T. Y. Fan

Nd:MgO:LiNbO3 spectroscopy and laser devices

Laser oscillation in Nd:MgO:LiNbO3 has been demonstrated. Thresholds as low as 3.6 mW and slope efficiencies up to 39% were achieved in a resonantly pumped miniature device. The electro-optical and nonlinear-optical properties of the host were also used to make active internal Q-switched and self-frequency-doubled lasers. Photorefractive damage is shown to be greatly suppressed compared with that for non-MgO-doped material. Absorption spectra, fluorescence spectra, and lifetime measurements are also reported.

Continuous-wave operation at 2.1 μm of a diode-laser-pumped, Tm-sensitized Ho:Y 3 Al 5 O 12 laser at 300 K

Room-temperature operation of a continuous-wave Tm-sensitized Ho:YAG laser at 2.0974 microm has been achieved under diode-laser pumping at 781.5 nm. Observed thresholds are as low as 4.4 mW, with a slope efficiency of 19% with 0.5% output coupling.

Continuous-wave operation of a room-temperature, diode-laser-pumped, 946-nm Nd:YAG laser

Single-stripe diode-laser-pumped operation of a continuous-wave 946-nm Nd:YAG laser with less than 10-mW threshold has been demonstrated. A slope efficiency of 16% near threshold was shown with a projected slope efficiency well above a threshold of 34% based on results under Rhodamine 6G dye-laser pumping. Nonlinear crystals for second-harmonic generation of this source were evaluated. KNbO(3) and periodically poled LiNbO(3) appear to be the most promising.

Efficient GaAlAs diode-laser-pumped operation of Nd:YLF at 1.047 micron with intracavity doubling to 523.6 nm

Diode-laser-pumped Nd:YLF lasers are demonstrated at 1.047 μm with less than 1-mW thresholds and internal quantum efficiencies approaching 70%. Operation at 1.053 μm has also been achieved. Intracavity second-harmonic generation using MgO:LiNbO3 has generated up to 145-μW output at 523.6 nm for 30.1 mW of diode-laser pump power.

Nd:MgO:LiNbO 3 continuous-wave laser pumped by a laser diode

Diode-pumped laser oscillation was achieved in Nd:MgO:LiNbO(3). The absorbed pump power thresholds were as low as 1.9 mW for the high-gain or pi polarization and 8 mW for the low-gain polarization. A cw output power of 2 mW was obtained for the pi polarization at lambda = 1.085 microm for 9 mW of absorbed pump power. A slope efficiency of 37% was achieved. The diode-pumped Nd:MgO:LiNbO(3) lasers operated for extended periods of time without exhibiting any reduction in output power.

Diode-pumped continuous-wave Nd:glass laser

We report on diode-laser pumping of monolithic Nd:glass laser oscillators. End pumping with a single-stripe diode laser, a threshold of 2.2 mW, and a slope efficiency of 42% were observed on a 2-mm-long oscillator with a mode radius of 35 microm. The oscillator generated 2.5 mW of single-ended output power in many (>20) axial modes.

Two-step excitation and blue fluorescence under continuous-wave pumping in Nd:YLF

Near-UV and blue fluorescence from the 4D3/2 and 4D5/2 manifolds in Nd:YLF has been observed at room temperature under cw pumping by a Rhodamine 590 dye laser. Excitation to these manifolds is attributed to two-step excitation involving excited-state absorption from the 4F3/2 metastable level. A similar phenomenon has also been observed in Nd:YAG and Nd:glass. The effective excited-state absorption cross section is measured to be (2 ± 1) × 10−20 cm2 at 587.4 nm in the π polarization, and the peak effective stimulated emission cross section is measured to be 5 × 10−20 cm2 at 411.7 nm, also in the π polarization. Estimated laser threshold at 411.7 nm for two-step pumping at 587.4 nm is 70 mW.

Energy transfer and inversion saturation in Tm, Ho: YAG

Abstract We report on the spectroscopic properties and the fundamental aspects of the Tm-Ho energy transfer in YAG under low and high excitation densities. Strong Tm-Ho interaction causes efficient down conversion of 781.5 nm pump light and saturation of the 2000 nm transition of Ho3+ in Tm,Ho:YAG laser crystals at 300 K.

Nonradiative Processes and Blue Emission in Nd:YLF

In addition to one-photon absorption and fluorescence in rare earth and transition metal ion-doped crystals and glasses, a number of other processes can occur such as two-step excitation and energy transfer which may affect laser operation. For example, concentration quenching in Nd3+ doped materials is an energy-transfer phenomenon, and energy transfer or two-step excitation can convert infrared photons to visible fluorescence [1] or visible lasers[2]. It has also been shown that energy-transfer upconversion (ETU), also known as Auger recombination, can increase laser threshold and change laser dynamics [3]. Both sequential two-photon excitation (STEP) and energy-transfer upconversion (ETU) have been identified in Nd3+ doped materials. These two processes are shown in Fig. 1. STEP involves absorption of one photon to an excited-state, followed by excited-state absorption (ESA) of a second photon to an even higher-lying level. In ETU, two nearby ions which are in excited-states interact causing one ion to relax while the other is simultaneously excited to a higher state. This is identical to concentration quenching except that one of the ions is in the ground state in concentration quenching. The transition rate for ESA increases with excited-state population density as does the rate for ETU. These processes may be especially important in resonant pumping because the excited-state densities can be quite high.

Diode Pumped Solid-State Laser Oscillators for Spectroscopic Applications

Solid state laser development has been paced by the improvement of pumping sources. From the helical lamps used to pump the early Ruby lasers, to the linear arc and pulsed flashlamps used to pump Nd:YAG lasers, solid state laser pump sources have improved steadily in power and efficiency. The latest development is pumping solid state lasers with diode lasers and diode laser arrays. The development of high power, efficient, long lived diode lasers promises a revolution in solid state laser technology.