscillators is not necessary for solving the coupled NLSE. The XPM compensation of WDM long-haul transmission by solving the coupled NLSE is experimentally demonstrated.At the optimum power level of fiber transmission, the total nonlinear phase shift is on the order of 1 radian. Therefore, for transoceanic fiber transmission systems which consist of many ((>)100) amplified fiber spans, the nonlinear effects in each span are weak. As a result, the optical waveform evolution is dominated by the dispersion. Taking advantage of the periodic waveform evolution in periodically dispersion managed fiber link, the DBP of K fiber spans can be folded into one span with K times the nonlinearity. This method can be called (")distance-folded DBP("). Under the weakly nonlinear assumption, the optical waveform repeats at locations where accumulated dispersions are identical. Consequently, the nonlinear behavior of the optical signal also repeats at locations of identical accumulative dispersion. Hence for a fiber link with arbitrary dispersion map, the DBP steps can be folded according to the accumulated dispersion. Experimental results show considerable savings in computation using this (")dispersion-folded DBP(") method. Simulation results show that the dramatically reduced computational load makes the nonlinearity-compensated dispersion-managed fiber link a competitive candidate for the next-generation transmission systems.
Show less - Date Issued
- 2011
- Identifier
- CFE0004492, ucf:49272
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004492
- Title
- High Energy, High Average Power, Picosecond Laser Systems to Drive Few-Cycle OPCPA.
- Creator
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Vaupel, Andreas, Richardson, Martin, Delfyett, Peter, Schulzgen, Axel, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
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The invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA...
Show moreThe invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA allows direct amplification of an almost-octave spanning bandwidth supporting few-cycle pulse durations at center wavelengths ranging from the visible to the mid-IR. The current record in peak power from a table-top OPCPA is 16 TW and the current record average power is 22 W. High energy, few-cycle pulses with stabilized carrier-envelope phase (CEP) are desired for applications such as high-harmonic generation (HHG) enabling attoscience and the generation keV-photon bursts.This dissertation conceptually, numerically and experimentally describes essential aspects of few-cycle OPCPA, and the associated pump beam generation. The main part of the conducted research was directed towards the few-cycle OPCPA facility developed in the Laser Plasma Laboratory at CREOL (University of Central Florida, USA) termed HERACLES. This facility was designed to generate few-cycle pulses in the visible with mJ-level pulse energy, W-level average power and more than 100 GW peak power. Major parts of the implementation of the HERACLES facility are presented.The pump generation beam of the HERACLES system has been improved in terms of pulse energy, average power and stability over the last years. It is based on diode-pumped, solid-state amplifiers with picosecond duration and experimental investigations are presented in detail. A robust system has been implemented producing mJ-level pulse energies with ~100 ps pulse duration at kHz repetition rates. Scaling of this system to high power ((>)30 W) and high peak power (50-MW-level) as well as ultra-high pulse energy ((>)160 mJ) is presented. The latter investigation resulted in the design of an ultra-high energy system for OPCPA pumping. Following this, a new OPCPA facility was designed termed PhaSTHEUS, which is anticipated to reach ultra-high intensities.Another research effort was conducted at CELIA (Univerist(&)#233; de Bordeaux 1, France) and aimed towards a previously unexplored operational regime of OPCPA with ultra-high repetition rates (10 MHz) and high average power. A supercontinuum seed beam generation has been established with an output ranging from 1.3 to 1.9 ?m and few ps duration. The pump beam generation has been implemented based on rod-type fiber amplifiers producing more than 37 W average power and 370 kW peak power. The utility of this system as an OPCPA pump laser is presented along with the OPA design.The discussed systems operate in radically different regimes in terms of peak power, average power, and repetition rate. The anticipated OPCPA systems with few-cycle duration enable a wide range of novel experimental studies in attoscience, ultrafast materials processing, filamentation, LIBS and coherent control.
Show less - Date Issued
- 2013
- Identifier
- CFE0004952, ucf:49570
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004952
- Title
- System for metal coated fiber fabrication.
