Intracavity Raman Laser Research Articles

All-solid continuous-wave Nd: YVO4-diamond intracavity Raman laser

We demonstrated a continuous intracavity diamond Raman laser operating by linear-cavity and V-cavity design. The diamond crystal as the Raman medium and Nd: YVO4 as the laser gain medium was utilized to achieve high beam quality Stokes output with narrow line width. By employing linear and V-shaped cavity, we achieved Stokes light outputs of 1.68 and 2.26 W, respectively. Compared to the linear cavity, the V-shaped cavity has a higher conversion efficiency of 11.07% and a narrower linewidth of 0.07 nm. Mechanism for linewidth of different cavity design and methods for further increasing power range and high quality are discussed.

Isolator-free 60 W diamond Raman laser at 607 nm.

We report an intra-cavity frequency doubled diamond Raman laser operating at 607 nm. A z-fold cavity design was configured to prevent back reflections into the fiber amplifier, which avoided the use of isolators in the pump beam path. A maximum output power of 60 W was generated in two output beams at an optical conversion efficiency of 28% from the 1045 nm pump. A maximum single-beam output power of 40 W was obtained using a highly reflecting end mirror for the visible. Output power and single frequency stability are negatively impacted by an increasing role of stimulated Brillouin scattering at output powers above 10 W.

High-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser operating at 1.7 µm

We report on a high-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser at 1.7 µm. Driven by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser, the highly efficient cascaded YVO4 Raman laser at 1715nm was obtained within the well-designed L-shaped resonator. Thanks to the absence of spatial hole burning in the stimulated Raman scattering process, significant spectral purification of second-Stokes radiation was observed by incorporating a fused silica etalon in the high-Q fundamental cavity. Under the repetition rate of 4 kHz, the highest average output power for single longitudinal mode operation was up to 2.2 W with the aid of precision vibration isolation and precision temperature controlling, corresponding to the pulse duration of ∼2.8 ns and the spectral linewidth of ∼330 MHz. Further increasing the launched pump power, the second-Stokes laser tended toward be always multimode, and the maximum average output power amounted to 4.8 W with the peak power of ∼0.8 MW and the spectral linewidth of ∼0.08 nm. The second-Stokes emission was near diffraction limited with M2 < 1.4 across the whole pump power range.

Ten-watt-level all-solid-state eye-safe intracavity Raman laser.

We demonstrate the first ten-watt-level eye-safe intracavity crystalline Raman laser, to the best of our knowledge. The efficient high-power eye-safe Raman laser is intracavity-pumped by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser. Benefiting from the unique bi-axial properties of KGW crystal, two sets of eye-safe dual-wavelength Raman lasers operating at 1461, 1645 nm and 1490, 1721nm are achieved by rotating the Raman crystal. Under the launched pump power of 84.9 W and the repetition rate of 4 kHz, the maximum first-Stokes output powers of 7.9 W at 1461 nm and 8.2 W at 1490 nm are acquired with the second-Stokes output powers of 1.4 W at 1645 nm and 1.5 W at 1721nm, respectively, leading to the eye-safe dual-wavelength Raman output powers of up to 9.3 and 9.7 W. Meanwhile, the pulse durations at the wavelengths of 1461, 1490, 1645, 1721nm are determined to be 4.8, 5.5, 4.3, and 3.6 ns, respectively, which give rise to the peak powers approaching about 410, 370, 80, 100 kW. These Stokes emissions are found to be near diffraction limited with M2 < 1.6 across the entire output power range.

A continuous-wave Nd:YVO 4 -KGW intracavity Raman laser with over 34% diode-to-Stokes optical efficiency

Abstract We demonstrate a continuous-wave (CW) Nd:YVO4-potassium gadolinium tungstate (KGW) intracavity Raman laser with a diode-to-Stokes optical efficiency of 34.2%. By optimizing the cavity arrangement and reducing the cavity losses, 8.47 W Stokes output at 1177 nm was obtained under an incident 878.6 nm diode pump power of 24.8 W. The influence of cavity losses on the power and efficiency of the CW Raman laser, as well as the potential for further optimization, was investigated based on the numerical model. The observation of thermally-induced output rollover was well explained by the calculation of the thermal lensing and cavity stability, indicating that the end-face curvature played an important role when the end-face of the crystal was highly reflective coated to make the cavity. A 10.9 W Stokes output under 40.9 W incident pump was also demonstrated with a cavity arrangement less sensitive to the end-face curvature, which is the highest output power of CW intracavity Raman lasers reported.

