Peter A. Budni

Efficient mid-infrared laser using 1.9-µm-pumped Ho:YAG and ZnGeP 2 optical parametric oscillators

We report >4.2-W mid-infrared (mid-IR) output (3.8 and 4.65 µm) and >2.1 W at 3.5 µm in ZnGeP2 (ZGP) optical parametric oscillators (OPO) pumped by a holmium-doped yttrium aluminum garnet (Ho:YAG) laser, directly pumped by a diode-pumped 1.9-µm thulium-doped yttrium lithium fluoride (Tm:YLF) laser. Optical-to-optical efficiency achieved is >7.2% (laser diode to mid-IR). In addition, a Ho:YAG-pumped ZGP OPO operation is achieved over a Ho:YAG temperature range of 80 °C at the 8-W (Ho:YAG) and 3-W (ZGP OPO) power levels.

High-power/high-brightness diode-pumped 1.9-/spl mu/m thulium and resonantly pumped 2.1-/spl mu/m holmium lasers

We report high power (>36 W) with beam propagation factor M/sup 2//spl sim/2 in a diode end-pumped Tm:LiYF/sub 4/ (Tm:YLF) laser generating output near the 1.91-/spl mu/m region. Using the 1.91-/spl mu/m emission and high brightness achieved with the Tm:YLF laser we resonantly end-pump the Holmium /sup 5/I/sub 7/ manifold in Ho:YAG and demonstrate /spl sim/19 W of continuous-wave (CW) output. The diode-to-Holmium optical to-optical conversion efficiency achieved is /spl sim/18%. Using a CW pumped and repetitively Q-switched configuration, the Tm:YLF pumped Ho:YAG laser achieves >16 W of output power with an M/sup 2//spl sim/1.48 at 15 kHz. A Q-switched frequency range of 9 to >50 kHz is also achieved.

Mid-infrared ZnGeP 2 parametric oscillator directly pumped by a pulsed 2 μm Tm-doped fiber laser

We have demonstrated what we believe to be the first mid-infrared optical parametric oscillator (OPO) pumped directly by a pulsed Tm-doped fiber laser. The Tm-fiber pump laser produces 30 ns pulses with a repetition rate of 30 kHz at a wavelength of 2 μm. The ZnGeP2 (ZGP) OPO produces 20 ns mid-IR pulses in the 3.4-3.9 μm and 4.1-4.7 μm spectral regions simultaneously. More than 658 mW of mid-IR output power has been generated with a total OPO slope efficiency greater than 35%.

Efficient 1645-nm Er:YAG laser

We report a resonantly fiber-laser-pumped Er:YAG laser operating at the eye-safe wavelength of 1645 nm, exhibiting 43% optical efficiency and 54% incident slope efficiency and emitting 7-W average power when repetitively Q switched at 10 kHz. To our knowledge, this is the best performance (conversion efficiency and average power) obtained from a bulk solid-state Q-switched erbium laser. At a 1.1-kHz pulse repetition frequency the laser produces 3.4-mJ pulses with a corresponding peak power of 162 kW. Frequency doubling to produce 822.5-nm, 4.7-kW pulses at 10 kHz was performed to demonstrate the lasers utility.

5-W repetitively Q-switched Er:LuAG laser resonantly pumped by an erbium fiber laser

We report a high-average-power, near-diffraction-limited Er:LuAG laser generating 5 W of power at 1.648 microm in either cw or repetitively Q-switched operation. When the laser is Q switched at 9 kHz, we measure 0.52 mJ/pulse. The laser is end pumped by a 20-W erbium fiber laser and achieves >30% optical conversion efficiency and >40% incident slope efficiency. This is, to our knowledge, the highest performance (average power and conversion efficiency) obtained from a bulk solid-state erbium laser.

