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  • Amplified Spontaneous Emission Source (ASE)

    ASE sources have very low coherence, corresponding to the large emission bandwidth. They contain a laser gain medium that is excited to emit and then amplify luminescent light. They are alternatively known as superluminescent sources.

    Their properties make them useful in applications such as fluorescence excitation, and spectroscopy.

    Amplitude Stability

    The amplitude stability or output power stability defines the variation of laser amplitude or output power over time. The time period over which this stability applies is usually defined. The total amplitude stability of a laser can have several components: noise from drive electronics, other lab electronics, or competing optical modes beating against each other; thermal effects where changes in the temperature of the laser or the environment cause a variation in the electro-optical efficiency of the laser or drive electronics; & drift where the mechanical alignment of the laser cavity changes with time. For those applications requiring high levels of amplitude stability, we have a wide range of solutions. Please contact us for advice or assistance.

    Analogue Modulation

    Analogue modulation enables the user to control the intensity of the output power. An external voltage signal, typically in the range of 0-5V, determines the laser output. The response of the laser power output to the input voltage is approximately linear.

    Average Output Power

    This is the total power emitted by a pulsed beam, averaged over one period. For a pulsed laser delivering peak power per pulse of Ppeak with a pulse width of Pw and pulse repetition frequency of f, the average output power, Pave, is defined as:

    Pave = Ppeak x Pw x f

    

    Bandwidth

    Frequency bandwidth

    The frequency bandwidth is the rate at which a system may operate within specification when operating in a pulsed or modulated mode. The frequency bandwidth is normally defined as the 3dB bandwidth, the point at which the performance decreases by a factor of 3dB (50%).

    Optical bandwidth or laser linewidth

    The optical bandwidth (laser linewidth) is the range of optical wavelengths over which laser emission occurs simultaneously. Even a highly monochromatic laser source produces a range of wavelengths over which it emits simultaneously.

    Bar Array

    Several different versions of bar-array packages are available depending on the power and temporal characteristics of the laser emission. These mounts offer close packing and high density of the emitted laser radiation. They allow multiple arrays to be stacked together to produce many kW of integrated laser output for pumping or materials processing applications. Temperature control, and heat removal is important for these lasers to operate within specification and with long lifetimes. These mounts are designed to be used with a third party heatsink or temperature control (such as recirculating water, Peltier effect TECs or forced air, or passive conduction).

    Beam Diameter

    There are two definitions of beam diameter, the FWHM beam diameter and the 1/e2 beam diameter.

    The 1/e2 Beam diameter of a laser beam is the diameter of a spot centred on the laser beam that contains 87.5% of the total output power of that laser. This beam diameter is commonly applied to lasers with uniformly circular Gaussian beams such as DPSS and Gas lasers.

    The FWHM beam diameter of a laser beam is the diameter of a spot centred on the laser beam that contains 50% of the total output power of that laser. This is generally applied to laser diodes, where the emission profile of the laser is not circular.

    Beam Dimensions

    The beam dimensions define the cross-sectional size of the beam, to be used alongside the beam shape. To define the edge of the beam, two modes may be used, FWHM and 1/e2 (see beam diameter).

    Beam Divergence

    Beam divergence relates to the rate at which a laser beam expands with distance from the emission aperture. It is usually defined in the far-field (i.e. beyond the beam waist).

    A beam is said to be collimated where the divergence is low, and the beam radius remains approximately constant.

    Beam divergence is given in degrees or milliradians and is specified as: either the full angle of the cone of the beam divergence from the laser ("full angle"); or the half angle of the cone of beam divergence ("half angle") from the laser.

    Beam Parameter Product

    The beam parameter product (BPP) is the product of a laser beam's divergence angle (half-angle) and the radius of the beam at its narrowest point (the beam waist). The BPP quantifies the quality of a laser beam, and how well it can be focused to a small spot.

    A Gaussian beam has the lowest possible BPP, λ / π, where λ is the wavelength. The ratio of the BPP of an actual beam to that of an ideal Gaussian beam at the same wavelength is denoted M² ("M squared"). This parameter is a wavelength-independent measure of beam quality.

    Beam Pointing Stability

    The beam pointing stability is a measure of the variation in the direction of a laser output beam, relative to a fixed point in an optical system.

