ADVANCED LASER BEAM DEFLECTION AND LASER INDUCED ACTIVATION

Restricted (Penn State Only)
Author:
Chao, Ju Hung
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 15, 2019
Committee Members:
  • Shizhuo Yin, Dissertation Advisor
  • Shizhuo Yin, Committee Chair
  • James Kenneth Breakall, Committee Member
  • Victor P Pasko, Committee Member
  • Jian Hsu, Outside Member
Keywords:
  • KTN
  • Beam Deflector
  • Multi-denominational beam deflector
  • High gain PCSS
  • Ruby fluorescence
Abstract:
A high-speed optical beam deflector based on potassium tantalate niobate (KTa1-xNbxO3 [KTN]) crystal, which has been used in swept-source optical coherence tomography (SSOCT), has been gaining interest for its potential application to laser measurement, sensing, imaging, printing, display, storage, and communication in advanced optical systems. The studies in this dissertation aimed to explore the unknown aspects of the KTN beam deflection technique and identify novel functionalities. Our investigation of the non-uniform charge distribution in KTN crystals led us to develop a method to quantitatively simulate space-charge-controlled (SCC) beam deflection in KTN crystals with non-uniform charge distribution. Our method of dividing charge densities in KTN crystals with respect to the distance from the KTN cathode was experimentally verified and found to be useful when designing SCC KTN beam deflectors with non-uniform charge distribution. We also discovered that 2-D beam deflection can be achieved on a single piece of KTN crystal by combining space-charge-controlled (SCC) deflection and temperature-gradient-controlled (TGC) deflection. When a temperature gradient is induced on an SCC KTN beam deflector in a direction perpendicular to the external electric field, 2-D beam deflection occurs in the KTN crystal. In addition to beam deflection, I studied the high-speed laser activation technique involving SI-GaAs and a photoconductive semiconductor switch (PCSS). I identified unconventional lock-on behavior during non-linear switching in PCSS by activating the PCSS with optical beams of multiple wavelengths simultaneously. After bonding the activating portion of the PCSS with a ruby crystal, the PCSS was triggered by a combination of a 532-nm laser pulse and a 694-nm fluorescent light. This resulted in an ultra-long lock-on time (i.e., on the order of milliseconds) three orders of magnitude longer than the typical lock-on behavior in the non-linear switching mode of PCSS.