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. The pulsed LIDTof the opticis significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. 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. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. Thank you very much! The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. The optic is exposed in 10 locations to this laser beam for 30 seconds (CW) or for a number of pulses (pulse repetition frequency specified). For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. Substrate materials often have multiple names, which vary depending upon the supplier of the bulk material. 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. For the 0.5" version a value of 27.5mm is listed. Thank you for participating in our feedback forum. Is there also a tested CW damage threshold for these achromat doublets? 12, 661 (1973). 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%. 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. While the broadband mirror wouldlikely be damaged by the laser, the more specialized laser line mirror isappropriate for use with this system. 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. So, the maximum energy density of this beam is ~0.7J/cm2. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. In addition, we can offer optics that exceed the specifications of our stock catalog offerings. 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? When using a white light source with a singlet lens, the focal point and circle of least confusion are blurred by chromatic aberration. 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. Hello, thank you for contacting Thorlabs. 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. Spherical and Chromatic aberrations will be most significantly increased in reverse, and the change is expected to be more noticeable for shorter focal lengths. Or use Achromat and drop Doublet, either way freeing up room to include the thread size on the mounting cell. Theoretical MTF shows how well a design can perform if the optic was built exactly to the design dimensions. As the contrast diminishes, the distinction between lines begins to blur. 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. 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). Damage threshold specifications are constant for all A-coated achromatic doublets, regardless of the size or focal length of the lens. Lett. 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 MTF shows the percentage of contrast as the spacing between these lines decreases. 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). 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. Thanks again for taking the time to comment and to help us improve the information we provide. 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. 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. 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. 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. I realized, that I mounted many achromatic doublets in my 4f imaging systems with the wrong orientation. 29, 517 (1998). Could you clarify from where f_b is measured, and whether it should be measured in the opposite direction to that drawn? Since the spot size is drawn using geometric ray tracing, spots much smaller than the Airy disk are not achievable due to diffraction. 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. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=1524&pn=SM2A6#3428. MTF curves calculated in Zemax typically present a weighted average with contributions from multiple wavelengths and are known as polychromatic MTF curves. There is 2.8mm from the -137.1mm radiused surface to the end of the external thread. For best performance, the side of the lens with the largest radius of curvature (flattest side) should face away from the collimated beam. LIDT in linear power density vs. pulse length and spot size. 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. Edge of housing to focal point is then ~70.09mm. This solution will allow you to easily thread in the SM2 to SM1 adapter(SM2A6). For the target selected, the contrast measured 82.3%. The calculation above assumes a uniform beam intensity profile. 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. Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. 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? Now compare the maximum power density to that which is specified as the LIDT for the optic. Most of the materials listed here are the Schott glass types with the exceptions of, Common microscope tube lens focal lengths. (532 nm, 10 ns pulse, 10 Hz, 0.566 mm). Chromatic aberration is due to the variation of refractive index with respect to wavelength. Below are some examples of how the performance of these lenses can be examined using the Zemax files. 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. These LIDT values are not valid for ultrashort pulses less thanone nanosecond in duration. 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. The screen captures to the right and left are actual measurements taken using a USAF 1951 resolution chart as the object. 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. For more information on cleaning optics, please see our Optics Cleaning tutorial. The figures also shows how the circle of least confusion for white light is reduced by using an achromatic doublet. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values. [4] N. Bloembergen, Appl. 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. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. Our entire, Achromatic Performance with AR Coating for 400 - 700 nm. I will reach out to you directly. For example, in Figure 2, a plot of the wavefront at the image plane reveals information regarding aberration correction by using the AC254-125-C. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately [3]. For applications that require higher damage thresholds, please consider our, The power density of your beam should be calculated in terms of W/cm. In this regime, the LIDTgiven as a linear power densitycan 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. In reality, most optics fall short of the theoretical due to manufacturing tolerances. Contrast at 100% would consist of perfectly black and white lines. 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. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. AC508-200-A: 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. The materials listed here are the Schott glass types. 