Bo C. Trieu

1 J/pulse Q-switched 2 µm solid-state laser

Q-switched output of 1.1 J/pulse at a 2.053 microm wavelength has been achieved in a diode-pumped Ho: Tm: LuLF laser with a side-pumped rod configuration in a master-oscillator-power-amplifier (MOPA) architecture. This is the first time to our knowledge that a 2 microm laser has broken the joule per pulse barrier for Q-switched operation. The total system efficiency reaches 5% and 6.2% for single- and double-pulse operation, respectively. The system produces an excellent 1.4 times transform-limited beam quality.

The Doppler Aerosol Wind (DAWN) Airborne, Wind-Profiling Coherent-Detection Lidar System: Overview and Preliminary Flight Results

AbstractThe first airborne wind measurements of a pulsed, 2-μm solid-state, high-energy, wind-profiling lidar system for airborne measurements are presented. The laser pulse energy is the highest to date in an eye-safe airborne wind lidar system. This energy, the 10-Hz laser pulse rate, the 15-cm receiver diameter, and dual-balanced coherent detection together have the potential to provide much-improved lidar sensitivity to low aerosol backscatter levels compared to earlier airborne-pulsed coherent lidar wind systems. Problems with a laser-burned telescope secondary mirror prevented a full demonstration of the lidar’s capability, but the hardware, algorithms, and software were nevertheless all validated. A lidar description, relevant theory, and preliminary results of flight measurements are presented.

Field testing of a high-energy 2-μm Doppler lidar

A 2-μm wavelength coherent Doppler lidar for wind measurement has been developed of an unprecedented laser pulse energy of 250-mJ in a rugged package. This high pulse energy is produced by a Ho:Tm:LuLiF laser with an optical amplifier. While the lidar is meant for use as an airborne instrument, ground-based tests were carried out to characterize performance of the lidar. Atmospheric measurements are presented, showing the lidars capability for wind measurement in the atmospheric boundary layer and free troposphere. Lidar wind measurements are compared to a balloon sonde, showing good agreement between the two sensors.

Highly efficient Q-switched Ho:YLF laser pumped by Tm:fiber laser

A highly efficient Q-switched Ho:YLF laser pumped by a Tm:fiber laser has been designed and demonstrated. When the pump power is 30 W, the pulse energy is 30 mJ at the repetition rate of 100 Hz.

Advanced 2-micron Solid-state Laser for Wind and CO2 Lidar Applications

Significant advancements in the 2-micron laser development have been made recently. 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 Diffrencial Absorption Lidar (DIAL) system for measuring atmospheric CO2 concentration profiles. The world record 2-micron laser energy is demonstrated with an oscillator and two amplifiers system. It generates more than one joule per pulse energy with excellent beam quality. Based on the successful demonstration of a fully conductive cooled oscillator by using heat pipe technology, an improved fully conductively cooled 2-micron amplifier was designed, manufactured and integrated. It virtually eliminates the running coolant to increase the overall system efficiency and reliability. In addition to technology development and demonstration, a compact and engineering hardened 2-micron laser is under development. It is capable of producing 250 mJ at 10 Hz by an oscillator and one amplifier. This compact laser is expected to be integrated to a lidar system and take field measurements. The recent achievements push forward the readiness of such a laser system for space lidar applications. This paper will review the developments of the state-of-the-art solid-state 2-micron laser.

Diode-pumped double-pulsed Ho:Tm:LuLF laser at 2.05 µm for CO 2 differential absorption lidar (DIAL)

It has been realized that eye-safe 2-mm all-solid-state lasers are important laser sources for an accurate measurement of the CO2 concentration in the atmosphere. Served as laser transmitters, they can be integrated into ground-based, airborne-base, and spaceborne-based CO2 Differential Absorption Lidars (DIALs) to accomplish the measurement. In addition, the lasers are also ideal laser pumping sources for a ZnGeP2 (ZGP) Optical Parametric Oscillator (OPO) or an Optical Parametric Amplifier (OPA) to achieve tunable laser output in 3~5 mm. In this spectrum region, the other important greenhouse gases, water vapor (H2O), carbon monoxide (CO), and methane (CH4) in the atmosphere can be measured. In this paper, we report a diode-pumped, double-pulsed, Q-switched, eye-safe Ho:Tm:LuLF laser at 2.05 mm developed for ground-based and airborne-based CO2 Differential Absorption Lidars (DIALs). The technology can be easily transferred to a space-borne CO2 DIAL in the future. The total output pulse energy of the laser is 220 mJ and 204 mJ per pair of pulses at 2 Hz and at 10 Hz respectively. The related optical energy conversion efficiency is 6.7% and 5.9% respectively.

Totally conductive-cooled diode-pumped 2-μm laser transmitter

Space Lidar applications benefits from efficient conductive cooled laser transmitters. Effective thermal management is a key challenge for high-energy laser development. In this paper, the design and performance of a totally conductive cooled 2µm laser is presented. Three heat pipes capable of removing 150 watts of heat both from the pump diode lasers and the rod were used in the design. A 2.5 m long ring resonator with two 5-m radii of curvature mirrors set a 2.36mm diameter TEMoo mode radius in the cavity. Despite the thermal gradient that was created in the Ho:Tm: LuLF crystal due to the cooling method and geometry, almost diffraction limited beam and up to 107 mJ of Q-switched output with a pulse length of 135ns was obtained. Such a laser transmitter can be used as a wind Lidar. It is especially suitable as a CO2 DIAL since two Q-switched pulses can be acquired for a single pump pulse due to the long lifetime of the Ho: 5I7 and 5I8 transition and the operating wavelength is near rich CO2 absorption lines.

A two micron coherent differential absorption lidar development

A pulsed, 2-μm coherent Differential Absorption Lidar (DIAL) / Integrated Path Differential Absorption (IPDA) transceiver, developed under the Laser Risk Reduction Program (LRRP) at NASA, is integrated into a fully functional lidar instrument. This instrument measures atmospheric CO2 profiles (by DIAL) from a ground platform. It allows the investigators to pursue subsequent in science-driven deployments, and provides a unique tool for Active Sensing of CO2 Emissions over Night, Days, and Seasons (ASCENDS) validation that was strongly advocated in the recent ASCENDS Workshop.

Diode-pumped one Joule per Q-switched pulse 2μm laser

This paper discusses the significant advancements in the 2-micron laser development. A world record one-Joule-per-pulse energy laser system and an advanced thermal management with fully conductive cooled laser technique are discussed.