Calcium Fluoride Broadband Plate Beamsplitters for the Mid-IR


  • Beamsplitter Coatings for either the 1 - 6 µm or 2 - 8 µm Range
  • Optimized for 50:50 Beamsplitting at 45°
  • Ø1/2", Ø1", 25 mm x 36 mm, and Ø2" Sizes

BSW520

2 - 8 µm Coating
Ø2"

BSW505

2 - 8 µm Coating
Ø1/2"

Backside
Uncoated

BSW511R

1 - 6 µm Coating
25 mm x 36 mm

BSW511

1 - 6 µm Coating
Ø1"

Related Items


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Plate Beamsplitter Selection Guide
Substrate Beamsplitter Coating
UV Fused Silica 250 - 450 nm
350 - 1100 nm
400 - 700 nm
532 nm and 1064 nm
600 - 1700 nm
700 - 1100 nm
1.2 - 1.6 µm
IR Fused Silica 0.9 - 2.6 µm
Calcium Fluoride 1 - 6 μm
2 - 8 μm
Zinc Selenide 1 - 12 μm
7 - 14 μm

Features

  • Beamsplitter Coating on Front Surface: 1 - 6 μm or 2 - 8 μm
  • Optimized for 50:50 Beamsplitting at a 45° Angle of Incidence (AOI)
  • Ø1/2", Ø1", 25 mm x 36 mm, and Ø2" Versions Available
  • Calcium Fluoride Substrate
  • 30 arcmin Wedged Back Surface on Round Beamsplitters Minimizes Ghosting

Thorlabs' 50:50 Calcium Fluoride Plate Beamsplitters have a broadband beamsplitter coating deposited on the front surface for either the 1 - 6 μm or the 2 - 8 μm spectral range, optimized for a 45° angle of incidence. A dielectric coating is used for long-term stability. These beamsplitters are available in Ø1/2", Ø1", or Ø2" versions. Additionally, a 25 x 36 mm verision specifically designed for mounting in microscopy filter cubes is available for the 1 - 6 µm range.

These plate beamsplitters utilize a calcium fluoride substrate, which offers many desirable physical and chemical properties. With an Abbe Number of 95, calcium fluoride exhibits low dispersion. It also has excellent water, chemical, and heat resistance. In dry environments, CaF2 can be used up to 1000 °C, but in the presence of moisture, degradation will occur for temperatures exceeding 600 °C. This crystal is also inert to organic chemicals and many acids.

To help reduce unwanted interference effects (e.g., ghost images) caused by the interaction of light reflected from the front and back surfaces of the optic, a 30 arcmin wedge has been added to our round broadband plate beamsplitters. The back surface of these beamsplitters has a 30 arcmin wedge; therefore the fraction of light that does get reflected from this surface will diverge. Please note that the surface with the beamsplitter coating is indicated by an arrow on the edge of the optic as shown on the Specs tab.

Thorlabs offers three types of non-polarizing beamsplitters: Non-polarizing Beamsplitting Cubes (mounted and unmounted), Pellicle Beamsplitters (mounted and unmounted), and the Plate Beamsplitters (see below and selection guide above). For a direct comparison of the performance of our non-polarizing beamsplitting cube, plate, and pellicle at 633 nm, see the Lab Facts tab.