    Beam Profile

    Profiling measures the spatial characteristics of a laser beam such as intensity distribution, diameter, divergence, and M squared.

    It is achieved by taking a section through a laser beam and building a spatial map of the energy distribution. This is often presented as a 3d Cartesian with X & Y as the orthogonal spatial axes across the beam and with the third assigned to intensity.

    By revealing the whole optical intensity profile, exact, accurate numerical values can be assigned to the physical properties of the beam.

    Knowing the intensity profile of a laser beam is important for many applications.

    Beam Quality

    Beam quality is defined as a measure of the ability to focus a laser beam down to its theoretical minimum spot size. This can be quantified using the M² factor.

    Beam Shape

    This is the shape of the spatial profile of the laser beam. It can affect how well the laser will work in a given application e.g : how the laser may be affected by different apertures; how well the laser may be focussed; which optics to use (spherical or cylindrical); and the maximum power density that can be achieved at the workspace.

    Bench top

    A bench top laser comprises a laser head and a freestanding power supply unit. The power supply unit (PSU) incorporates control electronics, matched to the laser head. A custom cable is provided to make the connection between the laser head and PSU. Extremely user friendly, this laser format is ready to use once plugged into a mains supply.

    All of our laser PSUs are suitable for use with standard 240V AC (single-phase) mains electricity. They are supplied with UK mains plugs, and are CE marked. The laser heads have through-holes for mounting to standard optical tables or rail systems. Additionally, we provide the following options where they are not standard:

    • Manual optical shutter
    • Emission indicator light
    • Heat sink
    • Forced air cooling
    • Collimation or focussing optics
    • Line generation optics
    • Optical fibre coupling

    The PSU is designed to be freestanding on a lab bench. Higher power laser systems use larger PSUs and may be built into a 19-inch rack. This could require an optional rack mounting kit. Please refer to the data sheet for details.

    Many of the following PSU features are standard, depending on the laser model:

    • Key activated on/off switch
    • On/off indication light
    • Safety interlock
    • Manual power amplitude adjustment
    • Output power level readout
    • Built in modulation control
    • RS232/IEEE/USB PC interface
    • External modulation input
    • 240VAC single phase power
    • 19 inch rack mounting kit
    • EU mains power plug

    The relevant datasheet should list the laser head and PSU features available. If you have a specific requirement for any of the features listed above and can't find the information you need, please contact us and we will be happy to help you.

    Birefringence

    A birefringent material has a refractive index that is dependent on the polarisation direction of the light that propagates through it. An optical beam passing through a birefringent material will generally be split into two components, an ordinary ray and an extraordinary ray, each of which has an orthogonal polarisation to the other.

    The axes of a birefringent material are classified "fast" where the refractive index is the lowest, with the slow axis referring to the orthogonal axis.

    Butterfly

    The butterfly package is an industry standard hermetically sealed laser diode package. The BFY package is comprised of laser welded gold plated Kovar. This has very similar expansion characteristics to the borosilicate glass used in the frit seals and optics to deliver the ultimate in robustness and reliability. The package is also provided with a fibre pigtail (either singlemode or polarisation preserving with an FC/PC or APC connector). Horizontal pins arranged symmetrically on both sides are provided for connection to a suitable laser diode & TEC controller. Several different pin-out configurations are provided as standard. Most options include: a Peltier effect TEC and thermistor for temperature measurement, control, and stabilisation; and a monitor photodiode for output power measurement, power control and mode hop free performance.

    

    C-mount

    The C-mount is a format of open laser diode chip mount. It is designed to remove heat from the laser diode and be cooled actively by adequate heat-sinking to a 3rd party supplier cooler. The C-mount is available in a number of different formats.

    Cavity Type

    DBR (Distributed Bragg reflector cavity)

    The distributed Bragg reflector cavity is a form of laser diode cavity that creates optical feedback which reduces the linewidth of the laser emission and the number of longitudinal modes that are present. It is similar to the DFB cavity but achieves higher wavelength coupling and offers the potential for much narrower linewidth generation.

    The narrow linewidth makes them suitable for spectroscopy and remote sensing applications.

    Some DBR laser diodes are wavelength tunable by drive current.

