Keith E. Murray

Diode-pumped Ho:Tm:LuLiF/sub 4/ laser at room temperature

A diode-pumped room-temperature Ho:Tm:LuLiF/sub 4/ laser achieved an optical efficiency of 9.4% under normal mode operation. Under similar experimental conditions. Ho:Tm:LuLiF/sub 4/ yielded 1.5 times greater optical efficiency than Ho:Tm:YLiF/sub 4/. Absorption spectra and lifetimes as a function of pump energy were measured for evaluation of this laser material.

Diode-pumped long-pulse-length Ho:Tm:YLiF 4 laser at 10 Hz

An optical efficiency of 0.052 under normal mode operation for diode-pumped Ho:Tm:YLiF(4) at a pulse repetition frequency of 10 Hz has been achieved. Laser output energy of 30 mJ in single Q-switched pulses with 600-ns pulse length were obtained for an input energy of 3 J. A diffusion-bonded birefringent laser rod consisting of Ho:Tm-doped and undoped pieces of YLF was utilized for 10-Hz operation.

ZnGeP 2 parametric amplifier

A ZnGeP2 parametric amplifier was constructed, and the small-signal gain of a 3.39-μm He–Ne laser in excess of 10 was measured. With a 2.06-μm Ho:Tm:Er:YLF laser having a nominal 50-ns pulse length as a pump, small-signal gain was measured as a function of pump power. When compared with the predicted gain, taking into account the beam profile of both the pump and the signal, good agreement was found at low pump powers. However, the observed gain was less than predicted at higher pump powers. Pump-induced loss at 3.39 μm, a phenomenon not observed in other nonlinear crystals such as AgGeSe2, causes the difference. Pump-induced loss was observed when the ZnGeP2 crystal was tilted away from the phase-matching angle. Pump-induced loss at 3.39 μm was characterized and found to be directly proportional to the pump energy.

Flash-lamp-pumped Ho:Tm:Cr:YAG and Ho:Tm:Er:YLF lasers: modeling of a single, long pulse length comparison.

Two methods of producing the long pulse lengths that promote efficient extraction of energy from low-gain, quasi-four-level lasers are analyzed. A long pulse length output can mitigate laser-induced damage effects and can be generated in quasi-four-level lasers by two disparate methods. One method utilizes Q-switching techniques in resonators designed to extend the pulse length and another utilizes the first pulse in a relaxation oscillation pulse train. Models for quasi-four-level lasers are derived here taking into account the nonnegligible thermal population of the lower laser level. Closed-form expressions are derived for both modes of operation of quasi-four-level laser systems so the parametric dependencies of both forms of operation become obvious, allowing facile comparison. In addition, a combined absorption and quantum efficiency, germane for flash-lamp pumping, is calculated for both Cr and Er sensitizers. Although the former has the advantage of broad absorption bands, the latter has the advantage of a quantum efficiency approaching 3.

Cr:Er:Tm:Ho:yttrium aluminum garnet laser exhibiting dual wavelength lasing at 2.1 and 2.9 μm: Spectroscopy and laser performance

Over 1.0 J of 2.1 μm laser energy and over 0.5 J of 2.9 μm laser energy have been demonstrated in a single flashlamp pumped solid state laser material, specifically Cr:Er:Tm:Ho:YAG. Flashlamp pumped laser operation of Ho:YAG at 2.1 μm and Er:YAG at 2.9 μm in various host materials is well known. We have developed an innovative laser system that operates at each of these wavelengths independently or simultaneously in a single solid state laser material with performance comparable to single wavelength systems Er:YAG and Cr:Tm:Ho:YAG. Variation of the flashlamp pump pulse length provides a method to discriminate between lasing at 2.1 and 2.9 μm. This effect results from Er→Tm→Ho energy transfer, the short lifetime of the upper lasing manifold in Er, the 4I11/2 manifold, and the relatively long upper laser level lifetime in Ho, the 5I7 manifold. This simple tuning method of achieving two widely separated wavelengths without the use of optical tuning elements has potential applications in remote sensing and me...

Long-pulse-length 2 μm diode-pumped YLiF 4 laser

A diode-pumped Ho:Tm:YLiF4 laser at room temperature has achieved an optical efficiency of 5.9% under normal-mode operation. Long pulse lengths, of the order of 1 μs, have been obtained by use of 4-m ring resonator, with laser energy output of 15 mJ in single Q-switched pulses for an input energy of 2.078 J.

Diode-pumped Ho:Tm:YLF laser pumping an AgGaSe 2 parametric oscillator

Tuning of both the pump laser, a Ho:Tm:YLF laser operating on the 5I7–5I8 transition, and an AgGaSe2 parametric oscillator has been demonstrated. Tuning of the Ho:Tm:YLF laser is complicated but not frustrated by the existence of both CO2 and H2O lines in the vicinity of the laser transition. Tuning of the parametric oscillator was achieved by tuning of the pump laser. Injection seeding of the parametric oscillator on the nonresonant signal was also demonstrated. In addition, the measured efficiencies of the parametric oscillator were compared for two different methods, measuring the parametric-oscillator output energy and measuring the energy depleted from the pump. By comparison of these measurements, the intrinsic efficiency of the parametric oscillator can be determined.

Nd:LuLF operating on the 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 transitions

Nd:LuLF, that is, Nd:LuLiF4, was grown with a Czochralski technique and characterized spectroscopically to include absorption and emission data and lifetime. Evaluation of this laser material for operation on the 4F3/2→4I11/2 and the 4F3/2→4I13/2 transitions was performed. Normal-mode laser performance was achieved on both the π and the σ polarizations for both transitions by use of a simple polarization-selective resonator. Both normal-mode and Q-switched performance was characterized on the 4F3/2→4I11/2 transition.

Flash-lamp-pumped Ho:Tm:Cr:YAG and Ho:Tm:Er:YLF lasers: experimental results of a single, long pulse length comparison

Flash-lamp-pumped, room-temperature Ho:Tm:Cr:YAG and Ho:Tm:Er:YLF are compared for single but long pulse operation, with pulse lengths of approximately 1.0 mus. Under similar operating conditions in normal-mode operation, a slope efficiency of 0.0331 was observed for Ho:Tm:Er:YLF compared with 0.0047 for Ho:Tm:Cr:YAG. For Q-switched operation, Ho:Tm:Er:YLF yielded a slope efficiency of 0.0075. In comparison, a slope efficiency of 0.0012 was obtained for Ho:Tm:Cr:YAG. Two methods of producing long pulse lengths are compared: pulse selection of normal-mode relaxation oscillations and Q-switching in a long resonator. Theoretical models developed in a companion paper for normal-mode relaxation oscillations and Q-switching in quasi-four-level solid-state lasers are in agreement with the experimental results.

Injection-Seeded Optical Parametric Oscillator

Injection seeding of an AgGaSe2 mid infrared optical parametric oscillator using a continuous wave HeNe laser operating at 3.39 µm has been demonstrated. A measurement of the resulting spectral bandwidth, 0.001 µm, was resolution limited. Pulse evolution time intervals were found to be significantly shorter when injection seeding was in effect while the efficiency was found to be significantly higher.