Beamsplitter Drawing
Note: Not Drawn to Scale
The drawing above only represents round optics;
rectangular optics do not have an arrow
nor a wedge.
Item # BSW501 BSW511 BSW511R BSW521 BSW505 BSW510 BSW520
Dimensions Ø1/2"
(12.7 mm)
Ø1"
(25.4 mm)
25 mm x 36 mm Ø2"
(50.8 mm)
Ø1/2"
(12.7 mm)
Ø1"
(25.4 mm)
Ø2"
(50.8 mm)
Dimensional
Tolerance
+0.0 mm / -0.2 mm ±0.1 mm +0.0 mm / -0.2 mm
Center Thickness (Nominal) 3.0 mm 5.0 mm 1.0 mm 8.0 mm 3.0 mm 5.0 mm 8.0 mm
Center Thickness Tolerance ±0.4 mm ±0.1 mm ±0.4 mm
Wedge Angle 30 arcmin - 30 arcmin
Substrate Calcium Fluoridea
Clear Aperture >Ø11.43 mm >Ø22.86 mm >22.5 mm x 32.4 mm >Ø45.72 mm >Ø11.43 mm >Ø22.86 mm >Ø45.72 mm
Surface Flatness <λ/4 at 633 nm Over Clear Aperture <λ/8 @ 633 nm
Over Clear Aperture
- <λ/4 @ 633 nm Over Clear Aperture
Transmitted Wavefront Error (TWE) - - <λ/4 @ 633 nm Over Clear Aperture - - - -
Coating on Surface 1 1 - 6 μm Beamsplitter Coating for 45° Incidence 2 - 8 μm Beamsplitter Coating
for 45° Incidence
Coating on Surface 2 None
Overall Performance Tabs = 50 ± 20%, Rabs = 50 ± 20%,
Tabs + Rabs > 95%,
|Ts - Tp| < 35% and |Rs - Rp| < 35%,
45° AOI
Tabs = 50 ± 15%, Rabs = 50 ± 15%,
Tabs + Rabs > 95%,
|Ts - Tp| < 35% and |Rs - Rp| < 35%,
45° AOI
Surface Quality 60-40 Scratch-Dig 80-50 Scratch-Dig
Damage Threshold Pulsed 0.5 J/cm(2.1 µm, 30 ns, 167 Hz, Ø0.027 mm)
10 J/cm2 (2.94 µm, 200 µs, 2 Hz, Ø0.485 mm) 
0.5 J/cm2 (3.3 μm, 6 ns, 30 kHz, Ø0.0483 mm)
CWb 100 W/cm (2.1 µm, Ø0.027 mm) -
  • Click link for detailed specifications on the substrate.
  • The power density of your beam should be calculated in terms of W/cm. For an explanation of why the linear power density provides the best metric for long pulse and CW sources, please see the Damage Thresholds tab.
Transmission of Uncoated CaF2
Click to Enlarge

Click Here for Raw Data

The transmission curve above was obtained using a 5 mm thick, uncoated sample of CaF2; the incident light was normal to the surface. Please note that this is the measured transmission, including surface reflections.

 


Click to Enlarge

Click Here for Raw Data for the 350 nm - 7 μm Wavelength Range

Click to Enlarge

Click Here for Raw Data for the 350 nm - 7 μm Wavelength Range

Above are the measured transmission (left) and reflectance (right) curves for the 50:50 broadband plate beamsplitters coated for 1 - 6 μm. Data was obtained for a 45° angle of incidence. The blue shaded region indicates the wavelength range for optimum performance. Performance outside of the specified range is not guaranteed and varies from lot to lot.

 


Click to Enlarge

Click Here for Raw Data for the 300 nm - 11 μm Wavelength Range

Click to Enlarge

Click Here for Raw Data for the 300 nm - 11 μm Wavelength Range

Above are the measured transmission (left) and reflectance (right) curves for the 50:50 broadband plate beamsplitters coated for 2 - 8 μm. Data was obtained for a 45° angle of incidence. The blue shaded region indicates the wavelength range for optimum performance. Performance outside of the specified range is not guaranteed and varies from lot to lot.

Thorlabs Lab Fact: Beamsplitter Package Matters

We present laboratory measurements of the polarization angle, split ratio, and total throughput power of a beam transmitted through Thorlabs plate, cube, and pellicle beamsplitters. While all non-polarizing beamsplitters function similarly, the exact performance is different for different types of beamsplitter. Each type of beamsplitter contains its own advantages and disadvantages compared to other types of beamsplitters. Appropriate choice of beamsplitter is essential to sensitive experimental systems. We present a complete analysis and comparison of optical parameters for three common types of non-polarizing beamsplitters.

For our experiment we used the former generation HRS015 stabilized HeNe laser (replaced by the HRS015B) as the light source for our investigation. A linear polarizer is used to set the laser beam's polarization axis to 45° in order to provide equal s- and p-polarized light incident on the beamsplitter. The beamsplitter under investigation was then placed in the beampath, and its split beams directed to appropriate detectors. The total power though the optic, polarization states, split ratios, and angle of incidence effects were investigated under this configuration.

Lab Facts Complete Summary

The plots below summarize the measured results for all three types of beamsplitters. From these graphs the performance of each optic can be easily compared to one another. The bottom left plot summarizes the results for the total power throughput for each optic. The total power throughput is measured as the fraction of input power. While the plate and pellicle beamsplitters perform rather similarly, the cube shows signs of absorption inside the optic. Additionally, this plot shows the relative insensitivity of throughput power to angle of incidence. The bottom middle graph summarizes the results for the output polarization angle for each optic. The cube shows the most similar polarization angles between the reflected and transmitted beams, with the plate producing the largest difference in polarization between beams. The bottom right plot summarizes the results for the split ratio, as a fraction of input power, for the beamsplitters. Here it can be shown that the plate beamsplitter demonstrates the most ideal for 50/50 power splitting. For details on the experimental setup employed and the results summarized here, please click here.

