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Hi-Shear Technology, Corp., (HSTC) has designed and built a Laser equivalent NASA Standard Initiator (LNSI). Langlie tests with a laser diode output initiating ZPP were conducted as a part of this effort. The test parameters include time to first pressure, laser power density requirements, and ignition time. The data from these laser tests on ZPP are presented.
A XeCl laser pumped iodine laser oscillator was developed which will be incorporated into the Master Oscillator Power Amplifier (MOPA) system. The developed XeCl laser produces output energy of about 60 mJ per pulse. The pulse duration was about 10 nsec. The kinetic model for the solar-pumped laser was refined and the algorithm for the calculation of a set of rate equations was improved to increase the accuracy and the efficiency of the calculation. The improved algorithm was applied to explain the existing experimental data taken from a flashlamp pumped iodine laser for three kinds of lasants, i-C3F7I, n-C4F9I, and t-C4F9I. Various solid laser materials were evaluated for solar-pumping. The materials studied were Nd:YAG, Nd:YLF, and Cr:Nd:GSGG crystals. The slope efficiency of 0.17 percent was measured for the Nd:YLF near the threshold pump intensity which was 211 solar constants (29W/sq cm). The threshold pump intensity of the Nd:YAG was measured to be 236 solar constants (32W/sq cm) and the near-threshold slope efficiency was 0.12 percent. True CW laser operation of Cr:Nd:GSGG was possible only at pump intensities less than or equal to 1,500 solar constants (203 W/sq cm). This fact was attributed to the high thermal focusing effect of the Cr:Nd:GSGG rod.
The ultra-stable beacon source (USBS) provides a laser-beam output with a very low angular jitter and can be used as an absolute angular reference to simulate a beacon in the laboratory. The laser is mounted on the top of a very short (approximately equal to 1 m) inverted pendulum (IP) with its optical axis parallel to the carbon fiber pendulum leg. The 85-cm, carbon fiber rods making up the leg are very lightweight and rigid, and are supported by a flex-joint at the bottom (see figure). The gimbal-mounted laser is a weight-adjustable load of about 1.5 kg with its center of rotation co-located with the center of percussion of the inverted pendulum. This reduces the coupling of transverse motion at the base of the pendulum to angular motion of the laser at the top. The inverted pendulum is mounted on a gimbal with its center of rotation coinciding with the pivot position of the inverted pendulum flexure joint. This reduces coupling of ground tilt at the inverted pendulum base to motion of the laser mounted at the top. The mass of the top gimbal is adjusted to give the pendulum a very low resonant frequency (approximately equal to 10 mHz) that filters transverse seismic disturbances from the ground where the base is attached. The motion of the IP is monitored by an optical-lever sensor. The laser light is reflected by the mirror on the IP, and then is detected by a quadrant photo-detector (QPD). The position of the beam spot on the QPD corresponds to the tilt of the IP. Damping of this motion is provided by two coil and magnet pairs. The bottom gimbal mount consists of two plates. The IP is mounted on the second plate. The first plate is supported by two posts through needles and can be rotated about the axis connecting the tips of the needles. The second plate hangs from the first plate and can be rotated about the axis perpendicular to the first plate. As a result, the second plate acts as a two-axis rotation stage. Its center of rotation is located at the effective bending point of the flex-joint. The second plate is pressed against two screw actuators by the weight of the IP. The screw actuators are orthogonal to each other and are used to adjust the inclination of the second plate. The actuators are driven by stepper motors. The whole IP system is housed in a box made of Lexan plastic plates to provide isolation from air currents and temperature variations. The signals from the sensors are processed and recorded with a PC using the xPC Target realtime environment of Math- Works. The control algorithms are written using the Simulink package from The MathWorks.
The repetitive Q-switched performances of an x-axis neodymium-doped lanthanum beryllate (Nd:BeL) laser and the current state-of-the-art Nd:YAG laser are compared. Output beam pulse energy, peak power, pulse width, beam divergence and mode pattern were measured for a gold-plated single elliptical cavity using a xenon flashlamp for excitation. The output of the Nd:BeL laser is found to exceed that of the Nd:YAG laser by a factor of two at Q-switched repetition rates on the order of 1 Hz, due to the smaller stimulated emission cross section of the x-axis Nd:BeL. When the repetition rate is increased to 10 Hz, the Nd:BeL output falls to a level three fifths lower than its low-rate value, while Nd:YAG output remained essentially constant. Analysis reveals that the decrease in output may be attributed to a depolarization loss due to thermally induced stress birefringence.
