A response from Laurie at Thorlabs to Simone.Rupp: Thank you for the comments you left on our website concerning our Mounted Visible Achromatic Doublets. 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. Reply from Sean at Thorlabs: Thank you for your feedback on our website presentation! Thanks. 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). 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. After exposure, the optic is examined by a microscope (~100X magnification) for any visible damage. [3] C. W. Carr et al., Phys. 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-E01broadband dielectric mirror and an NB1-K08Nd:YAG laser line mirror, respectively. The spacing between the lines at the object is usually represented as spatial frequency given in cycles/mm. Thorlabs' Cemented Visible Achromatic Doublets are available pre-mounted in engraved threaded mounts, making it easy to incorporate these optics into your setup. Pulsed Nanosecond Laser Example: Scaling for Different WavelengthsSuppose that a pulsed laser system emits 10 ns pulses at 2.5 Hz, each with 100 mJ of energy at 1064 nm in a 16 mm diameter beam (1/e2) that must be attenuated with a neutral density filter. A naive calculation of the average linear power density of this beam would yield a value of 0.5W/cm, given by the total power divided by the beam diameter: 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. This calculation assumes a uniform beam intensity profile. I realized, that I mounted many achromatic doublets in my 4f imaging systems with the wrong orientation. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. Whether your application has demanding imaging requirements or laser beam manipulation needs, these doublets should be considered. Thanks! When using a white light source with a singlet lens, the focal point and circle of least confusion are blurred by chromatic aberration. For the mounted Doublets it would be nice if you could drop the word Achromatic from the descirption and include the thread size on the cell instead. Is the off-axis and aspheric performance of 2" achromatic doublets superior compared to 1" optics of the same kind? Theoretical MTF shows how well a design can perform if the optic was built exactly to the design dimensions. That said, the aberrations will likely be different between a 1" and 2" version of the same focal length as they are not identical even within 1" of the center. Remember that absorption by optics or coatings can significantly reduce LIDT in some spectral regions. Yet the back focal plane must be located on the opposite side of the lens to where it is drawn. If the spot is within the Airy disk, the lens is typically considered to be diffraction limited. Response from Tim at Thorlabs: ~68.9mm and ~70.1mm. Use the SPW801Adjustable Spanner Wrench to incorporate the 5 mm, 6 mm, and 6.35 mm lenses into adapters and lens tube systems. 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. Substrate materials often have multiple names, which vary depending upon the supplier of the bulk material. 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 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. The number of locations that are damaged at a particular power/energy level is recorded. 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. Chromatic aberration is due to the variation of refractive index with respect to wavelength. Pulsed lasers with pulse lengths longer than 1 s can be treated as CW lasers for LIDT discussions. The figures also shows how the circle of least confusion for white light is reduced by using an achromatic doublet. Dispersion in the first (positive) element of the doublet is corrected by the second (negative) element, resulting in better broadband performance than spherical singlets or aspheric lenses. 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. The spot (circle of least confusion) from the doublet is 4.2 times smaller than the singlet spot size. Thanks again for taking the time to comment and to help us improve the information we provide. The damage threshold of an NDUV10A25 mm, OD 1.0, reflective neutral density filter is 0.05 J/cm2for 10 ns pulses at355nm, while the damage threshold of the similar NE10Aabsorptive filter is 10 J/cm2 for 10 ns pulses at 532 nm. Jale. A response from Adam at Thorlabs to a.heinrici: The infinite conjugate plate is located on the opposite side of the threaded portion of the mount. Please see our Visible Achromatic Doublets to purchase these lenses unmounted. 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 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. Hello, could you please also give front focal length information (eg as front WD) for the use of these lenses in 4f-configurations (I'd be interested in AC254-100 and AC512-150 in particular). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. This is why we don't spec a back-focal length as you've described. 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]. Or should I search for another source of wavefront distortion in my setup? Response from Buki at Thorlabs to r.m.dijkstra: Response from Bweh E at Thorlabs: We do provide the front and back focal lengths information for these lenses which you can use in a 4f imaging configuration. For applications in wavelength regimes less than 410nm, Thorlabs air-gap UV doublets provide excellent performance down to 240 nm. The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. Or use Achromat and drop Doublet, either way freeing up room to include the thread size on the mounting cell. [2] Roger M. Wood, Laser-Induced Damage of Optical Materials (Institute of Physics Publishing, Philadelphia, PA, 2003). [4] N. Bloembergen, Appl. 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. 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 beams with a high PRF both the average and peak powers must be compared to the equivalent CW power. The power density of your beam should be calculated in terms of W/cm. Do they fit properly in the 2-inch tube clamps and slip rings, such as the SM2TC or SM2RC? This represents 83% contrast at0.05 mm spacings between lines. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=120&pn=AC508-200-A#3597. 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. 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. For short pulses, energy density becomes a constant with spot size. 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. In this case, the absorptive filter is the best choice in order to avoid optical damage. Upon request, we can provide individual test information and a testing certificate. 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. A plot of MTF shows the percentage of contrast as the spacing between these lines decreases. 