The copper laser has undergone 20 years of development since first demonstrated in 1966 by Walter et al.1 The Lawrence Livermore National Laboratory, funded by the Department of Energy, has participated in copper-laser development since 1974 for application in atomic vapor laser isotope separation (AVLIS). Separation of isotopes from a uranium vapor stream using lasers requires several unique properties from the laser system. We have chosen copper-laser-pumped dye lasers as our baseline technology for this process. We discuss the operating characteristics of the copper laser with emphasis on suitability for AVLIS. These characteristics include: average power, pulse-repetition rate, optical pulse length, and electrical to optical efficiency. In the past 3 years, we have designed, built, and are at present running the Laser Demonstration Facility continuously. This facility has over 40 copper lasers. We discuss the copper-laser system as an extension of the operating characteristics of a single copper laser. Copper-laser oscillator amplifier chains, beam quality, and refurbish ent cycles are discussed. The overview is divided into five sections: an introduction to AVLIS, laser requirements for AVLIS, copper-laser chains, system maintenance and refurbishment, and conclusions.
The first fully automated mobile copper and gold vapour lasers for medical applications were developed in Australia. The history of this development program is presented in this paper. These lasers have been tested in several clinical programs and success with the gold vapour laser in cancer phototherapy using HpD has been achieved in various types of tumours. Trials have commenced on the use of the 578 nm yellow line of the copper vapour laser for dermatology and plastic surgery.
Recent advances are described which have resulted in improvements to the performance of copper vapour lasers (CVL), operating at 511nm and 578nm, with specific reference to ultra fast pulse amplification and high speed photography. Collaborative work between Oxford Lasers Ltd. and the University of Aachen has resulted in the development of a copper vapour pump laser with 10ns pulse width, peak power of order 150kW, repetition rate of up to 20kHz and an output beam divergence close to the diffraction limit. With optical fibre beam delivery systems, high levels of laser illumination can be achieved in locations inaccessable to conventional strobe sources. In textile manufacture for example, the spinning process in which individual fibres are incorporated into yarn has been studied. The 3Ons pulse length of the Oxford Lasers CU10 ensures that high resolution images of individual fine (10 micron) fibres are recorded. Advances in the design of the pulsed electronic circuitry have enabled not only extremely high repetition rate operation of the CVL to be achieved, but allows the frequency to be continuously varied over wide ranges. This ensures that maintaining synchronization with rotating prism cameras, even during the run-up phase of the camera, presents no problem. Improvements to the design of the laser head itself have led to operation at significantly higher overall efficiences (>1%) resulting in the upgrading of existing specifications. Advances in the cavity design have allowed these high powers to be realised as focusable laser light. The examples we present show how versatile the CVL technology has become in a rapidly expanding range of applications and illustrate the potential for the CVL to achieve the status as the 'work-horse' pulsed high power laser.
A flow visualization system has been developed to determine the air flow within the combustion chamber of a motored, axisymmetric engine. The engine has been equipped with a transparent quartz cylinder, allowing complete optical access to the chamber. A 40-Watt copper vapor laser is used as the light source. Its beam is focused down to a sheet approximately lmm thick. The light plane is passed through the combustion chamber, and illuminates oil particles which were entrained in the intake air. The light scattered off of the particles is recorded by a high speed rotating prism movie camera. A movie is then made showing the air flow within the combustion chamber for an entire four-stroke engine cycle. The system is synchronized so that a pulse generated by the camera triggers the laser's thyratron. The camera is run at 5,000 frames per second; the trigger drives one laser pulse per frame. This paper describes the optics used in the flow visualization system, the synchronization circuit, and presents results obtained from the movie. This is believed to be the first published study showing a planar observation of airflow in a four-stroke piston-cylinder assembly. These flow visualization results have been used to interpret flow velocity measurements previously obtained with a laser Doppler velocimetry system.
Copper vapor lasers are being used in forensic applications at more than thirty regional, state and national level forensic science laboratories (crime labs) in the United States, Israel and Japan. These high gain lasing medium systems provide desirable operational and maintenance features. The green line produced by copper vapor lasers allows use of latent fingerprint inherent and chemically induced luminescence techniques developed for argon ion lasers. The yellow line has developed latent fingerprints which would not luminesce at blue-green wavelengths, and is better suited for some forensic examinations such as ink differentiation involving forgeries and document alterations.
