Solid-state Raman Laser Research Articles

Dual-wavelength solid-state Raman laser at 555 and 579.5 nm for spectrophotometric determination of carboxyhemoglobin

For accurate measurement of carboxyhemoglobin level in the blood, a compact dual-wavelength laser at 555 and 579.5 nm with conversion efficiency up to 27.5% is originally developed by using Nd:YVO4/KGW/LBO laser with intracavity stimulated Raman scattering (SRS), second harmonic generation (SHG), and sum frequency generation (SFG). The SRS material is an Np-cut KGW crystal to produce the Stokes wave at 1159 nm from the fundamental wave at 1064 nm. The SHG of the Stokes wave and the SFG of the Stokes and fundamental waves are efficiently achieved by employing two LBO crystals. The temperature of the first LBO crystal is steadily fixed at the optimal phase-matching for generating the output power at 579.5 nm, whereas the temperature of the second one is varied to manipulate the power ratio between the yellow and green emissions. At the balanced temperature of the second LBO crystal, the output powers of the yellow and green emissions can simultaneously reach 5.5 W at a pump power of 40 W.

LD end-pumped passively Q-switched Nd:YLF/SrWO4/Cr4+:YAG solid-state Raman lasers based on Raman modes of 923 cm−1 and 334.5 cm−1

LD end-pumped passively Q-switched Nd:YLF/SrWO4/Cr4+:YAG solid-state Raman lasers based on Raman modes of 923 cm−1 and 334.5 cm−1

Compact continuous-wave solid-state Raman lasers at 707 and 714 nm for laser trapping and cooling of atomic strontium and radium.

Two compact laser sources at 707 and 714 nm are realized efficiently by using a diode-pumped a-cut Nd:YVO4 laser with intracavity stimulated Raman scattering and sum-frequency generation (SFG). The fundamental wave at 1342 nm is generated by the 4F3/2 → 4I13/2 transition in Nd:YVO4 crystal. The Raman Stokes waves at 1496 and 1526 nm were obtained by placing the c-axis of the Nd:YVO4 crystal along the Ng and Nm axes of an Np-cut KGW crystal, respectively. LBO crystals with critical phase matching are used to perform the intracavity SFG of fundamental and Stokes waves. At a pump power of 36 W, the maximum output powers at 707 and 714 nm can reach 2.72 and 3.14 W, corresponding to light-to-light conversion efficiencies of 7.5% and 8.7%, respectively. The developed 707 and 714 nm laser sources are practically useful in laser trapping and cooling related to atomic strontium and radium.

Picosecond synchronously pumped diamond Raman laser

With diamond crystals as Raman media, picosecond synchronously pumped solid-state Raman laser is theoretically studied in detail for the first time. High efficient working point and effective pulse compression working point are investigated. For both 532 nm and 1064 nm pumping, high Raman conversion efficiency can be achieved for negative cavity length detuning (∆x) and diamond crystal length of 5 mm. The higher efficiency can be obtained with longer Raman crystal, longer pumping pulse width and higher pumping power. For 532 nm pumping, effective pulse width compression can be realized for ∆x = 0 nearby and diamond crystal length of 10 mm. Shorter pulse width and higher peak power of 1st Stokes laser can be achieved with longer Raman crystal, shorter pumping pulse width and higher pumping power. The findings can contribute to the design and optimization of picosecond synchronously pumped diamond Raman lasers.

Folded-resonator LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser

A folded cavity of LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser is designed. The effects of the thermal focal length and resonator length on the resonator modes are analyzed. The appropriate mode sizes at laser crystal and Raman crystal are designated to realize low SRS threshold, high conversion efficiency and high beam quality. The folded-resonator LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser is realized, and the 1st Stokes laser at 1180 nm with high output power, high single pulse energy and high beam quality is obtained. The maximum output power of the 1st Stokes laser at 1180 nm is 2.89 W, optical–optical efficiency is 4 %, the single pulse energy is 0.96 mJ, and the shortest pulse is 35.5 ns. By analyzing the output spectrum and beam quality, it is shown that the beam spatial profile mode is well distributed, and the experimental results verify the rationality of the cavity mode design.

Numerical simulation on picosecond synchronously pumped solid-state Raman laser based on KGW crystal

Numerical simulation on picosecond synchronously pumped solid-state Raman laser based on KGW crystal

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.

Cascaded vector vortex mode generation from a solid-state Raman laser

Cascaded vector vortex mode generation from a Ba(NO3)2 Raman laser cavity pumped by a vector LG0,2 green laser was demonstrated for the first time to our knowledge. The generated Stokes outputs exhibited a second-order vector vortex beam as evidenced by linearly polarized flower-shaped spatial forms with four petals. The achieved optical conversion efficiencies of the first, second, and third Stokes outputs were 6.59%, 4.22%, and 0.11%, respectively, at a maximum pump energy of 3.6 mJ (360 mW).

