Bo Trieu

High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

High Energy Totally Conductive Cooled, Diode Pumped, 2µm Laser

This paper describes the design and performance a totally conductive cooled, space-qualify-able high-energy 2-µm laser. Over 230mJ normal mode energy and 107mJ of Q-switched energy has been achieved.

Advances in high-energy solid-state 2-micron laser transmitter development for ground and airborne wind and CO2 measurements

Sustained research efforts at NASA Langley Research Center (LaRC) during last fifteen years have resulted in a significant advancement in 2-micron diode-pumped, solid-state laser transmitter for wind and carbon dioxide measurement from ground, air and space-borne platform. Solid-state 2-micron laser is a key subsystem for a coherent Doppler lidar that measures the horizontal and vertical wind velocities with high precision and resolution. The same laser, after a few modifications, can also be used in a Differential Absorption Lidar (DIAL) system for measuring atmospheric CO2 concentration profiles. Researchers at NASA Langley Research Center have developed a compact, flight capable, high energy, injection seeded, 2-micron laser transmitter for ground and airborne wind and carbon dioxide measurements. It is capable of producing 250 mJ at 10 Hz by an oscillator and one amplifier. This compact laser transmitter was integrated into a mobile trailer based coherent Doppler wind and CO2 DIAL system and was deployed during field measurement campaigns. This paper will give an overview of 2- micron solid-state laser technology development and discuss results from recent ground-based field measurements.

Single longitudinal mode, high repetition rate, Q-switched Ho:YLF laser for remote sensing

An injection-seeded, Q-switched Ho:YLF laser has been developed. For 13W pumping from a CW Tm:fiber laser, the energy and width of single longitudinal mode pulse are 5.5mJ and 50ns, respectively. The repetition rate is 1.25kHz.

Efficient Operation of Conductively Cooled Ho:Tm:LuLiF Laser Oscillator/Amplifier

A conductively-cooled Ho:Tm:LuLiF laser oscillator generates 1.6J normal mode pulses at 10Hz with optical to optical efficiency of 20%. When the laser head module is used as the amplifier, the double-pass small-signal amplification excesses 25.

Fully conductively cooled, diode-pumped Ho:Tm:LuLiF 4 laser oscillator/amplifier

A fully conductively cooled and diode-pumped linear Ho:Tm:LuLiF laser oscillator can generate more than 1 J normal mode pulses at a 10 Hz pulse repetition rate where heat pipes are used for cooling pump diodes and laser crystal. As an amplifier, it can amplify the 80 mJ/180 ns pulses into 400 mJ pulses before the appearance of amplified spontaneous emission (ASE). The ASE threshold is about 5.6 J with a 40 mm long and side-polished laser crystal. For a 5 mJ input pulse and 5.6 J pump pulse, the double-pass gain exceeds 22.5. If the lateral surface of the laser crystal is fine ground, the ASE threshold can rise to higher than 8 J, but the efficiency will be lower due to large pump diffusion.

Highly efficient Ho:YLF laser pumpbed by Tm:fiber laser

The highly efficient 2-mum Ho:YLF laser has been demonstrated at room temperature. For 35 W pumping power, 19 W output power is obtained at the TEM00 mode. The slope and optical-to-optical efficiencies are 65% and 55%, respectively.

Design of a totally conductively cooled diode-pumped 2μm-laser amplifier

For space-based lidar applications, conductively cooled lasers have been identified as a critical technology for high energy, 2-micron laser transmitter. Effective thermal management is a challenge for high-energy, 2-micon lasers. In this paper, the design of a totally conductively cooled, diode pumped, 2-micron laser amplifier is presented. Based on the successful testing of a conductively cooled oscillator, concepts for a laser amplifier were developed. The newly designed amplifier consists of a 40 mm long Ho:Tm: LuLF rod being pumped by 4 banks of 5-radially arranged diode lasers totaling 80W pump power. Optical and thermal studies for the amplifier head are presented and discussed. Currently, the design of the amplifier head is being integrated into a complete amplifier subsystem for a conductive cooled Master Oscillator Power Amplifier (MOPA) laser.

Conductively cooled Ho:Tm:LuLiF laser amplifier

A conductively-cooled Ho:Tm:LuLiF laser head can amplify 80 mJ/340 ns probe pulses into 400 mJ when the pump pulse energy is close to amplified spontaneous emission (ASE) threshold, 5.6J. For a small signal, the double-pass amplification exceeds 25.

300mJ injection seeded compact 2 micron coherent lidar transmitter

The design of a compact coherent laser radar transmitter for tropospheric wind sensing is presented. This system is hardened for ground and airborne applications. As a transmitter for a coherent wind Lidar, this laser has stringent spectral line width and beam quality requirements. Although the absolute wavelength is not fixed, the output wavelength should avoid atmospheric CO2 and H2O absorption lines. The design architecture includes a seed laser, a power oscillator and a single amplifier. The laser material used for this application is a Ho:Tm:LuLF crystal. The 3-meter long folded ring resonator produces 100-mJ with a temporal pulse length around 185 ns. A final output of 300 mJ at a repetition rate of 10 Hz is achieved by using an amplifier in a double pass format. The operating temperature is set around 15°C for the pump diode lasers and 5°C for the rod. Since the laser design has to meet high-energy as well as high beam quality requirements, close attention is paid to the laser head design to avoid thermal distortion in the rod. A side-pumped configuration is used and heat is removed uniformly by passing coolant through a tube slightly larger than the rod to reduce thermal gradient. This paper also discusses issues related to beam distortion due to high repetition rate. In addition, energy, seeding technique, and beam quality evaluation of the engineering verification laser will be presented.