- Creator
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Zhang, Da, Amezcua Correa, Rodrigo, Schulzgen, Axel, Shah, Lawrence, University of Central Florida
- Abstract / Description
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For many specific applications, such as sensors, aerospace, chemical industry, deep-well oil-field industry, metal-coated fiber shows strong abilities to satisfy people's requirement. With in-line coating technology, we are able to coat Aluminum on the fibers.Using electromagnetic induction, we can easily heat an electrically conducting thing such as a metal with the eddy current. This process is defined as Induction heating. And we will melt the Aluminum by this induction heating during...
Show moreFor many specific applications, such as sensors, aerospace, chemical industry, deep-well oil-field industry, metal-coated fiber shows strong abilities to satisfy people's requirement. With in-line coating technology, we are able to coat Aluminum on the fibers.Using electromagnetic induction, we can easily heat an electrically conducting thing such as a metal with the eddy current. This process is defined as Induction heating. And we will melt the Aluminum by this induction heating during drawing the fibers on the tower. Introduce the fiber tower system. The drawing process of in-line technology is formed of the following steps: Position, Melting, Forming into fibers, Checking the diameter, Revising, Protective coatings. We will follow these to make the Aluminum coating fiber.With the help of the software which is 123D Design, I have four 3D model of the coating systems. Show the details of the all the coating systems such as the shape and the length of coated-fiber we can get.Talk about the photonic lantern which is the first project that I took part in when I joined the group. Show the mode profiles of our 6 to 1 lantern.
Show less - Date Issued
- 2017
- Identifier
- CFE0006677, ucf:51251
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006677
- Title
- Multi-Purpose device for analyzing and measuring ultra-short pulses.
- Creator
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Mehta, Naman Anilkumar, Schulzgen, Axel, Delfyett, Peter, Amezcua Correa, Rodrigo, University of Central Florida
- Abstract / Description
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Intensity auto correlator is device to measure pulse widths of ultrashort pulses on the order of picosecondsand femtoseconds. I have built an in-house, compact, portable, industry standard intensityauto correlator for measuring ultrashort pulse-widths. My device is suitable for pulse-widthsfrom 500 ps to 50 fs. The impetus for developing this instrument stemmed from our developmentof a multicore-fiber laser for high power laser applications, which also produces very short pulsesthat cannot be...
Show moreIntensity auto correlator is device to measure pulse widths of ultrashort pulses on the order of picosecondsand femtoseconds. I have built an in-house, compact, portable, industry standard intensityauto correlator for measuring ultrashort pulse-widths. My device is suitable for pulse-widthsfrom 500 ps to 50 fs. The impetus for developing this instrument stemmed from our developmentof a multicore-fiber laser for high power laser applications, which also produces very short pulsesthat cannot be measured with an oscilloscope. As techniques for measuring short pulse-widthshave been well studied, what made my journey exciting was the process of taking an idea and realizinga successful, cost-efficient device. In this study, I have analyzed a Q-switched laser and mymeasured pulse-width matched the theoretical value previously calculated. I have also analyzedour mode-locked multicore fiber laser and results were encouraging. The notion to build one intensityautocorrelator was based on our labs future work, which was with modelocked multicore fiberlaser, which at the moment is giving pulses on order of nanoseconds. Dr. Axel Schulzgen gavethe responsibility to build an intensity autocorrelator on my shoulders. As, Intensity autocorrelatorshave been around for long time, he encouraged me to make one in house, compact, portableintensity autocorrelator which measures pulse widths of 50 fs up to 500 ps quite easily.
Show less - Date Issued
- 2016
- Identifier
- CFE0006353, ucf:51508
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006353
- Title
- Pulsed Tm-Fiber Laser for Mid-IR Generation.
- Creator
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Kadwani, Pankaj, Richardson, Martin, Abouraddy, Ayman, Schulzgen, Axel, Peale, Robert, University of Central Florida
- Abstract / Description
-
Thulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation...