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 specifications to the right are measured data for Thorlabs' A-coated achromatic doublets. I would suggest purchasing the unmounted version of this lens (AC508-200-A) and mounting this into a 1" long lens tube (SM2L10). This graph was obtained from [1]. SM2A6: Please see the diagram under the reference drawing link below for details. Best regards 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. Response from Javier at Thorlabs to nkaddy: Thank you very much for submitting your request. As the contrast diminishes, the distinction between lines begins to blur. Additionally, for highly transparent materials, there is little to no drop in the LIDT with increasing PRF. SM2L10: An AC127-030-Cachromatic doublet lens has a specified CW LIDT of 350 W/cm, as tested at 1550 nm. A ray trace for spot size at the image plane of the AC254-250-C is shown below in Figure 3. Most of the materials listed here are the Schott glass types with the exception of. It would be very useful for me, possibly also for others, if those plot data (ideally for all the lenses, but at least the data used for the example plot of AC254-100-A) were made available. 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. This can be compared to the LIDT valuesfor aWPQ10E-980polymer zero-order quarter-wave plate, which are 5W/cm for CW radiation at 810nm and 5 J/cm2 for a 10 ns pulse at 810 nm. Our entire, Achromatic Performance with AR Coating for 400 - 700 nm. 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. Please contact TechSupport@thorlabs.com if you have any questions. 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. Where is the Focus (backward/forward) in relation to the edges of the housing? There is 2.8mm from the -137.1mm radiused surface to the end of the external thread. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). 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. A histogram such as that below represents the testing of one BB1-E02 mirror. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances. 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? 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]. Most of the materials listed here are the Schott glass types with the exceptions of, Common microscope tube lens focal lengths. The pulsed LIDTof the opticis significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. Testing may result in additional costs or lead times. However, on Achromats with 7.5 and 10 mm, the wrong orinetation seems to cause severe waverfront distortions. Average linear power density can be calculated using the equation below. In addition, they offer better broadband and off-axis performance than aspheric lenses. (532 nm, 10 ns pulse, 10 Hz, 0.566 mm). In CW applications, for instance, damage scales more strongly with absorption in the coating and substrate, which does not necessarily scale well with wavelength. A plot of the modulation transfer function is used as both a theoretical and experimental description of image quality. 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). Response from Jeremy at Thorlabs: The 2" mounted lens do have the same outer diameter as the regular SM2 lens tube. LIDT in linear power density vs. pulse length and spot size. Use the SPW801Adjustable Spanner Wrench to incorporate the 8 mm lenses into adapters and lens tube systems. In addition, we can offer optics that exceed the specifications of our stock catalog offerings. This specification is also commonly referred to as surface fit. These achromatic doublets, which are designed for use in the visible spectral region (400 - 700 nm), are computer optimized at infinite conjugate ratios. For a Gaussian output, these specifications result in a maximumenergy density of 0.1 J/cm2. 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). Dear Sir or Madam, The LIDT for an optic greatly depends on the type of laser you are using. 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. Rev. The MTF of a lens describes its ability to transfer contrast from an object to an image at various resolution levels. The pulse length must now be compensated for. Edge of housing to focal point is then ~70.09mm. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3383&pn=SM2L10#213. I did not manage to find out in which direction is the finite and in which the infinite conjugate is, Mounted Achromatic Doublets, AR Coated: 400 - 700 nm, f=7.5 mm, 5 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=10 mm, 5 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=15 mm, 5 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=10 mm, 6 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=13 mm, 6.35 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=15 mm, 6.35 mm Achromatic Doublet, M9x0.5 Threaded Mount, ARC: 400-700 nm, f=10 mm, 8 mm Achromatic Doublet, M12x0.5 Threaded Mount, ARC: 400-700 nm, f=16 mm, 8 mm Achromatic Doublet, M12x0.5 Threaded Mount, ARC: 400-700 nm, f=20 mm, 8 mm Achromatic Doublet, M12x0.5 Threaded Mount, ARC: 400-700 nm, f=30 mm, 8 mm Achromatic Doublet, M12x0.5 Threaded Mount, ARC: 400-700 nm, f=19 mm, 1/2" Achromatic Doublet, SM05-Threaded Mount, ARC: 400-700 nm, f=25 mm, 1/2" Achromatic Doublet, SM05-Threaded Mount, ARC: 400-700 nm, f=30 mm, 1/2" Achromatic Doublet, SM05-Threaded Mount, ARC: 400-700 nm, f=50 mm, 1/2" Achromatic Doublet, SM05-Threaded Mount, ARC: 400-700 nm, f=75 mm, 1/2" Achromatic Doublet, SM05-Threaded Mount, ARC: 400-700 nm, f=30 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=35 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=40 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=45 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=50 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=60 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=75 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=80 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=100 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=125 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=150 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=200 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=250 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=300 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=400 mm, 1" Achromatic Doublet, SM1-Threaded Mount, ARC: 400-700 nm, f=500 mm, 1" Achromatic Doublet, SM1-Threaded Mount. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. Below are some examples of how the performance of these lenses can be examined using the Zemax files. This lens can be mounted on any of our SM2-threaded mounts, for example the LMR2. The materials listed here are the Schott glass types. 