Thank you for contacting Thorlabs. I need to know the location of the back focal plane of AC508-200-A-MLd relative to the lens, however, on the reference document f, the focal length and f_b, the back focal length are both defined as being in the same direction, and both listed as positive. It will be available to a larger group shortly. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. A reply from Jens at Thorlabs: looking at the spec tab for the 1" 30mm focal lenght achromat (AC254-030-A1-ML) I see a value of 22.9mm. Use the SPW801Adjustable Spanner Wrench to incorporate the 5 mm, 6 mm, and 6.35 mm lenses into adapters and lens tube systems. Is is possiible to take out the lens, invert it and place it back or should i then buy the unmouted lens and for instance and SM2L10? Reply from Sean at Thorlabs: Thank you for your feedback on our website presentation! For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. -B coated doublets (650 - 1050nm): 810nm, 100W/cm^2 Achromatic Doublet Lenses have far superior optical performance to Singlet Lenses. Our entire, Achromatic Performance with AR Coating for 400 - 700 nm. Opt. 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 s pulse at 980 nm. Although you can use it backward/forward, using in the engraved direction will reduce aberrations by keeping the more curved side towards infinity. In this near IR achromatic doublet, the design wavelengths (706.5 nm, 855 nm, and 1015 nm) have each been traced through the lens and are represented by different colors. Is the off-axis and aspheric performance of 2" achromatic doublets superior compared to 1" optics of the same kind? I will reach out to you directly. The pulse length must now be compensated for. Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. When using a white light source with a singlet lens, the focal point and circle of least confusion are blurred by chromatic aberration. The damage threshold of cemented achromatic doublets is limited by the cement. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. This specification is also commonly referred to as surface fit. If this relatively long-pulse laser emits a Gaussian12.7 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 10-4J/cm2 per pulse. Using a collimated source incident on the curved side, I measure a length of about 23.5 mm from the flat side of the lens to the focal point. SM2A6: Working Distance is measured from the endof the externally threaded side of the mount, as shown in the reference drawing. 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. One way of displaying the theoretical level of correction is through plots of wavefront error and ray traces to determine spot size. Or are they only tested with a pulsed source as given by the specs? These lower thresholds are due to absorption or scattering in the cement or metal coating. 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. Jale. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. While the LIDT, when expressed in units of J/cm, 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]. Pulsed lasers with pulse lengths longer than 1 s can be treated as CW lasers for LIDT discussions. Hello, I purchased a pair of the 1" 30 mm focal length achromatic doublets coated for the visible and Im seeing a different value for focal distance from the flat side of the lens than the listed f_b of 27.5 mm. Is there also a tested CW damage threshold for these achromat doublets? For other products like achromatic triplets or cylindrical achromatic doublets there are focal length shift data available. Much like surface flatness for flat optics, spherical surface power is a measure of the deviation between the surface of the curved optic and a calibrated reference gauge. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. 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. [2] Roger M. Wood, Laser-Induced Damage of Optical Materials (Institute of Physics Publishing, Philadelphia, PA, 2003). Spherical and Chromatic aberrations will be most significantly increased in reverse, and the change is expected to be more noticeable for shorter focal lengths. I will email you an excel file that provides the focal length shift data you saw posted in our family image. Detailed information regarding each achromatic doublet can be found in the Zemax files included with the support documents for each doublet. Edge of housing to focal point is then ~70.09mm. If the spot is within the Airy disk, the lens is typically considered to be diffraction limited. In addition, they offer better broadband and off-axis performance than aspheric lenses. For reference a Gaussian beam typically has a maximum energydensity that is twice that of the 1/e2 beam. Upon request, we can provide individual test information and a testing certificate. While the question of beam quality requires a full model of the lens to answer, the short version is that these achromatic doublets are designed for infinite conjugate applications, and there is a preferred side for the focus and collimated beam to be on. From the center of the -137.1mm radiused surface to the focal point is 72.89mm. The figures below show two 50.0 mm focal length lenses, one plano-convex and the other an achromatic doublet. The LIDT scaling laws are determined from empirical relationships; their accuracy is not guaranteed. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. Please note there is an engraving which indicates the direction of light to collimate a point source. The spreadsheet will then calculate a linear power density for CW and pulsed systems, as well as an energy density value for pulsed systems. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values. Thorlabs' Cemented Visible Achromatic Doublets are available pre-mounted in engraved threaded mounts, making it easy to incorporate these optics into your setup. Mounts smaller than 1/2" are engraved with the part number only. Thank you for contacting Thorlabs, and I apologize for the confusion. The materials listed here are the Schott glass types. MTF curves calculated in Zemax typically present a weighted average with contributions from multiple wavelengths and are known as polychromatic MTF curves. Upon request, we can provide individual test information and a testing certificate. (532 nm, 10 ns pulse, 10 Hz, 0.566 mm). And the reference plane from which f_b is measured is unclear. The energy density of your beam should be calculated in terms of J/cm2. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). 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. Is it possible that you looked at the 0.5" version? Are the mounted 2-inch lenses mounted in the same kind of lens tubes (SM2L05, SM2M10, etc.) For applications that require higher damage thresholds, please consider our, The power density of your beam should be calculated in terms of W/cm. This graph was obtained from [1]. Both are 25.4 mm lenses with a 3 mm beam through the optical axis and one offset by 8.0 mm. 