Show moreThulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation describes the development of novel nanosecond pulsed thulium fiber laser systems with record high peak power levels in order to pump nonlinear mid-infrared generation. The peak power scaling in thulium fiber lasers requires new fiber designs with ultra large mode field area (MFA). Two different classes of prototype thulium doped photonic crystal fibers (PCF) were investigated for high peak power generation. The first prototype is a flexible-PCF with 50 ?m core diameter, and the second is a rod-type PCF with 80 ?m diameter core. A robust single stage master oscillator power amplifier (MOPA) source based on flexible-PCF was developed. This source provided narrow linewidth, tunable wavelength, variable pulse duration, high peak power, and high energy nanosecond pulses. The PCF-rod was implemented as a second stage power amplifier. This system generated a record level of ~1 MW peak power output with 6.4 ns pulse-duration at 1 kHz repetition rate. This thulium doped PCF based MOPA system is a state of the art laser source providing high quality nanosecond pulses. The single stage MOPA system was successfully implemented to pump a zinc germanium phosphide (ZGP) crystal in an optical parametric oscillator (OPO) cavity to generate 3 - 5 (&)#181;m wavelengths. The MOPA source was also used to demonstrate backside machining in silicon wafer. The PCF based laser system demonstrated an order of magnitude increase in the peak power achievable in nanosecond thulium doped fiber laser systems, and further scaling appears possible. Further increases in the peak power will enable additional capabilities for mid-IR generation and associated applications.
Show less - Date Issued
- 2013
- Identifier
- CFE0005100, ucf:50739
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005100
- Title
- Picosecond Yb-Doped Fiber Amplifier.
- Creator
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Zhu, Weibin, Amezcua Correa, Rodrigo, Schulzgen, Axel, Fathpour, Sasan, University of Central Florida
- Abstract / Description
-
Due to its versatility, rare earth doped fiber amplifier (RDFA) has attracted a lot of researchers worldwide in recent years. Depends on different kinds of rare earth ion, RDFA can be categorized into neodymium doped fiber amplifier (NDFA), erbium doped fiber amplifier (EDFA), thulium doped fiber amplifier (TDFA), and so forth. Among many kinds of RDFA, the ytterbium doped fiber amplifier (YDFA) has received even more interest, especially in high power application, mainly because of its broad...
Show moreDue to its versatility, rare earth doped fiber amplifier (RDFA) has attracted a lot of researchers worldwide in recent years. Depends on different kinds of rare earth ion, RDFA can be categorized into neodymium doped fiber amplifier (NDFA), erbium doped fiber amplifier (EDFA), thulium doped fiber amplifier (TDFA), and so forth. Among many kinds of RDFA, the ytterbium doped fiber amplifier (YDFA) has received even more interest, especially in high power application, mainly because of its broad gain bandwidth and high conversion efficiency which are due to its relatively simple electronic structure.The purpose of this research is to study the YDFA by developing a model and building a YDFA setup in free space configuration. The active fiber used in the setup is a few modes, polarization-maintaining double-cladding ytterbium-doped large mode area (LMA) fiber and the length is 1m. The pump used is a tunable 975nm laser diode and a 1064nm laser diode was used as the seed which has 630 ps pulse duration time and 9.59 kHz repetition rate. This setup produces 2.514W average power, corresponding to a pulse peak power of 423kW, with 15W absorbed pump power. The spectrum of the output power has also been investigated.
Show less - Date Issued
- 2017
- Identifier
- CFE0006678, ucf:51214
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006678
- Title
- Design of a hydrogen-filled hollow-core Raman fiber laser.
- Creator
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Qin, Yangyang, Amezcua Correa, Rodrigo, Schulzgen, Axel, Shah, Lawrence, University of Central Florida
- Abstract / Description
-
The purpose of this study is to investigate the design of a Raman fiber laser based on a molecule hydrogen-filled hollow-core fiber with non-touching single ring of capillaries structure. O-hydrogen vibrational frequency shift of 4155 cm-1 and rotational frequency shift of 587 cm-1 were employed to generate Raman scattering from a 1064nm pump source.A thorough exploration was made to show how all Raman fiber laser components made up: gas chamber, hollow-core fibers, windows. The whole process...
