Yuan Liang Lim

120-W continuous-wave diode-pumped Tm:YAG laser

We present a 120-W cw diode-pumped Tm:YAG laser. The Tm:YAG rod is side pumped by three diode arrays whose radiation is coupled through compound parabolic concentrators. The maximum optical-to-optical conversion efficiency of the 2.02-mum laser output is 25.2%, with a slope efficiency of 31.2%.

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.

Compact 21-W 2-µm intracavity optical parametric oscillator

We report on an intracavity optical parametric oscillator (OPO) placed within a compact diode-pumped Nd:YALO laser cavity. This OPO utilizes a pair of KTP crystals, which are diffusion bonded together in a walk-off-compensated configuration. We have generated up to 21.4 W of 2-mum radiation, operating in a few-kilohertz range.

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.

Room-temperature operation of a multiwatt Tm:YAG laser pumped by a 1-µm Nd:YAG laser

We present what is to our knowledge the first demonstration of a 4.7-W cw Tm:YAG. This proof-of-principle experiment clearly demonstrates the possibility of using a pump absorption that is 2 orders of magnitude (~0.0078 cm(-1)) less than that of the conventional pump absorption (typically >1 cm(-1)). This Tm:YAG laser is pumped intracavity within a Nd:YAG laser for multiple-pass absorption. The maximum conversion efficiency of 2.02 mum is 20%, with a slope efficiency of 35% with respect to the absorbed 1.064-mum power.

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.

Thermal investigation of a 120-W Tm:YAG laser

We demonstrated a 120-W side-pumped Tm:YAG laser with compound parabolic concentrators (CPCs) to couple the pump light into the laser rod. The optical-to-optical efficiency of this laser is 25.2% and the slope efficiency is 31.2%. At such high average power operation, we encountered severe thermal lensing in our Tm:YAG laser rod which prevented us from increasing the diode pump power due to the thermal rollover as the laser cavity become unstable. In this paper, Temperature was measured using IR camera. Temperature and stress distributions are obtained using finite element method. Those data can be used to estimate the fracture limit, the thermal lensing, the thermal distortion of the Tm:YAG laser and subsequently correct the thermal distortion using diffractive optical devices etc.

Greater than 100W diode-pumped Tm:YAG laser and its thermal issues

We discuss in this paper the serious thermal issues faced by a high average power (>100W) diode-side-pumped 2-micron Tm:YAG laser. An approach to quantify the thermal lensing with subsequent cavity designing to alleviate such thermal issues is presented. The simple approach outlined allows one to come up with appropriate cavity configurations quickly to overcome the thermal rollover and to power scale the laser. Such a technique is applicable to all high average power solid- state rod lasers which inevitably suffers from severe thermal aberrations.