Raman Crystal Research Articles

Compact actively Q-switched Nd:YVO4/YVO4 Raman laser at 1525 nm with frequency up to 150 kHz.

We develop a compact high-frequency actively Q-switched Nd:YVO4/YVO4 Raman laser at 1525 nm. The mode size stability and the mode overlapping are numerically analyzed to craft the resonator. Experimental results reveal that the compact cavity and the cavity dumping effect lead to the considerable narrowing of the pulse width. In addition, the quality factor of the cavity is significantly strengthened by using the YVO4 Raman crystal with a dichroic coating to minimize the scattering and absorption losses for the Stokes wave. Furthermore, we investigate the influence of the gate-on time of the Q-switcher on the output performance. Under the optimal condition, the average output power can be generally greater than 4.2 W at the pump power of 26 W for the repetition rate within 50-150 kHz, and the corresponding optical efficiency higher than 16.1%. The maximum peak powers can reach 53 kW and 25 kW for the repetition rates of 50 kHz and 100 kHz, respectively.

Sub-megahertz compact self-pulsed Raman laser

Broadband self-pulsed Raman laser operating at sub-megahertz (sub-MHz) has been widely used in optical sensing, high-spectral-resolution lidar, frequency-division multiplexing, and optical communication. However, it is a big challenge for achieving stable self-pulsed Raman laser oscillation in a wide pump power range. Here, we construct a compact Yb:YAG/YVO4 Raman laser for generating broadband self-pulsed laser operating at high repetition rate. The effects of cavity length (LC) and Raman crystal length (LR) on the performance of self-pulsed Raman laser have been investigated. By utilizing a 1.5 mm-thick YVO4 crystal as a Raman crystal, the repetition rate increases dramatically from 62 to 280 kHz when the LC decreases from 10 to 4 mm. Meanwhile, the pulse width of 0.66 μs and peak power of 1.1 W are achieved for the self-pulsed Raman laser with LC = 4 mm. For the 4 mm-long Raman laser cavity constructed with a 2 mm-thick YVO4 crystal, the pump power range enable for self-pulsed Raman laser oscillation extends from 1.8 to 3.9 W, the repetition rate has been further increased from 258 to 467 kHz. While the peak power and pulse width are 0.6 W and 0.98 μs, respectively. The Yb:YAG/YVO4 self-pulsed Raman laser oscillates in broadband multi-longitudinal-mode, the spectral bandwidth is 27.4 nm covering from 1051.1 to 1078.5 nm. Utilization of a tilted 2 mm-thick YVO4 crystal as output coupler to construct compact Yb:YAG/YVO4 self-pulsed Raman laser dramatically expands the pump power range for generating high repetition rate self-pulsed Raman laser. Sub-MHz self-pulsed Raman lasers with a wide spectral bandwidth have potential applications in materials processing, quantum information processing, and optical communications.

Palladium(II) and Platinum(II) Bis(Stibinidene) Complexes with Intramolecular Hydrogen-Bond Enforced Geometries.

The coordination capability of two N,C,N pincer coordinated stibinidenes, i. e. bis(imino)- [2,6-(DippN=CH)2C6H3]Sb (1) or imino-amino- [2-(DippN=CH)-6-(DippNHCH2)C6H3]Sb (2) toward palladium(II) and platinum(II) centers was examined. In the course of this study, seven new square-planar bis(stibinidene) complexes were synthesized and characterized by NMR, IR, Raman, UV-vis spectroscopy and single crystal (sc)-X-ray diffraction analysis. In all cases, both stibinidene ligands 1 or 2 adopt trans positions, but differ significantly in the torsion angle describing mutual orientation of aromatic rings of the stibinidenes along the Sb-Pd/Pt-Sb axes. Furthermore, majority of complexes form isomers in solution most probably due to a hindered rotation around Sb-Pd/Pt bonds caused by bulkiness of 1 and 2. This phenomenon also seems to be influenced by the absence/presence of a pendant -CH2NH- group in 1/2 that is able to form intramolecular hydrogen bonds with the adjacent chlorine atom(s) attached to the metal centers. The whole problem was subjected to a theoretical study focusing on the role of hydrogen bonds in structure architecture of the complexes. To describe the UV-vis spectra of these highly coloured complexes, TD-DFT calculations were employed. These outline differences between the stibinidene ligands, the transition metals as well as between the charge of the complexes (neutral or anionic).

