Lanthanide series ions are considered in the context of acquiring spectroscopic parameters and their application to modelling of quasifour-level lasers. Tm:Ho codoped crystals of YLiF4 (YLF) and the isomorphs LuLiF4 (LuLF) and GdLiF4 (GdLF) as 2.0 μm lasers are used for illustration of the experimental and theoretical techniques presented here. While these materials have similar physical properties, they differ in the strength of the crystal field at the site of optically active lanthanide dopant ions such as Tm3+ and Ho3+. This is due in part to the size of the Lu3+, Y3+, and Gd3+ ions, which comprise part of the host lattice, but ionicity plays a role as well. This selection of lanthanide: host materials provides a useful basis on which to assess laser materials with regards to changes in the strength of the crystal field at the dopant ion site. It is demonstrated that Tm:Ho:LuLF has a larger crystal field splitting than Tm:Ho:YLF and Tm:Ho:GdLF, leading to smaller thermal populations in the Ho lower laser level. To assess this effect quantitatively, the energy levels of the first ten manifolds in Ho:LuLF have been determined. Measurement of Ho:XLiF4 (X=Y,Lu,Gd) emission cross sections at 2.0 μm, Tm:XLiF4 pump absorption cross sections around 0.78 μm, manifold to manifold decay times and energy transfer parameters in Tm:Ho:XLiF4 systems are also determined to provide a consistent set of parameters to use in laser modeling. The techniques presented here are applicable to any lanthanide series ion in a crystalline host. A theoretical laser model has been developed that is easily adapted to any lanthanide ion in a crystal host. The model is used to predict diode side-pumped laser performance of Tm:Ho:LuLF and Tm:Ho:YLF using input parameters determined from the spectroscopy presented here. An explanation is presented for the improved performance of Tm:Ho:LuLF over Tm:Ho:YLF by modeling the laser. A demonstration that small changes in lower laser thermal population can substantially alter laser performance is noted, an effect that has not been fully appreciated previously.

A differential absorption lidar has been built to measure CO2 concentration in the atmosphere. The transmitter is a pulsed single-frequency Ho:Tm:YLF laser at a 2.05-microm wavelength. A coherent heterodyne receiver was used to achieve sensitive detection, with the additional capability for wind profiling by a Doppler technique. Signal processing includes an algorithm for power measurement of a heterodyne signal. Results show a precision of the CO2 concentration measurement of 1%-2% 1sigma standard deviation over column lengths ranging from 1.2 to 2.8 km by an average of 1000 pulse pairs. A preliminary assessment of instrument sensitivity was made with an 8-h-long measurement set, along with correlative measurements with an in situ sensor, to determine that a CO2 trend could be detected.

Water vapor and carbon dioxide are the most dominant greenhouse gases directly contributing to the Earth's radiation budget and global warming. A performance evaluation of an airborne triple-pulsed integrated path differential absorption (IPDA) lidar system for simultaneous and independent monitoring of atmospheric water vapor and carbon dioxide column amounts is presented. This system leverages a state-of-the-art Ho:Tm:YLF triple-pulse laser transmitter operating at 2.05 μm wavelength. The transmitter provides wavelength tuning and locking capabilities for each pulse. The IPDA lidar system leverages a low risk and technologically mature receiver system based on InGaAs pin detectors. Measurement methodology and wavelength setting are discussed. The IPDA lidar return signals and error budget are analyzed for airborne operation on-board the NASA B-200. Results indicate that the IPDA lidar system is capable of measuring water vapor and carbon dioxide differential optical depth with 0.5% and 0.2% accuracy, respectively, from an altitude of 8 km to the surface and with 10 s averaging. Provided availability of meteorological data, in terms of temperature, pressure, and relative humidity vertical profiles, the differential optical depth conversion into weighted-average column dry-air volume-mixing ratio is also presented.

A 2 microm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely tune and lock the wavelength at a desired offset up to 2.9 GHz from the center of a CO(2) absorption line. Once detuned from the line center the laser wavelength is actively locked to keep the wavelength within 1.9 MHz standard deviation about the setpoint. This wavelength control allows optimization of the optical depth for a differential absorption lidar (DIAL) measuring atmospheric CO(2) concentrations. The laser transmitter has been coupled with a coherent heterodyne receiver for measurements of CO(2) concentration using aerosol backscatter; wind and aerosols are also measured with the same lidar and provide useful additional information on atmospheric structure. Range-resolved CO(2) measurements were made with <2.4% standard deviation using 500 m range bins and 6.7 min? (1000 pulse pairs) integration time. Measurement of a horizontal column showed a precision of the CO(2) concentration to <0.7% standard deviation using a 30 min? (4500 pulse pairs) integration time, and comparison with a collocated in situ sensor showed the DIAL to measure the same trend of a diurnal variation and to detect shorter time scale CO(2) perturbations. For vertical column measurements the lidar was setup at the WLEF tall tower site in Wisconsin to provide meteorological profiles and to compare the DIAL measurements with the in situ sensors distributed on the tower up to 396 m height. Assuming the DIAL column measurement extending from 153 m altitude to 1353 m altitude should agree with the tower in situ sensor at 396 m altitude, there was a 7.9 ppm rms difference between the DIAL and the in situ sensor using a 30 min? rolling average on the DIAL measurement.

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.