Abstract

Continuous-wave optical parametric oscillators (OPOs) based on periodically-poled lithium niobate are outstanding light sources because they combine single-frequency operation with a wide tuning range. Studies demonstrate that in singly-resonant systems at high high pump levels, the spectrum of the resonant field comprises additional components [1,2]. Observed frequency shifts of about 45 and 100 cm⁻¹ are attributed to Raman lasing. In contrast to this interpretation, experiments on Raman scattering do not show optical phonons with frequencies below the prominent value of 250 cm⁻¹ [3]. To clarify this, we have used different phase-matching periods of 24.4 to 31.0 μm in our singly-resonant OPO leading to idler wavelengths from 2.33 to 5.32 μm. A frequency shift depending on the poling period would be a non-ambiguous proof that not a Raman effect is observed.

© 2009 IEEE