Competition between nonlinear processes excited by picosecond laser pulses in a disodium ditungstate Raman crystal for two excitation polarizations

Two nonlinear processes, namely, two-photon absorption (TPA) and stimulated Raman scattering (SRS) in Na2W2O7 crystal at a wavelength of 523.5 nm, are studied theoretically and experimentally depending on the polarization of the incident picosecond laser radiation. It was found that, due to the anisotropy of the band gap structure, the TPA coefficient at 523.5 nm strongly depends on the pump radiation polarization. For radiation along the c axis with polarization parallel to the a axis, the TPA coefficient was measured to be 1.28 cm GW−1, and no SRS process was registered. However, for polarization parallel to the b axis, no measurable TPA was detected and SRS with a gain of 6.5 cm GW−1 was observed. To the best of our knowledge, this is the first demonstration of the competition of two nonlinear processes in one crystal depending on its orientation.

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.

Self‐Frequency‐Mixing Raman Laser Based on RbTiOPO4

AbstractIn this work, the generation of yellow laser emission from a self‐frequency‐mixing Raman laser utilizing RbTiOPO4 (RTP) is reported. The RTP crystal is positioned within the cavity of a Nd:YAG/Cr4+:YAG composite, passively Q‐switched laser. By utilizing this intracavity configuration, Raman conversion of the fundamental laser wavelength to Stokes wavelengths and frequency mixing of these near‐infrared wavelengths to the visible wavelength range is achieved using a single RTP crystal. Multiple visible wavelengths are generated, with a primary line at 574.3 nm and additional weaker lines at 552.3 and 563.9 nm. An average output power of 180 mW is measured from the output coupler end of the laser setup (note that laser emission in the visible wavelength range is also generated toward the input end of the laser cavity) for an incident pump power of 11.4 W. The results demonstrate the potential of RTP as a self‐frequency‐mixing, Raman crystal, which may be used for the development of efficient and compact yellow lasers.

Continuous wave dual-wavelength Nd:YVO4 laser at 1342 and 1525 nm for generating a 714-nm emission

Continuous wave dual-wavelength lasers at 1342 and 1525 nm are developed by using separate Nd:YVO4 and YVO4 crystals to form compactly coupled cavities for fundamental and Raman waves, respectively. The design of the coupled cavity not only reduces the thermal lensing effect in the Nd:YVO4 crystal, but also improves the stimulated Raman scattering (SRS) efficiency in the undoped YVO4 crystal. In addition, the Raman crystal is coated to form a highly reflective mirror to minimize cavity losses. By using a plano-concave cavity with a pump power of 40 W, the output powers of the fundamental and Raman waves are 470 mW and 310 mW, respectively. Changed to a concave cavity, the output powers of fundamental and Raman waves are 220 mW and 510 mW, respectively. Basis on the dual-wavelength operation, the maximum output power at 714 nm can reach 2.0 W via the sum frequency generation. A light source at 714 nm can be used for laser spectroscopy of atomic and ionic radium isotopes.

High-order stimulated Raman scattering in KGd(WO4)2 employing aperture

An approach that employs the aperture in front of the Raman crystal for the generation of high-order stimulated Raman scattering (SRS) was proposed. Furthermore, first- to fifth-order anti-Stokes components (508, 486, 465, 447, and 430 nm) and first- to fifth-order Stokes components (559, 588, 621, 658, and 700 nm) were generated by a potassium gadolinium tungstate (KGW) Raman generator, which were the highest-order SRS generated in KGW. The effect of the aperture was discussed, and the angular dependence of Stokes was calculated theoretically and experimentally.

Design, growth, and characterization of Y2Mo4O15 crystals for Raman laser applications.

A new crystal Y2Mo4O15 with dimensions of 14 × 12 × 5 mm3 was successfully grown via a top-seeded solution growth (TSSG) method. The crystal structure shows that Y2Mo4O15 crystallizes in the monoclinic space group P21/c (No. 14, a = 6.8110(4) Å, b = 9.5833(6) Å, c = 10.5124(7) Å, β = 105.512(7)°, and Z = 2) with Mo4O15 and YO7 polyhedra as basic structural units. Optical transmittance spectra of the Y2Mo4O15 crystal exhibited a broad transmission range from 345 nm to 5575 nm. The group theory calculation and spontaneous Raman spectra show that the Y2Mo4O15 crystal has 63 IR-active modes (32Au + 31Bu) and 60 Raman-active modes (30Ag + 30Bg). The strongest Raman shift is located at 953 cm−1 caused by the asymmetric stretching vibrations of the Mo–O bonds. The spontaneous Raman spectra and the possibility of rare-earth doping to the Y2Mo4O15 crystal indicate the Y2Mo4O15 crystal to be a promising Raman and self-Raman crystal.