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. For best performance, the side of the lens with the largest radius of curvature (flattest side) should face away from the collimated beam. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application. 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. 12, 661 (1973). An infinity symbol denotes that this lens has an infinite conjugate ratio (i.e., if a diverging light source is placed one focal length away from the flatter side of the lens, the light rays emerging from the curved side will be collimated). These achromatic doublets, which are designed for use in the visible spectral region (400 - 700 nm), are computer optimized at infinite conjugate ratios. I want to know how can I mount it. Lateral and transverse aberrations are greatly reduced by the achromatic doublet. This is why we don't spec a back-focal length as you've described. SM2L10: 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. Now compare the maximum energy density to that which is specified as the LIDT for the optic. Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. Average linear power density can be calculated using the equation below. Beam diameter is also important to know when comparing damage thresholds. Damage threshold specifications are constant for all A-coated achromatic doublets, regardless of the size or focal length of the lens. 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. 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. Could you clarify from where f_b is measured, and whether it should be measured in the opposite direction to that drawn? Whether your application has demanding imaging requirements or laser beam manipulation needs, these doublets should be considered. Testing may result in additional costs or lead times. The illustration is correct in this case. As a result, both CW and pulsed LIDT values must be compared to the properties of the laser system to ensure safe operation. -A coated doublets (4000 - 700nm): 532nm, 100W/cm^2 Since shorter and longer wavelengths will have different resolution limits, and hence different individual MTF curves, quantitatively different polychromatic MTF curves may be produced depending on the wavelengths included in the curve's calculation. While the broadband mirror wouldlikely be damaged by the laser, the more specialized laser line mirror isappropriate for use with this system. The figures also shows how the circle of least confusion for white light is reduced by using an achromatic doublet. As described on the previous tab, the LIDT value of an optic scales with the square root of the wavelengthin the nanosecond pulse regime: This scaling gives adjustedLIDT values of 0.08 J/cm2 for the reflective filter and 14 J/cm2 for the absorptive filter. The Effective focal length is the focal distance from the principal plane within the optic. Both the positive and negative lenses have an infinite conjugate ratio (i.e., if a diverging light source is placed one focal length away from the flatter side of the lens, the light rays emerging from the curved side will be collimated). As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. The average energy density of each pulse is found by dividing the pulse energy by the beam area: As described above, the maximum energy density of a Gaussian beam is about twice the average energy density. This lens can be mounted on any of our SM2-threaded mounts, for example the LMR2. At the following link (http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2696&pn=AC254-100-A-ML#3441), below the section: 1" Mounted Achromatic Doublets, AR Coated: 400 - 700 nm, you should see these values with a reference drawing on the right. 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. Hello, thank you for contacting Thorlabs. In this ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism [2]. Since the spot size is drawn using geometric ray tracing, spots much smaller than the Airy disk are not achievable due to diffraction. LIDT in linear power density vs. pulse length and spot size. I want to use a 2" optic so I will need a step down SM2 to SM1 coupler but I am concerned that there are no accessible threads on the infinite conjugate face, are there? 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. For the target selected, the contrast measured 82.3%. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). 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. Additionally, a member of my team is currently working to add this information to the web page. 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. If focusing a collimated beam, the engraved arrow should point in the opposite direction of light propagation. For short pulses, energy density becomes a constant with spot size. Negative values are measured from the left side of the lens. Both of these LIDT values, while measured at 355nm, were determined with a 10ns pulsed laser at 10Hz. Remember that absorption by optics or coatings can significantly reduce LIDT in some spectral regions. For an explanation of why the linear power density provides the best metric for long pulse and CW sources, please see the, Engraved Threaded Housing Enables Easy Integration into Thorlabs Optomechanics, Housing on Lenses 1/2 and Larger Includes Focal Length and Coating Information, Focal Lengths Available: 7.5 mm to 1000 mm. But for the Mounted Visible Achromatic Doublets, there's just one example plot for one lens available, without the possibility to download the plot data. ARC: 400-700 nm, f=75 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=80 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=100 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=150 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=180 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=200 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=250 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=300 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=400 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f=500 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, f = 750 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400 - 700 nm, f=1000 mm, 2" Achromatic Doublet, SM2-Threaded Mount, ARC: 400-700 nm, Storage Box for Mounted 2" Round Optics (Max. The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. Choose from 7 diameters: 5 mm, 6 mm, 6.35 mm, 8 mm, 1/2", 1", or 2". The MTF of a lens describes its ability to transfer contrast from an object to an image at various resolution levels. AC508-200-A: Approximate intensity profile of your beam (e.g., Gaussian), Linear power density of your beam (total power divided by 1/e, Energy density of your beam (total energy divided by 1/e, Pulse repetition frequency (prf) of your laser. Hello! 