Show moreThe purpose of this study is to investigate the design of a Raman fiber laser based on a molecule hydrogen-filled hollow-core fiber with non-touching single ring of capillaries structure. O-hydrogen vibrational frequency shift of 4155 cm-1 and rotational frequency shift of 587 cm-1 were employed to generate Raman scattering from a 1064nm pump source.A thorough exploration was made to show how all Raman fiber laser components made up: gas chamber, hollow-core fibers, windows. The whole process of chamber design, modification and fabrication were demonstrated. Besides, two kinds of anti-resonant hollow-core fibers were studied and tested. The transmission and loss spectrum of these fibers were measured thus it's easier to make a choice. Through the whole thesis a Raman fiber laser can be set up and tested very soon.
Show less - Date Issued
- 2017
- Identifier
- CFE0006645, ucf:51213
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006645
- Title
- Characterization and Application of Isolated Attosecond Pulses.
- Creator
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Chini, Michael, Chang, Zenghu, Saha, Haripada, Chow, Lee, Schulzgen, Axel, University of Central Florida
- Abstract / Description
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Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few...
Show moreTracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on as-yet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for state-resolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics (-) on timescales shorter than the laser cycle (-) are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagnetically-induced absorption and transparency, and two-color multi-photon absorption to (")dark(") states of the atom. These features are observed in both bound states and quasi-bound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 15-25 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV (-) comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a world-record-breaking 67 as pulse.
Show less - Date Issued
- 2012
- Identifier
- CFE0004781, ucf:49802
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004781
- Title
- Metrology of Volume Chirped Bragg Gratings Recorded in Photo-Thermo-Refractive Glass for Ultrashort Pulse Stretching and Compressing.
- Creator
-
Lantigua, Christopher, Glebov, Leonid, Zeldovich, Boris, Schulzgen, Axel, University of Central Florida
- Abstract / Description
-
Chirped Bragg gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass provide a very efficient and robust way to stretch and compress ultra-short laser pulses. These gratings offer the ability to stretch pulses from hundreds of femtoseconds, to the order of 1 ns and then re-compress them. However, in order to achieve pulse stretching of this magnitude, 100 mm thick CBGs are needed. Using these CBGs to both stretch, and re-compress the pulse thus requires propagation through 200 mm of...
Show moreChirped Bragg gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass provide a very efficient and robust way to stretch and compress ultra-short laser pulses. These gratings offer the ability to stretch pulses from hundreds of femtoseconds, to the order of 1 ns and then re-compress them. However, in order to achieve pulse stretching of this magnitude, 100 mm thick CBGs are needed. Using these CBGs to both stretch, and re-compress the pulse thus requires propagation through 200 mm of optical glass. This therefore demands perfect control of the glass homogeneity, as well as the holographic recording process of the CBG. In this thesis, we present a study of the CBG parameters that lead to distortions in the quality of diffracted beams. We first present the challenges associated with measuring the quality of these beams and we show that such measurements are not easily achieved using commercial systems that rely on the ISO standard M2 method. Thus, we introduce a new metric of beam quality, which we have coined S2, that is a combination of both the M2 and power in the bucket metrics. Subsequently, we investigate the influence of the CBG parameters on the quality of diffracted beams. In particular, we examine the impact of small optical heterogeneities known as striae, as well as the impact of the optically and thermally induced distortions in the grating. We then use this data to improve the fabrication and characterization of 100 mm long CBGs.Finally, we characterize the performance of CBGs recorded in PTR for stretching and compression of femtosecond pulses using a custom autocorrelation system. We present data on high quality 100 mm long CBGs and an analysis on the correlation between beam quality and the final pulse duration after stretching and re-compressing the pulse.