Efficient continuous-wave Nd:YVO4/KGW intracavity Raman laser

We demonstrate an efficient Nd:YVO4/KGW intracavity Raman laser in continuous-wave (CW) scheme. With a V-shaped fundamental laser cavity and a short Stokes cavity in it, the oscillating beam sizes are designed to alleviate the thermal effect and to enhance the Raman gain for efficient CW operation. The output power of CW Stokes wave at 1177 nm reached 9.33 W under an incident laser diode pump power of 36.65 W, with corresponding optical efficiency being 25.5%. To the best of our knowledge, these are the highest Stokes output power and conversion efficiency of CW intracavity Raman lasers.

High-power dual-wavelength intracavity diamond Raman laser

Diamond crystals have garnered significant attention for applications in photonics, owing to their characteristics of ultra-high thermal conductivity, extremely broad spectral transmission range, and high Raman gain coefficient. These characteristics are particularly advantageous for the development of high-power, multi-wavelength lasers. In this work, we utilize single crystal diamond as a Raman gain medium, for intracavity wavelength-conversion of emission from a side-pumped, electro-optically Q-switched Nd:YAG module. Cascaded Raman conversion is demonstrated and dual-wavelength, pulsed laser emission at wavelengths of 1.2 μm (first-Stokes wavelength) and 1.5 μm (second-Stokes wavelength) is achieved (with a maximum combined pulse energy of 6.19 mJ). The relative ratio of output energy at the two Stokes orders could be varied by tuning the characteristics of the output coupling mirror and the length of the laser resonator. When operating at maximum pump power, the pulse width of the second-Stokes field was approximately half that of the first-Stokes field (second-Stokes ∼10 ns, first-Stokes ∼18 ns), resulting in maximum peak powers of 174 kW (at 1.2 μm) and 220 kW (at 1.5 μm). To the best of our knowledge, this is the highest reported peak power generated from a dual-wavelength, intracavity diamond Raman laser. This work highlights the diversity and utility of diamond as an effective wavelength-conversion component in high-power lasers, and stands as the current state-of-the-art in high pulse-energy, high peak-power, multi-wavelength intracavity Raman lasers.

Intra-Cavity Raman Laser Operating at 1193 nm Based on Graded-Index Fiber

Nonlinear Raman frequency conversion is an important technical scheme to obtain special optical band lasers based on conventional ion-doped lasers. In our work, we designed an intra-cavity Raman fiber laser based on graded index fiber (GRIF) as the Raman gain medium. Based on the fundamental-frequency 1080-nanometer laser, efficient first-order and second-order Stokes Raman lasers were obtained, respectively. When the power of the fundamental-frequency 1080-nanometer laser was 33.4 W, the output power of the second-order 1193-nanometer laser was 11.39 W. The corresponding conversion efficiency was 34.1%. To our knowledge, this is the first report of a second-order Raman output based on a GRIF and intra-cavity structure. In the experiment, the spectrum-purification process with the increase in power was also observed. Our experimental results prove that the intracavity Raman-laser system based on graded index fiber with a high optical conversion efficiency has important application potential for obtaining new special-application bands.

Intra-cavity diamond Raman laser at 1634 nm.

We demonstrated an eye-safe diamond Raman laser intra-cavity pumped by the 1.3 μm fundamental field for the first time, to the best of our knowledge. The first-Stokes laser at 1634 nm was converted from the 1342 nm fundamental laser, which was produced by an in-band pumped double-end diffusion-bonded a-cut Nd:YVO4 crystal. Under an incident pump power of 21.2 W and an optimal pulse repetition frequency of 25 kHz, the maximum average output power of 2.0 W was obtained with the pulse duration of 5.7 ns and the peak power of 14 kW. The first-Stokes emission was found to be near diffraction limited (M2 ≈ 1.3) and to have a narrow linewidth (∼0.05 nm FWHM; instrument limited).

Nanosecond pulsed deep-red laser source by intracavity frequency-doubled crystalline Raman laser.

