Compact Power Amplifier for Hybrid Fiber/Bulk Wind Lidar Transmitters

There is strong motivation to significantly reduce the complexity and size and to further improve the electrical-to-optical efficiency of eyesafe coherent lidar systems. Recent advances in fiber lasers and associated components allow for compact and rugged eyesafe transmitters, but the high-spectral-purity single frequency, and high beam quality output energy needed for efficient coherent lidar systems is limited to < 1 mJ in practical all-fiber implementations. This pulse energy is sufficient for many short-range or high-backscatter measurement applications, but to extend the measurement capability higher pulse energy is needed. This is due to a fundamental characteristic of coherent (heterodyne) detection in the weak signal regime, where the measurement sensitivity is proportional to the product of the pulse energy and the square root of the pulse repetition frequency (PRF). Stressing weak signal examples include measuring atmospheric winds from space platforms or measuring in the very low backscatter mid and upper troposphere from ground or airborne platforms. To utilize the positive attributes of a fiber-based transmitter, we propose to develop a very compact integrated bulk-crystal-based amplifier and lidar transmit/receive module that will boost the fiber transmitter output pulse energies to as much as 40 mJ per pulse at 400 Hz PRF and provide for efficient collection of the return signals. Our initial focus will be on 2 micron wavelength devices, but the basic architecture can be applied to other wavelength as well. Operationally flexible, highly ruggedized compact packaging with path-to-space will be emphasized. These innovations will apply directly to current NASA missions and instruments (Space-based Winds, Airborne and Ground Based Wind lidar, IPDA, LAS) and accelerate commercial development and availability of practical ground-based and airborne systems at Beyond Photonics and elsewhere.

Potential NASA applications of the proposed hybrid fiber/bulk power amplifier/lidar transceiver technology include on-going and future measurement of global winds from space; ground-based and airborne coherent lidar programs; eye-safe remote laser spectroscopy applications for measurement of atmospheric constituents like CO2, water vapor, and methane; tracking of fast-moving space debris and asteroid hazards; spacecraft docking applications; and other shortwave-IR wavelength instrument developments in the 1.5-to-2.0 micron wavelength region.

Non-NASA uses of hybrid fiber/bulk amplifier transmitters include DoD hard target and space debris tracking/imaging problems and research/industrial applications requiring very compact efficient front-end transmitter lasers and bulk amplifiers at SWIR wavelengths. Product development is planned for compact, high-performance remote-sensing products for winds and other remote sensing applications.

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