Show less - Date Issued
- 2013
- Identifier
- CFE0004876, ucf:49680
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004876
- Title
- Laser Filamentation Interaction with Materials for Spectroscopic Applications.
- Creator
-
Weidman, Matthew, Richardson, Martin, Schulzgen, Axel, Christodoulides, Demetrios, Sigman, Michael, University of Central Florida
- Abstract / Description
-
Laser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of...
Show moreLaser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of laser filamentation as a sampling tool for plasma based spectroscopy techniques. Within the scope of this study, single-shot ablation was compared with multi-shot ablation. The dependence of ablated mass on the number of pulses was observed to have a quasi-linear dependence on the number of pulses, advantageous for applications such as spectroscopy. Sample metrology showed that both physical and optical material properties have significant effects on the filament-induced ablation behavior. A relatively slow filament-induced plasma expansion was observed, as compared with a focused beams. This suggests that less energy was transferred to the plasma during filament-induced ablation. The effects of the filament core and the energy reservoir on the filament-induced ablation and plasma formation were investigated. Goniometric measurements of the filament-induced plasma, along with radiometric calculations, provided the number of emitted photons from a specific atomic transition and sample material.This work has advanced the understanding of the effects of single filaments on the ablation of solid materials and the understanding of filament-induced plasma dynamics. It has laid the foundation for further quantitative studies of multiple filamentation. The implications of this work extend beyond spectroscopy and included any application of filamentation that involves the interaction with a solid material.
Show less - Date Issued
- 2012
- Identifier
- CFE0004616, ucf:49940
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004616
- Title
- Nanocomposite Coating Mechanics via Piezospectroscopy.
- Creator
-
Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, Schulzgen, Axel, University of Central Florida
- Abstract / Description
-
Coatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of...
Show moreCoatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of nanocomposites and their coatings has been applied to give material property measurements, providing an understanding of particle reinforced composite behavior.Understanding the nanoparticle-coating-substrate mechanics is essential to interpreting the spectral shifts for stress sensing of structures. In the past, methods to experimentally measure the mechanics of these embedded nano inclusions have been limited, and much of the design of these composites depend on computational modeling and bulk response from mechanical testing. The PS properties of Chromium doped alumina allow for embedded inclusion mechanics to be revisited with unique experimental setups that probe the particles state of stress under applied load to the composite. These experimental investigations of particle mechanics will be compared to the Eshelby theory and its derivative theories in addition to the nanocomposite coating mechanics. This work discovers that simple nanoparticle load transfer theories are adequate for predicting PS properties in an intermediate volume fraction range. With fundamentals of PS nanocomposites established, the approach was applied to selected experiments to prove its validity. In general it was observed that the elastic modulus values calculated from the PS response were similar to that observed from macroscale strain measurements such as a strain gage. When simple damage models were applied to monitor the elastic modulus, it was observed that the rate of decay for the elastic modulus was much higher for the PS measurements than for the strain gage.A novel experiment including high resolution PS maps with secondary strain maps from digital image correlation is reviewed on an open hole tension, composite coupon. The two complementary measurements allow for a unique PS response for every location around the hole with a spatial resolution of 400 microns. Progression of intermediate damage mechanisms was observed before digital image correlation indicated them. Using the PS nanocomposite model, elastic modulus values were calculated. Introducing an elastic degradation model with some plastic deformation allows for estimation of material properties during the progression of failure.This work is part of a continuing effort to understand the mechanics of a stress sensing PS coating. The mechanics were then applied to various experimental data that provided elastic property calculations with high resolution. The significance is in the experimental capture of stress transfer in particulate composites. These findings pave the way for the development of high resolution stress-sensing coatings.
Show less - Date Issued
- 2014
- Identifier
- CFE0005614, ucf:50223
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005614
- Title
- Specialty Fiber Lasers and Novel Fiber Devices.