    DBR lasers tend to exhibit higher wavelength stability than DFB and FP lasers when operated across their full operating temperature range. This makes them useful for multiplexed optical communications.

    Some generations of DBR laser diodes deliver long coherence length. Such lasers are suitable for use in applications such as holography, interferometry and sensing.

    DFB (Distributed feedback cavity)

    The distributed feedback cavity is a form of laser diode cavity that includes a specific region within the laser that creates optical feedback. This has the effect of increasing the optical amplification at a given wavelength, and consequently reduces the linewidth of the laser emission, and the number of longitudinal modes that are present.

    The narrow linewidth makes them suitable for spectroscopy and remote sensing applications.

    Most DFB laser diodes are wavelength tunable by temperature and drive current variation.

    However they exhibit much higher wavelength stability across their operating temperature range. This makes them useful for multiplexed optical communications.

    Some generations of DFB laser diodes deliver long coherence length. Such lasers are suitable for use in applications such as holography, interferometry and sensing.

    Fabry Perot Cavity

    The Fabry Perot cavity is the simplest form of optical resonance cavity, based around two parallel plane reflectors. Light may only oscillate between the plane mirrors of the cavity if the modal wavelength conditions are fulfilled. Light of wavelengths that do not fulfil these conditions is emitted from the cavity. As a result the cavity acts as an optical filter. Changing the mirror separation changes the wavelength response of the filter (or Etalon). The performance of the cavity is principally defined by the reflectivity of the mirrors.

    When used as a laser cavity, a Fabry Perot cavity tends to deliver relatively broad linewidth when compared to other cavities, and multiple longitudinal modes

    Littman-Metcalf Configuration

    In an external cavity using the Littman-Metcalf configuration, the end mirror is also a diffraction grating, but it remains fixed at near grazing incidence. Instead, an additional mirror adjusts to tune the wavelength and to reflect the first-order diffracted beam back to the laser gain medium.

    This configuration tends to have lower output power than Littrow, as the zero-order reflection from the tuning mirror is lost. However, it can provide narrower line widths and broader tuning range. As the wavelength dependent diffraction occurs twice per round trip in the resonator, stronger wavelength selection results.

    Littrow Configuration

    The Littrow configuration of an external cavity features a diffraction grating as an external cavity end mirror. The emitted wavelength is tuned by adjusting the angle and position of the grating. The first-order diffracted beam is reflected back to the laser gain medium, giving optical feedback.

    This configuration allows independent control of the output power and the wavelength-dependent feedback from the external cavity.

    Monolithic Cavity

    A monolithic cavity is a laser cavity constructed from a single element, achieving greater alignment stability. This can reduce the effects of thermal drift, mechanical vibration and long term component reliability issues.

    MOPA Configuration

    MOPA stands for Master Oscillator Power Amplifier. A MOPA configuration combines a seed laser with an optical amplifier to boost output power whilst retaining many of the characteristics of the seed laser (such as the spatial mode, temporal mode, and coherence).

    Tapered Amplifier

    A tapered amplifier is a semiconductor optical device designed to amplify the signal of a low quality semiconductor source and to improve the resulting beam quality. The angle of the taper, and the length of the unamplified region are optimised to deliver high quality beams with low ASE noise.

    Chirp

    A chirped pulse is a pulse in which the frequency changes with time. A frequency increase is known as 'up-chirp', decrease as 'down-chirp'.

    Cladding Mode Free Fibre (CMF fibre)

    A cladding mode is an optical mode that propagates in the cladding of an optical fibre. This is an undesired effect as it: increases optical power loss; degrades output quality; increases optical system noise and instability; and in the worst case, causes damage to the components of an optical system.

    Cladding mode free fibre suppresses these modes.

    Coherence Length

    The coherence length is the distance over which the phase of the beam remains constant.

    It is the path length corresponding to the coherence time - the time over which coherence is lost.

    Multiplication of the coherence time by the vacuum velocity of light gives the coherence length. Alternatively, coherence length can be calculated by dividing the laser wavelength squared by the laser linewidth.

    Many applications require a long and stable coherence length such as holography and interferometry.

    However, long coherence length can lead to speckle and non-linear affects such as Brillouin scattering, which may be undesirable.