Investigation of high-energy extracavity Raman laser oscillator and single-pass Raman generator based on potassium gadolinium tungstate (KGW) crystal

Herein, a high-energy all-solid-state extracavity Raman oscillator and a high-energy single-pass Raman generator based on potassium gadolinium tungstate (KGW) crystal are theoretically and experimentally investigated. First, a high-energy 1064 nm nanosecond laser system with a maximum output energy of 7.03 J at a repetition rate of 1 Hz is built as the pumping source for stimulated Raman scattering (SRS). Then, the output spectra and energy of multiorder Stokes lasers from 1.16 to 1.49 μm are gradually detected as the 1064 nm pumping laser energy increases for both Raman laser structures. For the extracavity Raman oscillator, under a pumping energy of 1.8 J, three-order Stokes lasers with a maximum energy of 448 mJ are obtained when the electric field direction of the pumping laser is parallel to the Ng optical axis of the KGW crystal (E∥Ng). Moreover, to obtain a higher output of the Raman laser without damaging the cavity mirrors, a single-pass Raman generator is studied for comparison purposes. As the 1064 nm pumping laser energy of 2.8 J is injected, the measured maximum output energy of a two-order Stokes laser is ~ 676 mJ for the E∥Ng condition; this is the highest Stokes energy output of the nanosecond solid-state Raman lasers to the best of our knowledge.

Statistics of pulse enrgy fluctuations in a solid-state Raman laser

In this paper, we present the results of the study of the statistics of pulse energy fluctuations in a Raman laser under optical pump by the multimode nanosecond pulses. A system of coupled differential equations for slowly varying envelopes of the pump field and first three Stokes lines was integrated numerically with taking into account spatial inhomogeneity of the pump beam, spontaneous noise, and optical feedback. Data of the numerical simulation revealed a sharp increase in the fluctuation amplitude in the nonlinear regime of Raman frequency conversion when the optical length of the Raman cavity was matched with the cavity length of the multimode pump laser. At a mean 1st Stokes conversion efficiency of 3.5–3.8 %, the calculations showed an increase in the coefficient of variation (CV) of a random value from 9 % to 118 %. In the linear regime of Raman frequency conversion, when the conversion efficiency was 0.2–0.03 %, a further increase in the CV value up to 270–500 % was predicted. It is also numerically shown that the fluctuation statistics under the conditions of the cavity length matching is essentially non-Gaussian and described by the L-type probability density distributions (PDDs) with long tails and maxima located near zero. The numerical data were quantitatively confirmed by an experiment for a Raman laser on a barium nitrate crystal operated near the Raman threshold, when the 1st Stokes conversion efficiency did not exceed 0.3 %. A Raman cavity was formed by two flat mirrors providing a double-pass pump configuration. The Raman laser was excited by the linearly polarized frequency-doubled radiation of a Q-switched Nd:YAG laser generating multimode pulses with a duration of 7–8 ns. A Raman laser operating regime characterized by the hyperexponential PDDs with CVs reaching 480 %, which is 2–2.5 times higher than those observed earlier for the single-pass conditions of stimulated Raman scattering, was realized.

Cascaded Stokes polarization conversion in cubic Raman crystals.

We describe a theoretical approach based on Müller and tensor calculus for predicting the polarization state and gain of cascaded Stokes orders produced under coherent Raman scattering regime conditions. The formulation follows a Markovian-style implementation for F2g-type modes in Raman cubic crystals. The theoretical model is supported by experimental results that corroborate that the polarization and power of the cascaded Stokes orders can be effectively predicted using sequential calculus. We extend these results to a variety of crystal propagation directions, with the aim of facilitating the design of advanced solid-state Raman lasers.

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.

Recent progress on narrow-linewidth crystalline bulk Raman lasers

Narrow-linewidth, solid-state Raman lasers are of significant importance for numerous applications. In last decade, variety of methods have been utilized to suppress the spectral linewidth of Raman laser output. In this review we summarize the recent works of narrow-linewidth and/or single-frequency solid-state Raman lasers. The mechanisms and results are addressed while the positive and negative aspects of each technique are also discussed to give the readers a reference to choose a proper narrow-linewidth method for certain applications.

On Sagnac frequency splitting in a solid-state ring Raman laser.