- Creator
-
Jollivet, Clemence, Schulzgen, Axel, Moharam, Jim, Richardson, Martin, Mafi, Arash, University of Central Florida
- Abstract / Description
-
At the Dawn of the 21st century, the field of specialty optical fibers experienced a scientific revolution with the introduction of the stack-and-draw technique, a multi-steps and advanced fiber fabrication method, which enabled the creation of well-controlled micro-structured designs. Since then, an extremely wide variety of finely tuned fiber structures have been demonstrated including novel materials and novel designs. As the complexity of the fiber design increased, highly-controlled...
Show moreAt the Dawn of the 21st century, the field of specialty optical fibers experienced a scientific revolution with the introduction of the stack-and-draw technique, a multi-steps and advanced fiber fabrication method, which enabled the creation of well-controlled micro-structured designs. Since then, an extremely wide variety of finely tuned fiber structures have been demonstrated including novel materials and novel designs. As the complexity of the fiber design increased, highly-controlled fabrication processes became critical. To determine the ability of a novel fiber design to deliver light with properties tailored according to a specific application, several mode analysis techniques were reported, addressing the recurring needs for in-depth fiber characterization. The first part of this dissertation details a novel experiment that was demonstrated to achieve modal decomposition with extended capabilities, reaching beyond the limits set by the existing mode analysis techniques. As a result, individual transverse modes carrying between ~0.01% and ~30% of the total light were resolved with unmatched accuracy. Furthermore, this approach was employed to decompose the light guided in Large-Mode Area (LMA) fiber, Photonic Crystal Fiber (PCF) and Leakage Channel Fiber (LCF). The single-mode performances were evaluated and compared. As a result, the suitability of each specialty fiber design to be implemented for power-scaling applications of fiber laser systems was experimentally determined.The second part of this dissertation is dedicated to novel specialty fiber laser systems. First, challenges related to the monolithic integration of novel and complex specialty fiber designs in all-fiber systems were addressed. The poor design and size compatibility between specialty fibers and conventional fiber-based components limits their monolithic integration due to high coupling loss and unstable performances. Here, novel all-fiber Mode-Field Adapter (MFA) devices made of selected segments of Graded Index Multimode Fiber (GIMF) were implemented to mitigate the coupling losses between a LMA PCF and a conventional Single-Mode Fiber (SMF), presenting an initial 18-fold mode-field area mismatch. It was experimentally demonstrated that the overall transmission in the mode-matched fiber chain was increased by more than 11 dB (the MFA was a 250 ?m piece of 50 ?m core diameter GIMF). This approach was further employed to assemble monolithic fiber laser cavities combining an active LMA PCF and fiber Bragg gratings (FBG) in conventional SMF. It was demonstrated that intra-cavity mode-matching results in an efficient (60%) and narrow-linewidth (200 pm) laser emission at the FBG wavelength.In the last section of this dissertation, monolithic Multi-Core Fiber (MCF) laser cavities were reported for the first time. Compared to existing MCF lasers, renown for high-brightness beam delivery after selection of the in-phase supermode, the present new generation of 7-coupled-cores Yb-doped fiber laser uses the gain from several supermodes simultaneously. In order to uncover mode competition mechanisms during amplification and the complex dynamics of multi-supermode lasing, novel diagnostic approaches were demonstrated. After characterizing the laser behavior, the first observations of self-mode-locking in linear MCF laser cavities were discovered.
Show less - Date Issued
- 2014
- Identifier
- CFE0005354, ucf:50491
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005354
- Title
- LP fiber mode converters using holographic phase mask in photo-thermo-refractive glass.
- Creator
-
Patil, Aniket, Schulzgen, Axel, Delfyett, Peter, Amezcua Correa, Rodrigo, University of Central Florida
- Abstract / Description
-
In this study, an investigation was undertaken to research the use of holographic phase masks (HPMs) in photo-thermo-refractive (PTR) glass as mode converters for linearly polarized (LP) fiber modes. A Spatial Light Modulator (SLM) was used to generate higher-order transverse fiber modes LPm,n. Under proper incidence condition on the holographic device, LPm,n modes are diffracted and simultaneously converted into higher order or lower order LP modes. The process was analyzed by imaging the...
