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Near infrared laser illuminator for very long-range flash active imaging applications

For very long-range flash active imaging applications, a powerful and narrow beam divergence pulsed laser illuminator is needed. Conventional high fill factor 1-centimeter diode bars are not well suited to produce a homogeneous and narrow beam divergence in an easy way. In the present paper, a concept based on a QCW mini-bars laser diode stack, focusing lenses and beam homogenisation is presented. With fifteen 1.5 mm conductively cooled fast axis collimated mini-bars, a peak power of 803 Watt at a wavelength of 810 nm is achieved with a maximum duty cycle of 2 percent. After collimation, the laser beam on the scene shows very homogeneous rectangular illumination geometry with a ratio of 4:3 well adapted for active imaging purposes. The beam divergence is reduced to 3.35 × 2.53 mrd with a two lenses objective of focal length f = 573 mm and f-number f# = 4.8.