Kin Seng Lai

Multiwatt mid-IR output from a Nd:YALO laser pumped intracavity KTA OPO.

We have achieved 4.1W of 3.5-micron output from a non-critically phasematched (NCPM), type II, KTiOAsO4 (KTA) optical parametric oscillator (OPO) pumped within the cavity of a Q-switched diode-pumped Nd: YALO laser operating at 10kHz. We adopted the simplest configuration with a compact diode-pumped Nd: YALO module pumping the singly resonant KTA OPO. Besides 4.1W of 3.5um, 10.9W of 1.5 micron and 11.3W of 1-micron radiation were obtained simultaneously.

HIGH-EFFICIENCY MID-INFRARED ZNGEP2 OPTICAL PARAMETRIC OSCILLATOR IN A MULTIMODE-PUMPED TANDEM OPTICAL PARAMETRIC OSCILLATOR

We demonstrate a high-efficiency ZnGeP(2) optical parametric oscillator (OPO) pumped by another KTP OPO in a multimode-pumped tandem OPO configuration. The maximum optical-to-optical and slope efficiencies were 32% and 42.5%, respectively. Our setup also provides tunable multiband radiation in the 2.03-2.32-microm range and the 2.9-6.2-microm range simultaneously.

Analysis of a dynamical procedure on diode-end-pumped solid-state lasers

For solid-state lasers, we have determined that the overlap integrals V/sub th/, related to the threshold pump power, and V/sub slope/, related to the laser slope efficiency, dynamically change with pump power. The increase of diffraction loss is also caused by the dynamical change of the laser mode size, which alters the Fresnel number of the cavity. Subsequently, the threshold pump power and the laser slope efficiency also change dynamically. The dramatic increase of the laser mode radius at the laser crystal and the sudden decrease of the laser mode radius at the output mirror when operating near the stability limit make the laser output suddenly drop. A longer cavity will have a larger threshold pump power and a smaller total output power.

Multiwatt high-repetition-rate 2-µm output from an intracavity KTiOPO 4 optical parametric oscillator

We have obtained 6.5 W of 2-mum output from a near-degenerate, type II KTiOPO(4) (KTP) optical parametric oscillator (OPO) pumped within the cavity of a Q-switched diode-pumped Nd:YAG laser that operates at 3 kHz. We adopted the simplest configuration with a compact diode-pumped Nd:YAG module pumping the doubly resonant KTP OPO in its randomly polarized resonator with an acousto-optic Q switch. Attempts to increase the 2-mum output power by pumping this intracavity KTP OPO with a polarized laser beam by use of thermal birefringence compensation configurations are discussed.

Linearly polarized 100-W output from a diode-pumped Nd:YAlO laser

We demonstrate a compact cw diode-pumped Nd:YAlO laser that can produce 100 W of power at 1079 nm and 18.3 W at 1341 nm. Lasing and nonlasing thermal lensing data are presented.

Multiwatt KTiOPO4 optical parametric oscillators pumped within randomly and linearly polarized Nd:YAG laser cavities

We present 2 experiments on intracavity pumping of a KTiOPO4 (KTP) optical parametric oscillator (OPO) within a high power 1064nm Nd:YAG laser cavity producing multiwatt level 2-micron outputs. In such high power regime, the Nd:YAG rod laser suffers significant thermally-induced birefringence loss when it is linearly polarized. Hence in the first experiment, we present our intracavity KTP OPO pumped within the simple cavity of an unpolarized Nd:YAG laser. This simple configuration, with 1-micron high reflectors forming the Nd:YAG laser cavity and R equals 75 percent and 100 percent 2-micron mirrors forming the short flat-flat OPO cavity, delivered 6.5W of 2-micron output power at 3kHz Q-switched operation. Next we pumped our intracavity OPO within a more complex polarized Nd:YAG laser cavity. In this second experiment, we compensated for the thermally-induced birefringence loss in the Nd:YAG laser by using a re-entrant laser cavity with a Faraday rotator, and the OPO was pumped within one arm of this set-up. In this case, we also obtained approximately 6.5W of 2-micron output. FInally, studies of the temporal profiles of the 1 and 2-micron laser beams also revealed interesting multiple pulse features in such intracavity OPO output.

Linearly polarized 120-W output from a diode-pumped Nd:YALO laser

We present here a compact 120 W, continuous-wave (CW), diode-pumped Nd:YALO laser at 1079 nm. This linearly polarized output from the optically anisotropic Nd:YALO crystal is advantageous for pumping non-linear crystals. The 1 at% doped Nd:YALO laser rod, 4 mm diameter by 97 mm long, is cut along the b-axis, with both ends anti-reflection coated at 1079 nm and 1341 nm. It is water-cooled (16 degree(s)C) and side-pumped by 5 close-coupled CW diode arrays operating at 803 nm. We obtained 121 W output at the maximum diode pump power of 571 W. The optical slope efficiency is 60%. This is, to the best of our knowledge, the highest power obtained from a diode-pumped Nd:YALO laser. We have studied this thermal lensing at different diode pump powers in lasing and non-lasing configurations. The measured thermal lens decreased from 37.5 to 11 cm as the pump power increased from 185 to 542 W in the lasing configuration. In the non-lasing case, the corresponding thermal lens decreased from 35.5 to 9.5 cm. We have also successfully operated our Nd:YALO laser at 1341 nm. We obtained a maximum output of 60 W, to the best of our knowledge, the highest diode-pumped laser output at this wavelength.

A 150W 2-micron diode-pumped Tm:YAG laser

We present a 150W CW diode-side-pumped 2-micron TmiYAG laser. Temperature dependence on performance of this quasi-3-level laser is investigated, together with characterization of the thermal lensing and cavity designing for such high average power lasers.

High-power diffusion-bonded walk-off-compensated KTP OPO

Recently, we have obtained a 23.5 W of 2-micrometers intracavity OPO output which is, to the best of our knowledge, the highest power from an intracavity OPO reported in the literature. To achieve such high average power 2-micrometers OPO output in a simple and compact laser system, we have adopted the diffusion-bonded walk-off compensated (DBWOC) KTP OPO pumped by the anisotropy Nd:YALO laser. The walk-off compensated twin KTP crystals reduce the aperture effect due to Poyntings walkoff in the critically phase-matched parametric generation. At the same time, it increases the acceptance angle for the nonlinear interaction, resulting in more efficient OPO conversion. In addition, the diffusion-bonded configuration eliminates the optical losses at the in/out facets and the need for alignment of the crystals. In order to low down the OPO threshold and increase the effective gain of KTP OPO, we bonded two pairs of crystals together. In this paper, we will compare the recent results of the 2-micrometers KTP OPO results with different pairs of DBWOC KTP OPO. With two pairs of DBWOC KTP device, we observed 78% higher 2-micrometers average output power compared to one pair of KTP device.

Compact mid-IR intracavity OPO

In this paper, we report a compact mid-IR intracavity OPO, which has 4.1 W of 3.5-micron output from a non-critically phase-matched (NCPM), type II, KTiOAsO4 (KTA) optical parametric oscillator (OPO). This KTA OPO was pumped within the cavity of a Q-switched diode-pumped Nd:YALO laser operating at 10 kHz. We adopted the simplest configuration with a compact diode-pumped Nd:YALO module pumping the singly resonant KTA OPO. Besides 4.1 W of 3.5 um, 10.9 W of 1.5 micron and 11.3 W of 1-micron radiation were obtained simultaneously.