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High-Power MicroSpot® Focusing Objectives for UV Lasers![]()
LMUL-20X-UVB 20X, Long Working Distance, UV Achromatic Objective LMU-40X-NUV 40X, UV Achromatic Objective Application Idea Two Focusing Objectives Mounted in a CSN200 Dual-Objective Nosepiece. Related Items ![]() Please Wait
Features
Applications
Thorlabs' High-Power UV MicroSpot® Focusing Objectives are designed for use with UV excimer lasers and other ultraviolet sources in on-axis laser focusing and microimaging applications. The objectives contain lens elements made from high-quality, low-absorption, excimer-grade fused silica and CaF2. These lenses are AR coated and optically designed for narrowband or broadband wavelength ranges (see the focal shift and AR coating performance graphs below). The objectives feature M26 x 0.706 or RMS (0.800"-36) threading; to use these objectives with a different thread standard, please see our microscope objective thread adapters. Focusing objectives can be used in a variety of applications where intense optical power is necessary. Focused excimer sources in particular have uses in eye surgery, photolithography, and industrial laser cutting. Each section below lists some ideal applications for each group of our objectives. When incorporating these objectives into a system, note that the specified magnification for each objective is calculated assuming use with a 200 mm focal length tube lens, such as the TTL200-UVB. The graphs below show the transmission and focal length shifts (FLS) for our UV focusing Objectives. Transmission graphs show the total transmission through each objective. The shaded regions indicate the wavelength range for the AR coating applied to the elements of each objective. Long Working Distance, Achromatic UV Focusing Objective![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. Thorlabs offers custom V-coatings for our LMUL objectives upon request. These coatings can be designed to provide peak performance at select laser wavelengths while still giving moderate transmission at visible wavelengths. The axial focal length shift given above will still be valid for the given magnification of the custom objective. Contact Tech Support to request quotes and lead times for these custom coatings. Achromatic UV Focusing Objectives![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. Narrowband UV Focusing Objectives![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. Narrowband UV Focusing Objectives with Laser Line AR Coatings![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() Click to Enlarge Click Here for Raw Data The shaded region of this graph identifies the specified wavelength range of the AR coating. ![]() When viewing an image with a camera, the system magnification is the product of the objective and camera tube magnifications. When viewing an image with trinoculars, the system magnification is the product of the objective and eyepiece magnifications.
Magnification and Sample Area CalculationsMagnificationThe magnification of a system is the multiplicative product of the magnification of each optical element in the system. Optical elements that produce magnification include objectives, camera tubes, and trinocular eyepieces, as shown in the drawing to the right. It is important to note that the magnification quoted in these products' specifications is usually only valid when all optical elements are made by the same manufacturer. If this is not the case, then the magnification of the system can still be calculated, but an effective objective magnification should be calculated first, as described below. To adapt the examples shown here to your own microscope, please use our Magnification and FOV Calculator, which is available for download by clicking on the red button above. Note the calculator is an Excel spreadsheet that uses macros. In order to use the calculator, macros must be enabled. To enable macros, click the "Enable Content" button in the yellow message bar upon opening the file. Example 1: Camera Magnification Example 2: Trinocular Magnification Using an Objective with a Microscope from a Different ManufacturerMagnification is not a fundamental value: it is a derived value, calculated by assuming a specific tube lens focal length. Each microscope manufacturer has adopted a different focal length for their tube lens, as shown by the table to the right. Hence, when combining optical elements from different manufacturers, it is necessary to calculate an effective magnification for the objective, which is then used to calculate the magnification of the system. The effective magnification of an objective is given by Equation 1:
Here, the Design Magnification is the magnification printed on the objective, fTube Lens in Microscope is the focal length of the tube lens in the microscope you are using, and fDesign Tube Lens of Objective is the tube lens focal length that the objective manufacturer used to calculate the Design Magnification. These focal lengths are given by the table to the right. Note that Leica, Mitutoyo, Nikon, and Thorlabs use the same tube lens focal length; if combining elements from any of these manufacturers, no conversion is needed. Once the effective objective magnification is calculated, the magnification of the system can be calculated as before. Example 3: Trinocular Magnification (Different Manufacturers) Following Equation 1 and the table to the right, we calculate the effective magnification of an Olympus objective in a Nikon microscope:
The effective magnification of the Olympus objective is 22.2X and the trinoculars have 10X eyepieces, so the image at the eyepieces has 22.2X × 10X = 222X magnification. ![]() Sample Area When Imaged on a CameraWhen imaging a sample with a camera, the dimensions of the sample area are determined by the dimensions of the camera sensor and the system magnification, as shown by Equation 2.
