MIT/LL development of broadband linear frequency chirp for high-resolution ladar

The development of a high-resolution laser radar (ladar) exhibiting sub-mm resolution would have a great impact on standoff identification applications. It would provide biometric identification capabilities such as three-dimensional facial recognition, interrogation of skin pore patterns and skin texture, and iris recognition. The most significant technical challenge to developing such a ladar is to produce the appropriate optical waveform with high fideltiy. One implementation of such a system requires a 1.5-THz linear frequency sweep in 75 mu s. Previous demonstrations of imaging with such waveforms achieved a 1 THz sweep in > 100 ms, and required additional corrections to compensate for sweep nonlinearity. The generation of high fidelity, temporally short frequency-swept waveforms is of considerable interest to the Dol) community. We are developing a technique that utilizes a novel method to generate a I THz sweep in 50 mu s from a mode-locked laser. As a proof-of-principle demonstration of this technique we have successfully generated a 20 GHz sweep in I Vs with a fidelity sufficient to produce better than -20 dB sidelobes for a range measurement without using any additional corrections. This method is scalable to produce the entire I THz sweep in 50 mu s.