Coherent has brought industrial reliability to cutting-edge scientific lasers
Coherent provides laser-based solutions specifically optimized for a wide range of applications in scientific research. These applications include ultrafast and high resolution spectroscopy, multiphoton microscopy and other laser-based imaging techniques, material and environmental sciences, pulsed-laser deposition and holography/interferometry.
As the world’s largest supplier of scientific lasers, Coherent offers state-of-the-art laser systems featuring CW, Q-Switched and mode-locked operation ranging in output wavelength from 190 nm to 20 microns. And all new scientific lasers from Coherent feature industrial stability and 24/7 reliability, enabled by the laser industry’s first comprehensive HALT/HASS program. Coherent lasers not only enable you to get better data, they enable your lab to produce more data.
Pump-probe experiments using picosecond or femtosecond lasers.
Generally, ultrafast spectroscopy refers to pump-probe experiments using picosecond or femtosecond lasers to get time-resolved spectral information.
Traditionally ultrafast spectroscopy was restricted to gas phase reactions, where molecules are considered to be isolated. It is therefore easier to distinguish spectral features and energy transfer mechanisms than in condensed phase systems. These experiments have lead to an ever increasing knowledge of gas phase reactions resulting in quantum control of reactions in the gas phase.
Since the development of reliable solid-state ultrafast lasers over 10 years ago, ultrafast spectroscopy is not limited to gas phase reactions. The ability to choose pulsewidth, wavelength, or amplify the traditional Ti:S output means ever more increasing applications in condensed phase systems as well.
Ultra short FIR pulses as a spectroscopic tool.
There are numerous processes that occur in the far-infrared (FIR) region of the spectrum that have not been studied directly due to the lack of availability of ultrashort FIR pulses. Recent developments have yielded ultrashort FIR pulses, referred to as THz pulses (0.1 to about 6 THz), and the full capability of this technique is just starting to take off. Techniques once limited to the UV, visible and IR region can now begin to be applied to the FIR region as well. Attention has been focused on generating these THz pulses and understanding the physics of generation and propagation; now the actual THz pulses can be used as a spectroscopic tool.
THz spectroscopy has applications in semiconductors, liquids, gases and 2-D imaging. Imaging is rapidly emerging as an exciting THz application, and images can be taken using transmission or reflection geometry. By analyzing the THz waveform in either the time domain (material homogeneity or thickness variations) or the frequency domain (frequency-dependent absorption) as well as by other methods, images identifying material properties can be constructed (J.V. Rudd, D. Zimdars, and M. Warmuth, Picometrix, Inc., “Compact, fiber-pigtailed, terahertz imaging system”). Polar liquids and gases are highly absorptive in the THz regime; therefore, these type of samples are readily suitable for THz imaging. Such imaging serves as a complement to existing imaging methods or allows substances that haven’t been studied previously to be imaged. Recent examples of published THz imaging applications include: identifying raisins in a box of cereal by water content; studying water uptake and evaporation in leaves; examining circuit interconnects in packaged ICs; reading text in envelopes or beneath paint; identifying tooth decay; locating water marks in currency (also from J.V. Rudd et al, “Compact, fiber-pigtailed, terahertz imaging system”).
The number of commercially available terahertz imaging systems is extremely few even though many applications are emerging for THz imaging. New techniques have been developed for the generation and detection of THz radiation based on frequency conversion using nonlinear optics. THz techniques combine pulsed ultrafast laser technology with optoelectronics to generate terahertz radiation with sub-picosecond pulse duration. A typical set-up includes a modelocked solid-state laser that produces pulses with 100 femtosecond pulsewidths. The Coherent Vitara laser can be used as the femtosecond optical excitation source; alternatively, the Mira Optima 900-F system may be used. The Vitara offers the advantage of using a hands-off, turnkey solution in a single, compact, rugged package that includes the Verdi diode-pumped solid-state pump laser operating at 532 nm and the modelocked Ti:S oscillator.
Low noise lasers enable interferometry with unprecedented precision.
Low noise laser systems allow the detection of very small length changes with a precision that was unattainable until just recently. High precision interferometry now enables the study of previously unobserved phenomena such as gravitational waves. The direct detection of gravitational waves stands at the beginning of a whole new field of astronomy, because such waves are emitted by very massive accelerated objects such as black holes, which are often not visible with conventional telescopes. For this purpose, large scale Michelson interferometers housed within vacuum systems with an arm length of several kilometers are being built at several sites around the world. A passing gravitational wave will cause a very small arm length change in such an interferometer. Great care has to be taken to suppress all other potential noise sources below the strength of the signal that is to be detected. Such unwanted noise sources are seismic noise, thermal noise, electronic noise , as well as noise associated with the laser. Multiple stage monolithic suspensions of the interferometer optics and advanced interferometer designs with arm cavities and additional power and signal recycling mirrors are being used to address these noise sources. The laser of choice in these high precision interferometers is usually the Mephisto laser due to its very low frequency noise.