Show moreIn this study, an investigation was undertaken to research the use of holographic phase masks (HPMs) in photo-thermo-refractive (PTR) glass as mode converters for linearly polarized (LP) fiber modes. A Spatial Light Modulator (SLM) was used to generate higher-order transverse fiber modes LPm,n. Under proper incidence condition on the holographic device, LPm,n modes are diffracted and simultaneously converted into higher order or lower order LP modes. The process was analyzed by imaging the far field on a CCD camera. It is demonstrated that using this novel method of converting transverse fiber modes several combinations of LP modes can be converted to each other with mode conversion efficiencies up to 70%. Mode purities were found to be around 85% for up conversion and around 90% for down conversion, respectively. It is noticed that this approach has several promising applications such as mode multiplexing, beam cleaning and power scaling of higher-order mode fiber lasers and amplifiers by combining mode conversion and beam combining.
Show less - Date Issued
- 2014
- Identifier
- CFE0005396, ucf:50459
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005396
- Title
- Transverse mode selection and brightness enhancement in laser resonators by means of volume Bragg gratings.
- Creator
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Anderson, Brian, Glebov, Leonid, Zeldovich, Boris, Schulzgen, Axel, Rahman, Talat, University of Central Florida
- Abstract / Description
-
The design of high power lasers requires large mode areas to overcome various intensity driven nonlinear effects. Increasing the aperture size within the laser can overcome these effects, but typically result in multi-transverse mode output and reduced beam quality, limiting the brightness of the system. As one possible solution, the angular selectivity of a diffractive optical element is proposed as a spatial filter, allowing for the design of compact high brightness sources not possible...
Show moreThe design of high power lasers requires large mode areas to overcome various intensity driven nonlinear effects. Increasing the aperture size within the laser can overcome these effects, but typically result in multi-transverse mode output and reduced beam quality, limiting the brightness of the system. As one possible solution, the angular selectivity of a diffractive optical element is proposed as a spatial filter, allowing for the design of compact high brightness sources not possible with conventional methods of transverse mode selection. This thesis explores the angular selectivity of volume Bragg gratings (VBGs) and their use as spatial transverse mode filters in a laser resonator. Selection of the fundamental mode of a resonator is explored using transmission Bragg gratings (TBGs) as the spatial filter. Simulations and experimental measurements are made for a planar, 1 cm long resonator demonstrating near diffraction limited output (M2 (<) 1.4) for aperture sizes as large as 2.0 mm. Applications to novel fiber laser designs are explored. Single mode operation of a multi-mode Yb3+ doped ribbon fiber laser (core dimensions of 107.8 ?m x 8.3 ?m) is obtained using a single transmission VBG as the filter in an external cavity resonator. Finally, a novel method of selecting a pure higher order mode to oscillate within the gain medium while simultaneously converting this higher order mode to a fundamental mode at an output coupler is proposed and demonstrated. A multiplexed transmission VBG is used as the mode converting element, selecting the 12th higher order mode for amplifications in an Yb3+ doped ribbon fiber laser, while converting the higher order mode of a laser resonator to a single lobed output beam with diffraction limited divergence.
Show less - Date Issued
- 2015
- Identifier
- CFE0005754, ucf:50103
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005754
- Title
- 2 micron fiber lasers: power scaling concepts and limitations.
- Creator
-
Sincore, Alex, Richardson, Martin, Amezcua Correa, Rodrigo, Schulzgen, Axel, Shah, Lawrence, University of Central Florida
- Abstract / Description
-
Thulium- and holmium-doped fiber lasers (TDF and HDF) emitting at 2 micron offer unique benefits and applications compared to common ytterbium-doped 1 micron lasers. This dissertation details the concepts, limitations, design, and performance of four 2 micron fiber laser systems. While these lasers were developed for various end-uses, they also provide further insight into two major power scaling limitations. The first limitation is optical nonlinearities: specifically stimulated Brillouin...
