Reflective Beam Expanders: 2X, 4X, and 6X
 Expand or Reduce Polychromatic Beams
 Protected Silver Mirrors for 450 nm to 20 µm
 2X, 4X, and 6X Magnifications
 Compatible with Cage Systems and Lens Tubes
BE06R
6X Magnification
BE02R
2X Magnification
Input Beam is Angled
Relative to Output Beam
Please Wait
Click to Enlarge
Alignment into BE04R Beam Expander using CPA1 Alignment Plate, SM1D12D RingActivated Iris, and 30 mm Cage Rods
Features
 Enlarge or Reduce the Diameter of a Collimated Beam by a Fixed Ratio
 2X, 4X, and 6X Options
 Chromatic Compensation Provided by Spherical Mirrors (See Left Graph Below)
 High Transmission from 450 nm to 20 μm
 Max Input Beam Diameter (1/e^{2}) of 3 mm for DiffractionLimited Performance
Thorlabs' Reflective Beam Expanders use a pair of prealigned protectedsilvercoated spherical mirrors to provide 2X, 4X, or 6X beam expansion or reduction. Unlike our transmissive beam expanders, they exhibit virtually zero chromatic aberration (as shown in the left graph below), making them especially suitable for broadband sources. The protected silver mirrors provide high reflectance over a broad spectral range (R_{avg} > 97.5% from 450 nm  2 µm and R_{avg} > 96% from 2 µm  20 µm), minimize the phase delays and absorption losses introduced by transmissive optics, and offer a low wavefront error of λ/10 (see the Specs tab for details). One particularly useful application of a reflective beam expander is to reduce the diameter of a polychromatic beam and then couple the light into multimode fiber using a reflective collimator.
Cage System and Lens Tube Compatibility  

Item #  BE02R(/M)  BE04R(/M)  BE06R(/M)  
Magnification  2X  4X  6X  
Input Port  Cage System  16 mm  16 mm  30 mm 
Lens Tube  SM05  SM05  SM05  
Output Port  Cage System  16 mm  30 mm  30 mm 
Lens Tube  SM05  SM1  SM30 
To simplify alignment, the input and output ports of each beam expander feature SM05 (0.535"40), SM1 (1.035"40), or SM30 (M30.5 x 0.5) threading for compatibility with our SMthreaded lens tubes, as well as four 440 tapped holes for compatibility with our 16 mm and 30 mm cage systems. The SM threading and cage compatibility of each beam expander is detailed in the table to the left.
To secure the reflective beam expanders to an optical table, use two CL2(/M), CL3(/M), or CL6 Table Clamps to hold the lip of the housing against the table's surface. The BE04R and BE06R beam expanders also feature through holes that accept 1/4"20 and M6 cap screws, which can be used to mount the beam expander to the table or elevate the beam expander in combination with Ø1" Pedestal Pillar Posts. If vertical mounting is desired, each reflective beam expander includes a mounting plate with four 832 (M4) tapped holes at 1" (25 mm) spacings, suitable for connecting the housing to Ø1/2" Posts.
Thorlabs also manufactures many other types of beam expanders, including Galilean beam expanders with variable or fixed zoom ratios. Both sliding and rotating adjustment mechanisms are available. For more information, please visit the Beam Expanders tab.
Click to Enlarge
The graph above shows that the BE02R's reflective design minimizes chromatic aberration. A diopter is a unit of measurement proportional to the reciprocal of the focal length.
Click to Enlarge
Excel Spreadsheet with Raw Data for Protected Silver
The graph above shows the reflectance per surface for unpolarized light. The shaded region denotes the range over which we recommend using these beam expanders.
Item #  BE02R(/M)  BE04R(/M)  BE06R(/M)  

Magnification  2X  4X  6X  
Reflectance^{a} (Avg.)  450 nm  2 µm: >97.5% 2  20 µm: >96% 

Max Input Beam Diameter^{b} (1/e^{2})  3 mm  
Wavefront Error (RMS)  λ/10 for a Ø1.5 mm Input Beam 
λ/10 for a Ø1.0 mm Input Beam 
λ/10 for a Ø0.5 mm Input Beam 

Angle Between Input and Output Beams 
11°  14°  16.4°  
Clear Input Aperture  Ø6 mm  
Surface Quality  4020 ScratchDig  
Damage Threshold  Pulsed  3 J/cm^{2} (1064 nm, 10 ns, 10 Hz, Ø1.000 mm)  
CW  500 W/cm (1.07 µm, Ø0.974 mm) 1500 W/cm (10.6 µm, Ø0.339 mm) 

