Self-frequency Raman Conversion Research Articles

Eye-Safe KGd(WO4)2:Nd Laser: Nano- and Subnanosecond Pulse Generation in Self-Frequency Raman Conversion Mode with Active Q-Switching

The shape of the multimode Stokes pulse generated by an eye-safe KGd(WO4)2:Nd laser with self-frequency Raman conversion and active Q-switching was shown to depend on the inhomogeneity of the active-medium pump. The laser generated a short and undistorted Stokes pulse of length ~2.5 ns that increased with increasing laser cavity length for a moderately inhomogeneous pump characterized by a higher population inversion in the center of the active element. The energy of the Stokes pulse (~11.5 mJ) varied little as the output-mirror reflectivity varied in the range 5–45%. The Raman pulse became distorted if the inhomogeneity of the pump was increased considerably. The degree of pump inhomogeneity was negligible with fundamental TEM00 mode selection. The laser generated subnanosecond Stokes pulses with peak power in the MW range.

Output power and intracavity intensity profiles of a quasi-continuous end-pumped Nd:YVO4 self-Raman mini laser

The paper presents experimental investigation and modeling of an end-pumped quasi-continuous-wave YVO4/Nd:YVO4 mini self-Raman laser. The dependence of the Stokes output power on the pump power in the range from 3 to 17.5 W has been measured. As much as 1.76 W of an average Stokes power, corresponding to a total optical-to-optical conversion efficiency of about 10%, has been obtained. The transverse profiles of the laser (at the fundamental wavelength) and the Stokes beam intensity have been recorded at the output mirror and in the vicinity of the boundary between the pure and Nd-doped parts of the Raman crystal. These distributions have been approximated by the sum of Gaussian and super-Gaussian distributions with corresponding weights. We propose a model of such lasers that takes into account the features of intracavity self-frequency Raman conversion in lasers with highly inhomogeneous non-Gaussian spatial distributions of the pump, laser, and Stokes beam intensity in the cavity. The results of modeling are in good agreement with the experimental data.

Efficient continuous-wave YVO4/Nd:YVO4 Raman laser at 1176 nm

We present a simple and compact continuous-wave (CW) 1176 nm laser based on self-frequency Raman conversion in continuous-grown YVO4/Nd:YVO4 composite crystal. With a composite crystal 30 mm in length, a maximum output power up to 1.84 W was achieved at the incident diode pump power of 23.6 W. Corresponding to overall optical conversion, the efficiency was 7.8% and the slope efficiency was 8.5%. The conversion efficiency has been doubled compared with the conventional Nd:YVO4 CW self-frequency Raman laser. The excellent performance of this laser shows that the long continuous-grown YVO4/Nd:YVO4 composite crystal is promising in the application of CW Raman lasers and ideal for miniaturization.

Dynamics of generation of a pulsed Nd3+:KGd(WO)2/V3+:YAG laser emitting in the self-frequency Raman conversion mode at λ = 1.538 μm

It has been shown that the generation of the 1st Stokes component (λ = 1.538 μm) in an Nd:KGW laser with a passive V:YAG $$ Q $$ -switch is multimodal and its dynamics have a complex spatio-temporal character. The SRS-generation features the impact excitation manifested as the formation of a high-intensity peak at the beginning of the pulse, the peak position relative to the subsequent part of the pulse depending on the radius of curvature of the end cavity mirror. The SRS-conversion of the fundamental laser radiation (λ = 1.351 μm) starts in the central region of the Nd:KGW-element and then spreads towards its boundaries. The total integral SRS-pulse of duration 15–25 ns represents an envelope of shorter (1–2 ns) time-shifted pulses generated by separate local areas of the active medium cross-section. The multimode character of generation results in gradual damage to the V:YAG $$ Q $$ -switch at the attained SRS-radiation energy of 8–14 mJ.

High-efficiency Q-switched dual-wavelength emission at 1176 and 559 nm with intracavity Raman and sum-frequency generation

An efficient Q-switched dual-wavelength laser with self-frequency Raman conversion in composite Nd:YVO(4) and intracavity sum-frequency generation in BBO is reported. With an input pump power of 17.5 W, average power of 0.53 W at the first-Stokes 1176 nm and average power of 1.67 W at the sum-frequency mixed 559 nm are simultaneously generated at a pulse repetition rate of 100 kHz, corresponding to a total conversion efficiency of 12.5%.

