P. B. Phua

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%.

Coupled tandem optical parametric oscillator (OPO):?an OPO within an OPO

We have demonstrated, for the first time to our knowledge, a coupled tandem optical parametric oscillator (OPO) configuration in which a second ZnGeP(2) OPO is placed within the resonator of the first, KTiOPO(4), OPO. A significant enhancement in the overall cascaded efficiency of this OPO compared with standard two-stage OPOs was observed. With a multimode Nd:YAG laser, an overall optical-to-optical efficiency (from 1.06 microm to the mid IR) of 5.2% was obtained from operating only ~1.4 times above oscillation threshold. The measured overall slope efficiency was attractively high at 35%. With a single set of mirrors we obtained a broad wavelength-tuning range from 2.7 to 8 microm.

High-average-power mid-infrared ZnGeP~2 optical parametric oscillator with a wavelength-dependent polarization rotator

A wavelength-dependent polarization rotator is used to transform the orthogonal polarizations of the signal and idler of a near-degenerate type II KTP optical parametric oscillator (OPO) into a common polarization state. This common polarization allows a single ZnGeP2 OPO to fully utilize the 2 microm signal and idler KTP OPO outputs in a mid-IR conversion. The simple design of the wavelength-dependent polarization rotator yields a compact source that simultaneously generates four mid-JR wavelengths collinearly with a total mid-IR average power of 5.5 W at a >15 kHz pulse repetition rate.

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.

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.

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.

High power radial polarization conversion using photonic crystal segmented half-wave-plate

We generated 110 watts of radial polarized laser beam from Yb fiber laser using photonic-crystal segmented half-wave-plate. This is a promising external radial polarization converter for fiber laser used in the laser cutting industry.

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.

Broadband 6 µm OPA Driven by Yb:CaF2 DPSSL System

6-μJ, 6-μm pulses compressible to 1.5 optical cycles are generated in multistage OPA driven by 500-Hz Yb:CaF₂-DPSSL. The system is favorable for verification of the predictions on λ-scaling of photoelectron wavepacket dynamics and atmospheric spectroscopy.

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.