Mirror Substrate  NBK7 
Excel Spreadsheet with Raw Data for Protected Silver
The graph above shows the reflectance per surface. The shaded region denotes the range over which we recommend using these beam expanders.
Excel Spreadsheet with Raw Data for BExxR(/M)
The graph above shows the simulated peaktovalley (PV) reflected wavefront error in units of wavelength for the BE02R(/M), BE04R(/M), and BE06R(/M) reflective beam expanders.
Damage Threshold Specifications  

Mirror Coating Designation  Damage Threshold 
P01 (Pulsed)  3 J/cm^{2} (1064 nm, 10 ns, 10 Hz, Ø1.000 mm) 
P01 (CW^{a})  500 W/cm (1.07 µm, Ø0.974 mm) 1500 W/cm (10.6 µm, Ø0.339 mm) 
Damage Threshold Data for Thorlabs' Protected Silver Mirrors
The specifications to the right are measured data for Thorlabs' Protected Silver Mirrors, which are used inside our Reflective Optical Beam Expanders. Damage threshold specifications are constant for a given coating type, regardless of the size of the mirror.
Laser Induced Damage Threshold Tutorial
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. 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 scratchdig 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 Method
Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.
First, a lowpower/energy beam is directed to the optic under test. 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). After exposure, the optic is examined by a microscope (~100X magnification) for any visible damage. The number of locations that are damaged at a particular power/energy level is recorded. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. This process is repeated until damage is observed. The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. A histogram such as that below represents the testing of one BB1E02 mirror.
The photograph above is a protected aluminumcoated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm^{2} (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage.
Example Test Data  

Fluence  # of Tested Locations  Locations with Damage  Locations Without Damage 
1.50 J/cm^{2}  10  0  10 
1.75 J/cm^{2}  10  0  10 
2.00 J/cm^{2}  10  0  10 
2.25 J/cm^{2}  10  1  9 
3.00 J/cm^{2}  10  1  9 
5.00 J/cm^{2}  10  9  1 
According to the test, the damage threshold of the mirror was 2.00 J/cm^{2} (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 LongPulse Lasers
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]. 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, laserinduced 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.
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:
 Wavelength of your laser
 Beam diameter of your beam (1/e^{2})
 Approximate intensity profile of your beam (e.g., Gaussian)
 Linear power density of your beam (total power divided by 1/e^{2} beam diameter)
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 nonuniform 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 Lasers
As 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 ultrashortpulse regime various mechanics, such as multiphotonavalanche 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.
Pulse Duration  t < 10^{9} s  10^{9} < t < 10^{7} s  10^{7} < t < 10^{4} s  t > 10^{4} s 

