Study of tunable resonances in laser beam divergence and beam deflection

TL;DR

This paper predicts and demonstrates new resonant properties in laser resonators affecting beam divergence and stability, with tunable frequencies and experimental validation through noise spectrum measurements.

Contribution

It introduces the theoretical prediction and experimental demonstration of tunable resonances in laser beam properties, expanding understanding of laser resonator dynamics.

Findings

Resonances occur in beam width and wavefront curvature over a tunable frequency range.

Experimental measurements show increased noise at predicted resonant frequencies.

Resonances are analogous to effects in ultrashort pulse lasers.

Abstract

New, fundamental resonant properties of laser resonators are theoretically predicted and experimentally demonstrated. These resonances occur either in the time dependence of the beam width and that of beam radius of curvature of the wavefront or in the time dependent pointing and position stability of the output light beam of a laser resonator. The resonant frequency can be tuned continuously from zero to the round-trip frequency in the first case; and from zero to the half of the round-trip frequency in the second case, by for example, moving one of the mirrors of the resonator. In both cases besides a resonant frequency its complementary frequency to the round-trip frequency is also resonant, and their shifted frequencies by multiples of the round-trip frequency are also resonant. In our experimental demonstration we measured the radiofrequency noise spectrum of the output laser beam, that was partially blocked by a knife-edge. We observed increased noise at the theoretically predicted frequencies. Similar resonances are predicted either in the time dependent pulse-width and phase modulation or time jitter and the central frequency of the ultrashort light pulses of the mode-locked lasers because of the analogy between the space description of the light beams and the time-description of the light pulses.