    Collimation

    A collimated beam has low divergence and a beam radius that is approximately constant. As all optical systems suffer from optical divergence, collimation can only be used to optimise the beam over a short distance.

    Compact OEM

    Our Compact OEM laser format combines the laser resonator and PSU in the smallest of all of our laser packages. Size is kept to a minimum as no power source is built in. Connection to a suitable DC voltage source is made via flying leads.

    Due to the small size, fewer features are available as options with this format. However, it is possible to provide the following:

    • Adjustable optics
    • Line generation optics
    • Alternative electrical connection options

    These laser heads are CE marked in accordance with CEI 60825.

    Continuous Wave, CW (laser output)

    CW lasers emit laser radiation constantly with time. The output power may be adjusted by the source or by the use of attenuators in the beam path, but emission continues until the laser is switched off or reaches the end of its lifetime.

    D

    D* (Detector Responsivity)

    Detectivity is a key figure of merit used for photodetectors. It is proportional to the inverse of the smallest signal that can be detected. Hence a larger D* indicates a more sensitive detector.

    DBR (Distributed Bragg reflector cavity)

    The distributed Bragg reflector cavity is a form of laser diode cavity that creates optical feedback which reduces the linewidth of the laser emission and the number of longitudinal modes that are present. It is similar to the DFB cavity but achieves higher wavelength coupling and offers the potential for much narrower linewidth generation.

    The narrow linewidth makes them suitable for spectroscopy and remote sensing applications.

    Some DBR laser diodes are wavelength tunable by drive current.

    DBR lasers tend to exhibit higher wavelength stability than DFB and FP lasers when operated across their full operating temperature range. This makes them useful for multiplexed optical communications.

    Some generations of DBR laser diodes deliver long coherence length. Such lasers are suitable for use in applications such as holography, interferometry and sensing.

    DFB (Distributed feedback cavity)

    The distributed feedback cavity is a form of laser diode cavity that includes a specific region within the laser that creates optical feedback. This has the effect of increasing the optical amplification at a given wavelength, and consequently reduces the linewidth of the laser emission, and the number of longitudinal modes that are present.

    The narrow linewidth makes them suitable for spectroscopy and remote sensing applications.

    Most DFB laser diodes are wavelength tunable by temperature and drive current variation.

    However they exhibit much higher wavelength stability across their operating temperature range. This makes them useful for multiplexed optical communications.

    Some generations of DFB laser diodes deliver long coherence length. Such lasers are suitable for use in applications such as holography, interferometry and sensing.

    Digital Modulation (TTL Modulation)

    Digital modulation enables the user to modulate the output power of the laser diode digitally between zero power and maximum power via an external 5V TTL input.

    Available as a standard or optional feature on most of our lasers, this can also be used to switch the laser on or off remotely.

    The modulation frequency, Hz, refers to the speed at which the laser can be switched on and off.

    Dispersion

    Is defined as the dependence of the phase velocity in a medium on the optical wavelength, the mode of propagation, or the polarisation.

    Chromatic dispersion is where the phase velocity depends on the optical wavelength. It is caused by a frequency-dependent refractive index, or waveguide dispersion. It manifests itself as pulse broadening, where the duration of a pulse increases as the different wavelengths within the pulse travel at different speeds through the medium of propagation.

    Intermodal dispersion results from different propagation characteristics of higher-order transverse modes in waveguides, such as multimode fibres.

    Polarization mode dispersion results from polarization-dependent propagation characteristics.

    DPSS Laser

    Diode-pumped solid state (DPSS) lasers use laser diodes rather than flash or arc lamps for optically pumping solid-state laser cavities. Although lamps are low cost and can provide high powers, they also give lower lifetimes, low power efficiencies and introduce unwanted thermal effects.
     

    In comparison, DPSS lasers have a compact footprint and deliver efficient power consumption. They also offer potentially long lifetimes, low noise and high beam quality.

    E

    Efficiency

    Quantum Efficiency

    The quantum efficiency of a photo-detector or camera is defined as the number of photon collisions that are required to produce and electron-hole pair, and relates to the overall sensitivity of the detection system.