Damage Mechanism  Avalanche Ionization  Dielectric Breakdown  Dielectric Breakdown or Thermal  Thermal 
Relevant Damage Specification  No Comparison (See Above)  Pulsed  Pulsed and CW  CW 
When comparing an LIDT specified for a pulsed laser to your laser, it is essential to know the following:
 Wavelength of your laser
 Energy density of your beam (total energy divided by 1/e^{2} area)
 Pulse length of your laser
 Pulse repetition frequency (prf) of your laser
 Beam diameter of your laser (1/e^{2} )
 Approximate intensity profile of your beam (e.g., Gaussian)
The energy density of your beam should be calculated in terms of J/cm^{2}. 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/e^{2} 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/cm^{2} at 1064 nm scales to 0.7 J/cm^{2} at 532 nm):
You now have a wavelengthadjusted 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).
[2] Roger M. Wood, LaserInduced Damage of Optical Materials (Institute of Physics Publishing, Philadelphia, PA, 2003).
[3] C. W. Carr et al., Phys. Rev. Lett. 91, 127402 (2003).
[4] N. Bloembergen, Appl. Opt. 12, 661 (1973).
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
Suppose that a CW laser system at 1319 nm produces a 0.5 W Gaussian beam that has a 1/e^{2} diameter of 10 mm. A naive calculation of the average linear power density of this beam would yield a value of 0.5 W/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. Therefore, a more accurate determination of the maximum linear power density of the system is 1 W/cm.
An AC127030C 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
Suppose that a pulsed Nd:YAG laser system is frequency tripled to produce a 10 Hz output, consisting of 2 ns output pulses at 355 nm, each with 1 J of energy, in a Gaussian beam with a 1.9 cm beam diameter (1/e^{2}). 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. So, the maximum energy density of this beam is ~0.7 J/cm^{2}.
The energy density of the beam can be compared to the LIDT values of 1 J/cm^{2} and 3.5 J/cm^{2} for a BB1E01 broadband dielectric mirror and an NB1K08 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/cm^{2} for the BB1E01 broadband mirror and 1.6 J/cm^{2} for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm^{2} 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
Suppose 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/e^{2}) that must be attenuated with a neutral density filter. For a Gaussian output, these specifications result in a maximum energy density of 0.1 J/cm^{2}. The damage threshold of an NDUV10A Ø25 mm, OD 1.0, reflective neutral density filter is 0.05 J/cm^{2} for 10 ns pulses at 355 nm, while the damage threshold of the similar NE10A absorptive filter is 10 J/cm^{2} for 10 ns pulses at 532 nm. As described on the previous tab, the LIDT value of an optic scales with the square root of the wavelength in the nanosecond pulse regime:
This scaling gives adjusted LIDT values of 0.08 J/cm^{2} for the reflective filter and 14 J/cm^{2} for the absorptive filter. In this case, the absorptive filter is the best choice in order to avoid optical damage.
Pulsed Microsecond Laser Example
Consider a laser system that produces 1 µs pulses, each containing 150 µJ of energy at a repetition rate of 50 kHz, resulting in a relatively high duty cycle of 5%. 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. As a result, both CW and pulsed LIDT values must be compared to the properties of the laser system to ensure safe operation.
If this relatively longpulse laser emits a Gaussian 12.7 mm diameter beam (1/e^{2}) 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/cm^{2} per pulse. This can be compared to the LIDT values for a WPQ10E980 polymer zeroorder quarterwave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm^{2} 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/cm^{2} 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 highpower CW beam.
Posted Comments:  
Clayton Bargsten
(posted 20210612 20:55:34.547) I see others asked about astig and wavefront errors introduced by using spheres offaxis years ago. This vital information really should be displayed by now. Can you please post plots of the distortions across the entire rated aperture (not just some tiny fraction of it that is below L/10)? I'd appreciate receiving this information quickly (esp for the 6x model) as I assume adding the info to the website will take time. Thank you.
As a suggestion: An asphere version would be a great addition to this product line to avoid aberrations  even if it is harder to align. cdolbashian
(posted 20210625 08:53:57.0) Thank you for reaching out to us at Thorlabs! I have contacted you directly regarding the design considerations, from financial to practical, taken when considering an aspheric reflective beam expander. Moreover, I have provided you with some blackbox files, usable for calculating the wavefront error over the full aperture size. Thank you for the feedback, and the suggestion for a future product! Comments like this are exactly how we expand the offerings in our catalogue. user
(posted 20210505 10:13:13.45) The mounting plate on the side of this part is listed as being 5mm thick but in the latest batch we received, it is 7mm thick. It seems your 3D model and drawings are now incorrect. YLohia
(posted 20210505 02:26:08.0) Thank you for noticing this. The product has been updated and the mounting plate is now 7mm thick, and unfortunately the drawings on the web has not been updated to reflect this change. We will update the drawings shortly. Gregory Futia
(posted 20200813 14:25:23.293) Are the threaded input and output ports guaranteed to be squared and centered on optimal alignment?
I have screwed irises ,SM1D12SZ at input and SM1D25 at output. After aligning the Airy patterns such that they close down at the same position the center of the expanded beam does not appear centered to the SM1D25 but slightly off. nbayconich
(posted 20200824 03:04:08.0) Thank you for your feedback. I will reach out to you directly to discuss your setup. Carlos Tapia Ayuga
(posted 20190606 05:46:28.313) Good morning,
In my laboratory we need a beam expander of 6x.
The laser that we use works on 10.6 um and with picosecond frequency. Is a 15kW laser.
We will use only with 2 or 3 fires.
The beam diameter is 1 mm, and the expander will be mounted at the exit of the laser.
What expander can you recommend us?
Thanks,
Carlos mdiekmann
(posted 20190619 09:40:08.0) Thank you for your feedback! We do not have data for ps pulses but we may be able to provide an estimation. The coating is our standard P01coating, so if you have used this laser with other mirrors with this coating, it should be suitable. You requested not to be emailed, so we kindly ask you to reach out to us at europe@thorlabs.com with the full laser parameters, and we will be happy to assist. user
