Abstract: Space-based ground-imaging lidar has become increasingly feasible with recent advances in compact fiber lasers and single-photon-sensitive Geiger-mode detector arrays. A challenge with such a system is imperfect pointing knowledge caused by angular jitter, exacerbated by long distances between the satellite and the ground. Unless mitigated, angular jitter blurs the 3D lidar data. Unfortunately, using mechanical isolation, advanced IMUs, star trackers, or auxiliary passive optical sensors to reduce the error in pointing knowledge increases size, weight, power, and/or cost. Here, the 2-axis jitter time series is estimated from the lidar data. Simultaneously, a single-surface model of the ground is estimated as nuisance parameters. Expectation Maximization separates signal and background detections, while maximizing the joint posterior probability density of the jitter and surface states.

Abstract: Space-based ground-imaging lidar has become increasingly feasible with recent advances in compact fiber lasers and single-photon-sensitive Geiger-mode detector arrays. A challenge with such a system is imperfect pointing knowledge caused by angular jitter, exacerbated by long distances between the satellite and the ground. Unless mitigated, angular jitter blurs the 3D lidar data. Unfortunately, using mechanical isolation, advanced IMUs, star trackers, or auxiliary passive optical sensors to reduce the error in pointing knowledge increases size, weight, power, and/or cost. Here, the 2-axis jitter time series is estimated from the lidar data. Simultaneously, a single-surface model of the ground is estimated as nuisance parameters. Expectation Maximization separates signal and background detections, while maximizing the joint posterior probability density of the jitter and surface states.

Abstract: Methods and apparatus are disclosed for directing optical radiation to make multiple passes across an extended region of an electro-optic material, where during each pass the electro-optic material converts a portion of the optical radiation into terahertz radiation, and where the optical radiation is directed into the electro-optic material to cause an amplitude of the terahertz radiation generated from one or more earlier passes of the optical radiation to be constructively enhanced by the terahertz radiation generated from a later pass of the optical radiation.

Abstract: Methods and apparatus are disclosed for directing optical radiation to make multiple passes across an extended region of an electro-optic material, where during each pass the electro-optic material converts a portion of the optical radiation into terahertz radiation, and where the optical radiation is directed into the electro-optic material to cause an amplitude of the terahertz radiation generated from one or more earlier passes of the optical radiation to be constructively enhanced by the terahertz radiation generated from a later pass of the optical radiation.