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. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). For reference a Gaussian beam typically has a maximum energydensity that is twice that of the 1/e2 beam. The damage threshold of cemented achromatic doublets is limited by the cement. Achromatic optics with customer-defined sizes, focal lengths, substrate materials, cement materials, and coatings are all available as customs. 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. 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. Response from Buki at Thorlabs to r.m.dijkstra: 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. 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. Opt. Substrate materials often have multiple names, which vary depending upon the supplier of the bulk material. Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. SM2L10: By doublets with a focal lenght >30 mm, I actually could not see any difference in image quality even though they were placed wrongly. Use the SPW801Adjustable Spanner Wrench to incorporate the 5 mm, 6 mm, and 6.35 mm lenses into adapters and lens tube systems. This specification is also commonly referred to as surface fit. Therefore, a more accurate determination of the maximum linear power density of the system is 1W/cm. Achromatic doublet lenses have a much reduced sensitivity to centration on the beam axis when compared to spherical singlets and aspheric lenses. For other products like achromatic triplets or cylindrical achromatic doublets there are focal length shift data available. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3383&pn=SM2L10#213. 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. This is the plane from which it is measured in the diagram. 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). For long pulses to CW, linear power density becomes a constant with spot size. I need the infinite conjugate face to be coupled into an SM1 tube system. And the reference plane from which f_b is measured is unclear. 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. 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. The specifications to the right are measured data for Thorlabs' A-coated achromatic doublets. Upon request, we can provide individual test information and a testing certificate. Both of these LIDT values, while measured at 355nm, were determined with a 10ns pulsed laser at 10Hz. The pulse length must now be compensated for. 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. 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. Negative values are measured from the left side of the lens. Working Distance is measured from the endof the externally threaded side of the mount, as shown in the reference drawing. 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. This graph was obtained from [1]. It is important to note that these lenses use spherical, not aspheric surfaces. Is it possible that you looked at the 0.5" version? This graph was obtained from [1]. Thorlabs' Cemented Visible Achromatic Doublets are available pre-mounted in engraved threaded mounts, making it easy to incorporate these optics into your setup. The circle surrounding the distribution of ray intercepts represents the diameter of the Airy disk. Thorlabs' achromatic doublets are optimized to provide a nearly constant focal length across a broad bandwidth. Dear Sir or Madam, 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. Beam diameter is also important to know when comparing damage thresholds. The spacing between the lines at the object is usually represented as spatial frequency given in cycles/mm. Best regards Edge of housing to focal point is then ~68.86mm. Is the off-axis and aspheric performance of 2" achromatic doublets superior compared to 1" optics of the same kind? As a result, both CW and pulsed LIDT values must be compared to the properties of the laser system to ensure safe operation. Hello, thank you for contacting Thorlabs. In this example, the wavefront error is theoretically on the order of 3/100 of a wave. I will email you an excel file that provides the focal length shift data you saw posted in our family image. As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right). 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. 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 represents 83% contrast at0.05 mm spacings between lines. Whether your application has demanding imaging requirements or laser beam manipulation needs, these doublets should be considered. 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. Yet the back focal plane must be located on the opposite side of the lens to where it is drawn. The LIDT scaling laws are determined from empirical relationships; their accuracy is not guaranteed. 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. Now compare the maximum energy density to that which is specified as the LIDT for the optic. A plot of the modulation transfer function is used as both a theoretical and experimental description of image quality. 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. Thanks for your help. Use the SPW801Adjustable Spanner Wrench to incorporate the 8 mm lenses into adapters and lens tube systems. Are the mounted 2-inch lenses mounted in the same kind of lens tubes (SM2L05, SM2M10, etc.) The contrast is around 83% at a spatial frequency of about 20 cycles/mm. Mounts smaller than 1/2" are engraved with the part number only. Where is the Focus (backward/forward) in relation to the edges of the housing? I am wondering about the outside diameter of the (engraved) tubes used for the mounted lenses. 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. 91, 127402 (2003). 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). 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. Do they fit properly in the 2-inch tube clamps and slip rings, such as the SM2TC or SM2RC? http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=120&pn=AC508-200-A#3597. 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. Testing may result in additional costs or lead times. The AC508-200-A-ML uses a 0.5" long lens tube, and due to the thickness of the lens itself, there is very little usable thread. If the spot is within the Airy disk, the lens is typically considered to be diffraction limited. 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. Positive values are measured from the right side of the lens as shown in the reference drawing.
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