Zoom Beam Expanders: UV Fused Silica


  • 0.5X - 2.5X or 1X - 4X Continuous Beam Expansion
  • Sliding Lens Design Minimizes Beam Walk-Off
  • UV Fused Silica Optics for High-Power Applications
  • Four AR Coatings Available

ZBE11

0.5X - 2.5X Magnification,
980 - 1130 nm V Coating

Input

Output

ZBE22

1X - 4X Magnification,
495 - 570 nm V Coating,
Output Side

ZBE2UVB

1X - 4X Magnification,
240 - 360 nm AR Coating,
Input Side

Related Items


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0.5X - 2.5X ZoomBeam Expander
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The 0.5X - 2.5X magnification beam expanders have an externally SM1-threaded output. The input is internally SM05-threaded and externally SM1-threaded.
1X - 4X Zoom Beam Expander
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The 1X - 4X magnification beam expanders have an externally M43 x 0.5-threaded output. The input is internally SM05-threaded and externally SM1-threaded.

Features

  • 0.5X - 2.5X or 1X - 4X Continuous Beam Expansion
  • Collimation Remains Constant During Magnification Change
  • Four AR Coating Options Covering Common Laser Lines:
    • 240 - 360 nm Broadband
    • 330 - 370 nm V Coat
    • 495 - 570 nm V Coat
    • 980 - 1130 nm V Coat
  • Sliding Lenses Minimize Beam Walk-Off
  • Housing with Fixed Mechanical Length and Non-Rotating Ends
  • Engraved Magnification and Focusing Distance Scales
  • Magnification and Collimation Adjustment Rings can be Locked with Included Hex Key
  • Threaded Apertures for Easy Integration into Optical Systems

Thorlabs' UV Fused Silica (UVFS) Zoom Beam Expanders can continuously expand or reduce the diameter of a collimated beam in a range of 0.5X - 2.5X or 1X - 4X. These zoom beam expanders use a low-aberration, air-spaced sliding lens design optimized to provide diffraction-limited performance and minimize the impact on the M2 value of the expanded beam. Unlike variable beam expanders, zoom beam expanders do not need to be refocused when the magnification is adjusted since the collimation remains constant.

The sliding lens design allows for the magnification and focusing distance to be adjusted while minimizing the beam walk-off effect that is inherent to lens adjustments. The red rings, shown in the photos to the right, are used to adjust the magnification and focus distance of the output beam; once the desired beam size and collimation is obtained, the rings can be locked by tightening the locking screws using the included 0.050" hex key.

For a collimated input beam, the output beam remains collimated when changing the magnification adjustment ring engraved with the expansion ratios. An expanded beam can be focused or adjusted to a divergent beam using the focusing distance adjustment ring. The scale of the focusing distance ring is engraved with certain distances in meters, measured from the mounting plane of the front thread of the housing. The closest focusing distance for the 0.5X - 2.5X expanders is ±0.7 m and for the 1X - 4X expanders is ±2 m.

The optics used in each beam expanders have one of four AR coatings to minimize reflections at the air-to-glass interfaces. Beam expanders with Item #s ending in UVB feature a broadband AR coating designed for 240 - 360 nm. The other beam expanders use optics with one of three V-coatings, named for the shape of the reflectance curve, which reaches an Ravg < 0.2% per surface over the design wavelength range and slopes steeply upwards on either side. This coating design provides a lower reflectance over a narrower operating range when compared to a broadband AR coating. The V-coatings for these Zoom Beam Expanders are centered around one of three wavelengths chosen to match Nd:YAG laser lines: 355 nm, 532 nm, or 1064 nm. See the Specs and AR Coatings tabs for more information on the coating performance.

Mounting Options
The 0.5X - 2.5X and 1X - 4X Zoom Beam Expanders have a smooth mounting surface with the same diameter as our Ø1" lens tubes. Post mounting options include the SM1RC(/M) Lens Tube Slip Ring and SM1TC Lens Tube Clamp. Alternatively, the Zoom Beam Expanders can be integrated in one of our cage systems via the CP36 30 mm Cage Plate or by using the SM2A21 mounting adapter with the LCP09 60 mm cage plate. Details are provided below. We also offer the SM2A30 adapter, which allows the input to be mated with components using the M43 x 0.5 thread standard.

The threaded input and output apertures allow additional lenses and filters to be installed easily along the optical axis of the beam expander. The input of each zoom beam expander has internal SM05 (0.535"-40) and external SM1 (1.035"-40) threads for ease of use with Thorlabs' lens tubes and other optical components. The output threading types are given in the tables below. All housings are designed so that the mounting surface and threaded ends do not rotate when turning either the Magnification or the Focusing Distance adjustment ring, allowing the user to adjust the magnification and the divergence without disturbing any attached optics and maintain pointing stability.