A novel transverse-discharge copper-vapor laser has been developed. A specific laser energy density of 50 μJ/cm3 has been achieved in a volume of 0.6xlx20 cm3 . This corresponds to a laser power density of 5 kW/cm3 for a 10-ns laser pulse. A 10-kHz operation has been demonstrated in a steady state mode.
Continuous technological progress has occurred in improving the operational lifetime, decreasing the size, increasing the output power and improving the reliability of low- to medium-power CO2 lasers. A summary of the progress which has led to the present state-of-the-art, along with a projection of future technological trends in low- to medium-power CO2 lasers, is presented. The summary includes a discussion of RF excitation technology, folded waveguide lasers and waveguide array technology.
This paper deals with experimental results concerning injection phase locked homogeneously broadened continuous lasers. Power output and gain of the injected wave are reported and compared with the power output supplied by the same amplifier set up in a conventional cavity.
We have investigated the characteristics of a new electrode system developed for fast transvers-flow CO2 laser. The bar type electrode system makes it possible to reduce the number of electrodes and to increase the input discharge energy as compared with the conventional pin type electrode system. The oscillation mode at low laser output power is dramatically improved by adjusting the electrode arrangement.
An indepth analysis of commercial medium to high power CO2 lasers has been conducted. Systems are compared according to power levels. Available technical specifications and operating requirements such as beam quality and stability, physical size, serviceability and operating and maintenance costs are contrasted. These key factors are used to analyze currently available industrial laser designs.
The past, future and present developments of CO2 medical lasers are discussed, with special regard to tissue interaction and the impact of the inability of present day technology to provide an adequate means of fiber delivery.
New interest has developed in shorter wavelength visible and infrared helium-neon lasers. Performance characteristics of the green (543 nm), yellow (594 nm) and several infrared transitions are reported and discussed.
Atmospheric methane surveys may outline prospective oil and natural gas reservoirs. Methane sensing can also be applied to detect gas leakage of pipelines or landfills. We describe a field-device capable of measuring small changes in methane concentration in the near-surface atmosphere for such surveys. The detection of methane uses the attenuation of the 3.3922 μm He-Ne laser line in a pressurized flow cell through which air circulates at a regulated pressure of about 3 atmospheres. A second He-Ne laser line at 3.3912 μm, which is only weakly absorbed by methane, is used as a reference for ratio recording to compensate for laser intensity fluctuations and scattering by water or dust. The device is operated from a moving vehicle. Thus, sampling is continuous, i.e., large areas can rapidly be surveyed. Field tests showed the device to be rugged enough to withstand the rigors of off-road travel as well as summer heat.
Employing the ultraviolet lines from a krypton ion cw laser as steady-state excitation source, we tested McClure's method for measur-ing the triplet extinction coefficients εT of organic compounds on anthracene and pyrene. Our values for anthracene εT = 82 X 103 ℓ/mole cm at 426 nm and pyrene εT = 37 X 103 ℓ/mole cm at 413 nm agree well with values obtained by other methods. McClure derived his linear relationship from kinetic considerations. One simply measures triplet optical densities (ODT) at a fixed wavelength (e.g., at a triplet absorption maximum) as function(s) of different cw laser excitation intensities (powers) Iex. A plot of 1/ODT against 1/Iex yields a straight line. Extrapolating to the intersection of the ordinate (1/Iex = 0, or Iex = ∞) yields 1/ODT∞. ODT∞ = NsεT d. At infinite excitation intensity Iex, the concentration of the triplet state molecules NT is equal to the original concentration Ns of the ground state concentration. d is the thickness of the sample. This allows one to obtain εT. The success of this method requires the production of high concentrations of triplet state molecules, NT, as well as steady-state excitation. cw lasers fulfill all these requirements. We discuss the spectroscopic equipment employed for measuring triplet optical densities in some detail. Methods for reducing heat gradients (noise) in liquid nitrogen and laser excitation spot sizes are reviewed. We varied the cw laser illumination density (laser power/area) by setting the focusing lens at different distances from the sample, and measured 1/ODT as a function of 1/Iex. As long as the size of the excitation area was not below a critical size, all the straight lines obtained at different lens settings converged well into only one value of 1/ODT∞. Measurements were also performed at different concentrations of the solutes.