The effects of neutron irradiation on several properties of both single and multiple stripe laser diodes have been examined. Prior to fast neutron irradiation, total light output as a function of laser current, threshold current, near-field pattern, far-field pattern, and laser output wavelength spectra were measured at room temperature. These measurements were then repeated at intermittent neutron fluence levels. It was observed that the threshold current increased with neutron fluence for all devices examined. In contrast, neutron irradiation had only an indirect effect on the remainder of the laser diode properties in that the higher currents required for operation after irradiation caused variations in these properties.
Specifications for the pointing stabilization system of the large space telescope were used in an investigation of the feasibility of reducing ring laser gyro output quantization to the sub-arc-second level by the use of phase locked loops and associated electronics. Systems analysis procedures are discussed and a multioscillator laser gyro model is presented along with data on the oscillator noise. It is shown that a second order closed loop can meet the measurement noise requirements when the loop gain and time constant of the loop filter are appropriately chosen. The preliminary electrical design is discussed from the standpoint of circuit tradeoff considerations. Analog, digital, and hybrid designs are given and their applicability to the high resolution sensor is examined. the electrical design choice of a system configuration is detailed. The design and operation of the various modules is considered and system block diagrams are included. Phase 1 and 2 test results using the multioscillator laser gyro are included.
A method of pumping a COhZ laser by a hot cavity was demonstrated. The cavity, heated by solar radiation, should increase the efficiency of solar pumped lasers used for energy conversion. Kinetic modeling is used to examine the behavior of such a COhZ laser. The kinetic equations are solved numerically vs. time and, in addition, steady state solutions are obtained analytically. The effect of gas heating filling the lower laser level is included. The output power and laser efficiency are obtained as functions of black body temperature and gas ratios (COhZ-He-Ar) and pressures. The values are compared with experimental results.
Work toward developing a diffraction limited, single frequency, modulated transmitter suitable for coherent optical communication or direct detection communication is discussed. Diode pumped, monolithic Nd:YAG nonplanar ring oscillators were used as the carrier beam. An external modulation technique which can handle high optical powers, has moderate modulation voltage, and which can reach modulation rates of 1 GHz was invented. Semiconductor laser pumped solid-state lasers which have high output power (0.5 Watt) and which oscillate at a single frequency, in a diffraction limited beam, at the wavelength of 1.06 microns were built. A technique for phase modulating the laser output by 180 degrees with a 40-volt peak to peak driving voltage is demonstrated. This technique can be adapted for amplitude modulation of 100 percent with the same voltage. This technique makes use of a resonant bulk modulator, so it does not have the power handling limitations of guided wave modulators.
An optically pumped single mode laser, e.g., Nd:YAG crystal (20) with planoconcave mirrors is increased in efficiency by an order of magnitude to about 8% by optics (25, 27) for focusing the high power multimode output of laser diode arrays (21, 22) into the mode volume (20') of the laser medium (20). A plurality of these optically pumped single mode lasers (1-4) may be cascaded in a ring with dichroic mirrors (M.sub.1 -M.sub.4) at the corners for coupling in the laser diode arrays, each having its own means for spatially tailoring its beam to concentrate pump distribution inside the lasing mode volume of the medium. An InGaAlAs pump diode (30) with its wavelength the same as the lasing medium makes the ring unidirectional.
An optically pumped single mode laser, e.g. Nd:YAG crystal (20) with planoconcave mirrors is increased in efficiency by an order of magnitude to about 8% by optics (25, 27) for focusing the high power multimode output of laser diode arrays (21, 22) into the mode volume (20') of the laser medium (20). A plurality of these optically pumped single mode lasers (1-4) may be cascaded in a ring with dichroci mirrors (M.sub.1 -M.sub.4) at the corners for coupling in the laser diode arrays, each having its own means for spatially tailoring its beam to concentrate pump distribution inside the lasing mode volume of the medium. An InGaAlAs pump diode (30) with its wavelength of the same as a lasing medium makes the ring unidirectional. The questions raised in reexamination request No. 90/002,473, filed Oct. 10, 1991, have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1,570(e).