In related experiments, fundamental quantum optic effects and the generation and application of squeezed light are studied. The observation of these effects is only possible when an ultra stable low noise laser system is available.
When a higher output power is needed, the Mephisto MOPA is available with the same frequency stability. Interferometry applications at different wavelength such as 1319 nm or 532 nm are also possible.
Instead of detecting changes in the arm length of an interferometer, some standard institutes and research facilities require the measurement of an absolute length with very high precision. To achieve this, an absolute frequency standard, as well as extremely low frequency noise are required. The iodine stabilized Prometheus laser fulfills these requirements.
This type of spectroscopy analyzes fluorescence as a function of wavelength when the laser is tuned to an electronic absorption of the sample.
This type of spectroscopy analyzes fluorescence as a function of wavelength when the laser is tuned to an electronic absorption of the sample. In general, luminescence involves the emission of electromagnetic radiation by a material after that material has absorbed energy from a light source. Luminescence is described as fluorescence when the time lag between excitation and emission is on the order of 10 nanoseconds. Laser-induced fluorescence (LIF) can be used for a wide array of applications, including the qualitative and quantitative measurements of the concentrations of molecules in a sample and the mapping of energy level diagrams.
Fluorescence studies are usually conducted with tunable continuous wave (cw) laser systems; the use of frequency-doubled Ti:Sapphire (Ti:S) lasers enhance the experimental capabilities of cw fluorescence measurements. For broadband fluorescence studies of samples in the solid or liquid states, linewidths between 2 and 400 GHz are usually suitable.
For fluorescence spectroscopic experiments in the gas phase, the most important laser parameter may be the linewidth. For reliable high-resolution fluorescence studies, which dictate linewidths under 10 MHz and high output power, Coherent’s Ring Laser is designed for optimum performance with Ti:S gain media (Ti:dye). Systems such as the MBR-110 ring lasers operate reliably over extended periods of time with linewidths as low as 75 kHz.
One of the most important contributions to fluorescence spectroscopy has been the availability of ultrafast lasers capable of picosecond and femtosecond pulses in time-resolved fluorescence measurements. Lasers such as the Mira Optima 900 have allowed direct excitation of materials within the lifetime of an excited state.
Narrow linewidth lasers with broad tuning range enable advances in high resolution spectroscopy.
Laser-based atomic spectroscopy is the measurement of absorption, emission, or scattering of electromagnetic radiation by atoms and molecules (or atomic and molecular ions) to study these species and their related physical processes. The interaction of radiation with matter causes redirection of the radiation and/or transitions between the energy levels of atoms and molecules. There are three types of events that are often studied with lasers: absorption, fluorescence and scattering.
Absorption happens when photons are absorbed by the atom and its electrons are promoted to higher energy levels. Absorption can be studied measuring the amount of laser light transmitted by the sample as a function of the wavelength. Fluorescence happens when the excited electron decays back to its original state by emitting a photon of light at a longer wavelength (smaller energy) than the exciting photon from the laser. Scattering may be elastic (like Rayleigh and Mie scattering) or inelastic. Inelastic scattering takes places in atoms, molecules or lattices where part of the photon energy is transferred to/from the medium in processes like Raman or Brillouin scattering. In this section we consider mostly absorption and fluorescence spectroscopy and steady-state phenomena with high spectral resolution, rather than time-resolved studies, where pico- or femtosecond pulses are used. For a description of Raman scattering applications, please go to the section “Raman Spectroscopy”.
There are many high-resolution spectroscopic techniques. For example, the laser wavelength can be tuned to an electronic absorption of the sample and the resulting fluorescence can be analyzed as a function of wavelength. Alternatively, if laser excitation at an initial wavelength is introduced to a sample, absorption/transmission spectroscopy can be used to monitor the amount of light transmitted through the sample. If the excitation wavelength is scanned, an absorption spectrum can be analyzed. Many distinctions of this spectroscopy exist.