We demonstrated a deep-red laser source by intracavity frequency-doubled crystalline Raman laser for the first time, to the best of our knowledge. The actively Q-switched 1314 nm Nd:LiYF4 laser was first converted to the eye-safe Raman laser using a KGd(WO4)2 (KGW) crystal, which was subsequently frequency-doubled in a bismuth borate crystal. Benefiting from the KGW bi-axial properties, the deep-red laser source was able to lase separately at two different spectral lines at 730 and 745 nm. Under an optimal repetition rate of 4 kHz, the maximum average powers of 1.7 and 2.0 W were attained with good beam quality of M2≈1.7. The corresponding pulse durations were determined to be 3.0 and 2.8 ns with the peak powers up to approximately 140 and 180 kW, respectively.

High-peak-power narrowband eye-safe intracavity Raman laser.

We demonstrated a narrowband eye-safe intracavity Raman laser by incorporating a fused silica etalon into the fundamental resonator. The KGd(WO4)2 (KGW) Raman laser was pumped by an actively Q-switched Nd:YLF laser at 1314 nm. Thanks to the KGW bi-axial properties, two distinct eye-safe Raman lasers operating at 1461 and 1490 nm were obtained separately by rotation of the KGW crystal. At an optimized pulse repetition frequency of 4 kHz, the maximum average output powers of 3.6 and 4.0 W were achieved with the peak powers up to approximately 330 and 480 kW, respectively. The eye-safe Stokes emissions were narrow linewidth (∼0.05 nm FWHM; measurement limited) and near diffraction limited (M2 < 1.4). The powerful narrowband eye-safe Raman lasers are of interest for applications as diverse as laser range finding, scanning lidar and remote sensing.

Numerical modeling of the intracavity coherent anti-Stokes Raman laser

The space-dependent rate equations of intracavity coherent anti-Stokes Raman lasers are deduced by adding the term describing the coherent anti-Stokes scattering effect to the rate equations of the intracavity Raman laser. The intracavity photon densities of the fundamental and first Stokes lights and the initial population-inversion density are assumed to be Gaussian spatial distributions. The rate equations are normalized and solved numerically, and a group of general curves is generated. The influence of normalized parameters on the pulse parameters of the output anti-Stokes laser is investigated. The normalized rate-equation theory and numerical results will be of help in the design of high-performance intracavity coherent anti-Stokes Raman lasers.

Analysis of actively Q-switched infrared Raman lasers with crystalline media of multi-Raman-modes

Actively Q-switched intracavity Raman lasers can generate multi-wavelength infrared laser based on rich modes of crystalline Raman media. Assuming the intracavity photon densities and initial population inversion densities to be of Gaussian spatial distributions, the space-dependent rate equations of actively Q-switched intracavity Raman lasers with two Raman modes are deduced. The rate equations are solved numerically to investigate the influences of normalized variables on pulse energy, peak power, pulse duration, and conversion efficiency of Raman laser outputs, respectively. There are obvious discrepancies between the results of two Raman modes. The dependence of Raman laser conversion efficiency at 1103 nm on normalized initial population inversion density is numerically calculated, the experimental results are consistent with the numerical ones, and the optimum conditions are proposed theoretically in the end.

High peak power, multi-wavelength, passively Q-switched Raman lasers based on Yb:YAG/Cr4+:YAG composite crystal

Stable, multi-wavelength, high peak power, passively Q-switched Raman lasers based on Yb:YAG/Cr4+:YAG composite crystal and c-cut YVO4 crystal have been demonstrated under quasi-continuous-wave laser diode end-pumping. A Raman laser with a pulse energy of 50 μJ and a pulse width of 0.88 ns is obtained. The corresponding pulse peak power reaches 56.9 kW, which to our best knowledge is the highest peak power achieved in intracavity Raman lasers with Yb3+ ion-doped crystals as the gain medium. Stable pulse trains of the fundamental lasers and Raman lasers were achieved at different pump pulse energies. These findings have potential applications in nonlinear frequency conversion, photodynamic therapy, industrial processing and terahertz wave generation.

High-peak-power eye-safe orthogonally-polarized dual-wavelength Nd:YLF/KGW Raman laser.

