Kazuhiro Asai

Coherent 2 μm differential absorption and wind lidar with conductively cooled laser and two-axis scanning device

A coherent 2 microm differential absorption and wind lidar (Co2DiaWiL) was developed to measure CO(2) concentration and line-of-sight wind speed. We conductively cooled a pumping laser head to -80 degrees C and diode arrays to approximately 20 degrees C. A Q-switched laser outputs an energy of 80 mJ (pulse width 150 ns (FWHM), pulse repetition frequency up to 30 Hz). CO(2) measurements made over a column range (487-1986 m) for 5 min accumulation time pairs achieved 0.7% precision. Line-of-sight wind speeds for ranges up to approximately 20 km and returns from a mountainside located 24 km away from the Co2DiaWiL were obtained.

Lasing characteristics and optimizations of a diode-side-pumped Tm, Ho:GdVO 4 laser

A diode-pumped Tm, Ho:GdVO4 laser with a side-pumping configuration is demonstrated for the first time to our knowledge. Optimum Tm and Ho dopant concentrations for GdVO4 are somewhat lower than those for garnet and fluoride crystals. With a 3% Tm, 0.3% Ho:GdVO4 crystal an output energy of 31.2 mJ and a slope efficiency of 14.5% were obtained in normal-mode operation at room temperature.

Latitudinal distribution of aerosols and clouds in the western Pacific observed with a lidar on board the Research Vessel Mirai

We observed vertical distributions of aerosols and clouds with a lidar on board R/V Mirai and analyzed latitudinal features using the data of four cruises in the western Pacific. According to the measured backscattering coefficient, aerosol density was generally high at latitudes above 25° N where the westerly from the Asian continent prevailed. The wavelength dependence of the retrieved aerosol backscattering showed that the characteristics of aerosols in the continental air mass were clearly different from those at lower latitudes. Aerosol concentration in the boundary layer varied significantly in the lower latitudes and was correlated with surface wind speed. The wavelength dependence of aerosol backscattering indicated that aerosol particles were larger when surface wind speed was high.

Pulsed laser action in Tm,Ho:LuLiF/sub 4/ and Tm,Ho:YLiF/sub 4/ crystals using a novel quasi-end-pumping technique

A number of good quality thulium and holmium-codoped LuLiF/sub 4/ and YLiF/sub 4/ single crystals were successfully grown by the Czochralski crystal growth method under a CF/sub 4/ atmosphere. Using a novel diode-pumped, quasi-end-pump scheme incorporating two lens ducts, pulsed laser action is achieved in 5%Tm, 0.5% Ho:LuLiF/sub 4/ and 5%Tm, 0.5% Ho:YLiF/sub 4/ crystals, at various pulse repetition frequencies and temperatures. At 10 Hz and at an operating temperature of 273 K, slope efficiencies (optical to optical efficiencies) with respect to the incident pump energies of 12.9% (9.2%) and 7.4% (5.2%) were demonstrated in the grown Tm, Ho:LuLiF/sub 4/ and Tm, Ho:YLiF/sub 4/ crystals, respectively. Free running laser output energies in excess of 30 mJ (LuLiF/sub 4/) and 17 mJ (YLF) were measured.

Room-temperature Tm, Ho:LuLiF 4 laser with a novel quasi-end-pumping technique

A novel diode-pumped, efficient, quasi-end-pumping scheme that uses two lens ducts to achieve homogeneous pumping in a gain medium was proposed and evaluated. With this technique, room-temperature laser action at a pulse repetition frequency up to 20 Hz was demonstrated in 5%Tm, 0.5%Ho:LuLiF(4), which we grew by the Czochralski method. At 10 Hz a long-pulse laser output energy in excess of 24 mJ and a slope efficiency with respect to the incident pump energy of 10.7% were obtained.

Lidar network observation of Asian dust (Kosa) in Japan

We have organized a network campaign for the observation of Asian dust in the spring of 1997 and 1998 in Japan. Through the communication with electric mail, we have successfully observed Kosa events by lidar, sunphotometer, and particle counter, etc. These data must be useful to analyze the transport mechanism of Asian dust and validate the satellite observations.

