Modelling of passively Q-switched lasers with intracavity Raman conversion

We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fun-damental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. Prom these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd^3＋：GdVO4 self-Raman laser is presented to demonstrate the usage of the curves and related formulas.

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

We demonstrate a continuous-wave(CW)Nd:YVO_(4)-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.

Study on 660-nm quasi-continuous-wave intracavity frequency-doubled NdrYAG laser

A quasi-continuous-wave intracavity frequency-doubled Nd:YAG laser which operates at 660 nm is studied. By using a flat-flat laser cavity, 2 Kr-lamps, KTP crystal and an acousto-optically Q-switch, 2-W output power at 660 nm is obtained. The relationship between laser cavity length and output power is analyzed.

Theory of intracavity-frequency-doubled solid-state four-level lasers

The spatial distributions of the pumping,the population inversion density,and the intracavity photon densities of the fundamental and the second harmonic are taken into account in the rate equations of the intracavity-frequency-doubled cw lasers.By normalizing the related parameters,it is shown that the general solution of these space-dependent rate equations is dependent upon three dimensionless parameters:the pump to laser-mode size ratio,the normalized pump level,and a parameter written as ηSHG,which is related to the ability of the nonlinear crystal to convert the fundamental to the second harmonic.By numerically solving these rate equations,a group of general curves are obtained to express the relations between the solution and the three dimensionless parameters.In addition,the optimal pump to laser-mode size ratio and the optimal ηSHG are determined.A comparison with the result obtained under the plane-wave approximation is also given.

Intracavity biosensor based on the Nd:YAG waveguide laser: tumor cells and dextrose solutions

This work demonstrates the Nd:YAG waveguide laser as an efficient platform for the bio-sensing of dextrose solutions and tumor cells. The waveguide was fabricated in an Nd:YAG crystal with the cooperation of ultrafast laser writing and ion irradiation. The laser oscillation in the Nd:YAG waveguide is ultrasensitive to the external environment of the waveguide. Even a weak disturbance leads to a large variation of the output power of the laser.According to this feature, an Nd:YAG waveguide coated with graphene and WSe_2 layers is used as substrate for the microfluidic channel. When the microflow crosses the Nd:YAG waveguide, the laser oscillation in the waveguide is disturbed and induces fluctuation of the output laser. According to the fluctuation, the microflow is detected with a sensitivity of 10 mW/RIU.

Gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging for detection of submucosal gastric cancer:in vitro study

This paper presents photoacoustic and ultrasonic dual-mode imaging for real-time detection of submucosal gastric cancer with a combination of gastroscopy.The diagnostic capacity was directly addressed via several phantoms and ex vivo experiments.Results demonstrated that superficial and submucosal gastric cancer can be diagnosed with a perceptible depth of 6.33 mm,a lateral accuracy of 2.23 mm,and a longitudinal accuracy of 0.17 mm though capturing the morphology of angiogenesis,which is a main character of the therioma-related change.The capability of gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging system will own great potential in improving the clinical diagnostic rate of submucosal gastric cancer.

First-Stokes and second-Stokes multi-wavelength continuous-wave operation in Nd:YVO4/BaWO4 Raman laser under in-band pumping

A continuous-wave Nd:YVO4/BaWO4 Raman laser generating simultaneous multi-wavelength first-Stokes and second-Stokes emissions is demonstrated for the first time, to the best of our knowledge. Investigations concerning different pump spot sizes and crystal lengths were conducted to improve the thermal effect and pump absorption. Three first-Stokes lasers at 1103.6, 1175.9, and 1180.7 nm and two second-Stokes lasers at 1145.7 and 1228.9 nm are obtained simultaneously using the Raman shifts of 925 cm-1 and 332 cm-1 in BaWO4 and 890 cm-1 in YVO4. At the incident pump power of 23.1 W, 1.24 W maximum Raman output power is achieved,corresponding to an optical conversion efficiency of 5.4%. We also present a theoretical analysis of the competition between different Stokes lines.