An innovative Active Laser Imaging (ALI) vision system is presented. We report the experimental data of a short range
ALI able to achieve range measurements and to recognize people up to 5 km away, according to Johnson's criterion. We
also report the simulation data of a long range ALI working in excess of 10 km. The ALI uses a laser to illuminate an
area and a telescope to collect the scattered light into an InGaAs camera. The laser has been developed internally; it is an
eye safe class I pulsed laser operating at about 1.5 μm; its divergence and direction are changed according to the scene
and environmental conditions. The ALI can be used in active mode, with the laser on, or in passive mode using external
short wave infrared (SWIR) illumination sources. The data collected by the ALI and a thermal IR camera show the
ability of ALI to look across glasses and to read writings and the impossibility of thermal IR camera to do the same. We
describe the software models developed to emulate the ALI, the scenes, and the environmental conditions. The models
have been validated by experimental data and used to design the ALI.
The key features and performances of a compact, lightweight, high power Er3+:Yb3+ glass laser transmitter are reported on. The theory employed to get an optimal design of the device is also described. In free running regime high energies of about 15mJ in 3ms long pulses were obtained, with an optical efficiency close to
85%. When q-switched by a Co: MALO crystal of carefully selected initial transmittivity, a high peak power in excess of
500 kW was obtained in about 9ns pulse duration, with an optical efficiency of 60%.
The laser was successfully run with no significant power losses at repetition rates up to 5Hz due to a carefully designed
heat sink which allowed an efficient conduction cooling of both the diode bars and the phosphate glass.
The transmitter emits at a wavelength of 1535nm in the
so-called "eyesafe" region of the light spectrum thus being
highly attractive for any application involving the risk of human injury as is typically the case in remote sensing
activities. Moreover, the spectral band around 1,5mm corresponds to a peak in the athmospheric transmittance thus being
more effective in adverse weather conditions with respect to other wavelengths.
Actually, the device has been successfully integrated into a rangefinder system allowing a reliable and precise detection
of small targets at distances up to 20Km. Moreover, the transmitter capabilities were used into a state of the art infrared
laser illuminator for night vision allowing even the recognition of a human being at distances in excess of 5Km.