Yao Baoquan

A Graphene-Based Passively Q-Switched Ho:YAG Laser

A 2.09-μm in-band pumped passively Q-switched Ho:YAG laser is demonstrated. Single layer graphene deposited on a quartz substrate is used as the saturable absorber for the Q-switched operation. The minimum pulse width of 2.11 μs is obtained at an average output power of 100 mW, corresponding to a pulse repetition frequency of 57.1 kHz and the pulse energy of 1.75 μJ. The beam quality factors M2 of the Q-switched laser are 1.18 and 1.22 in the horizontal and longitudinal direction, respectively. The optical-to-optical conversion efficiency of the passively Q-switched laser is 4.3%, which is the highest conversion efficiency in the 2 μm wavelength, to the best of our knowledge. It shows clearly that the Ho:YAG crystal is a potential gain medium in the 2 μm range for the graphene application.

High Efficiency Continuous-Wave Tm:Ho:GdVO4 Laser Pumped by a Diode

We report a high efficiency cw diode-pumped cryogenic Tm(5 at.%), Ho(0.5 at.%):GdVO4 laser. The pumping source is a fibre-coupled laser diode with fibre core diameter of 0.4 mm and numerical aperture of 0.3, supplying power 14.8 W at 793.6 nm. For input pump power of 13.6 W at 794.2 nm, the maximum output power of 4.2 W, optical-to-optical conversion efficiency of 31% and slope efficiency 38% have been attained at 2.0485 μm. To our knowledge, the operating performance is the best among the previously reported Tm:Ho:GdVO4 lasers. We also analyse the influence of pump wavelengths (from 792 nm to 794.2 nm) on the output power, the optical-to-optical conversion efficiency increases with the longer pump wavelength which is closer to the absorption peak of 797 nm in Tm,Ho:GdVO4.

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Long-wave infrared (IR) generation based on type-II (o→e+o) phase matching ZnGeP2 (ZGP) and CdSe optical parametric oscillators (OPOs) pumped by a 2.05 μm Tm,Ho:GdVO4 laser is reported. The comparisons of the bire-fringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency (PRF) with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.

A 2.048-μm Tm,Ho:GdVO4 Laser Pumped Doubly Resonant Optical Parametric Oscillator Based on Periodically Poled Lithium LiNbO3

A multi-grating periodically poled LiNbO3 (PPLN) doubly resonant optical parametric oscillator (DROPO) pumped by a 2-?m laser is demonstrated experimentally. Employing acousto-optically Q-switched Tm,Ho:GdVO4 laser with pump pulse of 25?ns and repetition rate of 10?kHz as pump sources firstly, the noncritically quasi-phase-matched (QPM) tunable mid-IR output in 3.87?4.43??m is produced. Wavelength tuning is achieved with crystal temperature tuning from 50?180?C. When the incident average pump power is 3?W at 2.048??m, the total OPO output power of 195?mW at wavelength 3.88??m is obtained, corresponding to optical-to-optical conversion efficiency up to 6.5%.

Diode Pumped Operation of Tm,Ho:YVO4 Microchip Laser

A cryogenic and room-temperature diode pumped Tm,Ho:YVO4 microchip laser with 0.5 mm crystal length lasing around 2 μm is demonstrated for the first time to our knowledge. Under cryogenic temperature of 77K, as much as 1.2 W output and slope efficiency of 35% with respect to absorbed pump power are obtained. At temperature of 5°C the maximum output power of 48mW is obtained at an absorbed pump power of 503 mW, representing a 9.5% optical to optical conversion efficiency. In addition, as much as 8 mW single-frequency output lasing at 2052.6 nm is achieved at room temperature of 15° C.

LD-cladding-pumped 50 pm linewidth Tm 3+ -doped silica fiber laser

We report on a Tm(3+)-doped fiber laser source operating at 1936.4 nm with a very narrow linewidth (50 pm) laser output. Up to 2.4 W cw laser power was obtained from an 82 cm long Tm(3+)-doped multimode-core fiber cladding pumped by a 792 nm laser diode (LD). The fiber laser cavity included a high-reflective dichroic and a low-reflective FBG output coupler. The multimode fiber Bragg grating (FBG) transmission spectrum and output laser spectrum were measured. By adjusting the distance between the dichroic and the Tm(3+)-doped fiber end, the multipeak laser spectrum changed to a single-peak laser spectrum.

A Laser-Diode-Pumped Widely Tunable Single-Longitude-Mode Tm:YAP Laser at Room Temperature

A laser-diode-pumped widely tunable single-longitude-mode Tm:YAP laser in 2 μm eye-safe region is built. Continuous tunable range from 1899 nm to 2025 nm is achieved with the maximum laser output power of 225 mW at 1989 nm. In addition, the Tm:YAP laser operating under multimode and single-mode conditions is discussed.

Judd--Oflet analysis of spectrum and laser performance of Ho:YAP crystal end-pumped by 1.91-μm Tm:YLF laser

The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd-Ofelt intensity parameters Omega(2) = 1.42 x 10(-20) cm(2), Omega(4) = 2.92 x 10(-20) cm(2), and Omega(6) = 1.71 x 10(-20) cm(2), this paper calculated the fluorescence lifetime to be 6 ms for I-5(7) -> I-5(8) transition, and the integrated emission cross section to be 2.24 x 10(-18) cm(2). It investigates the room-temperature Ho:YAP laser end-pumped by a 1.91-mu m Tm:YLF laser. The maximum output power was 4.1 W when the incident 1.91-mu m pump power was 14.4W. The slope efficiency is 40.8%, corresponding to an optical-to-optical conversion efficiency of 28.4%. The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.

High Efficient Continuous-Wave Ho:YAG Laser Pumped by a Diode-pumped Tm:YLF Laser at Room Temperature

We present a high efficient continuous wave Ho:YAG laser pumped by a diode-pumped Tm:YLF laser with a Fabry–Perot etalon tuning at 1.91 μm. The maximum output power reaches 7.2 W when the absorbed pump power is 10.8 W. The slope efficiency (relative to the absorbed power) is 74.1%, and the Tm:YLF to Ho:YAG optical conversion efficiency of 60%, then the diode-to-Holmium optical conversion efficiency achieved is 21.0%. The wavelength is 2090 nm when the transmission of output coupler is larger than 20%. The beam quality factor is M2 ~ 1.15 measured by the travelling knife-edge method.

Widely Tunable cw Diode-Pumped 1.9-μm Tm:GdVO4 Laser at Room Temperature

A widely tunable cw diode-pumped room-temperature Tm:GdVO4 laser is built. Output power of 2.8 W and a slope efficiency of 22% pumped by a 18 W Fibre-coupled diode laser at 795 nm have been obtained. Continuous tunability from 1820 nm to 1946 nm is achieved. In addition, the factors that contribute to the efficiency of oscillation are studied.