Toshikazu Itabe

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.

Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Received 4 May 2008; revised 9 June 2008; accepted 18 June 2008; published 23 July 2008. [1] Dual-Doppler lidar and heliborne sensors were used to investigate the three-dimensional (3D) structure of the wind field over Sendai Airport in June 2007. The 3D structures of several-hundred-meter-scale horizontal convective rolls (HCRs) in the sea-breeze layer were observed by the dual-Doppler lidar. The scale of the HCRs determined by the heliborne sensors roughly agreed with that determined by the dual-Doppler lidar. Analysis of the dual-Doppler lidar data showed that the region of upward flow in the HCRs originated in near-surface low-speed streaks. This structure is consistent with the results of large-eddy simulations of the atmospheric boundary layer. The aspect ratios of the HCRs were close to those predicted by linear theories. Citation: Iwai, H., et al. (2008), Dual-Doppler lidar observation of horizontal convective rolls and near-surface streaks, Geophys. Res. Lett., 35, L14808, doi:10.1029/ 2008GL034571.

Diode-pumped 2-μm pulse laser with noncomposite Tm,Ho:YLF rod conduction-cooled down to -80°C.

Q-switched operation of a diode-side-pumped, conduction-cooled Tm,Ho:YLF laser oscillator with 100-mJ output at a pulse repetition rate of 20xa0Hz and an eye-safe wavelength of 2-μm was achieved. The noncomposite Tm,Ho:YLF laser rod was conduction-cooled down to -80°C through thermal contact of In films from Cu heat sinks, and the laser diode arrays were conduction-cooled to approximately 20°C using Cu heat sinks in a vacuum container. A ring resonator of 3.86xa0m length with an acousto-optic Q-switch was used. The pulse width was 125xa0ns, and optical-to-optical efficiency was approximately 7% for an output of 100xa0mJ. The laser is used at 2.05xa0μm for applications of Doppler wind lidar measurements, CO2 differential absorption lidar measurements, and aerosol profiling.

Conductive-cooled 2micron laser for CO2 and wind observations

We have developed 2micron Q-switched lasers with conductive-cooled side pumped laser head. Q-switched output of 100mJ at 20Hz has been achieved in a Tm,Ho:YLF laser oscillator with a composite rod. The experiments showed that very good thermal conduction is held between rod and heat sink. This laser head may be used for laser amplifier of 500mJ output. Another type of Tm,Ho:YLF laser head has been developed for the oscillator of 50-100mJ output at 20-40Hz. These 2micron lasers are applied to coherent lidar systems, which will be used to measure atmospheric CO2 and wind profiling.

Normal-mode and Q-switched operations of a conductively cooled Tm,Ho:LLF laser with a triangular-prism rod

A conductively cooled pump head with a triangular-prism laser rod is proposed and discussed. A pump absorption efficiency of ~80% and better pump intensity distribution were expected from the results of simulations. An output energy of 95 mJ and an optical-to-optical conversion efficiency of 10% were obtained at a pulse repetition frequency of 5 Hz in normal-mode operation. Using a fused-silica acousto-optic Q-switch, the laser produced an output energy of 21 mJ in a single Q-switched pulse. No parasitic oscillation occurred even when the laser rod with polished lateral surfaces was used in Q-switched operations.

Development of a high energy, quasi-three-level Nd:YVO4 laser at 914 nm for deep-blue light generation

A deep-blue light source is useful for various vegetation studies because strong absorption features of chlorophyll a and b exist in this wavelength region. Second-harmonic generation of quasi-three-level Nd-doped lasers operating around 900 nm allows us to produce high-energy deep-blue light suitable for remote sensing of vegetation. Currently, we are developing a high-energy, Q-switched Nd:YVO4 laser operating at 914 nm. Preliminary experiments were performed in a four-level Nd:YAG laser operating at 1064 nm. An output energy of 42 mJ in a single Q-switched pulse with 11-ns pulse length was obtained for a incident pump energy of 653 mJ at 10 Hz.

Development of 2-micron airborne coherent Doppler lidar at NICT

We have studied a 2-micron airborne coherent Doppler lidar to observe wind profile downward from flying object. We investigated the algorithms required to extract the Doppler-shifted frequency compensating for a speed of the flying object. The airborne experiments were conducted to demonstrate the feasibility of the airborne coherent Doppler lidar from a flying object in 2002, 2004 and 2006. We extracted the Doppler-shifted frequency corresponding to aircraft speed with developed algorithms and obtained wind profiles through airborne experiment. To examine wind profiles measured by the airborne coherent Doppler lidar, we compared those profiles with profiles measured by a GPS-dropsonde and a windprofiler. Although the volume measured by the airborne coherent Doppler lidar system differed spatially and temporally from those by other instruments, the wind profiles observed by the airborne coherent Doppler lidar agreed well with those observed by other instruments.

Development of coherent Doppler lidar for wind profiling

Space-borne Doppler lidar is expected to make wind profile observations on a global scale with an accuracy of 1 to 2 m/s. It may solve the problem of the shortage of the accuracy and distribution in the current wind data. We have studied an eye-safe coherent Doppler lidar (CDL) model that could be deployed on the exposed facilities of Japanese Experiment Module (JEM) and that would meet the science requirements. We have good prospects of 500mJ output at 10Hz in a conduction cooling sub-scale laser, which could be a small model of space-borne laser for JEM/CDL. We are making studies on improving the system’s efficiency, reducing its weight, and establishing the fundamental technologies involved. Research on another possibility, e.g. a free flyer, for a demonstration mission besides of JEM/CDL is also valuable to be considered. Development of algorithm for application of coherent lidar system is also in progress through air-borne experiments and ground-based observations.

Conductive-cooled 2-micron laser development for wind and CO2 measurements

We have developing two types of 2micron conductive-cooled lasers for wind and CO2 measurements. One type of lasers is side pumped Tm,Ho:YLF laser operated at 20-40Hz. The laser rod is cooled down to -80C and laser diodes are operated at normal temperature in a vacuum container. With this type of laser, we have built up a coherent lidar system which is used to measure wind and CO2 concentration. Ho:YLF laser end-pumped by Tm:fiber laser is another type oscillator which will be operated at high repetition rate of 200-300 Hz in normal temperature. The laser will have an amplifier. These lasers are conductive-cooled, solid-state, eye-safe and suitable for space applications.

Dust profiles of the atmospheric boundary layer observed by a laser ceilometer at Shapatou, China in 2004

Dust profiles have been observed by a laser Ceilometer (MEISEI CT25K) at Shapatou, China which is located at the edge of the Tengger Desert. The observation was conducted throughout one year of 2004 successfully and showed the behaviors of the atmospheric dust profile from near the surface to about the 1000-m height. The results of the observation were compared with several other meteorological data, such as surface, radio sonde and sky radiometer measurements. In particular, the dust profiles observed on calm and fair weather days were analyzed and compared with other meteorological data. The dust profile at the calm and fare weather day in the desert area is mainly influenced by thermal convection due to strong surface heating in the warm season. The dust amount lower than the 500-m height decreases in the daytime and recovers in the nighttime. The data of the sky radiometer shows that the total amount of the dust at the same calm and fair-weather days is almost constant during the daytime. The observational evidence was explained in the paper.