Sasa Zhang

Highly efficient Raman frequency converter with strontium tungstate crystal

A highly efficient extracavity Raman laser pumped by the infrared nanosecond laser pulses is presented utilizing the recently recommended Raman medium-strontium tungstate crystal (SrWO/sub 4/). The maximum conversion efficiency of the first and second Stokes pulses both reached about 50%, and the maximum total conversion efficiency of the first and second Stokes was obtained to be 70% in the experiment. The conversion efficiency dependence on the polarization and the temporal characteristics of the Stokes and pump pulses were also studied. A theoretical model for the solid-state extracavity Raman laser was established based on the radiation transfer equations describing stimulated Raman scattering processes, and solved numerically. This model can accurately predict the energy transfer dynamics observed in extracavity Raman lasers.

Theoretical and experimental study on the self-Raman laser with Nd:YVO/sub 4/ crystal

The intracavity photon densities and the initial population inversion density were assumed to be Gaussian distributions in the rate equations of the laser diode end-pumped actively Q-switched intracavity Raman laser. These space-dependent rate equations were solved numerically. In the experiment, an efficient self-Raman laser was realized based on the multifunctional Nd:YVO4 laser crystal with the acoustooptic Q-switch. The output, temporal, and spectral characteristics of the self-Raman laser were investigated experimentally in detail. The performance of the self-Raman laser was studied numerically, and the theoretical results showed the main trends of the intracavity Raman laser, which are in agreement with the experimental ones

High power and highly efficient Nd:YAG laser emitting at 1123 nm

A diode-end-pumped continuous-wave (CW) Nd:YAG laser emitting at 1123 nm is realized efficiently in a 25-mm-long cavity. A composite Nd:YAG (cNd:YAG) crystal is selected as the gain medium. With an incident diode power of 26.1 W, an output power of up to 9.3 W is obtained, corresponding to an optical-to-optical conversion efficiency of 35.6%. The laser performances at 1123 nm are compared between composite Nd:YAG and common Nd:YAG crystals. The results show that composite Nd:YAG is a better choice for 1123-nm laser generations.

Self-frequency-doubled KTiOAsO4 Raman laser emitting at 573 nm

A self-frequency-doubled KTiOAsO4 (KTA) Raman laser is realized in a diode-end-pumped acousto-optically Q-switched intracavity Raman laser configuration. A 30-mm-long x-cut KTA crystal is used as the Raman medium, and its 671 cm(-1) Raman mode is employed to finish the conversion from 1064 nm fundamental laser to 1146 nm Raman laser. Self-frequency doubling of the Raman laser is accomplished in the same KTA crystal, and a 573 nm yellow laser is obtained. With an incident diode power of 10.9 W and a pulse repetition rate of 20.8 kHz, a yellow-laser power of 0.82 W is obtained. The conversion efficiency from diode power to yellow-laser power is 7.5%.

Theoretical and experimental research on the multi-frequency Raman converter with KGd(WO4)2 crystal.

An efficient multi-frequency extracavity Raman laser for nanosecond pulses was realized by taking advantage of the anisotropic optical property of the KGd(WO4)2 crystal. The conversion efficiencies of the converter were investigated versus the pump pulse energy, pump polarization, and output coupling rate experimentally and theoretically. Based on the coupled radiation transfer equations, a theoretical model was deduced to predict the performance of solid-state extracavity Raman lasers. This model was solved numerically to analyze the operation of the extracavity Raman laser with the KGd(WO4)2 crystal, and the numerical results had a good agreement with the experimental ones.

A diode side-pumped KTiOAsO 4 Raman laser

A KTiOAsO(4) Raman laser is realized within a diode side-pumped acousto-optically Q-switched Nd:YAG laser. Efficient nanosecond first-Stokes generations at 1091.4 nm are obtained with three 30-mm-long KTA crystals. Under an incident diode power of 60.9 W and a pulse repetition rate of 4 kHz, a first-Stokes power of 4.55 W is obtained, corresponding to a diode-to-Stokes conversion efficiency of 7.5%. The single pulse energy is up to 1.14 mJ and the peak power is 18.0 kW.

Coexistent optical parametric oscillation and stimulated Raman scattering in KTiOAsO4

Coexistent optical parametric oscillation (OPO) and stimulated Raman scattering (SRS) are demonstrated in an X-cut KTiOAsO(4) (KTA) crystal. The 30-mm-long KTA crystal is placed within a diode-end-pumped acousto-optically (AO) Q-switched Nd:YAG laser cavity to construct an intracavity optical parametric oscillator. Coexistent Raman conversion of the fundamental wave is observed from the KTA crystal. With a diode power of 7.43 W and a pulse repetition rate (PRR) of 20 kHz, a signal (1535.0 nm) power of 0.92 W is obtained, corresponding to a diode-tosignal conversion efficiency of 12.4%. A first-Stokes (1091.4 nm) power of 0.17 W is obtained.

Measurement and analysis of water vapor inside optical components for optical fiber H2O sensing system.

Water vapor existing inside internal end-face gaps of optical components of an optical fiber H2O sensing system makes it possible to influence the measurement accuracy and stability. The influence principle has been briefly analyzed based on the structure of three main optical components: a distributed feedback laser diode (DFB-LD), a collimator, and a photoelectric diode (PD). With application of a differential technique, the influence of water vapor inside the DFB-LD can be removed. With reasonable recombination of the collimator and the PD in a dual-beam detection system, the influence of water vapor inside the collimator and the PDs end-face gaps has been suppressed from more than 1.57×10(-3) to as low as -2.175×10(-5) in absorbance. After H2O isolation processing water vapor inside the end-face gaps of the DFB-LD, the collimator, and the PD can be utilized as a reference to design a simple but feasible H2O sensor. As a result, good linearity with an R2 of 0.9964 has been realized in a concentration range of 39-2110 ppm during an application test, and a long-term test of the designed H2O sensor against the S8000 with a difference of 10 ppm has been achieved.

An Improved Denoising Method in RDTS Based on Wavelet Transform Modulus Maxima

This paper proposed and demonstrated an improved wavelet transform modulus maxima (WTMM) denoising method to decrease the temperature error without decreasing spatial resolution in Raman distributed temperature sensors. In this scheme, the WTMM were obtained by combining those on the high and low decomposition scales, and the temperature signal was reconstructed using the WTMM. Experimental results show that the new proposed method has better denoising effect than the conventional one, allowing for the temperature error reduction of ~2 °C at 30 °C and 60 °C without decreasing spatial resolution comparing to original data.

Fiber-optic vibration sensor system

A vibration measuring system based on a matched-fiber Bragg grating (FBG) is demonstrated, and the cross sensitivity of the temperature and strain was reduced by packaging the matched-sensing and interrogation FBG in the same shell, theory, system structure, and experimental results are presented. The experimental results demonstrated that the system has a good response to the 8–80 Hz vibration signal; it responds well to an acceleration of as low as 0.05 m/s2, the system was deployed in a coalmine, and good experimental result were received. Because the system has the advantage of intrinsic safety and an easy multiplex, it has good prospects in the mining and petrochemical industry.