James C. Barnes

Tetragonal vanadates YVO4 and GdVO4 – new efficient χ(3)-materials for Raman lasers

Abstract Efficient room temperature multiple Stokes and anti-Stokes picosecond generation in tetragonal YVO4 and GdVO4 host crystals for lasing trivalent lanthanides (Ln3+) has been observed for the first time. All measured stimulated Raman scattering (SRS) wavelengths in the visible and near infrared are identified and attributed to the SRS-active vibration modes of these vanadates.

High efficiency nanosecond Raman lasers based on tetragonal PbWO4 crystals

Abstract We report on laser action in linear and ring Raman oscillators based on novel χ (3) -active PbWO 4 crystals with scheelite structure ( ω R =901 cm −1 ). These resonators are pumped by the fundamental and the second harmonic wavelengths, respectively, of a Q-switched Nd 3+ :Y 3 Al 5 O 12 laser. In these preliminary measurements, conversion efficiencies as high as 20% are observed. To our knowledge, this is the first such demonstration of Raman lasing in lead tungstate in the nanosecond regime. Raman lasers based on PbWO 4 are very promising for several applications, including the generation of wavelengths in the uv (in conjunction with other nonlinear processes) for ozone differential absorption lidar. This material has optical transparency from ≈0.33 to ≈5.5 μm, making it also potentially useful for trace gas detection in the infrared. Furthermore, it has a high damage threshold and is not hydroscopic. Some new data on picosecond high-order Stokes and anti-Stokes generation are also presented. In particular, our SRS experiments with a 1-μm Nd 3+ :Y 3 Al 5 O 12 pump laser demonstrate multiple anti-Stokes emission up to the 10th component with λ ASt10 =0.5433 μm.

Injection seeding. I. Theory

Injection seeding has proven to be a practical method of controlling the spectral output of a laser in an efficient and reliable manner. To achieve satisfactory injection seeding performance, a sufficiently large seed must be employed. To characterize the required seed, an injection seeding theory is developed here which establishes two interrelated concepts, threshold for injection seeding and spectral purity of the laser output. Rather than utilizing numerical techniques to solve the differential equations, closed-form expressions for the threshold are developed for not only common continuous wave injection seeding but pulsed injection seeding as well. In addition, effects of alignment of the seed to the resonator, both in position and angle, and effects of frequency mismatch, or difference between the seed and the resonant frequencies of the resonator, are taken into account. Expressions for the threshold utilize readily measurable experimental parameters. Spectral purity of the laser output and its consequences on the required seed power or energy are also explored. >

Pulsed injection control of a titanium-doped sapphire laser

Injection control of a tunable Ti:sapphire laser using a narrow-bandwidth pulsed dye laser operating at a wavelength removed from the peak of the Ti:sapphire-laser gain curve is reported. The free-running Ti:sapphire laser had broadband laser emission from 750 to 790 nm. Injection at 727 nm resulted in essentially complete energy extraction at that wavelength in a 2.5-pm bandwidth matching the injection source.

Development of the Lidar Atmospheric Sensing Experiment (LASE)—An Advanced Airborne DIAL Instrument

The Lidar Atmospheric Sensing Experiment (LASE) Instrument is the first fully-engineered, autonomous Differential Absorption Lidar (DIAL) System for the measurement of water vapor in the troposphere (aerosol and cloud measurements are included). LASE uses a double-pulsed Ti:Sapphire laser for the transmitter with a 30 ns pulse length and 150 mJ/pulse. The laser beam is “seeded” to operate on a selected water vapor absorption line in the 815-nm region using a laser diode and an onboard absorption reference cell. A 40 cm diameter telescope collects the backscattered signals and directs them onto two detectors. LASE collects DIAL data at 5 Hz while onboard a NASA/Ames ER-2 aircraft flying at altitudes from 16–21 km. LASE was designed to operate autonomously within the environment and physical constraints of the ER-2 aircraft and to make water vapor profile measurements across the troposphere to better than 10% accuracy. LASE has flown 19 times during the development of the instrument and the validation of the science data. This paper describes the design, operation, and reliability of the LASE Instrument.

Injection seeding. II. Ti:Al/sub 2/O/sub 3/ experiments

Experiments have been designed and performed to determine the effects on the seeding efficiency of injection seed energy and power, alignment, and spatial mode matching between single longitudinal mode seed lasers and a power oscillator. The absorption features of H/sub 2/O have allowed the characterization of the seeding efficiency by selectively absorbing the laser output energy corresponding to the seed wavelength. This enabled the accurate measurement of the residual unseeded laser output energy. Both a pulsed and a continuous wave seed source were used for these experiments. This work compares the results of the experiments with a theory for injection seeding developed in the previous paper. >

A self-injection locked, Q-switched, line-narrowed Ti:Al/sub 2/O/sub 3/ laser

Line-narrowing, Q-switched, and self-injection locking are studied independently and as a system. Line narrowing is shown both theoretically and experimentally to depend on the inverse square root of the pulse evolution time interval. Q switching of the Ti:Al/sub 2/O/sub 3/ laser is demonstrated and the laser output energy as a function of the Q-switch delay is investigated. Self-injection is demonstrated and the operation of the laser is explored as a function of loss and the Q-switch delay. Self-injection locking is demonstrated and the performance as a function of the Q-switch delay is determined. >

Master oscillator power amplifier performance of Ti:Al/sub 2/O/sub 3/

An improved Ti:Al/sub 2/O/sub 3/ amplifier model is reported. Amplifier performance under various pump and probe fluence conditions is also reported. It is claimed to be in good agreement with the numerical model predictions. >

High-energy, efficient, 30-Hz ultraviolet laser sources for airborne ozone-lidar systems

Two compact, high-pulse-energy, injection-seeded, 30-Hz frequency-doubled Nd:YAG-laser-pumped Ti: sapphire lasers were developed and operated at infrared wavelengths of 867 and 900 nm. Beams with laser pulse energy >30 mJ at ultraviolet wavelengths of 289 and 300 nm were generated through a tripling of the frequencies of these Ti:sapphire lasers. This work is directed at the replacement of dye lasers for use in an airborne ozone differential absorption lidar system. The ultraviolet pulse energy at 289 and 300 nm had 27% and 31% absolute optical energy conversion efficiencies from input pulse energies at 867 and 900 nm, respectively.

An all solid-state 2-/spl mu/m laser system for space coherent wind lidar

We describe a 2-/spl mu/m diode-pumped, room temperature Ho:Tm:YLF laser and end-pumped amplifier system. The Ho:Tm:YLF oscillator utilized a multiple folded resonator with eight mirrors. A Q-switched output energy of 109 mJ pulse was obtained at 6 Hz. This new design makes the laser a smaller size, which can be used in space application. The effects of the laser operating temperature, thermal focusing and resonator structure rigidity on the performance of the laser were also investigated. In order to increase the laser system energy and efficiency, an end-pumped Ho:Tm:YLF disk amplifier was designed. Preliminary results showed that the efficiency of this laser amplifier could be better than 3% during Q-switch operation, a factor of three increase over side-pumped amplifier configuration. The laser system performance and its potential use for remote sensing of wind are presented.