Novel Single Frequency and Broadly Tunable Laser Sources Developed at Coherent Technologies Inc. for Remote Sensing Appl
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Novel Single Frequency and Broadly Tunable Laser Sources developed at Coherent Technologies Inc. for Remote Sensing Applications Mark W. Phillips Coherent Technologies Inc. Louisville CO 80027 ABSTRACT This paper provides an overview of novel single frequency and broadly tunable laser technology being developed at Coherent Technologies, Inc. (CTI) for long-range remote sensing of hard targets and distributed targets from ground based and airborne platforms. In all these applications, the need for high beam quality and efficient high power operation is paramount. For many of the applications, it is also critical to control and measure frequency content of the emitted and collected light to a high degree of accuracy. For example, a sub-kHz linewidth is typically required for velocity and vibration imaging, and sub-MHz linewidth for some differential absorption lidar (DIAL) type measurements. INTRODUCTION Over the past 2-3 years, Coherent Technologies has been developing rapidly step-tunable single frequency lasers (60GHz/ms) and variable pulse format high power transmitters for range-resolved, micro-Doppler imaging of rapidly moving objects. The rapidly tunable single frequency laser sources allow full correction in coherent-based laser sensors for Doppler frequency shifts between the sensor and the target, including between objects in low earth orbit. The residual frequency spectrum of return light from the target can then be probed in detail using the waveform-agile transmitter to determine highresolution rotation and vibration signatures. For DIAL type-applications, CTI has been developing tunable sources providing several watts of power in the mid-wave and longwave IR, based on optical parametric oscillators and amplifiers pumped by high power, rapidly-tunable Cr:ZnSe lasers. This architecture provides a practical way of addressing multiple wavelengths across the IR bands of interest in a repeatable manner, using a sensor with no moving parts. As an example of how these laser sources have been integrated into ground-based and airborne remote sensors, CTI has recently fielded an airborne mid-IR chemical sensor based on parametric oscillators pumped by fixed frequency Nd:YLF lasers, for the purpose of gas-line leak detection. In terms of broad-impact laser activity, CTI has been developing high power (100Wclass), high efficiency self-imaging waveguide lasers and amplifiers that provide a simple means for converting the low brightness output from laser diode bars into the high brightness output of near-diffraction-limited CW and pulsed laser sources. Sources are being developed at 1, 1.5 and 2 microns to support multiple coherent and direct detection remote sensing applications. These devices, in combination with fiber-preamplifiers, are expected to provide a compact, robust, and practical solution for fielding a wide variety of future lidar systems on airborne and space-based platforms.
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FREQUENCY-AGILE SINGLE FREQUENCY LASER SOURCES A major effort is underway at Coherent Technologies to develop l
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