Paul Petzar

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.

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.

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.

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.

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.

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.

2.5 MHz line-width high-energy, 2μm coherent wind lidar transmitter

The design of a diode pumped, injection seeded MOPA with a transform limited line width and diffraction limited beam quality is presented. This lidar transmitter produces over 300mJ energy at 10 Hz repetition rate.

Phase-Conjugated 2-μm Laser System

For the first time, beam quality improvement of 2 μm laser using fiber based phase conjugation mirror has been demonstrated. Single frequency operation is necessary to lower threshold. The reflectivity of the PCM is ~50%.