Beamsplitter Selection Guide

Thorlabs' portfolio contains many different kinds of beamsplitters, which can split beams by intensity or by polarization. We offer plate and cube beamsplitters, though other form factors exist, including pellicle and birefringent crystal. For an overview of the different types and a comparison of their features and applications, please see our overview. Many of our beamsplitters come in premounted or unmounted variants. Below is a complete listing of our beamsplitter offerings. To explore the available types, wavelength ranges, splitting/extinction ratios, transmission, and available sizes for each beamsplitter category, click More [+] in the appropriate row below.

Plate Beamsplitters

Non-Polarizing Plate Beamsplitters
Polarizing Plate Beamsplitters
  • 45° AOI Unless Otherwise Noted
  • 30 arcmin Wedge on Round Optics Only
  • Designed for use with P-polarized light.

Cube Beamsplitters

Non-Polarizing Cube Beamsplitters
Polarizing Cube Beamsplitters

Pellicle Beamsplitters

Non-Polarizing Pellicle Beamsplitters

Crystal Beamsplitters

Polarizing Crystal Beamsplitters
  • Mounted in a protective box, unthreaded ring, or cylinder.
  • Available unmounted or mounted in a protective box or unthreaded cylinder.

Other

Other Beamsplitters
Damage Threshold Specifications
Item # Damage Threshold
BSW501
BSW511
BSW511R
BSW521
Pulsed: 0.5 J/cm2 (2.1 µm, 30 ns, 167 Hz, Ø0.027 mm)
Pulsed: 10 J/cm2 (2.94 µm, 200 µs, 2 Hz, Ø0.485 mm)
CWa: 100 W/cm (2.1 µm, Ø0.027 mm)
BSW505
BSW510
BSW520
Pulsed: 0.5 J/cm2 (3.3 μm, 6 ns, 30 kHz, Ø0.0483 mm)
  • The power density of your beam should be calculated in terms of W/cm. 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.

Damage Threshold Data for Thorlabs' CaF2 Plate Beamsplitters

The specifications to the right are measured data for a selection of Thorlabs' CaF2 broadband plate beamsplitters. Damage threshold specifications are constant for these CaF2 beamsplitters, regardless of the size of the beamsplitter.

 

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 scratch-dig spec, surface free of contamination, etc.). Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. For more information on cleaning optics, please see our Optics Cleaning tutorial.

Testing Method

Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.

First, a low-power/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 BB1-E02 mirror.

LIDT metallic mirror
The photograph above is a protected aluminum-coated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm2 (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage.
LIDT BB1-E02
Example Test Data
Fluence # of Tested Locations Locations with Damage Locations Without Damage
1.50 J/cm2 10 0 10
1.75 J/cm2 10 0 10
2.00 J/cm2 10 0 10
2.25 J/cm2 10 1 9
3.00 J/cm2 10 1 9
5.00 J/cm2 10 9 1

According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, Ø0.803 mm). Please keep in mind that these tests are performed on clean optics, as dirt and contamination can significantly lower the damage threshold of a component. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances.

Continuous Wave and Long-Pulse 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, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). Absorption is either due to an intrinsic property of the optic or due to surface irregularities; thus LIDT values are only valid for optics meeting or exceeding the surface quality specifications given by a manufacturer. While many optics can handle high power CW lasers, cemented (e.g., achromatic doublets) or highly absorptive (e.g., ND filters) optics tend to have lower CW damage thresholds. These lower thresholds are due to absorption or scattering in the cement or metal coating.

Linear Power Density Scaling

LIDT in linear power density vs. pulse length and spot size. For long pulses to CW, linear power density becomes a constant with spot size. This graph was obtained from [1].

Intensity Distribution

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:

  1. Wavelength of your laser
  2. Beam diameter of your beam (1/e2)
  3. Approximate intensity profile of your beam (e.g., Gaussian)
  4. Linear power density of your beam (total power divided by 1/e2 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 non-uniform intensity profiles and roughly calculate a maximum power density. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right).

Now compare the maximum power density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. A good rule of thumb is that the damage threshold has a linear relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 10 W/cm at 1310 nm scales to 5 W/cm at 655 nm):

CW Wavelength Scaling

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 ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism [2]. In contrast, pulses between 10-7 s and 10-4 s may cause damage to an optic either because of dielectric breakdown or thermal effects. This means that both CW and pulsed damage thresholds must be compared to the laser beam to determine whether the optic is suitable for your application.

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:

Energy Density Scaling

LIDT in energy density vs. pulse length and spot size. For short pulses, energy density becomes a constant with spot size. This graph was obtained from [1].