An actively Q-switched eye-safe orthogonally-polarized dual-wavelength intracavity Raman laser was demonstrated for the first time, to the best of our knowledge. The gain balanced dual-wavelength operation at 1314 and 1321 nm within an in-band pumped Nd:YLF laser was realized by slightly titling the cavity mirrors. Owing to the KGW bi-axial properties, two sets of simultaneous orthogonally-polarized dual-wavelength Raman lasers at 1470, 1490 nm and 1461, 1499 nm were achieved by simply rotating the KGW crystal for 90°, respectively. With an incident pump power of 30 W and an optimized pulse repetition frequency of 5 kHz, the maximum dual-wavelength Raman output powers of 2.6 and 2.4 W were obtained with the pulse widths of 5.8 and 6.3 ns, respectively, corresponding to the peak powers up to 89.7 and 76.5 kW.

Simultaneous three Raman shift passively Q-switched intracavity Raman laser based on the overlapping Raman shift of 259 cm−1 in c-cut GdVO4 and YVO4

A diode-pumped passively Q-switched intracavity Raman laser is experimentally investigated, in which a c-cut Nd:GdVO4 crystal is used as a self-Raman medium and a c-cut Nd:YVO4 crystal is only used as a Raman medium. Simultaneous laser pulse outputs at 1096, 1176, 1177 nm corresponding to the first-Stokes light at 259, 882 and 890 cm−1 are acquired. 1128 nm light corresponding the second-Stokes light at 259 cm−1 is obtained and occupies the majority of the output power. The Stimulated Raman Scattering at 259 cm−1 takes place in both the GdVO4 and the YVO4 crystals. With an incident pump power of 7.74 W and a pulse repetition frequency of 30.5 kHz, the average output powers at 1096, 1128, 1176 and 1177 nm are 47.6, 446, 27 and 44.2 mW, respectively.

Diode-end-pumped solid state ZnWO4 Raman laser at 2254 nm

A diode-end-pumped actively Q-switch intracavity Raman laser with a Tm:YLF laser gain medium and a ZnWO4 Raman gain crystal is demonstrated for the first time. Under the pump power of 30 W at 793 nm, the average output power of 184 mW at first Stokes wavelength of 2254 nm was obtained at a pulse repetition of 2.5 kHz. The corresponding pulse width and output peak power are 5.8 ns and 12.79 kW, respectively. Near-diffraction limited beam quality was observed (M2 ⩽ 1.46).

Dual-wavelength intracavity Raman laser driven by a coaxially pumped dual-crystal fundamental laser.

An actively Q-switched dual-wavelength intracavity Raman laser based on a coaxially pumped dual-crystal (Nd:YAG and b-cut Nd:YAP) fundamental configuration was theoretically and experimentally investigated. Stable dual-wavelength Stokes output at 1176 nm and 1195 nm was subsequently obtained by the Raman conversion from an a-cut YVO4 crystal. A total average power of 1.8 W was produced at 10 kHz pulse repetition frequency under an incident diode pump power of 15.8 W, in which the power levels at the two Stokes wavelengths were nearly equivalent. The power proportion and the interval between the dual-wavelength Stokes pulses could be manipulated actively by changing the pump focal position or pump wavelength.

Resonantly pumped mid-infrared Ho:YAG/BaWO4 intracavity Raman laser at 2640 nm

We report on a mid-infrared 2640 nm intracavity Raman laser based on BaWO4 Raman conversion in a resonantly pumped actively Q-switched Ho:YAG laser. At the pulse repetition frequency of 1 kHz, the threshold pump power is as low as 2.1 W at 1.91 μm. Increasing the incident pump power to 3.6 W, the pulse energy and the pulse width are 105 µJ and 7.32 ns respectively, which corresponds to a peak power as high as 14.4 kW. When the pulse repetition frequency is increased to 5 kHz, the maximum average output power of 473 mW is achieved under a 9.8 W incident pump power. The mid-infrared pulse laser has potential applications in chemical sensing, environmental monitoring, and laser medicine.

Diode-Pumped Actively Q-Switched Nd:YVO4/RTP Intracavity Raman Laser at 1.49 µm

For the first time, a diode-pumped actively Q-switched Nd:YVO4/RbTiOPO4 (RTP) intracavity Raman laser at 1.49 µm was demonstrated to the best of our knowledge. Experimentally, a dual-end diffusion-bonded YVO4–Nd:YVO4–YVO4 crystal was employed as the laser medium to generate 1.34 µm laser radiation, and an RTP crystal as the Raman medium to enable the frequency conversion, by which radiation at 1.49 µm was achieved successfully. With an incident pump power of 10.4 W, an average output power of 502 mW was obtained at a pulse repetition rate of 15 kHz, corresponding to a conversion efficiency of 4.8%.