The camera sensor dimensions can be obtained from the manufacturer, while the system magnification is the multiplicative product of the objective magnification and the camera tube magnification (see Example 1). If needed, the objective magnification can be adjusted as shown in Example 3. As the magnification increases, the resolution improves, but the field of view also decreases. The dependence of the field of view on magnification is shown in the schematic to the right. Example 4: Sample Area
Sample Area ExamplesThe images of a mouse kidney below were all acquired using the same objective and the same camera. However, the camera tubes used were different. Read from left to right, they demonstrate that decreasing the camera tube magnification enlarges the field of view at the expense of the size of the details in the image.
Damage Threshold Data for High-Power Focusing Objectives AR CoatingsThe limiting factor in the damage threshold for these objectives is their anti-reflection coating. The specifications to the right are measured data for the anti-reflection coatings deposited onto the optical surfaces of our high-power focusing objectives.
Laser Induced Damage Threshold TutorialThe following is a general overview of how laser induced damage thresholds are measured and how the values may be utilized in determining the appropriateness of an optic for a given application. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. The LIDT for an optic greatly depends on the type of laser you are using. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. Note that the guideline presented here assumes room temperature operation and optics in new condition (i.e., within scratch-dig spec, surface free of contamination, etc.). Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. For more information on cleaning optics, please see our Optics Cleaning tutorial. Testing MethodThorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications. ![]() The photograph above is a protected aluminum-coated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm2 (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage. ![]()
According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, Ø0.803 mm). Please keep in mind that these tests are performed on clean optics, as dirt and contamination can significantly lower the damage threshold of a component. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances. Continuous Wave and Long-Pulse LasersWhen an optic is damaged by a continuous wave (CW) laser, it is usually due to the melting of the surface as a result of absorbing the laser's energy or damage to the optical coating (antireflection) [1]. Pulsed lasers with pulse lengths longer than 1 µs can be treated as CW lasers for LIDT discussions. When pulse lengths are between 1 ns and 1 µs, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). Absorption is either due to an intrinsic property of the optic or due to surface irregularities; thus LIDT values are only valid for optics meeting or exceeding the surface quality specifications given by a manufacturer. While many optics can handle high power CW lasers, cemented (e.g., achromatic doublets) or highly absorptive (e.g., ND filters) optics tend to have lower CW damage thresholds. These lower thresholds are due to absorption or scattering in the cement or metal coating. LIDT in linear power density vs. pulse length and spot size. For long pulses to CW, linear power density becomes a constant with spot size. This graph was obtained from [1]. ![]() Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. Unfortunately, this is highly dependent on factors such as absorption and thermal diffusivity, so there is no reliable method for determining when a high PRF laser will damage an optic due to thermal effects. For beams with a high PRF both the average and peak powers must be compared to the equivalent CW power. Additionally, for highly transparent materials, there is little to no drop in the LIDT with increasing PRF. In order to use the specified CW damage threshold of an optic, it is necessary to know the following:
Thorlabs expresses LIDT for CW lasers as a linear power density measured in W/cm. In this regime, the LIDT given as a linear power density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size, as demonstrated by the graph to the right. Average linear power density can be calculated using the equation below. The calculation above assumes a uniform beam intensity profile. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right). Now compare the maximum power density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. A good rule of thumb is that the damage threshold has a linear relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 10 W/cm at 1310 nm scales to 5 W/cm at 655 nm): While this rule of thumb provides a general trend, it is not a quantitative analysis of LIDT vs wavelength. In CW applications, for instance, damage scales more strongly with absorption in the coating and substrate, which does not necessarily scale well with wavelength. While the above procedure provides a good rule of thumb for LIDT values, please contact Tech Support if your wavelength is different from the specified LIDT wavelength. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application. Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). Testing may result in additional costs or lead times. Contact Tech Support for more information. Pulsed LasersAs previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Pulsed lasers often do not heat the optic enough to damage it; instead, pulsed lasers produce strong electric fields capable of inducing dielectric breakdown in the material. Unfortunately, it can be very difficult to compare the LIDT specification of an optic to your laser. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values. Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. In this ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism [2]. In contrast, pulses between 10-7 s and 10-4 s may cause damage to an optic either because of dielectric breakdown or thermal effects. This means that both CW and pulsed damage thresholds must be compared to the laser beam to determine whether the optic is suitable for your application.
