Compact KTA-based intracavity optical parametric oscillator driven by a passively Q-switched Nd:GdVO4 laser

High Power and Efficient 4.43 μm BaGa4Se7 Optical Parametric Oscillator Pumped at 1064 nm

A high power and efficiency mid-infrared optical parametric oscillator based on a BaGa4Se7 crystal is demonstrated in this paper. It was pumped by a 500 Hz Q-switched Nd:YAG laser at room temperature. Without cooling, up to 0.76 W output power at 4.43 μm was generated with respect to the incident pump power (1064 nm) of 5.52 W, corresponding to an optical-to-optical conversion efficiency of 13.7%. The corresponding slope efficiency was as high as 18.7%. The pulse width of the signal wave was 5.2 ns at the pump pulse of 13.7 ns. To the best of our knowledge, this is to date the highest output power achieved at 4–5 μm from a 1064 nm pumped BGSe OPO laser. Considering that no additional cooling system was applied, this work provides a good solution for a high-efficient, compact or even portable mid-infrared solid-state laser device.

Theoretical and experimental studies on output characteristics of an intracavity KTA OPO

An acousto-optically Q-switched Nd:YVO(4)/KTiOAsO(4) (KTA) intracavity optical parametric oscillator (OPO) is efficiently realized in singly resonated scheme. With an end-pumping diode power of 25.9 W, output signal (1535 nm) power of 3.77 W and idler power (3467 nm) of 1.18 W are obtained at a pulse repetition rate of 50 kHz. A rate-equation model is set up to simulate the output power and time characteristics of both signal and idler waves. And both the numerical and experimental results show that the idler pulse width is shorter than the signal one in a singly resonant OPO.

Autofluorescence spectroscopy for evaluating dysplasia in colorectal tissues

The aim of this study was to assess the applicability of autofluorescence (AF) spectroscopy as a method for the diagonosis of normal, benign and malignant of dysplasia in colorectal tissues experimentally. By improvement of optical design in laser pulse generator, wavelength-adjustable output was acquired and the optimal wavelength was defined as 380 nm. With 380-nm pulsed laser excitation, AF spectra of normal, benign and malignant colorectal tissues were recorded in the spectra region from 460-570 nm in vitro. The spectral analysis for discrimination among the different types of tissues was carried out using principal component analysis (PCA)-based Neural networks algorithm. The performance of analysis was pretty good with sensitivity, specificity and accuracy found to be 100%,90% and 96.7%, respectively. The AF spectroscopy may serve as an excellent tool for the evaluation of dysplasia in colorectal clinical diagnosis.

Passively Q-switched photonic crystal fiber laser and intracavity optical parametric oscillator

We report on a passively Q-switched photonic crystal fiber (PCF) laser with Cr(4+):YAG as a saturable absorber. Under a pump power of 14.2 W, the maximum pulse energy is up to 630 microJ with a pulse width of 36 ns at a repetition rate of 5.6 kHz. With an intracavity optical parametric oscillator, the passively Q-switched PCF laser is used to generate the signal wave at 1515 nm. The output pulse energy of the signal wave is found to be 140 microJ with a pulse width as short as 1.0 ns at a repetition rate of 3.3 kHz. The very short pulse width leads to the peak power up to 140 kW.

Influence of the time modulation of the pump laser caused by mode beating on optical parametric process

Numerical simulation and analysis about the influence of the time modulation of the pump laser caused by mode beating on optical parametric process are presented with OPA and OPG as examples. It is shown that the output power of the generated beams from optical parametric process is modulated in the time domain and exhibits large power fluctuations, when a Q-switched laser oscillating on several random longitudinal modes is used as the pump laser. Irregular spike sequences of the generated beams are observed. We also find that the output power of the light from optical parametric process becomes more stable and exhibits a less fluctuation, when the number of the longitudinal modes (n) increases.

High-efficiency intracavity Nd:YVO4\KTA optical parametric oscillator with 3.6 W output power at 1.53 microm

An efficient intracavity KTA optical parametric oscillator (OPO) driven by diode-end-pumped acousto-optical Q-switched Nd:YVO(4) laser is demonstrated. The mode mismatch between fundamental cavity and OPO cavity caused by the thermal lens effect in Nd:YVO(4) crystal as the pump power increased was studied. To lessen mode mismatch, a thermal lens-like cavity mirror made of plane BK7 glass induced by idler absorption was introduced into the OPO cavity. Under a diode pump power of 20 W, a maximum 1535nm light output power of 3.6 W was achieved at the pulse repetition rate of 60 kHz, corresponding to a diode-to-signal conversion efficiency of 18%. This is the highest efficiency reported for eye-safe laser based on intracavity OPO.