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The laser damage threshold (LDT) or laser induced damage threshold (LIDT) is the limit at which an optic or material will be damaged by a laser given the fluence (energy per area), intensity (power per area), and wavelength. LDT values are relevant to both transmissive and reflective optical elements and in applications where the laser induced modification or destruction of a material is the intended outcome.
For long pulses or continuous wave lasers the primary damage mechanism tends to be thermal. Since both transmitting and reflecting optics have non-zero absorption, the laser can deposit thermal energy into the optic. At a certain point, there can be sufficient localized heating to either affect the material properties or induce thermal shock.
Dielectric breakdown occurs in insulating materials whenever the electric field is sufficient to induce electrical conductivity. Although this concept is more common in the context of DC and relatively low frequency AC electrical engineering the electromagnetic fields from a pulsed laser can be sufficient to induce this effect, causing damaging structural and chemical changes to the optic.
For very short, high power pulses, avalanche breakdown can occur. At these exceptionally high intensities, multiphoton absorption can cause the rapid ionization of atoms of the optic. This plasma readily absorbs the laser energy, leading to the liberation of more electrons and a run-away "avalanche" effect, capable of causing significant damage to the optic.
Optical systems can mitigate the effects of laser damage both by increasing the LDT of the optics used and by changing the laser beam characteristics. The use of high reflectivity (HR) dielectric mirrors instead of metal mirrors is a common strategy. Further, the beam can be expanded, reducing the fluence present on optics. Finally, the beam can be temporally stretched, i.e. "chirped", to reduce the power incident on the optic. The use of chirped beams was the key innovation in chirped pulse amplification, a technique which permits the generation of petawatt class beams which was awarded the 2018 Nobel Prize in Physics.
Some applications make use of laser breakdown directly, necessitating knowledge of the materials' LDT properties. Some examples include:
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A laser diode is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.
Q-switching, sometimes known as giant pulse formation or Q-spoiling, is a technique by which a laser can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high (gigawatt) peak power, much higher than would be produced by the same laser if it were operating in a continuous wave mode. Compared to modelocking, another technique for pulse generation with lasers, Q-switching leads to much lower pulse repetition rates, much higher pulse energies, and much longer pulse durations. The two techniques are sometimes applied together.
Ti:sapphire lasers (also known as Ti:Al2O3 lasers, titanium-sapphire lasers, or Ti:sapphs) are tunable lasers which emit red and near-infrared light in the range from 650 to 1100 nanometers. These lasers are mainly used in scientific research because of their tunability and their ability to generate ultrashort pulses. Lasers based on Ti:sapphire were first constructed and invented in June 1982 by Peter Moulton at the MIT Lincoln Laboratory.
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle.
Laser cutting is a technology that uses a laser to vaporize materials, resulting in a cut edge. While typically used for industrial manufacturing applications, it is now used by schools, small businesses, architecture, and hobbyists. Laser cutting works by directing the output of a high-power laser most commonly through optics. The laser optics and CNC are used to direct the laser beam to the material. A commercial laser for cutting materials uses a motion control system to follow a CNC or G-code of the pattern to be cut onto the material. The focused laser beam is directed at the material, which then either melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high-quality surface finish.
Kerr-lens mode-locking (KLM) is a method of mode-locking lasers via the nonlinear optical Kerr effect. This method allows the generation of pulses of light with a duration as short as a few femtoseconds.
In optics, the Pockels effect, or Pockels electro-optic effect, is a directionally-dependent linear variation in the refractive index of an optical medium that occurs in response to the application of an electric field. It is named after the German physicist Friedrich Carl Alwin Pockels, who studied the effect in 1893. The non-linear counterpart, the Kerr effect, causes changes in the refractive index at a rate proportional to the square of the applied electric field. In optical media, the Pockels effect causes changes in birefringence that vary in proportion to the strength of the applied electric field.
Chirped pulse amplification (CPA) is a technique for amplifying an ultrashort laser pulse up to the petawatt level, with the laser pulse being stretched out temporally and spectrally, then amplified, and then compressed again. The stretching and compression uses devices that ensure that the different color components of the pulse travel different distances.
