Citation
Mittelstein, Michael (1989) Theory and experiments on unstableresonator and quantum well GaAs/GaAlAs lasers. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd02082007125156
Abstract
Structures of GaAs/GaA1As lasers and their performance characteristics are investigated experimentally and theoretically. A selfconsistent model for the longitudinal gain and intensity distribution in injection lasers is introduced. The model is applied to unstableresonator semiconductor lasers to evaluate their lateral losses and quantum efficiencies, and an advanced design is presented. Symmetric, unstableresonator semiconductor lasers are manufactured and a virtual source point inside the laser more than an order of magnitude narrower than the width of the near field is demonstrated. Young's doubleslit experiment is adopted for lateral coherence measurements in semiconductor lasers. A high degree of lateral coherence is found, indicating operation of the unstableresonator lasers in predominantly one mode.
In the pulsed measurements on broadarea, singlequantumwell, gradedindex waveguide, separateconfinementheterostructure lasers, very high quantum efficiencies, very low losses, and very high output powers are observed. The devices are found to exhibit beam divergence narrower than two times the diffraction limit in singlelobed, farfield patterns. Using these singlequantumwell lasers, the "second quantizedstate lasing" is found experimentally, and a simple model is developed to explain it.
A general model for the gain spectrum and required current density of quantumwell lasers is introduced. The eigenfunctions and eigenvalues of the charge carriers and optical mode of the transverse structure are used to derive the gain spectrum and current density from the Einstein coefficients. The twodimensional density of states for the charge carriers and the effective width of the optical mode (not the width of the quantum well) are identified as the dominant parameters. The model includes a new heuristic approach to account for the observed smeared onset of subbands, eliminating convolution calculations.
Applications of the model for a typical structure, a conventional double heterostructure and an advanced structure are presented. Structures providing two and threedimensional confinement are discussed and are directly compared to conventional and quantumwell structures in terms of laser parameters. The length scale of confinement structures for the optical mode is found to be two orders of magnitude larger than the corresponding length scale for carrier confinement, implying that the singlequantumwell laser is the most adapted structure.
The gainflattened condition that singlequantumwell lasers exhibit near the onset of the second quantizedstate lasing is introduced. An external gratingtuned resonator is analyzed, and the coupled cavity formalism is employed to examine conditions for continuous tuning. Predictions for tuning ranges of conventional, doubleheterostructure and singlequantumwell lasers are made, and the superiority of the latter on account of pump current density is clarified. Experimentally, broadband tunability exceeding a 10% spectral tuning range of an uncoated quantumwell laser in a simple gratingtuned resonator is demonstrated.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Degree Grantor:  California Institute of Technology 
Division:  Engineering and Applied Science 
Major Option:  Applied Physics 
Thesis Availability:  Restricted to Caltech community only 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  3 March 1989 
Record Number:  CaltechETD:etd02082007125156 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd02082007125156 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  553 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  02 Mar 2007 
Last Modified:  26 Dec 2012 02:30 
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