Yingxin Bai

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.

Joule-level double-pulsed Ho:Tm:LuLF Master-Oscillator-Power-Amplifier (MOPA) for potential spaceborne lidar applications

Spaceborne coherent Doppler wind lidars and CO2 Differential Absorption Lidars (DIALs) at eye-safe 2-μm spectral range have been proposed for several years for accurate global wind and carbon-oxide concentration profiling measurement. These lidar systems require Joule level laser pulse energy from laser transmitter and high efficiency. In this paper, we report a diode-pumped Ho:Tm:LuLF Master-Oscillator-Power-Amplifier (MOPA) developed to demonstrate Joule level output pulse energy. The MOPA consists of one master oscillator and two power amplifiers. The master oscillator was Q-switched and can be operated at single pulse mode or double pulse mode respectively. The single pulse operation is used for a coherent Doppler wind lidar and the double pulse operation for a CO2 Differential Absorption Lidar (DIAL). The output pulse energy of the master oscillator is 115 mJ for the single pulse operation and 186 mJ for the double pulse operation. To extract more energy from the pumping pulses and increase the efficiency of the MOPA, the first amplifier was set at a double pass configuration. The second amplifier was set at a single pass configuration to avoid the damage problem of the Ho:Tm:LuLF laser rod. Total output pulse energy of 0.63 J with an optical efficiency of 4.1% for single pulse operation and 1.05 J with an optical efficiency of 6.9% for double pulse operation were demonstrated.

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.

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.

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.

High-energy diode-pumped Ho:Tm:LuLiF4 laser for lidar application

Two-micron lasers can be used in a variety of remote sensing and medical applications. In recent years, such lasers have been used for remote sensing of wind and CO2 to expand our understanding of the global weather system. The detection of clear air turbulence and wake vortex from aircraft has been proven to enhance air travel safety. In this paper, we present the design and performance of a high-energy diode pumped solid-state 2-micron laser transmitter. There has been a large body of work on 2 μm laser crystals using Tm and Ho ions doped in YLF and YAG hosts, but the use of LuLiF4 as a host is relatively recent. Studies comparing Ho:LuLiF4 and Ho:YLF show that both crystals have similar emission cross-sections for both 2.05 μm and 2.06 μm transitions. Tm:Ho:LuLiF4 has proven to produce 15%-20% more energy than Tm:Ho:YLF. This is primarily attributed to the variation of the thermal population distribution in the Ho: 5I7 and 5I8 energy levels. The laser crystal used for this experiment is grown in the crystalline a-axis. The resonator is a bow tie ring configuration with 3-m length. One of the mirrors in the resonator has a 3.5m curvature, which sets up a 1.8 mm TEMoo mode radius. The output mirror reflectivity is 72% and it is the dominant source of the resonator loss. An acousto-optic Q-Switch with Brewster angle switches the Q of the oscillator and defines the polarization of the laser output. This laser has a potential to produce a multi joule energy and replace the traditionally used Ho: Tm: YLF crystal.

Sensitive Infrared Signal Detection by Upconversion Technique

Abstract. We demonstrated upconversion assisted detection of a 2.05-μm signal by sum frequency generation to generate a 700-nm light using a bulk periodically poled lithium niobate crystal. The achieved 94% intrinsic upconversion efficiency and 22.58% overall detection efficiency at a pW level of 2.05  μm pave the path to detect extremely weak infrared (IR) signals for remote sensing applications.

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.