Power spectral characteristic of a microchip Nd:YAG laser subjected to frequency-shifted optical feedback

Abstract

We systematically investigated the power spectrum of a Nd:YAG laser with external frequency-shifted feedback and identified three factors dominating the spectrum, namely, the feedback level, the pumping level of the laser diode (LD), and the shifted frequency introduced in the external cavity. For very weak feedback, the laser power spectrum presents two peaks at frequencies of and ω r , which are the shifted frequency and relaxation oscillation frequency, respectively. When the feedback level is increased to an intermediate level, the laser presents a series of nonlinear effects to cause harmonic and parametric oscillation; for strong feedback, only harmonic peaks are observed in the spectrum. The impact of the pumping levels and the amount of frequency shifting are also experimentally investigated. Especially, even at a weak feedback level, when the frequency approaches ω r , strong nonlinear effects still appear in laser dynamics to make the laser power present only harmonic oscillation. A theoretical analysis is provided which agrees well with the experimental results.

Nonlinear modification of the laser noise power spectrum induced by frequency-shifted optical feedback

“…10 17 times weaker than the laser intra-cavity power) has been detected [6]. When the optical feedback becomes stronger, nonlinearities appear in the laser dynamics [15,16]. They can cause the apparition of chaos, bi-stability and hysteresis phenomenon with the tuning (back and forth) of the frequency shift of the optical feedback [17].…”

“…where I and N are respectively the laser intensity (photon unit) and the population inversion (atom unit In the presence of a strong optical feedback, the laser intrinsic dynamics and in particular the relaxation oscillation frequency is modified and will depend on the modulation conditions ( to induce non-linear dynamical behaviors (which give rise to the generation of harmonic and parametric dynamical frequencies) in the laser output power modulation [13,15,16]. In contrast, the "weak feedback" regime corresponds to the situation where the modulation frequency is far away from the By comparison with the work made in [15,16], which is focused on the study of the signal power spectrum, the present work analyzes how the noise power spectrum of the laser is modified…”

“…In contrast, the "weak feedback" regime corresponds to the situation where the modulation frequency is far away from the By comparison with the work made in [15,16], which is focused on the study of the signal power spectrum, the present work analyzes how the noise power spectrum of the laser is modified…”

Response of microchip solid-state laser to external frequency-shifted feedback and its applications

“…For weak feedback, when both the frequency-shifted lights at Ω and Ω/2 are reflected/scattered back into the laser resonator, the laser output is modulated at two frequencies separately as follows: where ΔI is the laser intensity modulation; κ is the feedback level; G(Ω) is a frequency-dependent gain amplification factor1215161718 that reaches its maximum γ c /γ 1 when Ω approaches f R ; Ω = 80 kHz is the frequency shifting; ϕ is the phase of the light carrying the information of the measured targets; and φ 0 is the fixed initial phase. The subscript symbols m and r represent the measurement and reference arms, respectively.…”

“…We have previously reported on the frequency characteristics of an Nd:YAG laser subjected to frequency-shifted feedback18. Only the frequency distribution in the low frequency region (i.e., in the frequency range around the laser's own relaxation oscillation frequency) was observed, and laser intensity information was not collected.…”