High-power Laser and Amplifier Lidar Transmitters

High-power Laser and Amplifier Lidar Transmitters

Participants: Michael A. Krainak, Graham R. Allan, Mark A. Stephen, James B. Abshire, Jonathan A. Rall

Fiber lasers and fiber-amplifiers are truly an enabling technology for NASA's space flight remote sensing applications. Fiber lasers and fiber-amplifiers are light, compact and efficient, however work is still required on power-scaling and pulse-energies for NASA specific applications, such as altimetry and atmospheric spectroscopy. Fiber lasers and amplifiers offer numerous advantages for both near-term and future deployment on instruments on Earth Science Remote Sensing orbiting satellites. Advantages include: 1) no optical alignment required 2) strong leverage from the telecommunications industry and the US Defense Department 3) multi-year continuous- operation proven-reliable pump laser diodes 4) numerous pump laser diode and fiber laser/amplifier suppliers 5) upsurge in performance (including orders of magnitude power increases) over the last few years with predicted equal future increases 6) distributed thermal load 7) low parts count 8) radiation- tolerant devices available 9) space-qualified versions available (Figure 1 and Table 1)

Figure 1. Lucent 10 W space-qualified erbium fiber amplifier.

10) large wavelength range available 11) tunable and diverse wavelength reliable low-cast space- qualified single-frequency laser diode seed sources available 12) scalable to very high powers with both single-device and multi-device architectures 13) truly eye-safe (wavelengths longer than retinal thermal damage) versions available 14) compatibility with a number of atmospheric trace gas (e.g. H2O, CO2, O2) spectral features 15) high wall-plug efficiency (> 20%).

Table 2. Lucent 10 W space-qualified fiber amplifier.

Lucent space-qualified erbium-fiber-amplifier specifications

Most of our current research is focused on the use of fiber amplifier systems for atmospheric spectroscopy (H2O, CO2, O2). An important issue is the peak power limit for narrow linewidth (< 10 MHz) pulsed operaion of fiber amplifiers. Stimulated Brillouin Scattering (SBS) is typically the limiting factor (Figure 1).

Figure 2. SBS limits for single-frequency operation of Lucent (12 micron core diameter) fiber amp.

To achieve higher pulse peak powers (> 100 W) at narrow linewidth (< 10 MHz) we have com- missioned a large mode area (25 micron core diameter) erbium fiber amplifier from Keopsys Inc..

We are also pursuing 1) high-power (> 10 W) Nd doped fiber amplifers in the 920-940 nm wavelength range for use in water vapor DIAL systems, 2) > 1 mJ fiber lasers for laser altimetry 3) two-color frequency doubled systems for a normalized difference vegetation index lidar.