Kenji Tatsumi

Double-clad Nd-doped fiber amplifiers for transmitter of interorbit communications

Since Nd-doped fiber amplifiers could be used as power amplifiers for high data rate optical inter-orbit communications, we have fabricated and studied a square shaped double clad Nd-doped fiber for the 1.06 micrometers amplifier characteristics. The output signal power is not saturated up to 1 watt level using the single frequency broad linewidth signal source. It is, however, saturated at a few hundred milliwatts by a stimulated Brillouin scattering effect using narrow linewidth non-modulated linewidth signal source. The maximum output power of 1.17 Watts is obtained with extraction efficiency of 37 percent from absorbed pump power. The net gain is estimated more than 25dB.

Diode-pumped solid state laser for spaceborne water vapor DIAL

For future spaceborne water vapor DIAL systems, we started a laser design study in 1994. New laser materials such as Cr:LiSAF are very attractive, but at present there are no high power diode lasers for direct pumping those materials. Therefore we determined to develop a high power diode-pumped Nd:YLF laser and Ti:sapphire laser for water vapor DIAL. The output energy of Nd:YLF laser is expected to be 550 mJ at 1053 nm and 400 mJ at 527 nm with a maximum repetition rate of 150 Hz. A Ti:sapphire laser will be pumped by the SHG of the Nd:YLF laser. Tuning of the Ti:sapphire laser to a strong absorption line (ON1), a weak absorption line (ON2) of water vapor and an off line (OFF) is made by an injection seeder which consists of two single longitudinal mode laser diode modules. Two on-line laser diodes are locked to water vapor absorption lines using an absorption cell or a photo-acoustic cell. These three laser lines (ON1, OFF and ON2) are transmitted into the atmosphere with a triple pulse technique for measurements of water vapor profiles from the ground up to 10 km. The laser spectral width of the on line is expected to be 0.5 pm with a stability of 0.05 pm. The output energy of each laser line is to be more than 100 mJ. This laser system will be developed within three years, and then incorporated as an airborne water DIAL.