Second-harmonic generation of Nd:YAlO3/YVO4 Raman laser optimization for orange emission

The orange emission at 597 nm produced by the second-harmonic generation of an acousto-optic Q-switched Raman laser was reported. A diode-pumped Nd:YAlO3 laser emitting at 1080 nm was employed to intra-cavity drive the pure YVO4 Raman crystal to obtain the first-Stokes wavelength at 1195 nm. The second-harmonic optimization of the first-Stokes laser is compared between the coupled cavity and the shared cavity. The results show that the shared cavity has more advantages than the coupled cavity for its better mode matching between fundamental cavity and Raman cavity at higher power. At an absorbed pump power of 5.96 W and the pulse repetition frequency of 15 kHz, average output power of 587 mW and conversion efficiency of 9.8% were obtained for the orange emission at 597 nm in the Nd:YAlO3/YVO4/LBO laser system. The 597 nm laser has special application in the fields as polymer materials analysis and biomedical optics.

BaGeO3: A Mid-IR Transparent Crystal with Superstrong Raman Response.

Stimulated Raman scattering processes based on Raman crystals offer a simple and effective method to generate mid-IR lasers. However, currently available mid-IR Raman crystals are extremely scarce. Herein, a new type of mid-IR Raman crystal, BaGeO3, is reported. It crystallizes in the monoclinic space group C2/c with Ba2+ cations and [Ge3O9]6- rings as basic building units and features high transparency from 2.5 to 5.5 μm and a Raman response larger than that of diamond. The BaGeO3 crystal has 45 IR-active modes (22Au + 23Bu) and 42 Raman-active modes (20Ag + 22Bg). The wide mid-IR transparent window is attributed to the low phonon energy of the second-order IR-active Au ⊗ Bg mode. The strongest Raman band, located at 799 cm-1, arises from the symmetrically stretching vibration of the [Ge3O9]6- extra-ring Ge-O bonds. The findings provide new insights into the crystallographic and Raman spectroscopic characteristics of high-performance mid-IR Raman crystals.

皮秒多脉冲泵浦KGW红外多波长拉曼激光器

Picosecond infrared multi-wavelength Raman laser which adopted multi-pulse pumped KGW crystal was reported. A mathematical model was developed to investigate the effect of multi-pulse burst pumping regime on the vibrational mode of the Raman active molecule. The simulated results show that the response oscillation of the Raman active molecule to the multi-pulse burst pumping regime is more active and durable compared with the traditional single pulse pumping regime, which promotes the weakened molecule oscillation to return the natural frequency multiple times. The enhancement effect is beneficial to improve the Raman gain, reduce the Raman threshold, and increase the Raman conversion efficiency. During the experiment of picosecond multi-pulse pump KGW Raman crystal, the three-pulse burst pumping regime improves the Raman gain more than two times, reduces the threshold of stimulated Raman scattering more than 50%, and increases the Raman conversion efficiency more than 16% for 768 cm–1 Raman mode and 22% for 901 cm–1 Raman mode. Based on the three-pulse burst pumping regime, a 1 kHz mJ-level picosecond infrared multi-wavelength Raman laser was designed, which achieved the pulse energy of 1.39 mJ, the maximum Raman conversion efficiency of 29.6% for the 768 cm–1 vibrational mode of KGW, and the pulse energy of 1.38 mJ, the maximum Raman conversion efficiency of 25.7% for the 901 cm–1 vibrational mode of KGW. In addition, the Raman laser can radiate up to eight infrared Raman lines simultaneously for both the two vibrational modes of the KGW crystal, which covers the range of 800–1 700 nm.

Raman Spectra of Quartz and Pb4+-Doped SiO2 Crystals at Different Temperature and Pressure

In order to seek for new Raman crystals, the manuscript presented the discussion on the Raman frequency of α-quartz, β-quartz, as well as Pb4+-doped SiO2 crystals at different temperature and pressure. The results demonstrated that as the pressure increased, the Raman lines shifted towards higher frequency for α-SiO2 crystal, while for β-SiO2 crystals, the main lines moved to lower frequency. Several new peaks were generated from the Pb4+-doped α-SiO2 crystals. The Pb4+-doped β-SiO2 crystals presented strong and ample Raman beams in the low-frequency range. The airfoil-shaped spectra appeared and broadened at high temperature and pressure. It could be inferred that the Pb4+-doped SiO2 crystals were excellent Raman crystal candidates.

1 kHz dual sub-pulse train picosecond radially polarized beam KGW Raman generator capable of achieving multiple optical communication wavelength

A dual sub-pulse train 1064 nm picosecond radially polarized beam pump KGW single-pass Raman generator was designed. The Stokes lines of both the 768 cm−1 and 901 cm−1 vibrational modes of the KGW Raman-active crystal were excited simultaneously. The Raman generator radiated up to seven Stokes lines in the infrared spectrum, which covered multiple optical communication channels. The overall Stokes average power reached 1.01 W, and the maximum Raman overall conversion efficiency was 23.1%. The interaction between the optical field and the Raman crystal was discussed from two perspectives of line width compression and beam quality.