A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. Hence a fiber Bragg grating can be used as an inline optical fiber to block certain wavelengths, can be used for sensing applications, or it can be used as wavelength-specific reflector.
This is a list of acronyms and other initialisms used in laser physics and laser applications.
Extreme ultraviolet radiation or high-energy ultraviolet radiation is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths shorter that the hydrogen Lyman-alpha line from 121 nm down to the X-ray band of 10 nm, and therefore having photons with energies from 10.26 eV up to 124.24 eV. EUV is naturally generated by the solar corona and artificially by plasma, high harmonic generation sources and synchrotron light sources. Since UVC extends to 100 nm, there is some overlap in the terms.
Ultrafast laser spectroscopy is a spectroscopic technique that uses ultrashort pulse lasers for the study of dynamics on extremely short time scales. Different methods are used to examine the dynamics of charge carriers, atoms, and molecules. Many different procedures have been developed spanning different time scales and photon energy ranges; some common methods are listed below.
A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are related to doped fiber amplifiers, which provide light amplification without lasing.
The Vulcan laser is an infrared, 8-beam, petawatt neodymium glass laser at the Rutherford Appleton Laboratory's Central Laser Facility in Oxfordshire, United Kingdom. It was the facility's first operational laser.
In laser science, an output coupler (OC) is the component of an optical resonator that allows the extraction of a portion of the light from the laser's intracavity beam. An output coupler most often consists of a partially reflective mirror, allowing a certain portion of the intracavity beam to transmit through. Other methods include the use of almost-totally reflective mirrors at each end of the cavity, emitting the beam either by focusing it into a small hole drilled in the center of one mirror, or by redirecting through the use of rotating mirrors, prisms, or other optical devices, causing the beam to bypass one of the end mirrors at a given time.
A photoionization mode is a mode of interaction between a laser beam and matter involving photoionization.
A laser beam profiler captures, displays, and records the spatial intensity profile of a laser beam at a particular plane transverse to the beam propagation path. Since there are many types of lasers—ultraviolet, visible, infrared, continuous wave, pulsed, high-power, low-power—there is an assortment of instrumentation for measuring laser beam profiles. No single laser beam profiler can handle every power level, pulse duration, repetition rate, wavelength, and beam size.
An optical modulator is an optical device which is used to modulate a beam of light with a perturbation device. It is a kind of transmitter to convert information to optical binary signal through optical fiber or transmission medium of optical frequency in fiber optic communication. There are several methods to manipulate this device depending on the parameter of a light beam like amplitude modulator (majority), phase modulator, polarization modulator etc. The easiest way to obtain modulation is modulation of intensity of a light by the current driving the light source. This sort of modulation is called direct modulation, as opposed to the external modulation performed by a light modulator. For this reason, light modulators are called external light modulators. According to manipulation of the properties of material modulators are divided into two groups, absorptive modulators and refractive modulators. Absorption coefficient can be manipulated by Franz-Keldysh effect, Quantum-Confined Stark Effect, excitonic absorption, or changes of free carrier concentration. Usually, if several such effects appear together, the modulator is called electro-absorptive modulator. Refractive modulators most often make use of electro-optic effect, other modulators are made with acousto-optic effect, magneto-optic effect such as Faraday and Cotton-Mouton effects. The other case of modulators is spatial light modulator (SLM) which is modified two dimensional distribution of amplitude & phase of an optical wave.
Thermopile laser sensors are used for measuring laser power from a few µW to several W. The incoming radiation of the laser is converted into heat energy at the surface. This heat input produces a temperature gradient across the sensor. Making use of the thermoelectric effect a voltage is generated by this temperature gradient. Since the voltage is directly proportional to the incoming radiation, it can be directly related to the irradiation power.
A plasma mirror is an optical mechanism which can be used to specularly reflect high intensity ultrafast laser beams where nonlinear optical effects prevent the usage of conventional mirrors and to improve laser temporal contrast. If a sufficient intensity is reached, a laser beam incident on a substrate will cause the substrate to ionize and the resulting plasma will reflect the incoming beam with the qualities of an ordinary mirror. A single plasma mirror can be used only one time, as during the interaction the beam ionizes the subtrate and destroys it.
