Self-Guided Operation of Green-Pumped Singly Resonant CW OPO based on Bulk MgO:PPLN

1. Self-Guided Operation of Green-Pumped Singly Resonant CW OPO based on Bulk MgO:PPLN In-ho Bae,1 Han Seb Moon,1 Sebastian Zaske,2 Christoph Becher,2 Seung Kwan Kim,3 Seung-Nam Park,3 and Dong-Hoon Lee3,* 1Department of Physics, Pusan National University, Busan 609-735, Rep. Korea 2Universität des Saarlandes, Fachrichtung 7.3 (Technische Physik), 66123 Saarbrücken, Germany 3Division of Physical Metrology, Korea Research Institute of Standards and Science (KRISS), Daejeon 305-340, Rep. Korea * Email: dh.lee@kriss.re.kr

2. Contents • Introduction • Singly resonant CW OPO setup • CW OPO Cavity degin • Experimental results • Wavelength tuning curve • Thermal wave-guide effect • Output power characteristics • Continuous tuning range • Thermal absorption time • Spatial mode profile • Pump mode profile • Summary

3. Introduction Continuous-wave (CW) optical parametric oscillators (OPOs) based on quasi-phase-matching (QPM) broad wavelength coverage wide single-frequency tuning range correlations between the signal and idler output beams Nonlinear crystal Cavity design thermal lensing and de-phasing limitation of parametric efficiency, spatial mode quality, spectral tuning property, and stability of CW OPOs

4. Singly resonant OPO setup HR : high reflectivity HWP : half-wave plate ISO : isolator A : aperture OSA : optical spectrum analyzer BD : beam dump MgO: PPLN Pump : 532 nm Signal : 770~890 nm Oven Idler : 1330~1680 nm Translator Polling period Λ 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm XY stage

5. Wavelength tuning curve Idler : 1330~1680 nm Signal : 770~890 nm We fitted experimental results by using Sellmeier equations for 5% MgO-doped congruent PPLN in Ref. [1]. [1] Gayer et. al. Appl. Phys. B 91, 343–348.

6. Thermal wave-guide effect • Resonance frequency of the TEMnmq Mode Laser Resonator Stability Diagram • Transverse mode spacing • Resonator g parameters & Stability condition R = 50 mm, limited cavity length : 100 mm L > 100 mm  unstable cavity In our case, unstable cavity is above 122 mm.

7. Output power characteristics

8. Continuous tuning range 115.4 mm 109.4 mm 98 mm

9. Thermal absorption time Leff 93.4 mm Leff 115.4 mm

10. Spatial mode profile Leff 109.4 mm Leff 98 mm Leff 115.4 mm

11. Pump mode profile before after

12. Summary We operated Self-Guided singly resonant CW OPOs that was assisted by thermal wave guide effect. We got 400 ~ 600 MHz and 600 ~ 800 MHz for continuous tuning range under the stable and unstable cavity condition, respectively. The spatial mode of the CW OPOs were improved by thermal effect in unstable cavity and the Gaussian mode profile was achieve at the maximum cavity length. In the near future, CW – OPOs with unstable cavity method will be used to find atomic transition spectrum though optimization and stabilization of continuous tuning range.