The Nova laser, in operation since December 1984, is capable of irradiating targets with light at 1.05 Âµm, 0.53 µm, and 0.35 Âµm. Correct alignment of these harmonic beams uses a system called a target plane imager (TPI). It is a large microscope (four meters long, weighing one thousand kilograms) that relays images from the target chamber center to a video optics module located on the outside of the chamber. Several modes of operation are possible including: near-field viewing and far-field viewing at three magnifications and three wavelengths. In addition, the entire instrument can be scanned in X,Y,Z to examine various planes near chamber center. Performance of this system and its computer controls will be described.
The Large Optics Generator recently installed at the University of Arizona was purchased to grind symmetrical optics up to 8 meters and segments up to 15 meters in diameter and with a sag of up to 1.5 meters. To do this with accuracies of a few microns rms requires every trick in the book and leads to such farcical statements as: "You turned off the lights last night and that cost me 18 microns!" The techniques and solutions to many accuracy and stability problems are applicable to any large mechanical system that needs optical type tolerances or stability. The quantization of such items as a footstep on a two foot thick foundation and the sideways spread of a 1.7" x 3.5" steel bar when a bolt that goes through it is tightened can be potent reminders of what is needed to maintain micron accuracies. Verification of the smoothness of the large table bearing, mechanical alignment of the ways, minimization of backlash deflection and tilts, thermal time constants, characterization of the inaccuracies and computer corrections are all areas that could be of use in the design, adjustment and use of optical system. The Large Optics Generator may be unique, but its problems are not.
The NNTT concept is a multiple mirror type telescope consisting of an array of four 7.5-meter diameter telescopes which are coaligned and cophased by means of an internal optical metering device. As a result, the NNTT acts like a single telescope with a 15-meter collecting diameter and a 21-meter resolution diameter. This paper describes this coalignment/ cophasing system.
The Lockheed Beam Alignment Assembly (BAA) is designed to be a space qualifiable, long life, low bandwidth beam stabilization system. The BAA will stabilize a wandering pulsed laser beam with an input beam tilt of ±750 microradians and translation of ±2.5 mm by two orders of magnitude at the bandwidth of interest. A bandwidth of three hertz was selected to remove laser and optical train thermal drifts and launch induced strain effects. The lambda over twenty RMS wavefront will be maintained in the optics at full power under vacuum test, to demonstrate space qualifiability and optical performance.
The Nova laser is a high-power, pulsed, neodymium-glass system used for inertial confinement fusion and X-ray laser research at the Lawrence Livermore National Laboratory. The control system aligns the ten 250-m-long beams by closing approximately 300 automatic loops. TV alignment sensor images are image processed to extract laser beam and reference information. Two-dimensional techniques that have been applied to process these images include correlation, convolution, gradient, centroid, Hough transform, and histogram equalization. These techniques combine to form algorithms that are relatively insensitive to image Intensity. This paper describes practical image processing methods and reliability measures developed for automatic alignment.
Orthogonally acting phase-locked loops operating at distinct, well-separated dither frequencies are used to automatically align (maximize output power) an argon ion pump laser, its pointing into a ring dye laser, and optimize a dye laser beam coupling into a single mode fiber of 4 micron core diameter. Such a system of feedback loops or combination of them is an ATOM (Alignment Through Orthogonal Maxima).
The characterization of x-ray laser radiation requires the measurement of the radiation wavelengths, their brightness, and their temporal evolution. The spectrometer used for this application includes a focusing, grazing-incidence ellipsoidal mirror, a transmission grating for spectral resolution, and a soft x-ray streak camera to time-resolve and record the spectrum. This paper describes the bench alignment of the spectrometer and its alignment at the laser facility before each shot. Particular emphasis is put in the fact that only optical techniques were used for both alignments, relying on the correlation between the behavior of each component at optical and x-ray wavelengths.
A new surface measuring instrument has been developed which is capable of measuring surface errors to the submicron level. RMS noise in measuring the surface error was found to decrease as [integration time]-1/2. The instrument can measure surface errors to within 10 microns in a small test region in only a few seconds of integration. The instrument could therefore be used to align radio telescope panels to high precision in real time.
During optical alignment, whether internal to the optical instrument as part of the design, or external as references to other items, some physical movement must occur. This motion can be generated by an energy input of manual, electrical or thermal means. When a fine adjustment is performed during an optical alignment, the resolution, accuracy, repeatability and stability of the procedure enter into the error analysis. Companies do not like to publish information on their error analyses, nor on any details on their original fine adjustment concepts which they have evolved over the years. It is hoped that this article in some way might loosen this situation by allowing the author to expose some of the design considerations that he has come across over the years. Some of the major areas of coverage are these: • Displacement Amplification: The magnification of the fine adjustment to facilitate observation • Influences on the Adjustment: The same type of environmental phenomena affect the individual adjustment that affect the entire optical instrument • Restraining Motion: The problem of making an adjustment and then clamping, thereby causing a misadjustment due to the clamping action • Adjustment Error Budget: The various types of adjustment errors, and their effect on the overall adjustment error budget.
Two complimentary methods for aligning a linear array of detectors are described. The alignment procedure effectively projects a set of reference coordinators as defined by the intersection of a laser beam with the interface of a pair of matched cube beamsplitters. The fractional (radiometric) error associated with this alignment procedure should be much less than 0.1%.
The Radian Group, Inc., manufactures The Radian System, a specialized 35mm motion picture projection system producing an image on a hemispherical gray screen, typically a planetarium dome. The optical system consists of a reflector-backed xenon arc, a relay lens, field antics, and a fisheye lens. Well-considered alignment is required to simultaneously focus the image and nroduce uniform illumination.
An apparatus and procedure for the boresight alignment of the transmitter and receiver optical axes of a laser radar system are described. This accurate technique is applicable to both shared and dual aperture systems. A laser autostigmatic cube interferometer (LACI) is utilized to align a paraboloid in autocollimation. The LACI pinhole located at the paraboloid center of curvature becomes the far field receiver track and transmit reference point when illuminated by the transmit beam via a fiber optic pick-off/delay line. Boresight alignment accuracy better than 20 prad is achievable.
An instrument developed to accurately measure small rotations (twist about an optical axis) uses a Faraday rotator to modulate the polarization of a HeNe laser beam. Twist sensors located in the beam path consist of a calcite polarizer (analyzer), a silicon detector and associated electronics. The sensors measure relative changes of the sensor analyzer and the null position of the modulated source beam. Reference measurements of the laser intensity and beam modulation are made to avoid accurately characterizing the modulation amplitude. This instrument has a sensitivity of 0.2 microradians at 5 Hz bandwidths over a 17.5 milliradians measuring range. This is accomplished by controlling the beam wander, reducing the laser divergence, and utilizing synchronous detection.
Synchronous demodulation was applied to the Laser Optical Line of Sight system (LOLOS) used to measure deflections of a canister used in underground testing. The purpose of this was to achieve greater sensitivity and resolution than that found in the original system. Electronics and optical equipment were built or acquired to evaluate the concept. Under laboratory conditions sensitivity to lateral and angular displacements were improved by more than an order of magnitude.