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Nonlinear Optical Response of Simple Molecules and TwoPhoton Semiconductor Lasers
 Date Issued:
 2015
 Abstract/Description:
 This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a twophoton laser using a bulk semiconductor gain medium. Within the BornOppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both boundelectronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, whitelight continuum generation, alloptical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the thirdorder response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or twophoton absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the boundelectrons. Thus both the boundelectronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a twophoton gain medium. A twophoton laser has been a goal of nonlinear optics since shortly after the original laser's development. In this case, twophotons are emitted from a single electronic transition rather than only one. This processes is known as twophoton gain (2PG). Semiconductors have large twophoton absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ??_a?10??_b. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pumpprobe experiments. This constitutes, to my knowledge, the first report of nondegenerate twophoton gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate threephoton absorption (ND3PA), in both cases are theoretically analyzed. Experimental measurements of ND3PA agree with this analysis and show that it is enhanced much more than ND2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the twophoton gain, preventing the possibility of a twophoton semiconductor laser.
Title:  Nonlinear Optical Response of Simple Molecules and TwoPhoton Semiconductor Lasers. 
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Name(s): 
Reichert, Matthew, Author Vanstryland, Eric, Committee Chair Hagan, David, Committee CoChair Likamwa, Patrick, Committee Member Peale, Robert, Committee Member University of Central Florida, Degree Grantor 

Type of Resource:  text  
Date Issued:  2015  
Publisher:  University of Central Florida  
Language(s):  English  
Abstract/Description:  This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a twophoton laser using a bulk semiconductor gain medium. Within the BornOppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both boundelectronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, whitelight continuum generation, alloptical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the thirdorder response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or twophoton absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the boundelectrons. Thus both the boundelectronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a twophoton gain medium. A twophoton laser has been a goal of nonlinear optics since shortly after the original laser's development. In this case, twophotons are emitted from a single electronic transition rather than only one. This processes is known as twophoton gain (2PG). Semiconductors have large twophoton absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ??_a?10??_b. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pumpprobe experiments. This constitutes, to my knowledge, the first report of nondegenerate twophoton gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate threephoton absorption (ND3PA), in both cases are theoretically analyzed. Experimental measurements of ND3PA agree with this analysis and show that it is enhanced much more than ND2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the twophoton gain, preventing the possibility of a twophoton semiconductor laser.  
Identifier:  CFE0005874 (IID), ucf:50871 (fedora)  
Note(s): 
20150801 Ph.D. Optics and Photonics, Optics and Photonics Doctoral This record was generated from author submitted information. 

Subject(s):  Nonlinear optics  Nonlinear optical spectroscopy  Nonlinear optical materials  Kerr effect  Ultrafast nonlinear optics  Multiphoton processes  Semiconductor nonlinear optics  Raman effect  Coherent transients  
Persistent Link to This Record:  http://purl.flvc.org/ucf/fd/CFE0005874  
Restrictions on Access:  public 20150815  
Host Institution:  UCF 