Tunable Alexandrite Laser Research Articles

Alexandrite lasers with blue-diode-pumping.

The availability of high-power and high-brightness blue diode lasers makes them attractive as low-cost pump sources for broadly tunable Alexandrite lasers. In this paper we investigate the performance of an Alexandrite laser pumped by a high-power fiber-delivered blue diode module. Output power 1.84 W is achieved, the highest power from blue diode pumped Alexandrite to date. Excellent pump absorption is demonstrated of scrambled pump polarization on both a-axis and b-axis of Alexandrite crystal. Wavelength tuning and dual wavelength operation is produced using the self-birefringent filtering of the Brewster-cut Alexandrite crystal. An analysis is made of laser efficiency and mode formation including the creation of higher-order Laguerre-Gaussian vortex modes (LG01 and LG02). Performance is compared to red diode pumping and prospects for further optimization and power-scaling are discussed.

371-385 nm tunable alexandrite continuous-wave laser

371-385 nm tunable alexandrite continuous-wave laser

Development of the megahertz planar laser-induced fluorescence diagnostic for plasma turbulence visualization

A megahertz laser-induced fluorescence-based diagnostic system for measuring ion density fluctuations in two spatial dimensions is described. Well resolved spatial and temporal two-dimensional (2D) images of turbulent structures will be useful in understanding ion turbulence in magnetically confined plasmas which is a key factor in the performance of fusion experimental devices. A sheet beam of a megahertz repetition rate tunable Alexandrite laser is used to excite ion emission from argon plasma. The fluorescence emitted from the plane of the laser beam is detected with a narrow band interference filter and intensified ultrafast charge coupled device camera providing 2D images of relative ion density fluctuations every microsecond. It is expected that the edge plasma on fusion devices will be accessible to this technique.

Numerical study of passive Q switching of a tunable alexandrite laser with a Cr:Y_2SiO_5 solid-state saturable absorber

Passive Q switching of a tunable alexandrite solid-state laser with a Cr:Y2SiO5 solid-state saturable absorber is numerically studied over a major portion of the alexandrite tuning range. The theory of passive Q switching with a slowly relaxing saturable absorber is studied and utilized for evaluating the performance of the Cr:YSO Q-switched alexandrite laser system. With a typical laser configuration, a Q-switched laser pulse of 262 mJ in 23 ns is obtained.

Narrow-band tunable alexandrite laser with passive Q switching

An alexandrite laser with a self-injection of narrow-band radiation into its cavity was developed. A Fabry — Perot interferometer and a diffraction grating were used as dispersive components in an additional cavity. The cavity was switched by an LiF crystal with F3- colour centres. The laser generated a single pulse of ~ 180 ns duration and of 1.5 mJ energy, and with a spectrum 5 × 10-3 cm-1 wide. The laser emitted in the spectral range 720 — 780 nm.

Long-pulse ultraviolet-laser sources based on tunable alexandrite lasers

A long-pulse ultraviolet (UV) laser source has been demonstrated. It was obtained by the harmonic generator of a flashlamp-pumped alexandrite laser operating in the normal-pulse mode. We obtained tunable UV light in the wavelength region 365-390 nm. A 375-nm output generated 90 mJ. The pulsewidth was 240 /spl mu/s. The UV-laser output was successfully transmitted through a 3-m-long step-index-type silica fiber with a core diameter of 600 /spl mu/m.

Collinear and non-collinear sum-frequency mixing in?-BBO for a tunable 195?198 nm all-solid-state laser system

We attained tunable UV laser radiation between 195 and 198 nm by sum-frequency mixing two synchronized flashlamp-pumped solid-state Q-switch lasers, a Nd:YAG laser frequency quadrupled to 266 nm and a tunable (730–770 nm) alexandrite laser. UV pulse energies of 0.12 mJ with repetition rates of 10 Hz were attained in collinear, as well as non-collinear sum-frequency interaction in aβ-Barium Borate (BBO) crystal with a conversion efficiency of 2.5%. Theoretical models for the non-collinear phase-matching interaction were investigated at UV wavelengths below 200 nm.

Measurements of Atmospheric Water Vapor with an Alexandrite Lidar.

A differential absorption lidar (DIAL) for the detection of atmospheric water vapor was developed based on a tunable alexandrite laser. Theoretical estimation shows that the bandwidth of laser radiation and accuracy of the wavelength tuning critically affect detection errors. We propose a new accurate tuning method on the resonance line of H2O at 725.8 nm using the opto-galvanic effect in a Xe discharge tube, and compared it with an absorption method and a photo-acoustic method. The DIAL experiment demonstrates the detection range up to 9.5 km with a detection error of less than 50%. The H2O distributions measured were agreed with sonde data.