  1. Wavelength of your laser
  2. Energy density of your beam (total energy divided by 1/e2 area)
  3. Pulse length of your laser
  4. Pulse repetition frequency (prf) of your laser
  5. Beam diameter of your laser (1/e2 )
  6. Approximate intensity profile of your beam (e.g., Gaussian)

The energy density of your beam should be calculated in terms of J/cm2. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. In this regime, the LIDT given as an energy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. This calculation assumes a uniform beam intensity profile. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. For reference a Gaussian beam typically has a maximum energy density that is twice that of the 1/e2 beam.

Now compare the maximum energy density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately [3]. A good rule of thumb is that the damage threshold has an inverse square root relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 1 J/cm2 at 1064 nm scales to 0.7 J/cm2 at 532 nm):

Pulse Wavelength Scaling

You now have a wavelength-adjusted energy density, which you will use in the following step.

Beam diameter is also important to know when comparing damage thresholds. While the LIDT, when expressed in units of J/cm², scales independently of spot size; large beam sizes are more likely to illuminate a larger number of defects which can lead to greater variances in the LIDT [4]. For data presented here, a <1 mm beam size was used to measure the LIDT. For beams sizes greater than 5 mm, the LIDT (J/cm2) will not scale independently of beam diameter due to the larger size beam exposing more defects.

The pulse length must now be compensated for. The longer the pulse duration, the more energy the optic can handle. For pulse widths between 1 - 100 ns, an approximation is as follows:

Pulse Length Scaling

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, Laser-Induced 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.

Intensity Distribution
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/e2 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:

CW Wavelength Scaling

However, the maximum power density of a Gaussian beam is about twice the maximum power density of a uniform beam, as shown in the graph to the right. Therefore, a more accurate determination of the maximum linear power density of the system is 1 W/cm.

An AC127-030-C achromatic doublet lens has a specified CW LIDT of 350 W/cm, as tested at 1550 nm. CW damage threshold values typically scale directly with the wavelength of the laser source, so this yields an adjusted LIDT value:

CW Wavelength Scaling

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/e2). The average energy density of each pulse is found by dividing the pulse energy by the beam area:

Pulse Energy Density

As described above, the maximum energy density of a Gaussian beam is about twice the average energy density. So, the maximum energy density of this beam is ~0.7 J/cm2.

The energy density of the beam can be compared to the LIDT values of 1 J/cm2 and 3.5 J/cm2 for a BB1-E01 broadband dielectric mirror and an NB1-K08 Nd:YAG laser line mirror, respectively. Both of these LIDT values, while measured at 355 nm, were determined with a 10 ns pulsed laser at 10 Hz. Therefore, an adjustment must be applied for the shorter pulse duration of the system under consideration. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration:

Pulse Length Scaling

This adjustment factor results in LIDT values of 0.45 J/cm2 for the BB1-E01 broadband mirror and 1.6 J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm2 maximum energy density of the beam. While the broadband mirror would likely be damaged by the laser, the more specialized laser line mirror is appropriate for use with this system.

Pulsed Nanosecond Laser Example: Scaling for Different Wavelengths
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/e2) 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/cm2. The damage threshold of an NDUV10A Ø25 mm, OD 1.0, reflective neutral density filter is 0.05 J/cm2 for 10 ns pulses at 355 nm, while the damage threshold of the similar NE10A absorptive filter is 10 J/cm2 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:

Pulse Wavelength Scaling

This scaling gives adjusted LIDT values of 0.08 J/cm2 for the reflective filter and 14 J/cm2 for the absorptive filter. In this case, the absorptive filter is the best choice in order to avoid optical damage.

Pulsed Microsecond Laser Example
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 long-pulse laser emits a Gaussian 12.7 mm diameter beam (1/e2) at 980 nm, then the resulting output has a linear power density of 5.9 W/cm and an energy density of 1.2 x 10-4 J/cm2 per pulse. This can be compared to the LIDT values for a WPQ10E-980 polymer zero-order quarter-wave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm2 for a 10 ns pulse at 810 nm. As before, the CW LIDT of the optic scales linearly with the laser wavelength, resulting in an adjusted CW value of 6 W/cm at 980 nm. On the other hand, the pulsed LIDT scales with the square root of the laser wavelength and the square root of the pulse duration, resulting in an adjusted value of 55 J/cm2 for a 1 µs pulse at 980 nm. The pulsed LIDT of the optic is significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. However, the large average linear power density of the laser system may cause thermal damage to the optic, much like a high-power CW beam.


