1.55-µm high-peak, high-average-power laser amplifier using an Er,Yb:glass planar waveguide for wind sensing coherent Doppler lidar.

We have developed a high-gain, high-peak-power laser amplifier at an eye-safe 1.55 µm wavelength using an Er,Yb:glass planar waveguide for wind sensing coherent Doppler lidars (CDLs). Our planar waveguide is free from stimulated Brillouin scattering and realizes high gain thanks to its multi-bounce optical-path configuration. A peak power of 5.5 kW with a pulse energy of 3.2 mJ is achieved at the repetition frequency of 4 kHz, which leads to an average power of 12.8 W. The gain is more than 23 dB. The wind sensing at more than 30 km is demonstrated with a CDL using the developed amplifier.

Laser absorption spectrometer using frequency chirped intensity modulation at 1.57 µm wavelength for CO2 measurement.

We have demonstrated the laser-absorption spectrometer system using frequency chirped intensity modulation at 1.57 µm wavelength for measurement of CO(2) concentration. Using this technique, backscattered laser radiation from different ranges can be discriminated in the frequency domain of the electrical signal. We have reported the discrimination of two signals from the targets with different ranges. It is shown that stable measurements with short time fluctuation corresponding to 4 ppm (rms) were obtained with 32 s measurement intervals. Furthermore, there is qualitative good agreement on, at least, the diurnal changes between the results of the laser absorption spectrometer system and the in-situCO(2) sensor.

Feasibility study on 1.6 µm continuous-wave modulation laser absorption spectrometer system for measurement of global CO2 concentration from a satellite.

A feasibility study is carried out on a 1.6 µm continuous-wave modulation laser absorption spectrometer system for measurement of global CO(2)concentration from a satellite. The studies are performed for wavelength selection and both systematic and random error analyses. The systematic error in the differential absorption optical depth (DAOD) is mainly caused by the temperature estimation error, surface pressure estimation error, altitude estimation error, and ON wavelength instability. The systematic errors caused by unwanted backscattering from background aerosols and dust aerosols can be reduced to less than 0.26% by using a modulation frequency of around 200 kHz, when backscatter coefficients of these unwanted backscattering have a simple profile on altitude. The influence of backscattering from cirrus clouds is much larger than that of dust aerosols. The transmission power required to reduce the random error in the DAOD to 0.26% is determined by the signal-to-noise ratio and the carrier-to-noise ratio calculations. For a satellite altitude of 400 km and receiving aperture diameter of 1 m, the required transmission power is approximately 18 W and 70 W when albedo is 0.31 and 0.08, respectively; the total measurement time in this case is 4 s, which corresponds to a horizontal resolution of 28 km.

Performance improvement and analysis of a 1.6 µm continuous-wave modulation laser absorption spectrometer system for CO2 sensing.

In a previous study, we developed a 1.6 µm continuous-wave (cw) modulation laser absorption spectrometer system for CO(2) sensing and demonstrated the measurement of small fluctuations in CO(2) corresponding to a precision of 4 parts per million (ppm) with a measurement interval of 32 s. In this paper, we present the process to achieve this highly specific measurement by introducing important points, which have not been shown in the previous study. Following the results of preliminary experiments, we added a function for speckle averaging on the optical antenna unit. We additionally came up with some ideas to avoid the influences of etalon effects and polarization dependence in optical components. Because of the new functions, we realized a calibration precision of 0.006 dB (rms), which corresponds to a CO(2) concentration precision of less than 1 ppm for a 2 km path. We also analyzed the CO(2) sensing performance after the improvements described above. The measured short time fluctuation of the differential absorption optical depth was reasonably close to that calculated using the carrier-to-noise ratio of the received signal.

Semianalytic pulsed coherent laser radar equation for coaxial and apertured systems using nearest Gaussian approximation.

We present a semianalytic pulsed coherent laser radar (CLR) equation for coaxial and apertured systems. It combines the conventional CLR equation, numerical Fresnel integration (NFI), and nearest Gaussian approximation, using correction factors that correspond to beam truncation. The range dependence of the signal-to-noise ratio obtained by this semianalytic equation was found to agree well with the precise NFI solution for not only the focal range, but also the near-field range. Furthermore, the optimum beam truncation condition depending on the atmospheric refractive index structure constant is shown. The derived equation is useful for precisely predicting the CLR performance simply by its semianalytic expression.

Development of 1.6 microm continuous-wave modulation hard-target differential absorption lidar system for CO2 sensing.

We have demonstrated the 1.6 mum cw modulation hard-target differential absorption lidar system for CO(2) sensing. In this system, ON and OFF wavelength laser lights are intensity modulated with cw signals. Received lights of the two wavelengths from the hard target are discriminated by modulation frequencies in the electrical signal domain. The optical circuit is fiber based, and this makes the system compact and reliable. It is shown that a stable CO(2) concentration measurement corresponding to a fluctuation of 4 ppm (rms) (ppm is parts per million) has been achieved in 32 s measurement intervals and the 1 km path.

Master-oscillator power-amplifier scheme for efficient green-light generation in a planar MgO:PPLN waveguide.

We developed a new master-oscillator power-amplifier scheme consisting of a tapered semiconductor amplifier and a fiber-grating-stabilized laser diode for efficient green-light generation in a planar MgO:PPLN waveguide, and demonstrated cw green-light generation of 346 mW.

Blue light generation in a ridge waveguide MgO:LiNbO3 crystal pumped by a fiber Bragg grating stabilized laser diode.

We report cw blue light generation by using a periodically poled MgO:LiNbO(3) crystal with a ridge waveguide pumped by a fiber Bragg grating stabilized laser diode with 0.25 nm spectrum width in the coherent collapse regime. Blue light generation of 73 mW with 27% conversion efficiency and a wide temperature tolerance of 5.7 degrees C were attained.

Planar-waveguide quasi-phase-matched second-harmonic-generation device in Y-cut MgO-doped LiNbO3.

We designed a planar-waveguide quasi-phase-matched second-harmonic-generation device, which consists of a Y-cut periodically poled 5 mol.% MgO-doped LiNbO3 core and SiO2 claddings, that provided a 1.08 W green light with 30% conversion efficiency by using a 7 mm long sample at room temperature. The highest conversion efficiency of 49% at 0.88 W second-harmonic generation was attained by using an 18 mm long device.