    Slope Efficiency (Differential Efficiency)

    Slope efficiency of a laser is defined as the ratio of laser output power versus the input pump power. As this value is generally linear for most lasers operating in the lasing region, it is sufficiently expressed as a single ratio. However, at conditions below laser threshold and close to peak output power, the variation of output power with input power becomes non-linear and this approximation is no longer accurate.

    Wall Plug Efficiency

    The total electrical to optical power efficiency of a laser system.

    End Pumping

    Pump light is injected into the gain medium in the same axis as the propagation axis of the laser emission.

    Excimer Laser

    An excimer laser uses a gas mixture as the gain medium. This is typically a combination of a noble gas and a reactive gas. Pumped with a high voltage electric discharge in short pulses, the gases create excimers, pseudo molecules that only exist in an energized state. These usually emit laser light in the UV region.

    External Cavity Diode Laser

    External cavity diode lasers combine a laser diode with external optics that extend the resonant cavity beyond the laser diode.

    By extending the cavity, the laser linewidth is narrowed, phase noise is reduced and the wavelength can be adjusted.

    F

    Fabry Perot Cavity

    The Fabry Perot cavity is the simplest form of optical resonance cavity, based around two parallel plane reflectors. Light may only oscillate between the plane mirrors of the cavity if the modal wavelength conditions are fulfilled. Light of wavelengths that do not fulfil these conditions is emitted from the cavity. As a result the cavity acts as an optical filter. Changing the mirror separation changes the wavelength response of the filter (or Etalon). The performance of the cavity is principally defined by the reflectivity of the mirrors.

    When used as a laser cavity, a Fabry Perot cavity tends to deliver relatively broad linewidth when compared to other cavities, and multiple longitudinal modes

    Fast axis / slow axis

    A birefringent material has a refractive index that is dependent on the polarisation direction of the light that propagates through it. An optical beam passing through a birefringent material will generally be split into two components, an ordinary ray and an extraordinary ray, each of which has an orthogonal polarisation to the other.

    The axes of a birefringent material are classified "fast" where the refractive index is the lowest, with the slow axis referring to the orthogonal axis.

    FC/APC connector

    This is an industry standard optical fibre connector. It allows for quick connection of a device to an optical system in a way that is highly repeatable, stable and easy.

    APC "Angled Physical Contact" connectors are angle-polished. This prevents back-reflection into the optical system which can cause noise and instability.

    Fibre Coupling

    Fibre coupling is where the output power from a laser is coupled into the core of an optical fibre.

    Fibre coupling offers a number of advantages for example: remote location of the laser head from the work piece (e.g. surgery); combination of multiple wavelengths onto a single fibre (multiplexing in data and telecoms); improvement of beam quality (spatial filtering); and enclosing a large area (security and remote sensing).

    Most optical fibres have core diameters in the 5 to 500 micron range, depending on the spatial mode and the power handling requirements. The method of alignment needs to be precise and stable to ensure that maximum coupling is achieved and remains constant in many different environments and over long periods of time.

    Many different forms of fibre coupled laser are available ranging from pseudo-monolithic devices to uncoupled lasers with fibre accessories separated in space.

    Cladding Mode Free Fibre (CMF fibre)

    A cladding mode is an optical mode that propagates in the cladding of an optical fibre. This is an undesired effect as it: increases optical power loss; degrades output quality; increases optical system noise and instability; and in the worst case, causes damage to the components of an optical system.

    Cladding mode free fibre suppresses these modes.

    FC/APC connector

    This is an industry standard optical fibre connector. It allows for quick connection of a device to an optical system in a way that is highly repeatable, stable and easy.

    APC "Angled Physical Contact" connectors are angle-polished. This prevents back-reflection into the optical system which can cause noise and instability.

    Large Core Fibre coupling

    Large Core fibre coupling is a form of multimode fibre coupling, but is generally applied to fibres with cores greater than 100 microns. This form of fibre coupling allows numerous spatial modes and temporal modes of the laser beam to co-propagate.

    It is particularly useful for materials processing applications where large powers are to be handled within the fibre.

    Fibres can be aggregated together to form bundles, with each fibre providing a source of laser power.

    When compared with singlemode fibre coupling, beam quality and coherence are compromised, but much higher powers are achievable.