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.). In an achromatic doublet this effect is somewhat compensated for by using glasses of two different refractive indexes to cancel these aberrations. Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254andISO 21254 specifications.First, a low-power/energy beam is directed to the optic under test. Most of the materials listed here are the Schott glass types with the exceptions of, Common microscope tube lens focal lengths. Pulsed Microsecond Laser ExampleConsidera laser system that produces 1 s pulses, each containing 150 J of energy at a repetition rate of 50 kHz, resulting in a relatively high duty cycle of 5%. Thank you for participating in our feedback forum. MTF image quality is an important characteristic of lenses. The figures below show the effect on focal length for a number of different wavelengths of light through an achromatic doublet and a plano-convex singlet. Thanks, The specifications to the right are measured data for Thorlabs' A-coated achromatic doublets. Pulsed Nanosecond Laser Example: Scaling for Different Pulse DurationsSuppose that a pulsed Nd:YAG laser systemis frequency tripled to produce a 10 Hz output, consisting of 2ns output pulses at 355nm, each with 1J of energy, in a Gaussian beam with a 1.9cm beam diameter (1/e2). Please contact TechSupport@thorlabs.com if you have any questions. [3] C. W. Carr et al., Phys. 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. These LIDT values are not valid for ultrashort pulses less thanone nanosecond in duration. When 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]. Response from Jeremy at Thorlabs: The 2" mounted lens do have the same outer diameter as the regular SM2 lens tube. Refer to the Application tab above for information about the superior performance of achromatic doublets compared to singlet lenses. Do they fit properly in the 2-inch tube clamps and slip rings, such as the SM2TC or SM2RC? Achromatic doublet lenses have a much reduced sensitivity to centration on the beam axis when compared to spherical singlets and aspheric lenses. 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 inW/cm. [1] R. M. Wood, Optics and Laser Tech. These achromats are infinity-corrected, meaning they're designed to have collimated light on one side, and focused or divergent light from the other side. The engraved arrow points from the side of the lens with the larger radius of curvature (flatter side) to the side with the smaller radius of curvature and indicates the recommended direction of light propagation to collimate a point source. We do not have tested data for CW light but we have some guidelines to provide based on a 1mm diameter beam: When pulse lengths are between 1 ns and 1 s, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). They will fit into the SM2RC and SM2TC. For data presented here, a <1 mm beam size was used to measure the LIDT. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration: This adjustmentfactor results in LIDT values of 0.45J/cm2 for the BB1-E01 broadband mirror and 1.6J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7J/cm2maximum energy density of the beam. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3383&pn=SM2L10#213. [4] N. Bloembergen, Appl. For more information on cleaning optics, please see our Optics Cleaning tutorial. Thanks! A plot of MTF shows the percentage of contrast as the spacing between these lines decreases. Capacity: 10), M-F: 8 AM - 8 PM EDT, Sat: 9 AM - 1 PM EDT, 400 - 700 nm Unmounted Achromatic Doublets, 400 - 1100 nm Unmounted Achromatic Doublets, 650 - 1050 nm Unmounted Achromatic Doublets, 1050 - 1700 nm Unmounted Achromatic Doublets, 400 - 1100 nm Mounted Achromatic Doublets, 650 - 1050 nm Mounted Achromatic Doublets, 1050 - 1700 nm Mounted Achromatic Doublets, Technical Support: techsupport@thorlabs.com, Click on the red Document icon next to the item numbers below to access the Zemax file download. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. In this regime, the LIDT given as anenergy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. The chart shows the theoretical MTF for our 25.4 mm, f=200 mm near IR achromatic doublet. I will reach out to you directly to discuss your application. Dear Sir or Madam, If you need this information at a particular wavelength, I can get this for you using Zemax. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. Rev. This calculator assumes a Gaussianbeam profile, so a correction factor must be introduced for other beam shapes (uniform, etc.). Achromatic optics with customer-defined sizes, focal lengths, substrate materials, cement materials, and coatings are all available as customs. Since the lens is secured using SM2RR retaining ring without any epoxy, unmounting the lens is indeed possible using the SPW604 spanner wrench. This system falls somewhere between the regimes of CW and pulsed laser induced damage, and could potentially damage an optic by mechanisms associated with either regime. Thanks again for taking the time to comment and to help us improve the information we provide. I need the infinite conjugate face to be coupled into an SM1 tube system. A histogram such as that below represents the testing of one BB1-E02 mirror. I have bought such lenses. According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, 0.803 mm). -C coated doublets (1050 - 1620nm): 1542nm, 200W/cm^2 I've added the threading size to all of the product descriptions on this page, and will see that all of our mounted optics descriptions are updated soon. In the mount there is 4.8mm from the 41.3mm radiused surface to the edge of the housing. The circle surrounding the distribution of ray intercepts represents the diameter of the Airy disk. In addition, we can offer optics that exceed the specifications of our stock catalog offerings. In order to illustrate the process of determining whether a given laser system will damage an optic, a number of example calculations oflaser induced damage threshold are given below. To receive more information or inquire about a custom order, please contact Tech Support. In the specification tables below, a positive radius of curvature indicates that the surface is opening to the right when the lens is oriented as shown in the reference drawing while a negative radius of curvature indicates that the surface is opening to the left. Or should I search for another source of wavefront distortion in my setup? 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.
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