Abstract

Bi-directional ultrashort pulse ring lasers can be seen as differential interferometers for the counter-circulating pulses. Interfering the two outputs produces a beat note at the frequency equal to the phase difference between the pulses divided by the round-trip time (v_beat = Δϕ/T_RT). These lasers have been demonstrated as gyroscopes, sensors of displacement (≪ 0.01 Å), changes of index (Δn << 10⁻⁹), etc.... ¹Mode- locked operation is essential because (i) the pulses traverse the “sample” at different times and (ii) the phase coupling between the counter-rotating beams is totally eliminated.² Such sensors should ideally be compact, diode pumped solid state laser. Linear solid state lasers are routinely mode-locked.³ However, losses introduced by the increased number of intra-cavity elements—required in a ring configuration—favor Q-switched mode-locked (QSML) operation, a tendency exacerbated for bi-directionality.

© 2002 Optical Society of America