    Multimode Fibre Coupling (MM Fibre)

    Multimode fibre coupling allows numerous spatial modes and temporal modes of the laser beam to co-propagate through the fibre.

    It is particularly useful for short reach and low data rate optical communications, and low power beam delivery systems for applications such as sensing and optical pumping.

    When compared with singlemode fibre coupling, beam quality and coherence are compromised, but higher powers are achievable.

    Multimode fibres are available with core diameters of 50microns, 62.5 microns, 100 microns and greater.

    Polarisation Preserving Fibre coupling / Polarisation Maintaining Fibre Coupling (PM Fibre)

    Polarisation preserving fibre coupling is a form of singlemode fibre coupling. It uses a special type of fibre where the structure of the fibre core is designed to ensure that a single linear polarisation state is propagated along the length of the fibre.

    Singlemode Fibre Coupling (SM fibre)

    Singlemode fibre coupling preserves the spatial mode and temporal mode of the laser beam by allowing only one (single) mode to propagate through the fibre. However, it does not preserve the polarisation state of the fibre, which is randomised.

    It can be used to convert multi-spatial mode beams into single-spatial mode beams at the expense of increased loss.

    It is particularly useful for optical communications, distributed sensors, and applications where excellent beam quality or coherence is required.

    Singlemode fibres tend to have the smallest dimensions, with core diameters typically less than 10 microns.

    Fibre Laser

    A fibre laser is a solid-state laser and is based around an optically pumped doped optical fibre.

    As the gain media has a large gain bandwidth, wide wavelength tuning ranges and ultrashort pulses are achievable. The high gain efficiency allows operation with small pump powers, giving high power efficiencies and contributes to their small size and power consumption.

    Their high output power, without amplifiers, eliminates spontaneously induced noise. This is particularly useful in sensing applications.

    Furthermore, the potential for long cavity length produces very narrow linewidth and high coherence with low phase noise. This is particularly useful for high-resolution interferometry.

    Single mode fibres give diffraction limited beam quality making them ideally suited to high performance material processing applications.

    High output power and compact size are the trademarks of fibre lasers. As fibre laser construction is inherently more robust than other laser types, it lends itself to industrial and portable applications.

    Free Spectral Range (FSR)

    The Free spectral range (FSR) is the spacing in optical frequency or wavelength between two successive reflected or transmitted optical intensity maxima or minima of an interferometer or diffractive optical element.

    Frequency bandwidth

    The frequency bandwidth is the rate at which a system may operate within specification when operating in a pulsed or modulated mode. The frequency bandwidth is normally defined as the 3dB bandwidth, the point at which the performance decreases by a factor of 3dB (50%).

    G

    Gas Laser

    These lasers use an electrically pumped gas mixture as the gain medium. Examples include lasers such as Helium-Neon, Argon Ion, Krypton ion that deliver outputs in the visible; Carbon Dioxide delivers outputs in the Infrared; and Nitrogen and a range of Excimer lasers output in the UV.

    Gas lasers have largely been replaced by the newer diode, DPSS and fibre laser technologies. However, they are still the only solution for very specific wavelengths.

    Group Delay

    The group delay is a measure of the time delay incurred by a single pulse containing a group of wavelengths or polarisations as they propagate through an optical medium. The entire group will be retarded as it propagates through an optically dense medium. The amount of delay is defined as the group delay. Some wavelengths or polarisations within the group are delayed more than others. This leads to "pulse broadening" (an increase of the pulse duration). The rate at which slower signals are slowed in relation to the fastest in the group is termed the differential group delay.

    H

    High Brightness

    The brightness of a laser beam is the ratio of the output power to the surface area of the laser beam. 'High brightness' refers to a laser having a large output power over a small active area and is particularly useful for increasing the SNR in optical imaging and the speed of material processing.

    L

    Large Core Fibre coupling

    Large Core fibre coupling is a form of multimode fibre coupling, but is generally applied to fibres with cores greater than 100 microns. This form of fibre coupling allows numerous spatial modes and temporal modes of the laser beam to co-propagate.

    It is particularly useful for materials processing applications where large powers are to be handled within the fibre.

    Fibres can be aggregated together to form bundles, with each fibre providing a source of laser power.