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.). Edge of housing to focal point is then ~68.86mm. The screen captures to the right and left are actual measurements taken using a USAF 1951 resolution chart as the object. For other products like achromatic triplets or cylindrical achromatic doublets there are focal length shift data available. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. The graph below shows the paraxial focal shift as a function of wavelength for the AC254-400-A, which is a 400 mm focal length, 25.4 mm achromatic doublet AR coated for the 400 - 700 nm range. 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. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. Is it possible that you looked at the 0.5" version? For reference a Gaussian beam typically has a maximum energydensity that is twice that of the 1/e2 beam. MTF curves calculated in Zemax typically present a weighted average with contributions from multiple wavelengths and are known as polychromatic MTF curves. Therefore, a more accurate determination of the maximum linear power density of the system is 1W/cm. Additionally, a member of my team is currently working to add this information to the web page. These LIDT values are not valid for ultrashort pulses less thanone nanosecond in duration. 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. Contact Tech Support for more information. Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. We also offer an infinity corrected tube lens with f = 200 mm, Substrate materials often have multiple names, which vary depending upon the supplier of the bulk material. This solution will allow you to easily thread in the SM2 to SM1 adapter(SM2A6). The chart shows the theoretical MTF for our 25.4 mm, f=200 mm near IR achromatic doublet. 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. In the mount there is 4.8mm from the 41.3mm radiused surface to the edge of the housing. Substrate materials often have multiple names, which vary depending upon the supplier of the bulk material. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=1524&pn=SM2A6#3428. 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. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. -A coated doublets (4000 - 700nm): 532nm, 100W/cm^2 Refer to the Application tab above for information about the superior performance of achromatic doublets compared to singlet lenses. I will reach out to you directly. In reality, most optics fall short of the theoretical due to manufacturing tolerances. Or are they only tested with a pulsed source as given by the specs? Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). 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. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right). I have bought such lenses. Thorlabs' spherical doublet lenses have been corrected for various aberrations, including spherical aberration, chromatic aberration, and coma. I'm having trouble understanding the lens reference diagram. For more information on cleaning optics, please see our Optics Cleaning tutorial. 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. Damage threshold specifications are constant for all A-coated achromatic doublets, regardless of the size or focal length of the lens. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values. The figures below show two 50.0 mm focal length lenses, one plano-convex and the other an achromatic doublet. Unfortunately, it can be very difficult to compare the LIDT specification of an optic to your laser. From the center of the 41.3mm radiused surface to the focal point it is 73.66mm. Hi, Contact Tech Support for more information. 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%. So, the maximum energy density of this beam is ~0.7J/cm2. Achromatic doublets are useful for controlling chromatic aberration and are frequently used to achieve a diffraction-limited spot when using a monochromatic source like a laser. Although you can use it backward/forward, using in the engraved direction will reduce aberrations by keeping the more curved side towards infinity. Detailed information regarding each achromatic doublet can be found in the Zemax files included with the support documents for each doublet. [1] R. M. Wood, Optics and Laser Tech. For an explanation of why the linear power density provides the best metric for long pulse and CW sources, please see the "Continuous Wave and Long-Pulse Lasers" section below. This indicates that the optical path length difference (OPD) is extremely small for rays going through the center of the lens and at nearly full aperture. In an achromatic doublet this effect is somewhat compensated for by using glasses of two different refractive indexes to cancel these aberrations. From the center of the -137.1mm radiused surface to the focal point is 72.89mm. As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Both are 25.4 mm lenses with a 3 mm beam through the optical axis and one offset by 8.0 mm. There is not a general rule about which will have better performance. 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 longer the pulse duration, the more energy the optic can handle. For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application. Except for AC080-030-ML, AC508-75-A-ML, ACT508-200-A-ML, ACT508-250-A-ML, ACT508-300-A-ML, ACT508-400-A-ML. CW Laser ExampleSuppose that a CW laser system at 1319 nm produces a 0.5 W Gaussian beam that has a 1/e2 diameter of10 mm. The figures below show a comparison of a plano-convex singlet focusing a 633 nm laser beam and an achromatic doublet focusing the same laser beam. Are the mounted 2-inch lenses mounted in the same kind of lens tubes (SM2L05, SM2M10, etc.) The design wavelengths used are the helium "d" (587.6 nm, yellow), hydrogen "F" (486.1 nm, blue/green), and hydrogen "C" (656.3 nm, red) lines since they reasonably represent the visible spectrum and are used to define the Abbe Number, Vd, of a material. Back-focal length can be an ambiguous term which can refer to two distinct measurements; either the focal length in reverse direction, or (as in this case) the focal distance as measured from the last optical surface along the optical axis. Please note there is an engraving which indicates the direction of light to collimate a point source. Lateral and transverse aberrations are greatly reduced by the achromatic doublet. This is accomplished by utilizing a multi-element design to minimize the chromatic aberration of the lens. 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. Therefore, an adjustment must be applied for the shorter pulse duration of the system under consideration.

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