Relaxation oscillation suppression in continuous-wave intracavity optical parametric oscillators

Generating dual-wavelength VECSEL by selecting birefringence filter material and the application toward mid-infrared region via intracavity OPO

A method for realizing a synchronized watt-level dual-wavelength vertical-external-cavity surface-emitting-laser (VECSEL) by using a tilted birefringence filter (BRF) is demonstrated. It is verified that by selecting suitable BRF material with different refractive index differences between extraordinary wave and ordinary wave, the dual-wavelength emission with a free spectrum range from sub-THz to tens of THz can be achieved. The output characteristics of such a dual-wavelength VECSEL are thoroughly investigated including its wavelength tunability and power difference. Finally, the intracavity optical parametric oscillator is applied to efficiently convert the dual-wavelength laser toward the mid-infrared region. The gain competition and longitudinal mode hopping performances for the multi-wavelength mid-infrared output are explored.

Low-threshold dual-wavelength CW mid-IR laser from shared intracavity quasi-phase-matched OPO

A low-threshold continuous wave dual-wavelength mid-infrared laser is demonstrated by using an intracavity optical parametric oscillator (OPO) with a dual-wavelength pump wave. To realize a high-quality dual-wavelength pump wave, a composite Nd:YVO₄/Nd:GdVO₄ gain medium is applied for a linear polarized state and synchronization output. With the quasi-phase-matching OPO process, it is found that the dual-wavelength pump wave shares equal signal wave oscillation and leads to a lower OPO threshold. Finally, a diode threshold pumped power of barely 2 W can be achieved for the balanced intensity dual-wavelength watt-level mid-IR laser.

Suppression of relaxation-oscillations in intra-cavity optical parametric oscillators by two-photon absorption

The applications of continuous-wave (cw), intra-cavity optical parametric oscillators (ICOPO) in molecular sensing and spectroscopy have been hampered by their relaxation-oscillation and power-stability problems. To solve these problems, we propose a two-photon-absorption (TPA) mechanism into ICOPOs. In a proof-of-principle experiment, we inserted a CdTe plate into an ICOPO as a TPA medium and demonstrated efficient suppression of relaxation-oscillations, obtaining an intensity-noise reduction of over 70 dB at the relaxation-oscillation frequency. To the best of our knowledge, this is the first demonstration of relaxation-oscillation suppression in ICOPOs based on TPA.

Widely tunable, continuous-wave, intra-cavity optical parametric oscillator based on an Yb-doped fiber laser

We report an optical parametric oscillator (OPO) intra-cavity pumped by an Yb-doped fiber laser. In comparison to an intra-cavity OPO based on a solid-state laser gain medium, the benefits of using a fiber-based scheme include a superior beam quality of the generated mid-infrared idler light at high power levels, a more efficient process of nonlinear frequency conversion, and the prospect of scaling to higher power. In a preliminary experiment, we obtained a slope efficiency of the down-converted power of as high as 66% with respect to the absorbed laser diode power. To the best of our knowledge, this is the first demonstration of an intra-cavity OPO based on a fiber laser.

Continuous-wave, singly-resonant, intracavity optical parametric oscillator based on a single-mode-laser-diode-pumped Yb:KYW laser

We report a continuous-wave (cw), intracavity, singly resonant optical parametric oscillator (ICSRO) based on an Yb:KYW laser pumped by a single-mode laser diode (LD). Pumping the ICSRO by a low-noise single-mode LD, combined with the reduced heat generation due to the lower quantum defect of the Yb:KYW laser system, effectively eliminated the onset of relaxation oscillations, which have been a long-standing problem in previous multimode-LD-pumped ICSROs, and resulted in a cw ICSRO being operated free of relaxation oscillations. At an LD power of 515 mW, the generated idler power was 21 mW at ∼3500  nm. To the best of our knowledge, this is the first demonstration of a single-mode-LD-pumped ICSRO.

Relaxation oscillation suppressed, narrow linewidth, high beam quality, 1319 nm long-pulsed duration laser

We first report a 1319 nm long-pulsed duration laser with relaxation oscillation suppressed by placing lithium triborate crystals into the laser cavity. Two more etalons were added into the laser cavity to further increase the difference in cavity loss between oscillating and non-oscillating modes. With very little reduction in average output laser power, the smooth temporal profile laser pulse was obtained with a pulse duration of 150 μs. The average output power was 5.45 W, and the beam qualities Mx2 and My2 were 1.12 and 1.20.

Continuous-wave intra-cavity singly resonant optical parametric oscillator with resonant wave output coupling

We report herein the enhancement in both power and efficiency performance of a continuous-wave intra-cavity singly resonant optical parametric oscillator (ICSRO) by introducing finite resonant wave output coupling. While coupling out the resonant wave to useful output, the output coupling increases the SRO threshold properly thus suppresses the back-conversion under high pump power. Therefore, the down-conversion efficiency is maintained under high pump without having to raise the threshold by defocusing. With a T = 9.6% signal wave output coupler used, the SRO threshold is 2.46 W and the down-conversion efficiency is 72.9% under the maximum pump power of 21.4 W. 1.43 W idler power at 3.66 μm and 5.03 W signal power at 1.5 μm are obtained, corresponding to a total extraction efficiency of 30.2%. The resonant wave out coupling significantly levels up the upper limit for the power range where the ICSRO exhibits high efficiency, without impeding its advantage of low threshold.

Continuous-wave mid-infrared intra-cavity singly resonant PPLN-OPO under 880 nm in-band pumping

We report herein a continuous-wave mid-infrared intra-cavity singly resonant optical parametric oscillator (ICSRO) which is the first example of ICSRO that utilize in-band pumped Nd-doped vanadate laser as pump source. A 1064 nm Nd:YVO₄ laser in-band pumped by 880 nm LD and a periodically poled lithium niobate (PPLN) crystal are employed as the parent pump laser and the nonlinear medium, respectively. The idler output wavelength tuning range is 3.66-4.22 µm. A maximum output power of 1.54 W at 3.66 µm is obtained at absorbed pump power of 21.9 W, with corresponding optical efficiency being 7.0%. The control experiment of ICSRO under 808 nm traditional pumping is also carried out. The results show that in-band pumped ICSRO has better performance in terms of threshold, power scaling, efficiency and power stability than ICSRO traditionally pumped at 808 nm.