Laser beam width, divergence, and propagation factor are three major parameters required to apply a source. This paper discusses the status of the draft standard ISO TC172/SC9/WG 1. The two methods, free beam and lens method, are described and experimentally shown to give near equal results for a single TEMoo source. For nearly collimated sources, a quick method requiring two beam widths is described to give the key parameters. Basic measurement devices including slit scan, pinhole scan, encircled energy, knife edge scan and their array equivalents are described. These methods are compared to the theoretical variance beam measurement device with the result that the slit scan produces the least inherent error, 0 to 4% for the first six laser modes, assuming zero slit width.
Several methods of measuring multi-mode beam propagation characteristics are discussed. The aim is to use the minimum number of measurements and the simplest equipment possible. In theory all the beam properties can be determined from three beam diameter measurements. But care must be taken where the diameter measurements are made to avoid large errors due to small diffraction effects.
Beam waist size, waist location and the times-diffraction-limit number, M2, are the most basic and fundamental parameters describing the propagation characteristics of laser beams. This information is useful in the engineering development of lasers and beam delivery systems, and provides a meaningful way to monitor, compare and control quality both in the manufacture and in the application of laser devices. An instrument that allows real-time access to this information is described.
A comprehensive diagnostic instrumentation suite was designed and successfully utilized to characterize the performance parameters from two coupled lasers. The characterization included such standard diagnostic measurements as: absolute and RMS power, polarization, jitter, near-field and far-field irradiance profiles, near-field phase, spectral content, and beam quality. Coupling strength between the two lasers was also measured as well as their mutual coherence, locking range, and the heterodyne frequencies between axial modes in the resonator.
Increasing use is being made of high-power laser plant to cut, weld, harden, coat and alloy metals. Diagnostic systems analyzing the focused and unfocused laser beam are essential for advanced development and operation of such high-power laser plant. The paper presents various technical options for diagnosing high-power laser beams, with particular attention to a measuring technique which enables focused and unfocused beams to be diagnosed at beam powers of more than 20 kW and intensities of more than 10 7 W/cm2. Laser-beam diagnostics support 3D graphic displays of the laser beam intensity distribution. These graphics indicate the beam position, beam radius and beam intensity. Beam-descriptive parameters such as the M2 quality factor or the Rayleigh length can also be determined.
CCD holography is to be used to measure the phase conjugation fidelity of an SBS experiment at TRW. The diagnostic has been shown capable of phase measurements with an RSS accuracy of 1/80 (lambda) . The technique and experiments designed to quantify its accuracy are described. The application of this technique to the SBS experiment and the peculiarities of doing the experiment in the IR are also discussed.
Several ways of measuring spot quality are compared. Examination in detail is made of various figures of merit such as full-width-at-half maximum (FWHM), full-width-at-1/e2 maximum, Strehl ratio, and encircled energy. The paper describes application for optical data storage, but results can be applied to other areas like space communications and high-energy lasers. The finding is that the optimum figure of merit in many cases is Strehl ratio.
A method was developed for relative distance measurements of long optical pathlengths of up to 40 m with good distance resolution up to +/- 5 nm ((lambda) /120 at 0.6238 (mu)) and moderate temporal resolution up to 250 Hz, sufficient to quantify low and moderate frequency piston jitter of a ring resonator. The measurement scheme used two frequency interferometry using laser probe beams and was based upon a fringe counting technique utilizing a modified Hewlett-Packard (HP) Model 5527 A distance measuring interferometer. Modifications included a much different interferometer than that available from HP and a high performance receiver front-end based upon an avalanche photodetector. The interferometric method enabled in-situ resonator piston jitter measurements, internal to the resonator optical train, which were insensitive to optical disturbances external to the resonator. In an experimental demonstration, portions of a ring resonator optical train were installed in a supersonic combustion driven laser test-bed and its vibrational characteristics analyzed using this method. Data was recorded and analyzed during quiescent, vacuum pumps-on and 'cold flow' conditions with variations of number and combination of optical mounts. The data indicated that a high quality state-of-the-art translation stage incorporated in the ring resonator design was not sufficiently stable for the ring resonator design requirements. The data also indicated that the facility disturbances during pumps-on and 'cold flow' conditions significantly increased piston jitter. On the other hand, the device flow disturbances of the laser probe beams crossing the gain flow region during 'cold flows' and disturbances due to table bending and twisting between two optic vacuum optic boxes were minimal. Facility disturbance data measured by accelerometers and tilt disturbances measured by a laser probe beam incident upon a position sensor are also included. A design is presented for an interferometer which can be integral to an operating unstable ring resonator.