Posted Comments:
Maxim Astapocixh  (posted 2020-02-05 11:05:57.83)
What material is coated this beamsplitter? Dielectric or metal?
YLohia  (posted 2020-02-06 04:41:53.0)
Thank you for contacting Thorlabs. These beamsplitters have dielectric coatings.
schmidt-engler  (posted 2018-04-26 11:29:32.417)
Dear Thorlabs, I am a big supporter of your "customer inspired" range. Would it also be possible to develop a customer inspired 1" CaF2 50% Beamsplitter for 2-8 µm in 3mm thickness? 5mm thickness of the BSW510 is too thick for our application and the customer inspired 1/2" 3mm thick BSW505 is too small. sincerely yours, Julian Schmidt-Engler
YLohia  (posted 2018-04-26 08:21:34.0)
Hello Julian, thank you for contacting Thorlabs. We do have the ability to provide what you are asking for as a custom item. Please reach out to your local Thorlabs Tech Support team (europe@thorlabs.com) with the desired quantity and specifications for a quote.
coleen  (posted 2015-08-20 14:19:58.147)
Does the 50% reflectivity include both front and rear reflections? Due to the wedge, the rear beam will be at a different angle from the front beam. Thanks, Coleen
besembeson  (posted 2015-09-25 01:32:26.0)
Response from Bweh at Thorlabs USA: The beamsplitter coating is only on the front surface that is marked on the optic. Yes there will be a very small deviation due to the 0.5deg wedge that eliminates unwanted interference in the reflected beam.
user  (posted 2015-04-21 07:50:07.33)
Sorry, but I cannot find the inscripted arrow on none of my newly ordered BSW520. Or am I missing something here..
besembeson  (posted 2015-08-28 09:24:13.0)
Response from Bweh at Thorlabs USA: The arrow should be there. Please contact us at techsupport@thorlabs.com if we need to replace item for you.
tcohen  (posted 2012-12-28 16:41:00.0)
Response from Tim at Thorlabs: Transmission measurements of the BSW520 show unpolarized 633nm %T to be ~1%.
user  (posted 2012-12-14 18:42:17.073)
As many of us working in the MIR use red aiming beams, it would be nice to know the transmission at 633 nm. Thanks.
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Calcium Fluoride Beamsplitter Coated for 1 - 6 µm

Specificationsa
Item # BSW501 BSW511 BSW511R BSW521
Size Ø1/2"
12.7 mm
Ø1"
25.4 mm
25 mm x 36 mm Ø2"
50.8 mm
Beamsplitting
Ratio
50:50
Wavelength
Range
1 - 6 µm
Substrate Calcium Fluorideb
Clear
Aperture (mm)
>Ø11.43 >Ø22.86 >32.4 x 22.5 >Ø45.72
Nominal Thickness (mm) 3.0 5.0 1.0 8.0
  • See Specs tab for complete specifications.
  • Click link for detailed specifications on the substrate.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
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BSW511 Support Documentation
BSW511Ø1" CaF2 Plate Beamsplitter, Coating: 1 - 6 µm, 5 mm Thick
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BSW511R Support Documentation
BSW511RCustomer Inspired! 25 mm x 36 mm CaF2 Plate Beamsplitter, Coating: 1 - 6 µm, 1 mm Thick
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BSW521 Support Documentation
BSW521Customer Inspired! Ø2" CaF2 Plate Beamsplitter, Coating: 1 - 6 µm, 8 mm Thick
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Calcium Fluoride Beamsplitters Coated for 2 - 8 µm

Specificationsa
Item # BSW505 BSW510 BSW520
Size Ø1/2"
12.7 mm
Ø1"
25.4 mm
Ø2"
50.8 mm
Beamsplitting
Ratio
50:50
Wavelength
Range
2 - 8 µm
Substrate Calcium Fluorideb
Clear Aperture (mm) >Ø11.43 >Ø22.86 >Ø45.72
Nominal
Thickness (mm)
3.0 5.0 8.0
  • See Specs tab for complete specifications.
  • Click link for detailed specifications on the substrate.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
BSW505 Support Documentation
BSW505Customer Inspired! Ø1/2" CaF2 Plate Beamsplitter, Coating: 2 - 8 µm, 3 mm Thick
$302.92
Today
BSW510 Support Documentation
BSW510Customer Inspired! Ø1" CaF2 Plate Beamsplitter, Coating: 2 - 8 µm, 5 mm Thick
$339.74
Today
BSW520 Support Documentation
BSW520Customer Inspired! Ø2" CaF2 Plate Beamsplitter, Coating: 2 - 8 µm, 8 mm Thick
$460.92
Today