When comparing an LIDT specified for a pulsed laser to your laser, it is essential to know the following: LIDT in energy density vs. pulse length and spot size. For short pulses, energy density becomes a constant with spot size. This graph was obtained from [1].
The energy density of your beam should be calculated in terms of J/cm2. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. In this regime, the LIDT given as an energy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. This calculation assumes a uniform beam intensity profile. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. For reference a Gaussian beam typically has a maximum energy density that is twice that of the 1/e2 beam. Now compare the maximum energy density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately [3]. A good rule of thumb is that the damage threshold has an inverse square root relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 1 J/cm2 at 1064 nm scales to 0.7 J/cm2 at 532 nm): You now have a wavelength-adjusted energy density, which you will use in the following step. Beam diameter is also important to know when comparing damage thresholds. While the LIDT, when expressed in units of J/cm², scales independently of spot size; large beam sizes are more likely to illuminate a larger number of defects which can lead to greater variances in the LIDT [4]. For data presented here, a <1 mm beam size was used to measure the LIDT. For beams sizes greater than 5 mm, the LIDT (J/cm2) will not scale independently of beam diameter due to the larger size beam exposing more defects. The pulse length must now be compensated for. The longer the pulse duration, the more energy the optic can handle. For pulse widths between 1 - 100 ns, an approximation is as follows: Use this formula to calculate the Adjusted LIDT for an optic based on your pulse length. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. Keep in mind that this calculation is only used for pulses between 10-9 s and 10-7 s. For pulses between 10-7 s and 10-4 s, the CW LIDT must also be checked before deeming the optic appropriate for your application. Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. Contact Tech Support for more information. [1] R. M. Wood, Optics and Laser Tech. 29, 517 (1998). In order to illustrate the process of determining whether a given laser system will damage an optic, a number of example calculations of laser induced damage threshold are given below. For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. To use the calculator, enter the specified LIDT value of the optic under consideration and the relevant parameters of your laser system in the green boxes. The spreadsheet will then calculate a linear power density for CW and pulsed systems, as well as an energy density value for pulsed systems. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. This calculator assumes a Gaussian beam profile, so a correction factor must be introduced for other beam shapes (uniform, etc.). The LIDT scaling laws are determined from empirical relationships; their accuracy is not guaranteed. Remember that absorption by optics or coatings can significantly reduce LIDT in some spectral regions. These LIDT values are not valid for ultrashort pulses less than one nanosecond in duration. ![]() A Gaussian beam profile has about twice the maximum intensity of a uniform beam profile. CW Laser Example However, the maximum power density of a Gaussian beam is about twice the maximum power density of a uniform beam, as shown in the graph to the right. Therefore, a more accurate determination of the maximum linear power density of the system is 1 W/cm. An AC127-030-C achromatic doublet lens has a specified CW LIDT of 350 W/cm, as tested at 1550 nm. CW damage threshold values typically scale directly with the wavelength of the laser source, so this yields an adjusted LIDT value: The adjusted LIDT value of 350 W/cm x (1319 nm / 1550 nm) = 298 W/cm is significantly higher than the calculated maximum linear power density of the laser system, so it would be safe to use this doublet lens for this application. Pulsed Nanosecond Laser Example: Scaling for Different Pulse Durations As described above, the maximum energy density of a Gaussian beam is about twice the average energy density. So, the maximum energy density of this beam is ~0.7 J/cm2. The energy density of the beam can be compared to the LIDT values of 1 J/cm2 and 3.5 J/cm2 for a BB1-E01 broadband dielectric mirror and an NB1-K08 Nd:YAG laser line mirror, respectively. Both of these LIDT values, while measured at 355 nm, were determined with a 10 ns pulsed laser at 10 Hz. Therefore, an adjustment must be applied for the shorter pulse duration of the system under consideration. