Argus laser
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Argus was a two-beam high power
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...
doped silica glass
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
with a output aperture built at
Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...
in 1976 for the study of
inertial confinement fusion Inertial confinement fusion (ICF) is a fusion energy process that initiates nuclear fusion reactions by compressing and heating targets filled with thermonuclear fuel. In modern machines, the targets are small spherical pellets about the size of ...
. Argus advanced the study of laser-target interaction and paved the way for the construction of its successor, the 20 beam
Shiva laser The Shiva laser was a powerful 20-beam infrared neodymium glass (silica glass) laser built at Lawrence Livermore National Laboratory in 1977 for the study of inertial confinement fusion (ICF) and long-scale-length laser-plasma interactions. Presu ...
. It was known from some of the earlier experiments in ICF that when large laser systems amplified their beams beyond a certain point (typically around the gigawatt level),
nonlinear optical Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typic ...
effects would begin to appear due to the very intense nature of the light. The most serious effect among these was " Kerr lensing", where, because the beam is so intense, that during its passage through either air or glass the
electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
of the light actually alters the
index of refraction In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...
of the material and causes the beam at the most intense points to "self focus" down to filament like structures of extremely high intensity. When a beam collapses into extremely high intensity filaments like this, it can easily exceed the optical damage threshold of laser glass and other optics, severely damaging them by creating pits, cracks and grey tracks through the glass. These effects became so severe after just the first few amplification stages of early lasers, that it was seen as essentially impossible to exceed the gigawatt level for ICF lasers without destroying the laser itself after just a few shots. In order to improve the quality of the amplified beams, LLNL had started experimenting with the use of
spatial filter A spatial filter is an optical device which uses the principles of Fourier optics to alter the structure of a beam of light or other electromagnetic radiation, typically coherent laser light. Spatial filtering is commonly used to "clean up" the ou ...
s in the single-beam
Cyclops laser Cyclops was a high-power laser built at the Lawrence Livermore National Laboratory (LLNL) in 1975. It was the second laser constructed in the lab's ''Laser'' program, which aimed to study inertial confinement fusion (ICF). The Cyclops was a singl ...
, built the previous year. The basic idea was to extend the laser device into a very long "beamline", over which any imperfections that accumulated in the beam would be successively removed after every amplification stage. A series of tubes with lenses on either end would focus the light down to a point (the focal point) where it would pass through a pinhole which would reject stray unfocused light, smoothing the beam and eliminating the high intensity spots which would have otherwise been further amplified causing damage to down-beam optics. The technique was so successful on Argus it was often referred to as being "the savior of laser ICF". After the success of Cyclops in beam smoothing, the next step was to further increase the energy and power in the resulting beams. Argus used a series of five groups of amplifiers and spatial filters arranged along the beamlines, each one boosting power until it reached a total of about 1 
kilojoule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...
and 1-2 terawatts per beam. These intensities would have been impossible to achieve without the use of spatial filtering. Argus was designed primarily to characterize large laser beamlines and laser-target interactions, there was no attempt to actually achieve the fusion ignition state in the device as this was understood to be impossible at the energies Argus was capable of delivering. Argus however, was used to further explore higher yields of the so-called "exploding pusher" type targets and to develop x-ray diagnostic cameras to view the hot plasma in such targets, a technique crucial to characterization of target performance on later ICF lasers. Argus was capable of producing a total of about 4
terawatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s of power in short pulses of up to about 100 picoseconds, or about 2 terawatts of power in a longer 1 nanosecond pulse (~2
kilojoules The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
) on a 100
micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
diameter fusion fuel capsule target. It became the first laser to perform experiments using
X-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...
produced by irradiating a
hohlraum In radiation thermodynamics, a hohlraum (a non-specific German word for a "hollow space" or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. This idealized cavity can be approximated in pra ...
. The reduced production of hard X-ray energy via the production of hot electrons while using
frequency doubled Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of ...
and tripled laser light (as opposed to the infrared light directly produced by the laser itself) was first noticed on Argus. This technique would also be later validated in the direct drive mode (at both the LLE and
Novette laser Novette was a two beam neodymium glass (phosphate glass) testbed laser built at Lawrence Livermore National Laboratory in about 15 months throughout 1981 and 1982 and was completed in January 1983. Novette was made using recycled parts from the dis ...
) and subsequently used to enhance laser energy to target plasma coupling efficiency in experiments on nearly all subsequent laser inertial confinement devices. Argus was shut down and dismantled in September 1981. Maximum fusion yield for target implosions on Argus was about 109
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s per shot.


See also

*
Laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
*
Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...
*
List of laser articles This is a list of laser topics. A * 3D printing, additive manufacturing * Abnormal reflection * Above-threshold ionization * Absorption spectroscopy * Accelerator physics * Acoustic microscopy * Acousto-optic deflector * Acousto-optic modul ...
*
List of laser types This is a list of laser types, their operational wavelengths, and their applications. Thousands of kinds of laser are known, but most of them are used only for specialized research. Overview Gas lasers Chemical lasers Used as directed-ener ...


External links

* https://web.archive.org/web/20041109063036/http://www.llnl.gov/50science/lasers.html * http://www.osti.gov/bridge/servlets/purl/16710-UOC0xx/native/16710.pdf * http://adsabs.harvard.edu/abs/1978ApOpt..17..999S {{Lasers Inertial confinement fusion research lasers Lawrence Livermore National Laboratory