A carbon dioxide gasdynamic laser was operated over a range of reservoir pressure and temperature, test-gas mixture, and nozzle geometry. A significant result is the dominant influence of nozzle geometry on laser power at high pressure. High reservoir pressure can be effectively utilized to increase laser power if nozzle geometry is chosen to efficiently freeze the test gas. Maximum power density increased from 3.3 W/cu cm of optical cavity volume for an inefficient nozzle to 83.4 W/cu cm at 115 atm for a more efficient nozzle. Variation in the composition of the test gas also caused large changes in laser power output. Most notable is the influence of the catalyst (helium or water vapor) that was used to depopulate the lower vibrational state of the carbon dioxide. Water caused an extreme deterioration of laser power at high pressure (100 atm), whereas, at low pressure the laser for the two catalysts approached similar values. It appears that at high pressure the depopulation of the upper laser level of the carbon dioxide by the water predominates over the lower state depopulation, thus destroying the inversion.
The paper discusses a program designed for the development of a GaAs IOC transmitter consisting of a monolithic surface laser whose output is coupled into patterned channel waveguides. Modulation and switching of the radiation occur in the waveguide circuit and are controlled separately. These structures are to be fabricated monolithically on a single semiconductor chip with each device amenable to integrated low-cost manufacture. The waveguide outputs of the IOC transmitter will be coupled to single mode optical fibers which form a transmission cable. The properties of the semiconductors (Ga,Al)As and (Ga,In)As permit performance of each of the basic functions included in the device considered. The concept of monolithic nondiscrete GaAs diode lasers is examined along with optical stripline channel waveguides and electro-optic channel waveguide modulators and switches.
The long path absorption spectroscopy (LPA) measurement of OH utilizes the strong UV absorption spectrum of the molecule with well resolved rotational lines around 308 nm. The light source consists of an Ar ion laser pumped CW dye laser, the output of which is frequency doubled to emit a spectrally smooth light profile of 0.1 nm FWHM at 308 nm. This is considerably broader than the sharp (0.0018 nm wide) absorption features of OH and also wider than the total spectral region (0.06 nm) scanned around the OH lines. For field measurements a Cassegrain-type telescope expands the small diameter of the original laser beam by a factor of 50 to about a 0.25-m diameter in order to reduce the divergence of the beam as well as its mean photon flux density, thus reducing the maximum self-generated OH concentration to 40,000 cu. cm. The light is passed into the open atmosphere and reflected at about 5 km distance resulting in a 10-km light path length. A telescope focuses the returning light onto the entrance slit of a monochromator the single exit slit of which is replaced by a mechanical scanning device operating at a scan repetition rate of 6.6 KHz. For a typical measurement (1h duration) some 20,000,000 scans are averaged, rendering the contribution of atmospheric turbulence to the spectral noise negligible.
A 100-W Beale free-piston Stirling engine was powered remotely by a CO2 laser for long periods of time. The engine ran on both continuous-wave and pulse laser input. The working fluid was helium doped with small quantities of sulfur hexafluoride, SF6. The CO2 radiation was absorbed by the vibrational modes of the sulfur hexafluoride, which in turn transferred the energy to the helium to drive the engine. Electrical energy was obtained from a linear alternator attached to the piston of the engine. Engine pressures, volumes, and temperatures were measured to determine engine performance. It was found that the pulse radiation mode was more efficient than the continuous-wave mode. An analysis of the engine heat consumption indicated that heat losses around the cylinder and the window used to transmit the beam into the engine accounted for nearly half the energy input. The overall efficiency, that is, electrical output to laser input, was approximately 0.75%. However, this experiment was not designed for high efficiency but only to demonstrate the concept of a laser-driven engine. Based on this experiment, the engine could be modified to achieve efficiencies of perhaps 25-30%.
Presented is an O-band silicon photonics dual-polarization coherent/IMDD modulator integrated with semiconductor optical amplifiers and tunable laser to enhance the short-reach link budget. The laser demonstrated output power >6 dBm and a <250 kHz linewidth over a 14 nm tuning range. Modulators paired with custom 64 Gbaud QPSK drivers exhibited improved analog link sensitivity compared to similar devices without integrated gain sections. They also demonstrated 53 Gbaud dual-polarization PAM4 operation when characterized with a linear driver and MaxLinear 100G/lane DSP board. Both optical links achieved BERs at the KP4-FEC threshold and overall transmitter assembly energy consumption <6.9 pJ/bit without any thermal control when at steady room temperatures.
High intensity interference patterns for lateral shearing interferometer with single plane parallel plate and gaseous laser source
Finite laser pulse time effects on temperature wave retardation in flash diffusivity techniques
Spectroscopic investigation of laser excited molecular spectra from powdered solids for meteor and reentry physics