This paper describes our leading experience in the clinical application of laser in the treatment of neonatal jaundice. Currently, the irradiation of jaundiced infants during neonatal life to fluorescent light is the most common treatment of neonatal hyperbilirubinemia. The authors have investigated the photodegradation of bilirubin by laser in vitro and in Gunn rats before embarking on its clinical application in the treatment of jaundice in the new born child. This work was done to study the theraputic effect of laser compared to the currently used phototherapy in the treatment of neonatal jaundice. We selected 16 full term neonates with jaundice to be the subject of this study. The neonates of the study were devided into two groups. The first group was treated with continuous phototherapy . The second group recieved photoradiation therapy with gas laser The laser used was a CW argon-ion laser tuned to oscillate at 488.0 nm wavelength. This wavelength selection was based on our previous studies on the effect of laser irradiation of Gunn rats at different wavelengths. Comparison of the results of both methods of treatment will be reported in detail. The advantages and limitations of laser photoradiation therapy for neonatal jaundice will be discussed.
This paper provides an introduction to the more common applications of ion laser systems. Applications discussed include photocoagulation, flow cytometry, laser disk mastering, laser doppler velocimetry, Raman spectroscopy, holography, laser light shows, large screen projection, fingerprint detection, and applications in printing such as color separation and scanning. All these applications are currently in widespread use. At the end of the paper a short review is provided of developing applications such as cardiovascular surgery and semiconductor processing.
A systematic survey of cw ion laser operation in Ne, Ar, Kr, and Xe was conducted, using a small commercial laser plasma tube. Primary attention was given to the ultraviolet spectral region. Laser output was observed on virtually every known cw laser line as well as 27 lines not previously reported in the literature. Tentative atomic transition assignments have been made for some of these. Scaling of cw uV laser performance to high current density was investigated. Tests in a large commercial Ar laser system gave useful power output (0.2-1.0W) at a number of "non-standard" wavelengths.
We describe the design of a device for on-line endpoint monitoring of oxide thickness in silicon wafer etching. The endpoint is sensed by continuous in situ determination the Si02 layer thickness. The design utilizes an air-cooled Ar-laser whose plane polarized light passes through a rotating half-wave plate which alternately switches the polarization from transverse electric to transverse magnetic. The thus modulated beam is specularly reflected from the silicon wafer. AC detection instrumentation measures the normalized reflectance intensity (ITE - ITM)/(ITE + ITM ) which is a measure of the SiO2 film thickness. The normalization compensates for light intensity fluctuations.
A high performance scanning laser lithography system has been developed for high speed writing of reduction reticles (the master patterns used expose semiconductor wafers). This system uses an Argon fan laser operating at 363.8 nm as the exposing light source. An overview of the system's optics will be presented and the laser performance required to meet the system specifications will be discussed.
Lasers have been used to machine semiconductors for many years (Fig. 1). The first practical application was scribing silicon wafers with a Q-switched YAG laser. Many others followed, with the use often determined by the features of the available lasers. This process has been modified slightly in recent years, with lasers being tailored to fill a perceived need.
Excimer lasers are finding increasing use in the area of laser materials processing. Of particular importance is the fact that excimers can remove material through ablation rather than by any purely thermal process such as those associated with YAG or CO2 processing. This paper reviews the basic mechanisms associated with excimer laser ablation and presents examples of practical applications of this new technique.
A practical calorimetric method suitable for the ultraviolet calibration of laser joulemeters is described. Excimer laser pulses are used as the light source for the calibration, and the method is inherently insensitive to instrumental nonlinearities and thermal losses. A study of the behavior of pyroelectric joulemeters under excimer irradiation demonstrates the advisability of periodic recalibration of these devices.