Picosecond Passively Q‐Switched Laser Generation via Whispering‐Gallery Mode Resonators

ABSTRACT As laser processing technology continues to expand into fields like medicine and information communication, there is a growing urgency for miniaturizing pulsed laser sources and integrating them into chip‐scale light sources. Currently, the miniaturization of pulsed lasers mainly relies on optical waveguide structures, achieved by integrating traditional Fabry‐Perot (F‐P) cavities with nonlinear modulation elements. Although this design can reduce the cross‐sectional area of the optical mode to a few square micrometers, the F‐P cavity‐based architecture requires optical waveguide lengths of several millimeters to centimeters, offering both theoretical possibilities and practical requirements for further device size reduction. Here, this work presents a passively Q‐switched picosecond pulsed laser based on whispering gallery mode (WGM) microcavities, with a diameter of only 28 µm. This WGM laser employs Cr,Nd:YAG as a self‐Q‐switched gain medium, generating 820‐picosecond pulses at 0.75 MHz with a 3.5 mW threshold. The study explores Q‐switched dynamics in a WGM resonator, showing how cavity size and Cr,Nd:YAG absorption affect pulse stability. The findings indicate that WGM cavities exhibit higher stability compared to Fabry‐Perot resonators, providing strong support for the development of more compact and efficient pulsed laser systems and suggesting promising applications in future miniaturized laser technologies.