Compact efficient high-power triple-color Nd:YVO4 yellow-lime-green self-Raman lasers

Multiphonon-coupling yellow laser in Yb:La2CaB10O19 crystal

Yellow lasers at 590 nm have many extensive applications in our daily life, but extremely difficult to attain by traditional solid-state laser technology, owing to the absence of highly-efficient transition channels at this spectral range. In this work, we proposed a cooperative lasing mechanism to obtain the yellow light emission, with multiphonon-assisted electronic transitions and phase-matched frequency-doubling. Based on the predictable configurational coordinate model, we can calculate the multiphonon-assisted emission step-by-step. Using Yb3+-doped La2CaB10O19 crystal as an example, it is capable of producing yellow laser at 581-590 nm, with a maximum output power of 4.83 W and a high slope efficiency of 31.6%. To the best of our knowledge, it represents the highest power of solid-state yellow laser realized in one single crystal pumped by a laser diode. This power scaling can be assigned to the amplified phonon-assisted emission beyond the fluorescence spectrum, and optimized crystal angle for phase-matching condition. Such a compact, low-cost, and high-power laser device, provides an alternative candidate for the spectral "yellow-gap" where no practical solid-state laser exists at present.

Compact efficient high-power continuous-wave Nd:YVO4/KGW/LBO Raman lasers for selectable wavelengths within 559-603 nm

Compact efficient high-power continuous-wave Nd:YVO4 Raman lasers for selectable wavelengths within 559-603 nm are achieved by using KGW crystal for intracavity stimulated Raman scattering (SRS) and lithium triborate (LBO) crystal for intracavity sum frequency generation (SFG) and second harmonic generation (SHG). The LBO crystal with the cut angle in the XY plane for the type-I phase matching is used to perform intracavity SHG or SFG. Experimental results reveal that the participated Stokes lines include the internal vibration mode at 901 cm-1, the external vibrational mode at 209 cm-1, and the combination mode of the 901 cm-1 and 209 cm-1 Raman shifts. By tuning LBO temperature for attaining the maximum output power, the output spectrum reveals the triple peaks of 588.7, 595.7, and 603.1 nm with the intensity ratio of 10:4:1. Under this circumstance, the output power can reach the highest value of 10.8 W at a pump power of 40 W. Furthermore, the output spectrum can be simply concentrated on the single peaks among 588.7 (orange), 565.7 (yellow), and 559.1 nm (lime) by tuning LBO temperature to fulfill the selection of the critical phase matching. The output powers at a pump power of 40 W can be up to 8.0, 6.1, and 9.8 W for the single-peak emission at 588.7, 565.7, and 559.1 nm, respectively. Finally, a dual-peak emission of 565.7 and 572.3 nm with total output power of 5.2 W can be generated by tuning LBO temperature to match the SFG for 572.3 nm.

Highly efficient continuous-wave solid-state Raman crystal lasers at 555 and 559 nm

High-power efficient continuous-wave Nd:YVO4/KGW Raman lasers at 555 and 559 nm are achieved by using a double-sided dichroic coating output coupler to improve the resonance quality factor. The Np-cut potassium gadolinium tungstate (KGW) is used to generate the Stokes waves at 1159 and 1177 nm by placing the polarization of the1064 nm fundamental wave parallel to the Ng and Nm axes, respectively. The lithium triborate (LBO) crystal with the cut angle in the XY plane for the type-I phase matching is used to perform the intracavity sum frequency generation for yielding the green light at 555 nm and the lime light at 559 nm at the optimal phase matching temperature. Experimental results were systematically accomplished to comprehend the optimal cavity length for the conversion efficiency. Under the optimal cavity length, the output powers can reach 6.6 and 6.3 W at a pump power of 22 W for the wavelengths of 555 and 559 nm, respectively. The conversion efficiencies can be up to 30% and 28.6% for 555 and 559 nm, respectively.

Intracavity frequency-doubled yellow laser in an electron-phonon-coupled Nd:YVO4 crystal

An approach to obtain a yellow laser is demonstrated for the first time to our knowledge by the employment of an Nd3+-doped YVO4 crystal and a LBO frequency-doubling crystal. Differing from the previous stimulated self-Raman radiation of Nd:YVO4, a direct 1176 nm lasing, without a high-intensity intracavity 1064 nm laser, was realized by utilizing an electron-phonon coupling effect and amplifying the thermally activated vibronic transitions. Combining with intracavity frequency-doubling, a yellow laser at 588 nm was obtained. At the pump power of 14.3 W, the output power of the yellow laser was 1.17 W, corresponding to a diode-to-visible efficiency of 8.2%. Moreover, for the first time, the yellow laser at 584 nm with output power of 164 mW was realized by tuning the filter, indicating the great potential of such an electron-phonon coupling laser for a wavelength extension in the yellow regime.

Generating multiple optical vortices in orange beams induced by selectively pumped frequency-doubled solid-state Raman lasers with mode conversion

We employ a selectively pumped solid-state laser with stimulated Raman scattering and second-harmonic generation to generate frequency-doubled lasing modes (FDLMs) at 588 nm. The FDLMs are transformed by using an external cylindrical mode converter to generate various structured beams with multiple optical vortices. Theoretical analyses clearly reveal the relationship between the mode components in the laser emission and the transverse displacement of the off-center pumping. We further verify that the experimental results for the transformed FDLMs can be numerically reconstructed with a theoretical model. By analyzing the phase structures of the converted beams, it can be demonstrated that the number of vortices rises from 2 to 19 with increasing off-center displacement.