We report on an accurate measurement of the frequency splitting of an optical rotating ring microcavity made out of calcium fluoride. By measuring the frequencies of the clockwise and counter-clockwise coherent Raman emissions confined in the cavity modes, we show that the frequency splitting is inversely proportional to the refractive index of the cavity host material. The measurement has an accuracy of 1% and unambiguously confirms the classical theoretical prediction based on special theory of relativity. This Letter also demonstrates the usefulness of the ring Raman microlaser for rotation measurements.

Characterization of ZnWO_4 Raman crystal

Stimulated Raman scattering (SRS) is an important technique for broadening the laser spectra. The Raman crystals with large dimensions and high thermal conductivity are favorable by SRS. Zinc tungstate (ZnWO4) belonging to a monoclinic system has been grown by the Czochralski method with the dimensions of Φ 35 mm × 70 mm. The thermal properties were evaluated and analyzed in several aspects, including the density, specific heat, thermal expansion coefficient, and thermal conductivity. Thermal conductivity was calculated to be 5.412 Wm−1K−1 along the c-axis, which is about two times larger than the famous BaWO4 and SrWO4. Meanwhile, the optical properties including transmission and Raman spectra and Raman shift were measured and the stimulated Raman scattering performance of ZnWO4 crystal was demonstrated. The results show that the thermal conductivity decreases with increasing temperature. Furthermore, the thermal focal lengths were theoretically estimated. Along the a direction, the light with a wavelength of 532 nm can be shifted to the light at 558.95 nm, which is in good accordance with the spontaneous Raman spectrum. All the analyses and results above show that ZnWO4 is a promising solid-state Raman laser crystal.

Optimization of an intracavity Q-switched solid-state second order Raman laser

In this paper, the model of an intracavity Q-switched second order Raman laser is established, the characteristics of the output 2nd Stokes are simulated. The dynamic balance mechanism among intracavity conversion rates of stimulated emission, first order Raman and second order Raman is obtained. Finally, optimization solutions for increasing output 2nd Stokes pulse energy are proposed.

Fresnoite Ba2TiSi2O8: A novel stimulated Raman scattering active crystal

Large Ba2TiSi2O8 crystals were successfully grown by the Czochralski technique. The stimulated Raman scattering properties of the Ba2TiSi2O8 crystals were investigated for the first time, and the first (558 nm) and second (587 nm) Stokes lines were generated in an ultracavity single-pass configuration excited by 532 nm picosecond pulses. The output energy and conversion efficiency of the scattering process as functions of pump energy were studied, and the highest conversion efficiency was found to be 31.8%. The experiments indicate that Ba2TiSi2O8 is a novel active crystal suitable for solid-state Raman laser applications.

Controllable continuous-wave Nd:YVO₄ self-Raman lasers using intracavity adaptive optics.

A controllable self-Raman laser using an adaptive optics (AO)-based control loop featuring an intracavity deformable mirror is reported. This method has the potential to alleviate thermal lensing within the Raman and laser gain media, and enable solid-state Raman lasers to reach new power levels. A proof-of-concept experiment using a Nd:YVO4 self-Raman laser and resulting in 18% enhancement of the first Stokes output power is reported. Moreover, wavelength selection between two Raman laser outputs (λ=1109 and 1176 nm) emanating from the 379 and 893 cm(-1) Raman shifts of YVO4, respectively, was achieved using this AO technique.

Diamond Raman laser with continuously tunable output from 3.38 to 3.80 μm.

We report a pulsed mid-infrared diamond Raman laser with output tuned from 3.38 to 3.80 μm through varying the optical parametric oscillator (OPO) pump wavelength. To our knowledge this is the longest reported wavelength from a solid-state Raman laser. We generated up to 80 μJ with good beam quality and 22% quantum conversion efficiency. Whilst the conversion process itself is efficient, approximately 40% of the generated Stokes light is lost to multiphonon absorption. By introducing a secondary pump beam at the anti-Stokes wavelength to initiate a seed at the Stokes wavelength through Raman resonant four-wave mixing, the laser threshold was reduced by approximately half, and the maximum output increased by 44% to 115 μJ.

Theoretical and experimental study on passively Q-switched intracavity frequency-doubled solid-state yellow Raman lasers

Normalized space-dependent rate equations of passively Q-switched intracavity frequency-doubled Raman lasers are deduced for the first time. The normalized rate equations are solved numerically to investigate the influences of the normalized variables on the yellow laser performance. The LD end-pumped passively Q-switched Nd:YAG/SrWO(4)/KTP/Cr:YAG yellow Raman laser is realized, and the maximum yellow laser output power is 350 mW with the incident pump power of 5.9 W with Cr:YAG of 85% initial transmission. The theoretical analysis and optimization are taken out for the experiment, and the theoretical results are in accordance with the experimental ones.