In this paper a description of the device for the analysis of spatial-temporal characteristics of technological lasers radiation is presented. The device construction is a measuring head connected with a personal computer through a special unit manufactured in the form of a separable board for IBM PC/XT/AT, and a personal computer proper. As a photodetector in measuring head the original 64-elements linear array is used, its operative mechanism is based on the phenomenon of an anisotropic thermo-EMF in textured metallic films. The spatial-temporal distribution of the laser LTN-102-SU radiation intensity obtained with the help of the complex is demonstrated.
A practical approach has been evaluated and is described for acquiring low-power beam samples from a high-power free electron laser (FEL) with optical fidelity suitable for performance evaluation. The analytical results for polarization and alignment sensitivities related to this sampling technique are discussed.
Precision multi-wavelength output beam diagnostics are currently under development for use in the Nova laser system. This diagnostic package will measure the energy, pulseshape, and near-field intensity distribution at wavelengths of 0.351 micrometers, 0.528 micrometers, and 1.05 micrometers.
A 0.74-m aperture laser diagnostic system has been designed and built and is an operational part of target irradiation experiments being conducted at the Nova Two Beam facility at Lawrence Livermore National Laboratory. These experiments examine the effects of laser beam conditioning on laser-plasma interaction, and include the use of full-aperture (0.74-m diameter) distributed phase element optics for fundamentally altering the irradiance distribution at either the second or third harmonic wavelengths of the Nova Nd:Glass laser system. The two beam laser diagnostic system (TBLDS) provides the suite of laser diagnostics essential to interpreting the results of these studies: (1) full-aperture energy measurement, (2) near-field imaging of planes up to 15 m ahead of the target chamber focusing lens, (3) far-field imaging of equivalent target planes within 5 mm on either side of `best focus', (4) time-resolved power measurement using 10 to 20-ps resolution streak camera systems, and (5) spectral measurement using a 1-m grating spectrometer with option for temporal streaking. The diagnostic is also equipped with a self-referencing interferometer for measuring the wavefront at various near-field planes; however, this feature is still under activation. The diagnostic system can flexibly handle either the fundamental, second or third harmonic wavelengths on alternate laser pulses, and an energy range of 50 Joules/pulse to 12.5 kJ/pulse. In this paper the design of the TBLDS, and present results from ongoing measurements of the Nova irradiance without wavefront modifications are discussed. The authors' numerical simulation techniques for modeling the laser irradiance at the target plane are also reviewed.
An integrated diagnostic mstrumentaüon suite has been developed for use in characterizing certain aspects of the interaction
of an infrared high energy laser beam with target materials. The diagnostics include the temporal history of the target surface
temperature at the focal plane, scattering and extinction by the target plume, high speed imaging of the microscopic particles
spalled off the target, and a high-speed real-time digital data acquisition system which provides overall control of the
A laptop personal computer and camera-based laser beam diagnostic system (LaserScan) has been developed which can easily be transported for field installation of lasers and laser systems. Simply, easily customized menus are tailored to specific user requirements employing powerful image processing routines. For pulsed lasers a novel flash detection system allows pulsed or modulated laser beams to be sampled without the requirement for external triggers. The laptop LaserScan systems incorporate an internal modem so data and image files can be easily saved on built-in high-density disk drives and transmitted by telephone to other locations. The laptop system can also be used with the SensorPhysics UV LaserCards and IR LaserCards to provide images of ultraviolet (220-360 nm) lasers and CO2 lasers. These low cost imaging media can be used without the image processing system as well.