Powerful Q-switched Raman laser at 589 nm with a repetition rate between 200 and 500 kHz

We demonstrate a highly powerful acousto-optically Q-switched Nd:YVO₄ yellow laser at 589 nm by using a N_p-cut KGW crystal and a phase-matching lithium triborate crystal to performance the intracavity stimulated Raman scattering and second-harmonic generation, respectively. We experimentally verify that the design of the separate cavity is superior to the conventional design of the shared cavity. By using the separate cavity, the optical-to-optical efficiency can be generally higher than 32% for the repetition rate within 200-500 kHz. The maximum output power at 589 nm can be up to 15.1 W at an incident pump power of 40 W and a repetition rate of 400 kHz.

Highly efficient solid-state Raman yellow-orange lasers created by enhancing the cavity reflectivity

A new, to the best of our knowledge, output coupler (OC) with enhancement of the cavity reflectivity is proposed to remarkably elevate the output powers and efficiencies of diode-pumped Nd:GdVO₄/KGW Raman yellow-orange lasers. The cavity reflectivity is effectively increased by using the double-sided dichroic coating on the OC. In comparison with the conventional single-sided coating, the conversion efficiency can be boosted from 15% to 26.3% in the experiment of a yellow laser at 578.8 nm, and the maximum output power can be increased from 5.7 to 10.5 W in the quasi-continuous-wave mode with 50% duty cycle and frequency of 500 Hz. Furthermore, in the operation of an orange laser at 588 nm, the maximum output power can be improved from 5.6 to 7.0 W by replacing the conventional OC with the new one.

Multifunctional Optical Crystals for All-Solid-State Raman Lasers

In the past few decades, the multifunctional optical crystals for all-solid-state Raman lasers have been widely studied by many scholars due to their compactness, convenience and excellent performance. In this review, we briefly show two kinds of multifunctional Raman crystals: self-Raman (laser and Raman effects) crystals and self-frequency-doubled Raman (frequency-doubling and Raman effects) crystals. We firstly introduce the properties of the self-Raman laser crystals, including vanadate, tungstate, molybdate and silicate doped with rare earth ions, as well as self-frequency-doubled Raman crystals, including KTiOAsO4 (KTA) and BaTeMo2O9 (BTM). Additionally, the domestic and international progress in research on multifunctional Raman crystals is summarized in the continuous wave, passively Q-switched, actively Q-switched and mode-locked regimes. Finally, we present the bottleneck in multifunctional Raman crystals and the outlook for future development. Through this review, we contribute to a general understanding of multifunctional Raman crystals.

Numerical analysis of synchronously pumped solid-state Raman lasers

Considering the spatial distribution of laser beams and phonon waves, the SRS coupling wave equations in the transient regime are derived and normalized for the first time. The synchronously pumped solid-state Raman laser is simulated numerically to investigate the influences of the cavity length detuning, output coupling rate, dispersion, Raman gain and dephasing time of Raman mode on laser performances. It is found that the intensive pulse compression of first Stokes laser in synchronously pumped solid-state Raman laser stems from pulse width gain narrowing and intensity oscillation effects. The cavity length detuning, dispersion, Raman gain and dephasing time considerably affect the pulse width gain narrowing and intensity oscillation processes. The theoretical results can help the design and optimization of synchronously pumped solid-state Raman laser to generate ultrafast Raman laser output efficiently.

High-power diode-pumped Nd:GdVO4/KGW Raman laser at 578 nm

A diode-pumped neodymium-doped gadolinium vanadate (Nd:GdVO₄) laser is developed as a compact efficient yellow light at 578 nm by means of intracavity stimulated Raman scattering (SRS) in a potassium gadolinium tungstate (KGW) crystal and the second-harmonic generation in a lithium triborate crystal. The SRS process with a shift of 768cm^-1 is achieved by setting the polarization of the fundamental wave along the N_g axis of the KGW crystal. The self-Raman effect arising from the Nd:GdVO₄ crystal is systematically explored by employing two kinds of coating specification for the output coupler. With a specific coating on the output coupler to suppress the self-Raman effect, the maximum output power at 578 nm can reach 3.1 W at a pump power of 32 W. Moreover, two different lengths for the Nd:GdVO₄ crystal are individually used to verify the influence of the self-Raman effect on the lasing efficiency.

Efficient solid-state Raman yellow laser at 579.5 nm

A highly efficient diode-pumped Nd:YVO₄/KGW Raman yellow laser is developed to produce a 6.8 W yellow light at 579.5 nm accompanied by a 3.2 W Stokes wave at 1159 nm under an incident pump power of 30 W. The intracavity stimulated Raman scattering with the shift of 768cm^-1 is generated by setting the polarization of the fundamental wave along the N_g direction of an N_p-cut KGW crystal. The Nd:YVO₄ gain medium is coated as a cavity mirror to reduce the cavity losses for the fundamental wave. More importantly, the KGW crystal is specially coated to prevent the Stokes wave from propagating through the gain medium to minimize the cavity losses for the Stokes wave.