    When compared with singlemode fibre coupling, beam quality and coherence are compromised, but much higher powers are achievable.


    A laser diode uses electrically pumped semiconductor gain medium.

    Laser diodes are highly sensitive light sources. The SK Group range of laser diode current controllers, laser diode temperature controllers and laser diode mounts allow the output power, wavelength and mode stability to be adjusted with high precision, resolution and stability. This enables sensitive control and measurement.

    Light Emitting Diode (LED)

    A light emitting diode is a semiconductor device that emits light through electroluminescence. LEDs emit low powers in the UV, visible and infrared parts of the spectrum. They are broadband sources that are suitable for applications such as illumination, fluorescence excitation, sensing and spectroscopy. They are also used in low data rate optical communications.

    Quantum Cascade Laser / External Cavity Quantum Cascade Laser

    A Quantum Cascade Laser (QCL) is a semiconductor laser that emits highly coherent radiation in the mid- to long-wave infrared region of the spectrum. QCLs are not diode lasers, but rather unipolar semiconductor devices consisting of hundreds of epitaxial grown layers forming a large number of quantum wells in the conduction band of the device. These are engineered to enable a cascade of photons emitted for each injected electron. QCLs generate light in the 4 µm to 25 µm region of the electromagnetic spectrum.

    An External Cavity Quantum Cascade Laser (ECqcL™) is a semiconductor laser source. It integrates quantum cascade gain media into an external cavity having wavelength dependent feedback. ECqcLs™ are available either as precision fixed-wavelength sources, or as broadly tunable lasers. A tunable ECqcL™ can tune across the entire gain profile of the QC chip, allowing for tunability of 10% to 25% of the center wavelength

    Solid State Laser

    Solid state lasers are based around a solid gain media such as ion-doped crystals or glasses, (e.g. Nd:YAG, Nd:YLF, Ti:sapphire, Nd:YVO4 etc...).

    These lasers have the ability to deliver highly coherent radiation in the UV, visible or Infrared ranges of the spectrum, in pulsed or CW forms and with high optical output power and quality. They also offer the ability to operate in highly singlemode states for applications requiring long and stable coherence.

    High powers can also be achieved, making them suitable for some materials processing applications.

    Superluminescent Light Emitting Diode (SLED)

    SLEDs are semiconductor devices that incorporate high-power gain sections to give amplified spontaneous emission. Similar in construction to laser diodes, but without optical feedback to cause laser action, they combine the high power and brightness of laser diodes with the low coherence of conventional light-emitting diodes.

    Light Emitting Diode (LED)

    A light emitting diode is a semiconductor device that emits light through electroluminescence. LEDs emit low powers in the UV, visible and infrared parts of the spectrum. They are broadband sources that are suitable for applications such as illumination, fluorescence excitation, sensing and spectroscopy. They are also used in low data rate optical communications.

    Linewidth

    As laser light is a narrow band of wavelengths rather than a single wavelength, a lasers linewidth is the full width at half maximum of its optical spectrum. This is measured in wavelength, wavenumbers or frequency.

    Narrow linewidths are required for various applications. Used in spectroscopy, narrow linewidths give high resolution to allow adjacent absorption lines to be resolved.

    However, for some applications a narrow linewidth is not suitable. For advice on your particular application, please contact us - we will be happy to help you.

    Littman-Metcalf Configuration

    In an external cavity using the Littman-Metcalf configuration, the end mirror is also a diffraction grating, but it remains fixed at near grazing incidence. Instead, an additional mirror adjusts to tune the wavelength and to reflect the first-order diffracted beam back to the laser gain medium.

    This configuration tends to have lower output power than Littrow, as the zero-order reflection from the tuning mirror is lost. However, it can provide narrower line widths and broader tuning range. As the wavelength dependent diffraction occurs twice per round trip in the resonator, stronger wavelength selection results.

    Littrow Configuration

    The Littrow configuration of an external cavity features a diffraction grating as an external cavity end mirror. The emitted wavelength is tuned by adjusting the angle and position of the grating. The first-order diffracted beam is reflected back to the laser gain medium, giving optical feedback.

    This configuration allows independent control of the output power and the wavelength-dependent feedback from the external cavity.