Lockheed Martin's Advanced Technology Center in Palo Alto has developed a prototype 8x8 NIR focal plane capable of
simultaneous Fourier processing per pixel. Experiments will be described in which 10 kHz Fourier processed frame rates
are used to drive a closed loop tracking servo loop. The pointing direction of one laser with wavelength λ1, and
amplitude modulation f1 is adjusted with a fast stirring mirror to track the motion of two targets illuminated by two other
lasers with wavelengths λ2 and λ3, amplitude modulated at two other distinct frequencies. Closed loop tracking control at
1kHz is demonstrated using only the single 8x8 focal plane to sense position of the three lasers simultaneously at all
pixels. Random noise generated by heat sources and a fan applied to the track laser beam path, and a white light source
with 100x larger signal then the received laser signal shown directly on the focal plane, has no effect on the track loop. A
final discussion will show the capability of the sensor to simultaneously measure range, as well as position.
White light interferometry techniques to obtain 3D surface profiles or rms surface roughness measurements for
microscopic instruments are used to develop an adaptive optics wavefront sensor for long range correction of lasers and
images. Combining these techniques with a high power incoherent or multiline laser and a radial shear interferometer, a
black fringe wavefront sensor (bfwfs) has been developed over the last two years at Lockheed Martin's Advanced
technology Center. The bfwfs will be described, and results of recent tests shown using a 16 channel device. The 16 ch
system is used to obtain measurements of open loop influence functions, and closed loop Bode plots using a Mems
mirror. The bfwfs device can be used for adaptive optics at long ranges on weight or volume limited platforms because
it allows high power incoherent lasers or other broadband sources to be combined with a parallel architecture and
inherently analog servo system. Results are reported in which a superluminescent laser diode (SLD) and a multiline cw
Argon laser are combined with a radial shear interferometer to measure phase at 200 Hz with 1/20 pv accuracy.
In this paper, we present the results of the phase diversity algorithm applied to simulated and laboratory data. We show that the exact amount of defocus distance does not need to be known exactly for phase diversity algorithm. We determine, through simulation, the optimum diversity distance. We compare the aberrations recovered with the phase diversity algorithm and those measured with a Fizeau interferometer using a HeNe laser. The two aberration sets agree with a Strehl of over 0.9. The contrast of the recovered object is found to be 10 times that of the raw image.
A portable low earth orbit satellite (LEO) tracking mount is described which has dimensions of 21' X 15' X 10' and weighs 58 pounds. Using 22 bit encoders on 9.5' worm gears, an integral microcontroller is capable of adjustable slew rates to six degrees per second. With a CCD and tracking software LEO pointing is demonstrated on f/10 eight inch telescope to less than 8 urad for periods of 10 seconds, and 50 urad for entire orbit passes. A closed loop one Hz video tracker is also described with automatic tracking of mag 7/8 satellites using a 12' telescope. Requiring only one operator, this system can be transported by a small car and be operational in a few hours. Possible uses and other recent work is also explained.
Experimental results will be shown in which an external acoustic-optic modulator is used with a high power single frequency cw argon laser operated at 488 nm and 514.5 nm to produce 150 - 300 MHz tunability on a 1.6 GHz carrier signal. Amplitude modulation with a visibility of 1 is demonstrated at 3.4 W488 nm and 5 W514 nm. Each of these wavelengths is tunable over 150 MHz or 300 MHz depending on the transducer. The crystal in each case is TeO<SUB>2</SUB>. At least 95% of the available laser power is modulated with a contrast of 100%, having a single-sideband power of -12 dBm with no measurable harmonics to less than -60 dBm. Thermal tests are discussed in which theory is compared to experimental data to investigate damage mechanisms. Two AOMs were tested until damage occurred at powers in excess of 6 Watts. Interferograms and sheargrams were used to measure phase changes as a function of heat load. Finally, a beam combining method will be explained in which recombined first and zero order beams from a single AOM are phased together to produce two collinear beams with output modulated power equal to the input power, except for small losses due to absorption.
The on axis intensity of a focused beam is a critical measurement of laser wavefront quality. This paper describes a simple method and device for measuring the Strehl ratio. The device requires a collimated beam of known input size and wavelength. The experimental Strehl ratio is determined by the power within the central 1/5 of the Airy disc diameter. Error sources are discussed, as well as experimental measurements.
A pulsed CO2 electric discharge fast flowing gain medium is used to test three unstable resonators which are forced to oscillate in an L = 3 azimuthal mode. This Higher Order Azimuthal Mode Unstable Resonator could be used to form a 'natural mode' resonator which would be unaffected by support struts necessary in an annular gain medium. Six equally spaced intracavity radial struts, and a suitable diameter on-axis obscuration, produce 180 degree phase changes between adjacent sectors of the six-sector near field pattern, and six radial lobes in the far field with no on-axis intensity. A phase plate, constructed by applying a half step coating to every other adjacent sector, corrects the far field.
This paper details experimental and numerical studies of the effect of astigmatism on the performance of an unstable ring resonator with eight mirrors, causing a round trip 180 deg beam rotation, or seven mirrors, producing a beam flip. The resonators were studied with integer and integer plus one half equivalent Fresnel numbers and with and without intracavity spatial filtering. The experiment was performed on a CW electric discharge, fast flow CO2 unstable ring resonator with two removable and orthogonal focal line apertures (FLAs). The astigmatism was produced by rotating one cylindrical focusing mirror with respect to the other, producing astigmatism oriented at 45 deg to the focal line axes. Intracavity power, near field intensity distribution, and far field power and beam quality measurements were taken. The far field beam quality behavior with astigmatism was not very sensitive to the Fresnel number, but was dramatically dependent on the number of mirrors.
During a series of experiments to test the concept of using an intracavity spatial filter to improve far field resonator performance, some interesting anomalies with established theory was discovered. A brief description of the gain medium and resonator geometries will be followed by a detailed discussion of the behavior.