Diode-pumped continuous-wave Nd:YVO4 laser with self-frequency Raman conversion

Continuous-wave operation of a diode-pumped Nd:YVO4 laser with self-frequency Raman conversion is demonstrated. The threshold of Raman generation was measured to be 1.3 W of laser diode power. The maximum output power of Stokes radiation at the wavelength of 1177 nm was up to 50 mW at a laser diode pump power of 2.3 W, corresponding to the slope efficiency of 5%. The beam quality M2 of the Stokes radiation was about 1.4. The fluctuations of the Stokes power were minimised down to 4%.

Compact efficient all-solid-state eye-safe laser with self-frequency Raman conversion in a Nd:YVO4 crystal.

An efficient compact eye-safe laser at 1525 nm is presented by use of self-frequency Raman conversion in a diode-pumped actively Q-switched Nd:YVO4 1342-nm laser. At an incident pump power of 13.5 W, the self-stimulated Raman laser produces 1.2 W of 1525-nm average output power at a repetition rate of 20 kHz. The corresponding peak power at 1525 nm is generally greater than 10 kW for repetition rates from 5 to 20 kHz.

Efficient subnanosecond diode-pumped passively Q-switched Nd:YVO4 self-stimulated Raman laser.

Generation of efficient subnanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:YVO4/Cr4+:YAG laser is demonstrated. Experimental results reveal that self-frequency Raman conversion can be achieved with a c-cut Nd:YVO4 crystal in a nearly hemispherical cavity. At 2.0 W of incident pump power, the self-stimulated Raman laser produces stable 710-ps pulses at a Stokes wavelength of 1178.6 nm with 7.2 microJ of pulse energy at a 17-kHz repetition rate.

Compact efficient self-frequency Raman conversion in diode-pumped passively Q-switched Nd:GdVO4 laser

I report the first demonstration of the generation of efficient sub-nanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:GdVO4/Cr4+:YAG laser. The conversion efficiency for the average power is 7% from pump diode input to self-Raman output and the slope efficiency is up to 14%. At an incident pump power of 2.0 W, the pulse duration, pulse energy, and peak power for the Stokes wavelength of 1175.6 nm were found to be 750 ps, 6.3 μJ, and 8.4 kW, respectively, with a pulse-repetition rate of 22 kHz.

Yb:KYW microchip laser with self-frequency Raman conversion

Passively Q-switched and cw operation regimes of a diode-pumped Yb:KYW microchip laser have been investigated. The maximum slope efficiency for cw operation of 23% relative to incident pump power has been achieved. Self-frequency Raman conversion for microchip cavity configuration has been realised.

Efficient diode-pumped passively Q-switched laser operation around 1.9 μm and self-frequency Raman conversion of Tm-doped KY(WO4)2

Passively Q-switched operation of Yb,Tm:KY(WO4)2 and Tm:KY(WO4)2 lasers diode pumped at 805 nm has been investigated. A thin plate of Cr:ZnS was used as a saturable absorber for passive Q switching. A maximum average output power of 116 mW emitted at 1.9 μm in comparison to 160 mW for the free-running regime at the same pumping level has been obtained with a slope efficiency of 26% with respect to the incident pump power. Using a Tm:KYW sample with broadband antireflection coatings and dichroic laser resonator mirror, the first Stokes component of Raman self-frequency conversion was observed at 2365 nm.

Passive Q switching and self-frequency Raman conversion in a diode-pumped Yb:KGd(WO_4)_2 laser

We report on the laser performance of a diode-pumped Yb:KGd(WO(4))(2) laser that is passively Q switched with a Cr(4+):YAG saturable absorber. Raman conversion of fundamental laser emission in the laser crystal was demonstrated. Q-switched 3.4-mu;J pulses with a pulse width of 85 ns were obtained at the 1033-nm fundamental wavelength and 0.4-mu;J pulses with a pulse width of 20 ns were produced in a first Stokes at 1139 nm.