(posted 20190320 12:15:00.81) Hi!
The smallest mirror in our expander (BE04R) seems to be damaged. Is there any possibility to purchase this mirror (i.e. the same model) to replace the damaged one? YLohia
(posted 20190408 11:03:07.0) Hello, we are sorry to hear about the damaged mirror. We have been in touch with you via email to gather the details of the damage and create an RMA case. Van Rudd
(posted 20190312 20:01:03.863) Do the protected silver mirrors in the beam expanders have the same CW damage level (500 W/cm^2) as your plano protected silver mirrors? mmcclure
(posted 20190314 08:03:19.0) Hello, thank you for contacting us. Yes, our reflective beam expanders use a pair of protectedsilvercoated (P01) mirrors, which have a CW damage threshold of 500 W/cm (1070 nm, Ø0.974 mm). We will add damage threshold values to the webpage. devans
(posted 20170612 13:36:06.313) Would it be possible to know the focus lengths of the mirrors? We are trying to model a system which incorporates the device we have bought. tfrisch
(posted 20170626 11:39:52.0) Hello, thank you for contacting Thorlabs. While the exact design of these beam expanders are proprietary, I can reach out to you with advice on how to best model it. Peh
(posted 20170601 23:08:26.17) Is it possible to buy the beam expander with uv enhanced Al coating? nbayconich
(posted 20170614 08:04:02.0) Thank you for contacting Thorlabs. We can provide these beam expanders with uvenhanced aluminum coating. I will contact you directly with more information. nd
(posted 20160224 09:57:36.44) PLease inform me if your product Reflective Optical Beam Expanders: 2X, 4X, and 6X is suitable for CO2 laser system, or not. besembeson
(posted 20160308 02:05:30.0) Response from Bweh at Thorlabs USA: The laser wavelength will be suitable. I will contact you regarding the power levels for your CO2 laser. The pulse damage threshold guide is 3.0 J/cm^2 at 1064nm, 10ns, 10Hz, Ø1.000 mm. cmrogers
(posted 20151007 17:53:19.923) Do you have information on the astigmatism introduced by using the spherical mirrors at nonnormal incidence? besembeson
(posted 20151014 08:56:39.0) Response from Bweh at Thorlabs USA: At normal incidence, there is only some spherical while at nonnormal incidence, distortion is dominant followed by astigmatism. It is highly recommended to align input beam properly. Beam will become truncated even for small nonnormal incidence angles. I will share Seidel diagrams for the BE04R via email at normal and 5deg incidence angles for comparison. tdzamba
(posted 20150826 16:05:27.637) Could you tell me the focal length of the two mirrors used? I am trying to understand the relationship between the angle of the incident and exit beams, if they are no exactly along boresight. Assume we are operating the beam expander in reverse (acting to reduce beam diameter). besembeson
(posted 20150925 04:09:38.0) Response from Bweh at Thorlabs USA: I will followup by email with this information. dmkim
(posted 20150826 09:43:57.32) If the input beam is not perfectly collimated, can the mirrors be adjusted to compensate for this? besembeson
(posted 20150925 03:49:47.0) Response from Bweh at Thorlabs USA: Adjusting the mirrors to compensate for "not perfectly collimated" beam is not possible. borondics.accounts
(posted 20150314 21:59:07.76) Hi,
I was wondering why you don't go through a focus? Just to save space or there is an optics reason for that too?
Are these spherical mirrors or parabolic?
Thanks! besembeson
(posted 20150421 06:56:56.0) Response from Bweh at Thorlabs USA: These utilize spherical mirrors, concave and convex combinations. With high power beams, going through the focus can lead to air ionization at the focus as the air super heats. bolek.zapiec
(posted 20140717 19:09:07.087) HI, Could you please verify that the BE02R/M is able to contract a beam ~5.5mm in diameter down to ~2.75mm in diffraction limited performance? Thanks besembeson
(posted 20140807 03:34:54.0) Response from Bweh E at Thorlabs. These expanders can be used to reduce beam diameters but one should always keep in mind that also the divergence will be increased (2X in your case) while doing this. The magnification factor of a beam expander is also the factor by which the beam is getting more divergent when used in reverse for beam reduction.
So depending on your input beam divergence the output beam will not stay 2.75mm for long time but will expand again and in worst case might be clipped at the housing. There is a certain distance between the mirrors and the housing edge.
In addition, there will be a very strong dependence on angle when running the beam expander in reverse. Therefore you should be able to XYalign the input beam while monitoring the output. This is also recommended when using the beamexpander to increase the beam diameter, but even more important in reverse.
If you are still interested I suggest that you order one and that you simply try it out and let me know how this works out for your application. user
(posted 20140205 07:25:08.387) Hi,I would like to know wether the beam expander is able to reduce the diameter of a 30 femtosecond laser beam without damage of the mirrors, if the pulse energy is 4 mJ, or the laser power is 4 W which consists of 1 KHz series of such pulses. Thank you. besembeson
(posted 20140207 04:04:31.0) Response from Bweh E at Thorlabs: We have not tested this with such high peak powers yet. What we specify as the damage threshold is 3.0 J/cm2 at 1064 nm, 10 ns, 10 Hz, Ø1.000 mm. Could you provide me the wavelength of your laser so i can look into this further? I didn't see am email contact for you. ferchu
(posted 20140130 14:41:59.067) Hi, I would like to know if the beam expander consist of two concave mirrors, or if it consist of 1 concave mirror and 1 convex mirror.
thank you for the prompt response. jlow
(posted 20140130 10:33:48.0) Response from Jeremy at Thorlabs: These are made with 1 convex and 1 concave mirror. 
Thorlabs offers fixed and variable magnification beam expanders, as well as zoom beam expanders that do not need to be refocused when the magnification is adjusted since the collimation remains constant. The table below provides a direct comparison of the options we offer. Please contact Tech Support if you would like help choosing the best beam expander for your specific application.
Beam Expander Description 
Fixed Magnification Laser Line, Sliding Lens 
Fixed Magnification Achromatic, Sliding Lens 
Fixed Magnification MidInfrared, Sliding Lens 
Zoom, Sliding Lens 

