Guangyuan He

High average power 2 μm generation using an intracavity PPMgLN optical parametric oscillator

An intracavity quasi-phase-matched optical parametric oscillator (OPO) has been developed for the purpose of generating radiation with high average power and high repetition rate in the 2 μm regime. The device is a degenerate OPO based on a 3 mm thick MgO-doped periodically poled LiNbO(3) (PPMgLN) crystal, which is pumped in turn within the cavity by a diode side-pumped, Q-switched 1 μm Nd:YAG laser operating at 10 kHz. Up to 20 W broadband 2 μm radiation can be generated with a compact configuration under the crystal temperature of 115 °C. The beam profile is close to circularly symmetric with M(2) ~ 10.

Generation of radially polarized beams based on thermal analysis of a working cavity

The laser oscillation and polarization behavior of a side-pumped Nd:YAG laser are studied theoretically and experimentally by a thermal model for a working cavity. We use this model along with the Magni method, which gives a new stability diagram, to show important characteristics of the resonator. High-power radially and azimuthally polarized laser beams are obtained with a Nd:YAG module in a plano-plano cavity. Special regions and thermal hysteresis loops are observed in the experiments, which are concordant with the theoretical predictions.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

Efficient high-peak-power and high-repetition-rate eye-safe laser using an intracavity KTP OPO

An efficient high-peak-power and high-repetition-rate intracavity KTP optical parametric oscillator pumped by a Q-switched Nd:YVO4 laser is demonstrated. We achieved 1.5 W output power of 1.5 μm at 10 kHz repetition rate with the pulse duration of 6 ns. The maximum peak power of 25 kW and the maximum pulse energy of 150 μJ have been obtained. The maximum conversion efficiency of 9.5% is achieved with respect to a laser diode power of 10.5 W.

Compact Efficient 2.1-

We present a compact efficient intracavity MgO:PPLN optical parametric oscillator (OPO) with a volume Bragg grating output coupler pumped by a Q-switched Nd:YVO4 laser operating in 2.1-μm region. Narrowband 2.1-μm output power of 3.7 W is achieved with a pulse duration <;2 ns at 15-kHz repetition rate. A maximum conversion efficiency of 19.5% from laser diode (LD) to 2.1 μm is obtained at 17.5-W LD pump power. The 2.1-μm beam quality factors M2 of 1.85 and 2.37 in horizontal and vertical directions are obtained. To the best of our knowledge, the efficiency is the highest ever achieved from an intracavity OPO in 2-μm region.

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A high average-power 2 μm laser with good beam quality based on an intracavity potassium titanium oxide phosphate (KTP) optical parametric oscillator (OPO) is demonstrated. A concave lens is used in the 1064 nm Nd:YAG pumped laser cavity to compensate for the thermal lensing of the laser rod. The cavity length of the KTP OPO is enlarged to improve the 2 μm beam quality. The maximum average output of the 2 μm laser is up to 18 W at 7 kHz with M 2 less than 6 and pulse width of 70 ns. The FWHM of the signal and idle lights are both less than 3 nm.

m Intracavity MgO:PPLN OPO With a VBG Output Coupler

A continuous-wave singly resonant optical parametric oscillator employing a volume Bragg grating as one of the end mirrors is demonstrated. Due to the high intracavity power, the minute absorption of the grating leads to the thermal induced surface deformation and reflection peak shift. In this letter, the former effect is confirmed to be a cause of beam quality degradation of the resonant signal, while the latter, together with the thermal effects of the nonlinear crystal, leads to unconventional behaviors of power and stability. To the best of our knowledge, the joint effects of the grating and the nonlinear crystal are studied for the first time in details by changing the thermal effects of grating in varied strengths.

High average-power 2 μm radiation generated by intracavity KTP OPO

We report a high-brightness and high-efficiency degenerate periodically poled MgO:LiNbO3 (PPMgLN) optical parametric oscillator (OPO), configured with a four-mirror standing-wave cavity and pumped by a Q-switched Nd:YVO4 laser. Attributed to the successful mode matching of four-mirror standing-wave cavity, we have obtained good beam qualities both in single-pass and double-pass geometry. The beam qualities of single-pass pump geometry are M2 ~ 1.6 and 1.7 in the horizontal and vertical directions, and the beam qualities of double-pass pump geometry are M2 ~ 1.8 and 1.9. Optical to optical conversion efficiencies of 38% and 55% are achieved, respectively. With a volume Bragg grating used as the output coupler, we achieved a narrow linewidth of less than 2 nm.

Joint Thermal Effects of VBG and Nonlinear Crystal in a Singly Resonant OPO

Generation of high stability and high power azimuthally polarized beams is demonstrated in a Nd:YAG laser by inserting an optimum aperture in the cavity. The location and the size of the aperture are optimized by analyzing the mode-radius, stability and mode selectivity of the cavity with a transfer matrix method. Experiments are performed in a Nd:YAG laser with a flat-flat resonator, and the results are concordant with the theoretical predictions. A 10 W azimuthally polarized beam with the standard deviation of the output power less than 0.6% is obtained.

2.1 μm four-mirror standing-wave optical parametric oscillator with high brightness and efficiency

A high efficiency near-degenerate periodically poled MgO:LiNbO3 optical parametric oscillator pumped by a nanosecond Nd:YVO4 laser is demonstrated. Under a 1.064 μm pump power of 7.2 W, an output power of 5.3 W with an optical-to-optical conversion efficiency of 74% and a slope efficiency of 82% in the 2 μm region is obtained in a double-pass-pumped doubly resonant geometry at 20 kHz repetition rate.