Threshold for strong thermal dephasing in periodically poled KTP in external cavity frequency doubling

Abstract

We present a measurements series of the efficiency of periodically poled KTP used for second harmonic generation in an external phase locked cavity. Due to the high absorption (0.01cm -1 ) in the PPKTP crystal at the pump wavelength a strong thermal dephasing of the periodically poled grating is observed for high pump powers. For four different resonator setups, it was experimentally found that a threshold parameter could be defined as the ratio between the focal intensity in the crystal and the single pass conversion efficiency. The value of this threshold for the onset of strong thermal dephasing was found to be 1.41·10 10 W 2 m -2 in our 30 mm long PPKTP sample. This threshold parameter marks the onset of thermally induced instability that leads to a degradation of the SHG conversion efficiency. Above the threshold the shape of the resonance peaks of the resonator changed from symmetrical into triangular making phase locking difficult.

Ultraviolet Laser Pulses with Multigigahertz Repetition Rate and Multiwatt Average Power for Fast Trapped-Ion Entanglement Operations

“…Cross-correlation frequency-resolved optical gating measurement gives a UV pulse duration on the order of a picosecond. At higher pump intensities thermal-dephasing induced power fluctuations in the PPKTP crystal become problematic, as reported in earlier studies [24,25]. As a consequence, it is difficult to gauge the exact power at the crystal output.…”