Expansions Available  2X, 3X, 5X, 10X, 20X^{a}  2X, 3X, 5X, 10X, 15X, 20X 
2X, 5X, 10X  0.5X  2.5X, 1X  4X 
AR Coating Range(s) (Item # Suffix) 
240  360 nm (UVB) 248  287 nm (266) 325  380 nm (355) 488  580 nm (532) 960  1064 nm (1064) 
400  650 nm (A) 650  1050 nm (B) 1050  1650 nm (C) 
7  12 μm (E3)  240  360 nm (UVB) 330  370 nm (3) 495  570 nm (2) 980  1130 nm (1) 
Mirror Coating (Range)  N/A  
Reflectance (per Surface)  R_{avg} < 0.2% (R_{Max} < 1.5% for UVB) 
R_{Max} < 0.5%  R_{avg} < 1.0%  R_{avg} < 0.2% (R_{Max} < 1.5% for UVB) 
Max Input Beam Diameter  2X: 8.5 mm 3X: 9.0 mm 5X: 4.3 mm 10X: 2.8 mm 20X: 2.0 mm 
2X: 8.5 mm 3X: 9.0 mm 5X: 5.0 mm 10X: 3.0 mm 15X: 2.5 mm 20X: 2.0 mm 
2X: 9.5 mm 5X: 6.7 mm 10X: 3.5 mm 
0.5X  2.5X: 10.9 to 8.0 mm 1X  4X: 10.9 to 8.8 mm 
Wavefront Error  <λ/4 (Peak to Valley)  
Surface Quality  105 ScratchDig  2010 ScratchDig  8050 ScratchDig  105 ScratchDig 
Beam Expander Description 
Variable Magnification, Rotating Lens 
Variable Magnification, Sliding Lens 
Reflective Beam Expander Fixed Magnification 

Expansions Available  2X  5X, 5X  10X  0.5X  2X  2X, 4X, 6X 
AR Coating Range(s) (Item # Suffix) 
400  650 nm (A) 650  1050 nm (B) 1050  1620 nm (C) 
400  650 nm (A) 650  1050 nm (B) 
N/A 
Mirror Coating (Range)  N/A  Protected Silver (450 nm  20 μm) 

Reflectance (per Surface)  R_{avg} < 0.5%  R_{avg} < 0.5%  R_{avg} > 96% 
Max Input Beam Diameter  2X  5X: 4.0 mm 5X  10X: 2.3 mm 
0.5X  2X: 6.0 mm to 3.0 mm  3 mm 
Wavefront Error  <λ/4  <λ/10^{a} (RMS)  
Surface Quality  2010 ScratchDig  4020 ScratchDig 