OSE Dissertation Defense by Mr. Mingyang Zhang on Exploration of Semiconductor Gain Medium, Resonator, Pump, and Frequency Stabilization for Laser Guide Star Applications
Departmental News
![Mr. Fatih Furkan](images/mingyang-zhang1.jpg)
Posted: June 6, 2024
Date and Time: Thursday, June 20th, 2024, from 10:00 AM - 11:30 AM
Location: PAIS, Room 2540
Dissertation Committee:
Dr. Alexander Albrecht, Committee Chair, Physics & Astronomy Department
Dr. Victor Acosta, Physics & Astronomy Department
Dr. Garrett Cole, Thorlabs
Dr. Daniel Feezell, Electrical and Computer Engineering Department
Abstract:
Laser Guide Star (LGS) is essential in adaptive optics system for ground-based astronomical observation. This dissertation presents the implementation of membrane external-cavity surface-emitting laser (MECSEL) as a compact and cost-effective LGS platform. The MECSEL gain chips employ multi-quantum-well structure with In0.38Ga0.62As quantum wells, GaAs barriers, GaAs0.94P0.06 strain compensation layers, and In0.49Ga0.51P window layers. The laser cavity configurations, including linear, V-shaped, and Z-shaped geometries, were analyzed through both numerical simulations and experimental investigations. An in-well pumping method was explored to reduce quantum defect, addressing the thermal rollover limitation for high power output. A comparative study between barrier pumping and in-well pumping demonstrated the superior performance of the in-well method in terms of slope efficiency and maximum output power. New multi-pass pumping structures were designed using Zemax modeling, with two specific configurations experimentally realized in MECSELs. A hybrid-MECSEL (H-MECSEL) design was introduced to simplify multi-pass pumping while enhancing thermal management. COMSOL modeling was employed to assess thermal management capabilities, and the thermal lensing within the H-MECSEL gain chip was studied for optimized laser cavity design.
The H-MECSEL, using 1070 nm in-well pumping, achieved approximately 30 W output power in free-running operation and 17.2 W with linewidth narrowed to a single longitudinal mode at 1178 nm. Intracavity frequency doubling yielded 10.3 W at 589 nm with TEM00 beam profile and 7 MHz linewidth. The entire system was integrated on a single breadboard, and dither locking with a sodium cell as a frequency reference was implemented. Doppler-free hyperfine transitions within the sodium D line were resolved using saturated absorption spectroscopy, and the H-MECSEL was stabilized to a hyperfine transition within sodium D2a for over an hour with watt-level output. Allan deviation calculations confirmed the stabilization efficacy. This dissertation demonstrates the feasibility of deploying semiconductor-based LGS systems in astronomical observatories.
Biography: