Y. J. Zhang

7.3 W of single-frequency output power at 2.09 μm from an Ho:YAG monolithic nonplanar ring laser

Single-frequency output power of 7.3 W at 2.09 mum from a monolithic Ho:YAG nonplanar ring oscillator (NPRO) is demonstrated. Resonantly pumped by a Tm-doped fiber laser at 1.91 mum, the Ho:YAG NPRO produces 71% of slope efficiency with respect to absorbed pump power and nearly diffraction-limited output with a beam quality parameter of M(2) approximately 1.1.

Continuous-wave laser action around 2-um in Ho3+:Lu2SiO5

Continuous-wave (cw) laser action around 2 μm in Ho3+-doped Lu2SiO5 (LSO) was demonstrated in this paper. Cryogenically cooled by liquid nitrogen, a 10-mm long Tm-sensitized (6% at.) Ho(0.4% at.):LSO produced a maximum output power of 3 W at 2.07 μm for incident diode power of 11 W at 786 nm, and a slope efficiency of 35% with respect to incident pump power. To achieve room-temperature operation of Tm, Ho:LSO laser, a 1-mm long microchip crystal was pumped by a high brightness diode, generating an output power of greater than 80 mW and a slope efficiency of 26% at 2.08 μm. Using a 1.91 μm Tm:YLF laser as an in-band pump source, room-temperature cw operation of singly-doped Ho: Lu2SiO5 laser at 2106 nm was attained with a maximum output power of 2.8 W and a slope efficiency of 35% corresponding to absorbed pump power.

Diode-pumped high-efficiency Tm:YLF laser at room temperature

High-efficiency continuous-wave (CW) Tm:YLF laser by the dual-end-pumping configuration is presented. Under the total input pump power of 24.0 W, the highest output power reaches 9.8 W in the wavelength range of 1910-1926 nm by use of 10% output coupling, corresponding to optical conversion efficiency of 40.9% and slope efficiency of 51.4%. The free-running laser spectrum of Tm:YLF is measured.

Double-clad Tm3+-doped silica fiber laser with Bragg grating inscribed directly into active core by femtosecond laser

We report for the first time to inscribe the Fiber Bragg Grating (FBG) in Tm3+-doped multimode double-clad silica fiber by 800 nm femtosecond laser with a phase mask. The 1.35 μm period Bragg grating is written into the fiber core, which is responded to the laser center wavelength located at nearly 1960 nm. Continuous wave total output power of 11.5 W is obtained under the launched pump power of 29.8 W, corresponding to a slope efficiency of 45.0% and a conversion efficiency of 38.6%.

Multi-peak output Tm-doped silica fiber laser based on femtosecond-written multi-mode fiber Bragg grating

The all-fiber Tm-doped double-clad laser was reported, incorporating a phase mask scanning technology writing FBG directly into the Tm-doped multi-mode fiber core as cavity mirror, using 800 nm femtosecond laser sources. A fiber grating of 12 mm length was realized with a period of 1.35 μm. Pumped by the 793 nm pigtail fiber output LD, the continuous wave (CW) power could scale to 25.4 W at 1.96 μm with the slope efficiency of 38% respected to the LD output power. The output laser spectrum exhibited multi-peak, due to the multi-mode FBG reflective characteristic.

6.17-W continuous wave operation of a 2132-nm c-cut Tm,Ho:YAP pumped by a laser diode of 794.3 nm

Continuous wave (CW) operation of a c-cut Tm (5 at %), Ho (0.3 at %):YAP laser at 2132 nm wavelength were reported in this paper. In the temperature of 77 K, the Tm,Ho:YAP crystal was double end-pumped by a 21.4 W fiber-coupled laser diode (LD) at the center wavelength of 794.3 nm. Different resonator lengths and output couplers for the total pump power were tried. The resonator length was 205 mm, and the maximum CW output power of 6.17 W was acquired, corresponding to an optical-optical conversion efficiency of 28.8% and a slope efficiency of 35.6%.

All-fiber clad-pumped Tm3+-doped fiber amplifier using high power fiber combiner

The diode laser (LD) clad-pumped 1947.6 nm continuous wave (CW) Tm3+-doped fiber amplifier is reported using the master oscillation power amplifier (MOPA) method. The injected seed laser is provided by an all-fiber LD-clad-pumped Tm3+-doped single-mode fiber laser, which has a nearly 2.4 W maximal output power and 0.1 nm ultra-narrow linewidth based on the intracore reflection FBG. Using the 25/400 µm double-clad LMA Tm3+-doped fiber as the gain fiber, the output maximal output power is 30.6 W from the fiber amplifier, with a slope efficiency of 39.1% respected to the LD total output power. A high power multi-mode fiber combiner is used to couple high power LD light into the gain fiber. The output wavelength is also located at 1947.6 nm, with the slightly expanded laser linewidth of 0.2 nm.

In-band pumped Ho:YAP laser by Tm-Doped fiber laser at 1936 and 1948 nm, respectively

We present for the first time a highly efficient Ho:YAP laser at 2117.9 nm, which is double-end inband pumped by two all-fiber Tm-doped fiber lasers at 1936 and 1948 nm. Using a single 50 mm long Ho:YAP rod in a simple L-shaped resonator geometry, a maximum laser output power of 10.1 W and a slope efficiency of 43.6% with respect to the incident pump power are acquired. The Ho:YAP crystals work under room temperature 24°C, and without any active thermal management. This experimental results verify the Ho:YAP crystals can be pumped by the versatile laser sources in the 1.9 μm regions.

Thermal focal length measurement of an LD-end-pumped Tm,Ho:GdVO4 laser

The thermal focal length of a Tm,Ho:GdVO4 crystal was measured in this paper. The pump laser was 25.73 W, and the thermal focal length was 692.6 mm; based on the thermal focal length of a Tm,Ho:GdVO4 crystal, a single end-pump continuous wave (CW) operation of Tm,Ho:GdVO4 laser was designed to demonstrate the effect of thermal focal length, and a 0.26-W output power was high in considering the thermal focal length than in unconsidering the thermal focal length with a 26.1-W pump power.

Efficiency improvement of multimode Tm3+ doped double cladding silica fiber laser by in-line biconical tapers

Efficiencies improvement of LD (laser diode) pumped multimode large mode area (LMA) Tm3+ doped double cladding silica fiber lasers with different in-line biconial tapers were reported. Two types of multimode Tm3+ doped fiber were used in this experiment. Each type of fiber was made into three fiber lasers, a uniform geometry fiber laser and two tapered fiber lasers with different taper parameters. Biconical tapers located several centimeters from the output end of the multimode fiber lasers were made by heating and stretching method. Although the threshold of the best tapered fiber laser was added 200 mW, the slope efficiency (25.3%) and the maximum output power (1.31 W) of the fiber laser increased by 10.3% and 350 mW respectively, in comparison with the un-tapered one. Pre and post output laser power ratio was 6.3–15.6. Simultaneously, the laser spectrum moved to shorter wavelengths. The same trends of these characteristics were also observed in the other three tapered fiber lasers.