워크오프 이중보상방법을 이용한 적외선-자외선 변환 효율 향상에 대한 연구

Abstract

ABSTRACT Study on infrared-to-ultraviolet conversion- efficiency enhancement using a walk-off double compensation method

Kun-Kook Kim Advisor : Prof. Jin-Tae Kim, Ph.D. Department of Photonic Engineering Graduate School of Chosun University

In this paper, we propose how to improve IR-UV conversion efficiency with walk-off double compensation. We theoretically describe process of sum-frequency generation and second-harmonic generation, and also phase matching condition in each process. A LBO crystal which has deep UV transparency and relatively small walk-off was used as a second-harmonic and sum-frequency generations. The IR beam of 1064 nm is partially converted to a green beam with 532 nm wavelength at second-harmonic generation process and then the generated green beam was mixed with residual IR beam to have 355 nm UV beam at sum-frequency generation process. The Walk-off generated during sum-frequency generation process was firstly compensated using a walk-off compensator. Then, second compensation was achieved by 2-crystal set. The first and second compensation improved output power of UV beam. IR beam of 3 W was converted into green beam of 1.53 W and thus maximum IR to green conversion efficiency was 51%. In sum-frequency generation, UV beam output power improved 1.4 times greater with walk-off compensator, and 2-crystal set as sum-frequency generation crystal improved 1.4 times greater output power than that using single crystal. The UV beam output power was 1.06 W and the IR to UV conversion efficiency was 35.3% when used both walk-off compensator and 2-crystal set. The measured beam sizes of X and Y directions were measured to be FWHM_X = 840 μm and FWHM_Y = 960 μm with double walk-off compensation, respectively. The beam shape after 2-crystal set is more similar to a circle than that using a single crystal. We theoretically and experimentally verified method of double walk-off compensation can improve the power and beam quality of output UV beam.