As part of the early development for NASA's Mars Laser Communication Demonstration (now canceled), we exposed
two InGaAs focal plane arrays (FPAs) to 22 krad(Si) dose at a rate of 4.6 rad(Si)/s using a 60Co gamma-ray source. Both
the SU320MS from Sensors Unlimited and the ISC9809 from FLIR Systems, Inc. operated throughout the test. The FPA
electronics were shielded from radiation; only the photosensitive InGaAs and its readout integrated circuit (ROIC) were
exposed. Background levels on both FPAs increased during the test. The SU320MS saturated and failed to respond to
infrared light after the test. The ISC9809's background increased but did not saturate. Phenomena exhibited during the
test included both isolated single-pixel hits and increased mean over the full FPA. Tests of the ISC9809 after irradiation
indicate no change in gain but an increase in mean dark current. In addition, 91% of the ISC9809 pixels also had
increased temporal noise. As a result of these tests, the ISC9809 was chosen for flight, but shielding was added to reduce
the level seen by the FPA to an estimated 6 krad(Si) for a 10-year lifetime in Mars orbit.
A high-speed imaging device based on a streak camera has been demonstrated, which provides multiple images from non-repeatable transient events of time scale >= 1 ns. It can be employed for pulsed laser beam diagnostics, measuring laser beam spatial and temporal structure on a single-pulse basis. The system currently has angular resolution of 16 X 16 pixels, with a time resolution of 250 ps. The laser beam width is sized to fill the input optic, and the image is dissected by a square array of optical fibers. At the other end of the fiber optic image converter, the 256 fibers form a line array, which is input to the slit of a streak camera. The streak camera sweeps the input line across the output phosphor screen so that position is directly proportional to time. The resulting 2-D image (fiber position vs. time) at the phosphor is read by an intensified (SIT) vidicon TV tube, and the image is digitized and stored. A computer subsequently decodes the image, unscrambling the linear pixels into an angle-angle image at each time. We are left with a series of snapshots, each one depicting the laser beam spatial profile (intensity cross-section) at succeeding moments in time. The system can currently record several hundred images over a span of 25 to 400 ns. This detector can study lasers of pulse width >= 1 ns and with a visible wavelength (200 - 900 nm). Candidate lasers include doubled Nd:YAG, excimer, ruby, nitrogen, metal vapor, and Ti:Sapphire. The system could also be simply configured as an 8 X 8 element wavefront sensor to record the cross-sectional distribution of phase, as well as amplitude. Finally, suggestions for system improvement are detailed, and the ultimate limitations of the method in terms of spatial and temporal resolution are discussed.
A high-speed imaging device has been built that is capable of recording several hundred images over a time span of 25 to 400 ns. The imager is based on a streak camera, which provides both spatial and temporal resolution. The system's current angular resolution is 16 X 16 pixels, with a time resolution of 250 ps. It was initially employed to provide 3-D images of objects, in conjunction with a short-pulse (approximately 100 ps) laser. For the 3-D (angle-angle-range) laser radar, the 250 ps time resolution corresponds to a range resolution of 4 cm. In the 3-D system, light from a short-pulse laser (a frequency-doubled, Q-switched, mode-locked Nd:YAG laser operating at a wavelength of 532 nm) flood-illuminates a target of linear dimension approximately 1 m. The returning light from the target is imaged, and the image is dissected by a 16 X 16 array of optical fibers. At the other end of the fiber optic image converter, the 256 fibers form a vertical line array, which is input to the slit of a streak camera. The streak camera sweeps the input line across the output phosphor screen so that horizontal position is directly proportional to time. The resulting 2-D image (fiber location vs. time) at the phosphor is read by an intensified (SIT) vidicon TV tube, and the image is digitized and stored. A computer subsequently decodes the image, unscrambling the linear pixels into an angle-angle image at each time or range bin. We are left with a series of snapshots, each one depicting the portion of target surface in a given range bin. The pictures can be combined to form a 3-D realization of the target. Continuous recording of many images over a short time span is of use in imaging other transient phenomena. These applications share a need for multiple images from a nonrepeatable transient event of time duration on the order of nanoseconds. Applications discussed for the imager include (1) pulsed laser beam diagnostics -- measuring laser beam spatial and temporal structure, (2) reflectivity monitoring during pulsed laser annealing of microelectronics, and (3) detonics or shock wave research, especially microscopic studies of shocks produced by laser pulses.
This paper compares two detectors for visible laser radar: a 1-D detector that resolves a target in range and a 3-D detector that resolves a target in angle and range. For both, a short pulse laser illuminates the target. For both, the receiver is based on a streak camera, which detects reflected light from the illuminated target and resolves the light in time.
The time resolution is 250 ps, so the target is resolved into 4 cm range cells. The 1-D detector focuses the reflected light to a point. The output
is the 1 -D, range-resolved projection of the target. The 3-D detector images the target on a focal plane, which is dissected by a fiber optic image converter attached to the streak camera. The output is a 3-D image of the target. For both detectors, we show data from two simple targets. The paper also compares two methods of remote sensing using these detectors:
2-D range tomography using data from the 1-D detector and angle-angle-range imagery using the 3-D data.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.