Hyung R. Lee

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.

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.

High pulse energy ZnGeP 2 singly resonant OPO

We report a high pulse energy singly resonant ZnGeP2 OPO, pumped by a Q-switched Ho:Tm:LuLiF4 2µm laser. It generates up to 17.3 mJ in the 4.3-10.1 µm ranges at conversion efficiency of 27.5%.

Parametric generation of tunable infrared radiation for remote sensing applications

We are developing a high energy, narrow linewidth, and tunable mid-IR laser source that can be used to measure the green house gases and toxic gases with sufficient sensitivity and accuracy. This system consists of three major components; a high energy seeded 2.05-micron pump laser, a parametric oscillator and amplifier tunable between 3 to 9 microns and a continuous wave Periodically Poled Lithium Niobate (PPLN) seed source for parametric oscillator. A high-energy 2.05-micron pump laser with 600-mJ output has been demonstrated. This laser is comprised of one oscillator and two amplifiers. It is operated in a double pulse format to increase the system efficiency. The high beam quality combined with the narrow linewidth feature makes it a superior pump source for the parametric oscillator and amplifier. A seed source for the parametric oscillator can be implemented by using a PPLN continuous wave Optical Parametric Oscillator (OPO). The efficiency of this PPLN OPO can be greatly increased because of the huge nonlinearly associated with the d33 element of the nonlinear tensor of this material and the non-critical phase matching. Recent significant material growth improvement of ZnGeP2 makes it possible to produce the crystal with sufficient low absorption at the 2.05 pump wavelength (<0.1cm-1). This crystal also has the characteristics of wide transparency range and large second-order nonlinearities. Such a crystal is one of the most promising nonlinear optical materials for efficient frequency conversion into the mid-IR spectral region. In this paper, the design and preliminary results of this laser system will be presented.

Birefringence compensation in a barium nitrate Raman laser

We are investigating pulsed barium nitrate (Ba(NO/sub 3/)/sub 2/) lasers and amplifiers for an ozone lidar system. Previously, we reported that the visible output of a Raman laser, pumped by a Q-switched, frequency-doubled Nd:YAG laser at 532 nm, is slightly depolarized. In this paper, we present quantitative depolarization measurements and demonstrate a simple technique to compensate for the crystal birefringence.

Compact ground-based UV DIAL system for measurements of tropospheric ozone

The development of a portable, eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar (DIAL) measurements in the troposphere is presented. This compact prototype instrument is intended to operate at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar technology to be widely deployed in networks, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. The chosen laser transmitter for the system is an all-solid state tunable frequency-doubled OPO which produces 25 mJ uv pulses. Progress with alternative solid-state uv laser sources based upon an IR-pumped OPO and based upon stimulated Raman scattering in barium nitrate will be discussed. The receiver incorporates highly efficient dielectric coatings, a parabolic primary and a narrow- bandpass grating-based filter. Dual analog and photon-counting detector channels are incorporated to extend the measurement range. All data acquisition and control hardware is incorporated in an industrial PC-based system. A flexible, user-friendly graphical user interface is written in LabVIEW for data acquisition and online processing and display.

An Injection-Seeded Narrow Linewidth Singly Resonant ZGP OPO

Injection seeding of a singly resonant ZnGeP2 mid-infrared OPO using a CW 3.39 µm laser or tunable near-infrared laser has been demonstrated. The injection seeded OPO provides a narrow idler wavelength linewidth of ~1 nm.

Nonlinear frequency up-conversion for mid-infrared single-photon detection

Remote sensing using mid-infrared wavelength has many applications in pollution surveillance and atmosphere studies. However, high gain, low noise detectors or single photon counters are not available in the mid-infrared wavelength range. One approach to obtain single-photon detection in mid-infrared wavelength is to convert the mid-infrared radiations into visible/near-infrared wavelengths where high efficiency and low dark current detectors are easily available. In this paper, the up-conversion of mid-infrared radiations based on the quasi-phase matching condition of periodically poled lithium niobate (PPLN) is investigated. The bandwidth and efficiency are the two essential parameters for the up-conversion process. The optimal pump wavelength λlasero and PPLN period Λ can be determined from conservations of energy and momentum. Once the λlasero and Λ are defined, the spectral bandwidth corresponding to the full width at half maximum of frequency up-conversion can be calculated. The spectral bandwidth of mid-infrared radiations can exceed 130 nm for a 25 mm PPLN crystal when the pump laser operates in the optimum wavelength. It is wide enough to cover both the on and off wavelengths of the species of interest in a Differential Absorption Lidar. The maximum up-conversion bandwidth usually corresponds to the longest PPLN period allowed by the quasi-phase matching condition. The conversion efficiency increases with the pump laser intensity. Both the external cavity pumping approach with cavity locking technique and the intra-cavity pumping approach can greatly increase the up-conversion efficiency.

Measurements of tropospheric ozone with a compact UV DIAL system

Current results from laboratory testing of an eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar measurements in the troposphere are presented. This compact prototype instrument is intended to be a prototype for operation at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar to be widely deployed, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. To achieve these goals, the system incorporates (1) an all- solid state compact OPO transmitter, (2) a highly efficient, narrow bandpass grating-based receiver, (3) dual analog and photon-counting detector channels, and (4) a PC-based data acquisition system.