Lasers play an important role in high-resolution spectroscopy because of their simultaneous high-power output beam and narrow linewidth. Atomic spectroscopy (both absorption and fluorescence) usually requires wavelengths between 100 nm and 2 micron. Tunable Titanium Sapphire lasers are ideally suited for atomic spectroscopy because they provide powers and tuning ranges unavailable with any other source. The natural tuning range of 700-1,000 nm can be extended using second harmonic generation to cover the region 350-500 nm. Coherent’s MBR family of CW tunable lasers offer all these wavelength ranges with different power levels and with various linewidths. The flagship model MBR-110 provides a very narrow 75 kHz linewidth, suitable for high-resolution studies. The laser output of the MBR lasers can be stabilized and scanned to provide accurate spectra of atomic species. The MBD-200 resonant ring frequency-doubler efficiently converts the MBR output to its second harmonic and further extends the available wavelength range.
Coherent’s Ion lasers (Innova 300 series) can be operated in single frequency at several blue and green wavelengths and provide linewidths narrower than 50 MHz. The single frequency Verdi DPSS laser produces up to 18 Watts at 532 nm and 20 W at 1064 nm. The specifically designed doubler MBD-266 can be used to convert the green output of Verdi to its second harmonic in the deep UV.
The development of methods to cool and trap atoms using laser light.
The control of atomic motion by laser light is an application that has exploded over the last few years. The possibility of reaching extremely low atomic kinetic-energy temperatures near absolute zero is perhaps the most astonishing achievement. Research in atom trapping and cooling has led to insights into the interaction of matter and radiation and a variety of applications in areas such as spectroscopy, atomic clocks, atomic interferometers, optics, lithography, and gravitational measurements.
Laser beams are used to chill atoms and trap them in space. At first it would seem that cooling atoms using a laser source would be unlikely, but the technique has readily been demonstrated by the Nobel prize-winning work of Steven Chu, William D. Phillips and Claude Cohen-Tannoudji. When an atom is illuminated by counter-propagating light and absorbs a photon, its momentum changes the atomic velocity. After many cycles of absorption and emission, the velocity of the atom becomes nearly zero. In each cycle the atom loses energy which corresponds to the Doppler shift. The kinetic energy of the atom can eventually be lower than one microKelvin. This atom can then be trapped by two opposing laser beams that have frequencies lower than the atom’s absorption maximum. As the atom moves in the direction of one of the laser beams it sees a frequency increase (Doppler effect). The frequency increase moves into the atom’s absorption band causing a momentum kick in the opposite direction. The atom is then fixed in space by the two beams. Cooling allows the atom to be held longer since its random thermal motions are minimized.
Laser cooling applications demand single-frequency operation in the visible (red) and IR wavelength region. Sodium, rubidium and cesium are the most common atoms used in cooling experiments, Coherent’s MBR-110 Monolithic Block Resonator is well suited to the study of these atoms.
Short and intense laser pulses provide unique benefits for many pulsed laser deposition applications.
Pulsed laser deposition (PLD) is a laser-based technique used to grow high quality thin films of complex materials on substrates like Silicon wafers. The material to be deposited (target) is vaporized by short and intense laser pulses and forms a plasma plume. Then, the vaporized target material from the plasma bombards the substrate and – under the right conditions – creates a thin homogenous layer on this substrate. For each laser shot, a layer of only a few nanometers of material is ablated to form the plasma plume in a process that typically last a few tens of picoseconds. To enable this process, nanosecond pulses with energies of tens or hundreds of millijoules are necessary and UV wavelengths are usually preferred. These requirements match well the performances of excimer lasers.
The first laser deposition experiments took place in the mid to late 1960s, but PLD gained tremendous interest after T. Venketesan in 1987 first applied this method to create high temperature superconductive (HTSC) films. Since then, many hundreds of lasers have been sold to drive research, process development and small-scale production of thin film devices, such as superconductive magnetic sensors (SQUIDs), thin film ferroelectrics and “high k” gate resistors, semiconductor alloys, carbon nano-tubes, and more.
Although visible or IR laser beams have been used for PLD applications, UV beams are now most commonly employed. Among UV pulsed lasers, excimer lasers provide a variety of short wavelengths combined with energy levels that fit perfectly most PLD applications. High laser pulse energy provides several benefits for pulsed laser deposition. First, it extends the range of possible target materials that can be used. Second, it enables a larger area on the target to be ablated with the desired fluence. In turn, this area enlargement increases the deposition rate and reduces the plume angle, resulting in higher deposition efficiency. Finally, higher pulse energy provides a larger process window, allowing a more consistent process.