Pump wavelength tuning of a near-infrared optical parametric oscillator

Optical parametric conversion in a potassium titanyl phosphate crystal with a tunable alexandrite laser was investigated as a function of pump wavelengths in the 700-800-nm region. Threshold energies and slope efficiencies for a doubly resonant oscillator configuration were measured for pump wavelengths of 744, 766, and 780 nm. Phase-matching conditions and a theoretical analysis using Sellmeier's equations provide good agreement with experimentally measured values of signal and idler wavelengths as a function of the pump wavelengths.

Lasing properties of chromium-aluminum-doped forsterite pumped with an alexandrite laser

The lasing properties of chromium-aluminum-doped forsterite were investigated using a tunable alexandrite laser as the pump source. Results of measurements of the lasing threshold, slope efficiency, spectral and temporal profiles of the laser pulse, and the time delay between the alexandrite pump pulse and the laser emission are presented for pump wavelengths of 770, 746, and 730 nm and different pump beam energies. Laser rate equations are developed to model the lasing center as a four-level system and applied to the case of 746-nm pumping.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Airborne and ground based lidar measurements of the atmospheric pressure profile

The first high accuracy remote measurements of the atmospheric pressure profile have been made. The measurements were made with a differential absorption lidar system that utilizes tunable alexandrite lasers. The absorption in the trough between two lines in the oxygen A-band near 760 nm was used for probing the atmosphere. Measurements of the 2-D structure of the pressure field were made in the troposphere from an aircraft looking down. Also, measurements of the 1-D structure were made from the ground looking up. Typical pressure accuracies for the aircraft measurements were 1.5-2 mbar with a 30-m vertical resolution and a 100-shot average (20 s), which corresponds to a 2-km horizontal resolution. Typical accuracies for the upward viewing ground based measurements were 2.0 mbar for a 30-m resolution and a 100-shot average.

Excited state absorption of pump radiation as a loss mechanism in solid-state lasers

The characteristics of optical pumping dynamics in laser-pumped, rare-earth-doped, solid-state laser materials are investigated by using a tunable alexandrite laser to pump Y/sub 3/Al/sub 5/O/sub 12/:Nd/sup 3+/ in an optical cavity. It is found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited-state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process is an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths. >

Energy transfer kinetics of singlet molecular oxygen: The deactivation channel for O2(b 1∑+g)

A tunable alexandrite laser was used to produce O2(b 1∑+g) in the gas phase, with quantitative measurement of O2(b 1∑+g) and O2(a 1Δg) densities achieved by detection of the b→X fluorescence and dimol emission signals, respectively. A simple kinetics analysis indicates that collisional deactivation of O2(b 1∑+g) by ground state oxygen molecules occurs with unit production of O2(a 1Δg). These results are in accord with previous assumptions regarding collisional deactivation of O2(b 1∑+b) based on spin conservation.

Tunable alexandrite lasers: Development and performance

Some major recent developments in alexandrite laser research are reviewed. Emphasis is placed on key material characteristics, and their relationship to laser performance. Alexandrite's favorable thermomechanical properties and high capacity for energy storage have led to laser performance levels that, in certain areas, exceed those of established solid-state laser sources. Here we review performance achievements for a variety of pulsed and CW laser configurations including single-mode, multimode, and mode-locked resonators, high-power amplifiers, and zig-zag slabs. In these configurations, operating performance levels have been demonstrated that are comparable to those of older, more familiar solid-state laser technologies. Alexandrite's broad tunability offers additional advantages. Together with nonlinear frequency conversion processes, alexandrite lasers provide high-brightness output over most of the UV, visible, and near IR.

Spectral characterization of a tunable alexandrite laser by rubidium absorption at 780 nm

Rubidium vapor was used to characterize the output of a tunable, pulsed alexandrite laser operating at 780 nm. Rubidium spectra were obtained at temperatures of 23, 50, 110, and 140°C. Excellent agreement was obtained with computer-synthesized spectra which yielded values for the effective laser bandwidth at different operating conditions. The model assumed a Voigt profile for the rubidium 5^{2}P_{3/2} \leftarrow 5^{2}S_{1/2} transition and a Gaussian profile for the laser pulse. The model also showed that the laser output was spectrally compact with no evidence of energy outside the narrow 780 nm central feature.

High efficiency cw laser-pumped tunable alexandrite laser

High efficiency cw alexandrite laser operation has been achieved. With longitudinal pumping by a krypton laser in a nearly concentric cavity, a 51% output power slope efficiency has been measured. Including the transmission at the input coupler mirror, a quantum yield of 85% has been attained above threshold. Tunability from 726 to 802 nm has also been demonstrated. The low loss and good thermal properties make alexandrite ideal for cw laser operation.