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration: This adjustment factor results in LIDT values of 0.45 J/cm2 for the BB1-E01 broadband mirror and 1.6 J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm2 maximum energy density of the beam. While the broadband mirror would likely be damaged by the laser, the more specialized laser line mirror is appropriate for use with this system. Pulsed Nanosecond Laser Example: Scaling for Different Wavelengths This scaling gives adjusted LIDT values of 0.08 J/cm2 for the reflective filter and 14 J/cm2 for the absorptive filter. In this case, the absorptive filter is the best choice in order to avoid optical damage. Pulsed Microsecond Laser Example If this relatively long-pulse laser emits a Gaussian 12.7 mm diameter beam (1/e2) at 980 nm, then the resulting output has a linear power density of 5.9 W/cm and an energy density of 1.2 x 10-4 J/cm2 per pulse. This can be compared to the LIDT values for a WPQ10E-980 polymer zero-order quarter-wave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm2 for a 10 ns pulse at 810 nm. As before, the CW LIDT of the optic scales linearly with the laser wavelength, resulting in an adjusted CW value of 6 W/cm at 980 nm. On the other hand, the pulsed LIDT scales with the square root of the laser wavelength and the square root of the pulse duration, resulting in an adjusted value of 55 J/cm2 for a 1 µs pulse at 980 nm. The pulsed LIDT of the optic is significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. However, the large average linear power density of the laser system may cause thermal damage to the optic, much like a high-power CW beam. Laser Safety and ClassificationSafe practices and proper usage of safety equipment should be taken into consideration when operating lasers. The eye is susceptible to injury, even from very low levels of laser light. Thorlabs offers a range of laser safety accessories that can be used to reduce the risk of accidents or injuries. Laser emission in the visible and near infrared spectral ranges has the greatest potential for retinal injury, as the cornea and lens are transparent to those wavelengths, and the lens can focus the laser energy onto the retina. Safe Practices and Light Safety Accessories
Laser ClassificationLasers are categorized into different classes according to their ability to cause eye and other damage. The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic, and related technologies. The IEC document 60825-1 outlines the safety of laser products. A description of each class of laser is given below:
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These objectives provide long working distances while keeping axial focal shift low. Their optical design is chromatically optimized in the UV wavelength range. Diffraction-limited performance is guaranteed over the entire clear aperture. These objectives are ideal for laser cutting, surgical laser focusing, and spectrometry applications. They can also be used for scanning and micro-imaging applications like brightfield imaging under narrowband, UV laser illumination. Each objective is shipped in an objective case comprised of an OC2M26 lid and an OC24 canister. Custom AR Coatings can be requested by contacting Tech Support; options include broadband NUV (325 nm - 500 nm), dual band (266 and 532 nm), and laser line (248 nm, 266 nm, 355 nm, or 532 nm). Please see the Graphs tab for more details.
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These 5X, 20X, and 40X objectives are chromatically corrected to minimize the axial focal shift across the AR coating wavelength range. Diffraction-limited performance can be achieved with beam diameters ≤70% of each objective's clear aperture. These objectives are ideal for focusing or collecting polychromatic light, making them well suited for use in spectrometry, wafer inspection, or surgical laser applications. Their small field of view limits their performance in imaging applications. The external RMS (0.800"-36) threads allow these objectives to be mounted to our fiber launch systems or to any of our flexure stages using a HCS013 RMS mount. An objective case (OC2RMS lid and OC22 canister) and aluminum cap (RMSCP1) are available for purchase separately.
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These objectives offer 3X, 10X, and 15X magnification. Due to their monochromatic optical design, a narrow-bandwidth laser within the AR coating wavelength range should be used to achieve optimal optical performance. Diffraction-limited performance can be achieved with beam diameters ≤70% of each objective's clear aperture. We also offer narrowband-coated versions of these objectives below. The external RMS (0.800"-36) threads allow these objectives to be mounted to our fiber launch systems or to any of our flexure stages using a HCS013 RMS mount. An objective case (OC2RMS lid and OC22 canister) and aluminum cap (RMSCP1) are available for purchase separately
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These 3X, 10X, and 15X objectives are treated with narrowband AR coatings centered around Excimer laser lines with <1% maximum reflectance per surface and high damage thresholds, making them ideal for laser cutting and micromachining components at high powers. The external RMS (0.800"-36) threads allow these objectives to be mounted to our fiber launch systems or to any of our flexure stages using a HCS013 RMS mount. An objective case (OC2RMS lid and OC22 canister) and aluminum cap (RMSCP1) are available for purchase separately.
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