Frequency expansion of orthogonally polarized dual-wavelength laser by cascaded stimulated Raman scattering.

In this Letter, the frequency expansion of an orthogonally polarized dual-wavelength laser, based on the cascaded stimulated Raman scattering, was demonstrated for the first time, to the best of our knowledge. The dual-wavelength fundamental laser generated from two separate Nd:YLF crystals was free of gain competition. Integrating the benefit of the two different orthogonally polarized Raman gain peaks in the KGd(WO4)2 (KGW) crystal, two sets of first-Stokes orthogonally polarized dual-wavelength Raman lasers were first achieved by rotating the Raman crystal for 90°. Furthermore, by simply replacing the Raman output coupler, we attained another two sets of second-Stokes orthogonally polarized dual-wavelength Raman lasers via the cascaded Raman shift. At a pulse repetition frequency of 5kHz, the maximum first-Stokes and second-Stokes dual-wavelength Raman output powers were 3.12 and 2.09W, with the combined peak powers of approximately 240 and 290kW, respectively.

10.3-W actively Q-switched Nd:YVO4/YVO4 folded coupled-cavity Raman laser at 1176 nm.

We report herein an efficient actively Q-switched Nd:YVO4/YVO4 intracavity Raman laser operating at 1176nm. Factors such as resonator geometry and pumping scheme are optimized to strengthen the power scalability and the conversion efficiency of the intracavity Raman laser. With a folded coupled cavity adopted to make full use of the high pump intensity on the Raman crystal, the first-order Stokes output of 10.32W at 1176nm is achieved under the incident pump power of 39W and pulse repetition frequency of 160kHz. The corresponding optical efficiency reaches 26.4%, and even higher efficiency of 27.8% is obtained at lower incident pump of 34.4W.

High-performance second-Stokes generation of a Nd:YVO4/YVO4 Raman laser based on a folded coupled cavity.

We report an actively Q-switched Nd:YVO4/YVO4 intracavity Raman laser at second-Stokes wavelength of 1313.6 nm, which is capable of operating efficiently under pulse repetition frequency higher than 80 kHz. A folded coupled cavity is adopted to optimize the fundamental and the Stokes resonators individually and make full use of the high pump intensity on the Raman crystal. With relatively high output coupling of 82% at 1313 nm, the average output power of 5.16 W at 1313 nm is achieved under the incident pump power of 36.7 W. The cascaded Raman emission at both the first- and second-Stokes wavelength of 1176 and 1313 nm is investigated to discuss the optimization of the second-Stokes generation.

Continuous-wave intracavity YVO4/BaWO4 Raman laser pumped by a wavelength-locked 878.9 nm laser diode

In this paper, the composite Nd:YVO4 laser crystal is in-band pumped by a wavelength-locked laser diode at 878.9 nm, with the purpose of reducing thermal effects and improving pump absorption simultaneously. By using the YVO4 and BaWO4 crystals as Raman media, the influences of crystal properties, resonator structure and stability on the performance of continuous-wave intracavity Raman laser are investigated experimentally and theoretically. The results show that the resonator stability greatly affects laser performance due to the long cavity length of intracavity Raman laser. By choosing the Raman medium with high Raman gain, we can not only obtain higher Raman conversion efficiency, but also reduce the thermal effect to a certain extent. Furthermore, the smaller the curvature radius of the output mirror in the plano-concave cavity structure, the greater the power density of the fundamental laser in the Raman crystal is and the wider the dynamic stability region of the resonator, and hence the higher output power of the Raman laser can be achieved. Finally, by using 30-mm BaWO4 crystal as Raman medium, a highest Raman output of 3.02 W is obtained at a pump power of 25.1 W, corresponding to a diode-to-Stokes optical conversion efficiency of 12%.

Crystal growth, electronic structure and optical properties of Sr2Mg(BO3)2

Single crystals of Sr2Mg(BO3)2 (SMBO) were grown by Kyropoulos method. X-ray powder diffraction (XRD) analysis, transmission spectrum, thermal properties, band structure, density of states and charge distribution as well as Raman spectra of SMBO were described. The as-grown SMBO crystals show wide transparency range with UV cut-off below 180nm. A direct band gap of 4.66eV was obtained from the calculated electronic structure results. The calculated band structure and density of states results indicated the top valence band is determined by O 2p states whereas the low conduction band mainly consists of Sr 5s states. Twelve Raman peaks were observed in the experimental spectrum, fewer than the number predicted by the site group analysis. Raman peaks of SMBO were assigned combining first-principle calculation and site group analysis results. The strongest peak at 917cm−1 in the experimental spectrum is assigned to symmetric stretching mode A1′(ν1) of free BO3 units. SMBO is a potential Raman crystal which can be used in deep UV laser frequency conversion.