Partial CO2 Column-Averaged Dry-Air Mixing Ratio from Measurements by Coherent 2-μm Differential Absorption and Wind Lidar with Laser Frequency Offset Locking

AbstractA coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) with a 2-μm single-frequency Q-switched laser with laser frequency offset locking was used for long-range CO2 measurement. The frequency stabilization of the single-frequency λ on pulsed laser was 1.0 MHz. Experimental horizontal CO2 measurement over a column range of 2.6–5.6 km and 900 shot pairs (1-min integration time) was conducted on 22 October 2009 to examine the detection sensitivity of the Co2DiaWiL. The achieved precision was less than 2.1%. The root-mean-square of the differences between the 30-min CO2 averages measured by the Co2DiaWiL and a ground-based in situ instrument was 0.9% (3.5 ppm). Experimental vertical CO2 measurements were conducted in February 2010 and January and February 2011. The partial CO2 column-averaged dry-air mixing ratios (XCO2) for an altitude between 0.4 and 1.0 km in 2010 and 2011 were 403.2 ± 4.2 and 405.6 ± 3.4 ppm, respectively. In the paper, the Co2DiaWiL results were well validated careful...

Pinatubo volcanic aerosols observed by lidar at Wakkanai, Japan

Dense stratospheric aerosol layers originating from the volcanic eruptions of Mt. Pinatubo in the Philippines on June 15, 1991 were observed at the Wakkanai radio observatory (45.4°N, 141.7°E) of the Communications Research Laboratory (CRL) using a Nd:YAG lidar system. These observations started in late August 1991, and the dense layer was first detected in early October 1991. The backscattering of the aerosol layers varied greatly in October and November 1991 then stabilized in December 1991. The integrated backscattering coefficient (IBC) at the beginning of 1992 was smaller than the values observed in October and November 1991. The IBC increased slightly during 1992, but began to decrease in 1993. The estimated surface area density of aerosol particles increased one to two orders of magnitude in late 1991 and early 1992 to about 10−7 cm2/cm3. The IBC and surface area started to decrease sooner at higher altitudes: in May 1992 from 25 to 30 km, in November 1992 from 20 to 25 km, and in February 1993 from 13 to 20 km in altitude. Calculation by Prather [1992] indicates that our estimated surface area correspond to about 30 to 50% less NOx. Almost same degree of decrease in NO2 was observed by Koike et al.[1993].

Measurements of the urban ozone vertical profile with an airborne CO 2 DIAL

An airborne DIAL system with two color pulsed CO(2) lasers has been developed for remote measurements of ozone distributions in an urban area. The airborne CO(2) DIAL is a nadir-directed and direct range-resolved system, since the system was designed to use aerosols between an aircraft and the ground surface as a distributed target. Flight tests were successfully conducted in September 1986 over Tokyo, Japan, at a flight altitude of 5000 ft (1.7 km). The airborne CO(2) DIAL instrument and its first measurements of the vertical profile of urban ozone are described.

Overview of Japan's spaceborne vegetation lidar mission

Vegetation LIDAR, which measures an accurate canopy height, has been studied by JAXA. Canopy height is a very important parameter to estimate forest biomass, and global measurement of accurate canopy height leads to better understanding of the global carbon cycle. The vegetation LiDAR is designed based on the assumption that it is to be mounted on the Exposed Facility (EF) of the Japanese Experiment Module (JEM, also known as “Kibo”) on the International Space Station (ISS). The vegetation LIDAR uses an array detector (2x2) for dividing the ground footprint, making it possible to detect the slope of the ground for improving the accuracy of canopy height measurement. However, dividing the footprint may cause a reduction in reflected lights and signal-to-noise ratio (SNR); hence, the vegetation LiDAR system needs high sensitivity and low-noise array detector module. We made a prototype of the array detector module and it satisfied the tentative target SNR which we set. This presentation will introduce the mission objectives, the LiDAR system including experimental prototypes of array detector module, and some results of the study.