Μm Differential Absorption Lidar Research Articles

Range-resolved detection of boundary layer stable water vapor isotopologues using a ground-based 1.98 µm differential absorption LIDAR.

This paper presents a first demonstration of range-resolved differential absorption LIDAR (DIAL) measurements of the water vapor main isotopologue H2 16O and the less abundant semi-heavy water isotopologue HD16O with the aim of determining the isotopic ratio. The presented Water Vapor and Isotope Lidar (WaVIL) instrument is based on a parametric laser source emitting nanosecond pulses at 1.98 µm and a direct-detection receiver utilizing a commercial InGaAs PIN photodiode. Vertical profiles of H2 16O and HD16O were acquired in the planetary boundary layer in the suburban Paris region up to a range of 1.5 km. For time averaging over 25 min, the achieved precision in the retrieved water vapor mixing ratio is 0.1 g kg-1 (2.5% relative error) at 0.4 km above ground level (a.g.l.) and 0.6 g kg-1 (20%) at 1 km a.g.l. for 150 m range bins along the LIDAR line of sight. For HD16O, weaker absorption has to be balanced with coarser vertical resolution (600 m range bins) in order to achieve similar relative precision. From the DIAL measurements of H2 16O and HD16O, the isotopic abundance δD was estimated as -51‰ at 0.4 km above the ground and -119‰ in the upper part of the boundary layer at 1.3 km a.g.l. Random and systematic errors are discussed in the form of an error budget, which shows that further instrumental improvements are required on the challenging path towards DIAL-profiling of the isotopic abundance with range resolution and precision suitable for water cycle studies.

Comparison of CO₂ Vertical Profiles in the Lower Troposphere between 1.6 µm Differential Absorption Lidar and Aircraft Measurements Over Tsukuba.

A 1.6 μm differential absorption Lidar (DIAL) system for measurement of vertical CO2 mixing ratio profiles has been developed. A comparison of CO2 vertical profiles measured by the DIAL system and an aircraft in situ sensor in January 2014 over the National Institute for Environmental Studies (NIES) in Tsukuba, Japan, is presented. The DIAL measurement was obtained at an altitude range of between 1.56 and 3.60 km with a vertical resolution of 236 m (below 3 km) and 590 m (above 3 km) at an average error of 1.93 ppm. An in situ sensor for cavity ring-down spectroscopy of CO2 was installed in an aircraft. CO2 mixing ratio measured by DIAL and the aircraft sensor ranged from 398.73 to 401.36 ppm and from 399.08 to 401.83 ppm, respectively, with an average difference of −0.94 ± 1.91 ppm below 3 km and −0.70 ± 1.98 ppm above 3 km between the two measurements.

Characteristics of the OPG System USIG Quasiphase-Matched Nonlinear Crystals for 1.6 μm CO2 Dial

We have developed a direct detection 1.6 μm differential absorption lidar (DIAL) technique to perform range-resolved measurements of vertical CO2 concentration profiles in the atmosphere. Our 1.6 μm DIAL system consists of the optical parametric generator (OPG) and amplifier (OPA) transmitter that excited by the LD pumped Nd:YAG laser with high repetition rate (500 Hz). The OPG system consists of a quasi-phase-matched (QPM) crystal and does not need a cavity. The output power of the OPA system is 6 mJ, the full width at half maximum (FWHM) of the spectrum is about 280 MHz and spectrum purity is 91.0 +- 0.2 ~ 0.5%. CO2 concentration error from fluctuation of the spectrum purity is 0.3% at 6 km altitude and 0.4 % at 10 km altitude.

Measurement of Lower-Atmospheric CO2Concentration Distribution Using a Compact 1.6 μm DIAL

Knowledge of present carbon sources and sinks including their spatial distribution and their variation in time is one of the essential information for predicting future CO2 atmospheric concentration levels. The differential absorption lidar (DIAL) is expected to measure atmospheric CO2 profiles in the atmospheric boundary layer and lower troposphere from a ground platform.We have succeeded to develop a compact 1.6 μm DIAL system for measuring CO2 concentration profiles in the lower atmosphere. This 1.6 μm DIAL system consists of the optical parametric generator (OPG) transmitter that excited by the LD pumped Nd:YAG laser with high repetition rate and the receiving optics that included the near-infrared photomultiplier tube operating at the analog mode and a 25 cm telescope. CO2 concentration profiles were obtained up to 2.5 km altitude.

Orthogonally polarized dual-wavelength single-longitudinal-mode Tm,Ho:LLF laser

We first report a diode-pumped continuous wave orthogonally polarized dual-wavelength single-longitudinal-mode laser with a single c-cut Tm,Ho:LuLiF₄ laser crystal. The simultaneous dual-wavelength single-longitudinal-mode laser near 2 μm is realized by using two uncoated intracavity Fabry-Perot etalons. The output wavelengths are 2064 nm in π-polarization and 2066 nm in σ-polarization respectively, which are orthogonal to each other. At the absorbed pump power of 1 W, the maximum single-longitudinal-mode output powers at 2064 and 2066 nm are 76 and 32 mW respectively. The orthogonally polarized dual-wavelength single-longitudinal-mode laser is possible to be applied to the 2 μm differential absorption lidar and the generation of THz radiation.

Development of a 16 μm differential absorption lidar with a quasi-phase-matching optical parametric oscillator and photon-counting detector for the vertical CO_2 profile

We have developed a 1.6 microm carbon dioxide (CO(2)) differential absorption lidar utilizing a quasi-phase-matching optical parametric oscillator (OPO) and a photon-counting detector. The operating wavelengths were chosen based on their low interference from water vapor and low temperature sensitivity. The online wavelength was in the (30012<--0001) band of CO(2), which was insensitive to atmospheric temperature. The established OPO laser achieved a 10 mJ, 200 Hz repetition rate at the online and offline wavelengths. Our observations confirmed the statistical error of 2% with 5 h of accumulation for the CO(2) density profile less than 5.2 km. Also, the statistical error of 1% at an altitude of 2 km was demonstrated. The results of the vertical CO(2) concentrations acquired using a 1.6 microm wavelength are presented.