Kilohertz AgGaSe 2 optical parametric oscillator pumped at2 μm

A high-repetition-rate high-average-power AgGaSe2 doubly resonant optical parametric oscillator has been demonstrated by using a 2-μm pump laser operating at 2.5 and 5 kHz. Energy conversion and slope efficiencies of 23% and 32%, respectively, were achieved. Sustained average power outputs as high as 740 mW were measured. Evidence of optical parametric oscillator output saturation and damage site formation at the crystal output face are effects attributed to thermal lensing in our AgGaSe2 crystal.

Advances in nonlinear optical crystals for mid-infrared coherent sources

Advances in growth of the birefringent crystals ZnGeP2 and CdSiP2, as well as all-epitaxial processing of orientation-patterned semiconductors GaAs (OP-GaAs) and GaP (OP-GaP), are extending solid-state laser output deep into the mid-infrared. These materials exhibit the highest nonlinear coefficients and broadest infrared transparency ranges among all practical nonlinear optical crystals. In this review paper we describe the attractive properties of these materials, along with the unique capabilities and novel crystal growth and processing that continue to provide record-breaking conversion efficiencies and output powers in the mid-infrared.

2-μm-pumped 8-12-μm OPO source for remote chemical sensing

A 100 Hz, optical parametric oscillator (OPO) lidar breadboard is designed, built and tested for remote chemical sensing in the 8 - 12 micrometers range. Continuous tuning is achieved by angle tuning a type II, silver gallium selenide (AgGaSe2) OPO crystal pumped in a single step by a 2.088-micrometers pump laser. The pump source for the OPO consists of a temperature stabilized, continuously pulsed, resonantly pumped Ho:YAG (2.088-micrometers ) laser, end-pumped by a diode- end-pumped Tm:YLF (1.9-micrometers ) laser. The 9 mm X 5 mm X 25 mm-long OPO crystal was mounted on a computer-controlled galvanometer scanner for rapid wavelength tuning (1.5 micrometers between shots). Continuous tunability was demonstrated from 7.9 to 12.6 micrometers with energies in the 50 - 400 (mu) J range. Quantum slope conversion efficiencies up to 40% were obtained. Far-field beam divergence measurement showed the output of the OPO to be 2.6 times diffraction limit. The improved OPO beam quality over previous studied tandem OPO systems is attributed to the reduced Fresnel number of the OPO cavity (idler resonating) and the better beam quality of the pump source. A LabWindows based data collection and analysis system is implemented. The effectiveness of the OPO as a source for chemical sensing is demonstrated by the collection of the absorption spectrum of ammonia.

Pulsed Tm-doped fiber lasers for mid-IR frequency conversion

Fiber lasers are an ideal pump source for nonlinear frequency conversion because they have the capability to generate short pulses with high peak-powers and excellent beam quality. Thulium-doped silica fibers allow for pulse generation and amplification in the 2-micron spectral band. This opens the door to a variety of nonlinear crystals, such as ZnGeP2 (ZGP) and orientation patterned GaAs (OPGaAs), which cannot be pumped by Yb- or Er-doped fiber laser directly due to high losses in the near-IR band. These crystals combine low losses with high nonlinearities and transparency for efficient nonlinear mid-IR converters. Using such nonlinear crystals and a pulsed Tm-doped master oscillator fiber amplifier (MOFA), we have demonstrated efficient mid-IR generation with watts of output power in the 3-5μm region. The Tm-doped MOFA is capable of generating from 10 to 100W of average output power at a variety of repetition rates (10kHz - >500kHz) and pulse widths (10ns - >100ns). Total mid-IR power is only limited by thermal effects in the nonlinear materials. The use of Tm-doped fiber-pumped OPOs shows the path toward compact, efficient, and lightweight mid-IR laser systems.

Multi-watt mid-IR fiber-pumped OPO

We have demonstrated a multi-watt mid-IR ZGP OPO pumped by a pulsed Tm-doped fiber laser operating at 1.995 um. 2 W of total mid-IR output power has been generated in the 3.4-3.9 mum and 4.0-4.7 mum spectral regions simultaneously.