Coherent’s COMPexPro and LPXpro laser series are designed for demanding high-pulse energy applications and are highly effective tools for pulsed laser deposition. They deliver the beam stability and energy stability performance required to achieve superior results in sophisticated thin film deposition experiments.
Laser pulses can vary over a very wide range of duration (milliseconds to femtoseconds) and fluxes, and can be precisely controlled. This makes pulsed laser ablation very valuable for both research and industrial applications.
Laser Ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave (CW) laser if the laser intensity is high enough. The depth over which the laser energy is absorbed, and thus the amount of material removed by a single laser pulse, depends on the material’s optical properties and the laser wavelength.
Laser pulses can vary over a very wide range of duration (milliseconds to femtoseconds) and fluxes, and can be precisely controlled. This makes laser ablation very valuable for both research and industrial applications.
The 193 nm solid-sampling-system GeoLasPro is a self-contained laser ablation system for sample introduction in high-resolution LA-ICP MS (laser ablation inductively-coupled plasma mass spectrometry). GeoLasPro integrates the COMPexPro 193 nm ablation laser including beam homogenizing and shaping optics, a sample chamber, and unmatched microscopic sample observation capability. 193 nm sampling speed can be varied in a wide range from 1 Hz up to 100 Hz.
GeoLasPro includes several innovative features that enhance the performance of the overall LA-ICP-MS system. For example, the new sample observation microscope is made perfectly co-linear with the laser beam delivery optics through the use of an all-mirror microscope objective, which is free of chromatic aberration. This objective is also able to operate at higher laser power without the risk of coating damage that can occur when using lens-based objectives. These beam delivery optics can achieve a homogenized spot with a diameter as small as five (5) microns, which is ideal for sampling small fluid inclusions. The optics also include interchangeable circular and square beam shaping masks providing high sampling flexibility.
GeoLasPro is designed for geological and nuclear physics research and for quality control of materials and pharmaceutical samples. Examples include analysis of fluid inclusions in minerals, age determination of samples by isotope ratio analysis and analyzing high purity semiconductor materials
.Advantages of Laser Ablation
Raman scattering is a valuable spectroscopic technique that can be applied to solid, liquid or gas samples.
The Raman effect occurs when a sample is irradiated with UV, visible or IR light and a small fraction of the incident radiation is scattered and shifted at frequencies that correspond to vibrational transitions specific of the sample.
The Raman signal is much weaker than the incident and scattered light, so it may be difficult to detect it, unless appropriate measures to enhance the signal/background noise ratio are taken. For example, when a laser source is tuned to match an electronic transition of the sample, the resonant effect increases the Raman scattering by several orders of magnitude. This so-called resonance Raman spectroscopy is often used for applications such as qualitative analysis and molecular structure determination of samples which exhibit electronic transitions in the visible region of the spectrum. For non-resonant Raman spectroscopy, the most commonly used sources are visible or IR laser sources in the range 500 nm to 1,000 nm; shorter wavelength are more likely to excite fluorescence that can easily hide the Raman scattered light, unless the fluorescence is carefully filtered out. For this reason, near-IR light is often used.
Laser sources for continuous wave (CW) Raman spectroscopy include laser diodes, diode-pumped lasers, optically pumped semiconductor lasers (OPSL), and ion lasers. For excitation at fixed wavelengths with CW solid-state lasers, Coherent offers the Sapphire SF single-frequency OPSL series with wavelengths at 488 nm and 532 nm. The Innova 300C and 70C series of small-frame argon or krypton ion lasers are also well suited for Raman experiments in the visible region of the spectrum. Innova 70C Spectrum is a mixed gas lasers that can generate a number of laser lines from the UV to the near IR.
Ultraviolet (UV) resonance Raman spectroscopy is a useful tool for the investigation of molecular structure, kinetics, and excited-state surfaces and dynamics. In particular, it finds numerous applications in systems of biological interest. The Innova series of frequency-doubled argon ion lasers - Innova FRED - is perfect match for resonance Raman spectroscopy because it produces several wavelengths in the range 229 nm to 257 nm. The very short wavelengths of these CW lasers minimize sample damage, compared with nanosecond pulses lasers, and minimize excitation of competing fluorescent signal.
A dynamic field of Raman studies is coherent anti-Stokes Raman scattering, or CARS. This technique uses two synchronized picosecond or femtosecond sources to stimulate a strong signal response at the so-called Anti-Stokes frequency. This happens only when the wavelengths of the two lasers are separated by a wavenumber matching the Raman transition of the sample. This technique is particularly suitable to detect lipids (fats) in microscopic cellular specimens. Ti:Sapphire (Ti:S) lasers and OPOs are well suited for CARS experiments: broad tunability and flexible pulse duration match the application requirements perfectly. Mira-900, Chameleon and Mira-OPO are ideal laser sources for CARS.
