Fig. 4
From: Pockels laser directly driving ultrafast optical metrology
Laser frequency stabilization. a Schematic of the experimental setup for PDH laser locking. The reference cavity is either a high-Q silicon nitride microring resonator or a H13C14N gas cell. To obtain the laser-scanned transmission spectrum of the reference cavity (c, e Top figures), a triangular waveform signal, produced by an AWG at a modulation speed of 200 Hz, is used to drive the TFLN laser external cavity, so as to linearly scan the laser frequency at a slow speed. To obtain the laser-scanned PDH error signal (c, e Bottom figures and d), A single-frequency sinusoidal RF signal is added to drive the laser external cavity, together with the triangular waveform signal. For feedback locking the laser, the AWG is switched off and the PDH error signal is directed to a PID servo whose output is used to drive the laser's external cavity. b Optical spectrum of laser output when laser external cavity is modulated by a sinusoidal RF signal at different frequencies, with an RF power of 7 dBm. c Laser-scanned transmission spectrum (top) and PDH error signal (bottom) of a resonance mode of the reference silicon nitride microresonator. d Laser-scanned PDH error signal of the silicon nitride resonator, at different RF modulation frequencies. e Laser-scanned absorption spectrum (top) and PDH error signal (bottom) of the H13C14N P16 line of the reference gas cell. A RF modulation speed of 630 MHz is used to obtain the figure of the PDH error signal. f Time-dependent laser frequency, measured by a wavemeter (Toptica Photonics, WS6-600 VIS/IR-I). The PID servo is switched on in the first and third hour and is switched off in the second hour. g Detailed time-dependent laser frequency at the three time sections in dashed area in (f)