Show moreThulium- and holmium-doped fiber lasers (TDF and HDF) emitting at 2 micron offer unique benefits and applications compared to common ytterbium-doped 1 micron lasers. This dissertation details the concepts, limitations, design, and performance of four 2 micron fiber laser systems. While these lasers were developed for various end-uses, they also provide further insight into two major power scaling limitations. The first limitation is optical nonlinearities: specifically stimulated Brillouin scattering (SBS) and modulation instability (MI). The second limitation is thermal failure due to inefficient pump conversion. First, a 21.5 W single-frequency, single-mode laser with adjustable output from continuous-wave to nanosecond pulses is developed. Measuring the SBS threshold versus pulse duration enables the Brillouin gain coefficient and gain bandwidth to be determined at 2 micron. Second, a 23 W spectrally-broadband, nanosecond pulsed laser is constructed for materials processing applications. The temporally incoherent multi-kW peak power pulses can also efficiently produce MI and supercontinuum generation by adjusting the input spectral linewidth. Third, the measured performance of in-band pumped TDF and HDF lasers are compared with simulations. HDF displays low efficiencies, which is explained by including ion clustering in the simulations. The TDF operates with impressive (>)90% slope efficiencies. Based on this result, a system design for (>)1 kW average power TDF amplifier is described. The designed final amplifier will be in-band pumped to enable high efficiency and low thermal load. The amplifier efficiency, operating bandwidth, thermal load, and nonlinear limits are modeled and analyzed to provide a framework for execution. Overall, this dissertation provides further insight and understanding on the various processes that limit power scaling of 2 micron fiber lasers.
Show less - Date Issued
- 2018
- Identifier
- CFE0007374, ucf:52105
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007374
- Title
- Novel solid state lasers based on volume Bragg gratings.
- Creator
-
Hale, Evan, Glebov, Leonid, Divliansky, Ivan, Schulzgen, Axel, Vodopyanov, Konstantin, Lyakh, Arkadiy, University of Central Florida
- Abstract / Description
-
Since their invention in 1960, lasers have revolutionized modern technology, and tremendous amounts of innovation and development has gone into advancing their properties and efficiencies. This dissertation reports on further innovations by presenting novel solid state laser systems based on the volume Bragg gratings (VBGs) and the newly developed holographic phase mask (HPMs) for brightness enhancement, dual wavelength operation, and mode conversion. First, a new optical element was created...
Show moreSince their invention in 1960, lasers have revolutionized modern technology, and tremendous amounts of innovation and development has gone into advancing their properties and efficiencies. This dissertation reports on further innovations by presenting novel solid state laser systems based on the volume Bragg gratings (VBGs) and the newly developed holographic phase mask (HPMs) for brightness enhancement, dual wavelength operation, and mode conversion. First, a new optical element was created by pairing the HPM with two surface gratings creating an achromatic holographic phase mask. This new optical device successfully performed transverse mode conversion of multiple narrow line laser sources operating from 488 to 1550 nm and a broadband mode locked femtosecond source with no angular tuning. Also, two types of HPMs were tested on high power Yb fiber lasers to demonstrate high energy mode conversion.Secondly, the effects of implementing VBGs for brightness enhancement of passively Q-switched systems with large Fresnel numbers was investigated. Implementing VBGs for angular mode selection allowed for higher pulse energies to be extracted without sacrificing brightness and pulse duration. This technique could potentially be applied to construct compact cavities with 1 cm diameter beams and nearly diffraction limited beam quality.Lastly, a spectral beam combining approach was applied to create Tm3+ and Yb3+ based narrowband dual-wavelength pump sources for terahertz generation, using VBGs as frequency selectors and beam combiners. Comparison of pulse duration and synchronization was done between passive and active Q-switching operation. An experimental set up for THz generation and detection using high sensitive detectors was created, and modeling of terahertz conversion efficiencies were done
Show less - Date Issued
- 2019
- Identifier
- CFE0007812, ucf:52333
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007812