Multiphoton Excitation (MPE) microscopy was first reported in 1990 (Denk, Strickler and Webb). Since then, it has grown to become an ubiquitous imaging technique when in-vivo, optical sectioning is key. In multiphoton microscopy, a fluorescent molecule – attached to the specimen or naturally present – is excited by two or three photon of infrared light. This is in contrast with confocal microscopy where the same type of molecules are excited by a single photon of blue-green or UV light. Multiphoton excitation offers several fundamental advantages over confocal microscopy: the IR light penetrates more deeply in the tissue because of lower absorption and scattering; the longer wavelength is less damaging and allows in vivo imaging also in human subjects; finally, the non-linear process excite fluorescence only on the focal plane and a the confocal aperture required with single-photon excitation is no more necessary. The sectional image of a living mouse brain, imaged to a depth of 800 micron with Coherent Chameleon Ultra II laser is an impressive paradigm of the capability MPE.
In parallel to MPE, several other non-linear techniques have become increasingly popular. These include Second Harmonic Generation (SHG) microscopy and Coherent Anti-Stokes Raman Spectroscopic (CARS) microscopy. This suite of non-linear techniques require the use of Ultrafast lasers, generating pulses of 100-200 fs and tunable over the near IR region of the spectrum. These lasers are inherently more complex than the blue-green lasers used for confocal microscopy and other bioinstrumentation applications.
Coherent recognizes that microscopists, neurologists and biologists should not have to become laser experts to do their work. For this reason we designed and manufacture and expansive line of lasers designed specifically for non-linear imaging. This way, MPE users can focus on their sample, not on the laser equipment.
Yields a series of high-resolution, high-contrast images that can be reassembled into a three-dimensional picture.
The microscope is confocal because the objective lens is used both to illuminate the sample and to image it. It is a scanning optical microscope because only one point of the sample is illuminated at a time. As the sample is scanned, the image is built up pixel by pixel. True optical sections of a sample are taken because of the short focal plane of the objective lens (as small as .5 microns). Any image data above or below the focal plane is prevented from reaching the detector. Levels of the sample are collected as the focal plane (Z axis) is raised or lowered. These levels are then computer-assembled into a three dimensional structure. Features of a confocal microscope include high-resolution, submicron microscopy, without the expense of an electron microscope, magnification ranging from 100x to 10,000x, and non-destructive examinations of living samples. Confocal Microscopes are used in the following applications:
Confocal Microscopes are used in the following applications:
The use of laser pulses to find range or other information of a distant target.
ght etection nd anging uses the same principle as RADAR. The LIDAR instrument transmits light out to a target. The transmitted light interacts with and is changed by the target. Some of this light is reflected or scattered back to the instrument where it is analyzed. The change in the properties of the light enables some property of the target to be determined. The time for the light to travel out to the target and back to the LIDAR is used to determine the range to the target.
There are three basic generic types of lidar:
Range finder LIDAR is used to measure the distance from the LIDAR instrument to a solid or hard target.
fferential bsorption LIDAR (DIAL) is used to measure chemical concentrations (such as ozone, water vapor, pollutants) in the atmosphere. A DIAL LIDAR uses two different laser wavelengths which are selected so that one of the wavelengths is absorbed by the molecule of interest whilst the other wavelength is not. The difference in intensity of the two return signals can be used to deduce the concentration of the molecule being investigated.
Doppler LIDAR is used to measure the velocity of a target. When the light transmitted from the LIDAR hits a target moving towards or away from the LIDAR, the wavelength of the light
reflected/scattered off the target will be changed slightly. This is known as a Doppler shift - hence Doppler LIDAR. If the target is moving away from the LIDAR, the return light will have a longer wavelength (sometimes referred to as a red shift), if moving towards the LIDAR the return light will be at a shorter wavelength (blue shifted). The target can be either a hard target or an atmospheric target - the atmosphere contains many microscopic dust and aerosol particles that are carried by the wind. These are the targets of interest to us as they are small and light enough to move at the true wind velocity and thus enable a remote measurement of the wind velocity to be made.
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Santa Clara, CA 95054 USA
Coherent has locations across the globe that are available to provide support for any product, service or inquiry.
Coherent has locations across the globe that are available to provide support for any product, service or inquiry.
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