Thorlabs also offers achromatic zoom beam expanders for broadband applications. Other beam expander options available are our UV fused silica, achromatic, and ZnSe fixed beam expanders, rotating lens and sliding lens variable beam expanders, and reflective beam expanders. For more information on our extensive line of beam expanders, please see the Beam Expanders tab.

Item # Prefix ZBE1 ZBE2
Expansion 0.5X - 2.5X 1X - 4X
Max Input Beam Diametera 10.9 mm @ 0.5X
8.0 mm @ 2.5X
10.9 mm @ 1X
8.8 mm @ 4X
Diffraction-Limited Input Beam Diametera,b 10.0 mm @ 0.5X
7.0 mm @ 2.5X
10.0 mm @ 1X
7.0 mm @ 4X
Closest Focusing Distancec ±0.7 m ±2 m
Pointing Stabilityd <1 mrad
Input Thread Internal: SM05 (0.535"-40)
External: SM1 (1.035"-40)
Output Thread External SM1 (1.035"-40) External M43 x 0.5e
Surface Quality 10-5 Scratch-Dig
Housing Dimensions
Input Housing Diameter 30.5 mm (1.20")f
Output Housing Diameter 30.5 mm (1.20")f 45.0 mm (1.77")
Housing Length 119.9 mm (4.72") 170.8 mm (6.72")
Mounting Optionsg SM1RC(/M), SM1TC, CP36, SM2A21 SM1RC(/M), SM1TC, CP36, SM2A21, SM2A30
  • For a collimated beam.
  • Maximum input beam diameter for output Peak-to-Valley Wavefront Error (WFE) <λ/4 at 633 nm.
  • For the zoom beam expanders with the UVB coating, the closest focusing distances are valid for 266 nm. For all other wavelength within the coating range (240 nm - 360 nm), the focus adjustment ring needs to be used to re-collimate the beam for the different magnifications and consequently the focusing range is limited.
  • Pointing stability during zooming for a collimated input beam aligned to the optical axis of the Zoom Beam Expander.
  • The SM2A30 thread adapter can be used to integrate these beam expanders with our SM2-Threaded Lens Tubes and 60 mm Cage System.
  • This is the same diameter as our SM1-Threaded Lens Tubes. See below for recommended mounting options.
  • The options in this row are available below. The beam expanders can also be integrated with various threaded components using our thread adapters.
AR Coating Specifications
Item # Suffix UVB 3 2 1
AR Coating Type 240 - 360 nm Broadband 355 nm V-Coat 532 nm V-Coat 1064 nm V-Coat
Average Reflectancea - <0.2% (330 - 370 nm) <0.2% (495 - 570 nm) <0.2% (980 - 1130 nm)
Max Reflectancea <1.5% (240 - 360 nm) <0.7% (325 - 380 nm)
<0.2% (335 - 362 nm)
<0.7% (488 - 580 nm)
<0.2% (503 - 553 nm)
<0.7% (960 - 1160 nm)
<0.2% (1000 - 1100 nm)
Typical Transmissionb >89% @ 248 nm
>92% @ 266 nm
>90% @ 355 nm
>95% @ 355 nm >96% @ 532 nm >96% @ 1064 nm
Damage Thresholdc 5.0 J/cm² (355 nm, 10 ns Pulse,
20 Hz, Ø0.342 mm)
10.0 J/cm² (355 nm, 10 ns Pulse,
10 Hz, Ø0.406 mm)
15.0 J/cm² (532 nm, 10 ns Pulse,
20 Hz, Ø0.213 mm)
20.0 J/cm² (1064 nm, 10 ns Pulse,
20 Hz, Ø0.395 mm)
  • Per surface.
  • For the entire system.
  • The maximum power that the beam expander can accept is limited by the AR Coating Damage Threshold.

The lenses in the UV fused silica zoom beam expanders have one of four AR coatings deposited on both sides of each optic in the beam expanders to minimize reflections at the air-to-glass interfaces. The graphs below show the reflectance per surface as a function of wavelength over an extended wavelength range. Each blue shaded region indicates the specified operating range of the coating; performance outside of this region is not guaranteed.

UVB Zoom Beam Expander Reflectance
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The reflectance per surface of the AR coating applied to the optics used in the ZBExUVB UVFS zoom beam expanders. The blue shaded region indicates the 240 - 360 nm operating range where Rmax < 1.5% per surface. Performance outside of this region is provided for reference only and is not guaranteed.
355 nm Zoom Beam Expander Reflectance
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Click Here for Raw Data
The reflectance per surface of the AR coating applied to the optics used in the ZBEx3 UVFS zoom beam expanders. The blue shaded region indicates the 330 - 370 nm operating range where Ravg < 0.2% per surface. Performance outside of this region is provided for reference only and is not guaranteed.
532 nm Zoom Beam Expander Reflectance
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Click Here for Raw Data
The reflectance per surface of the AR coating applied to the optics used in the ZBEx2 UVFS zoom beam expanders. The blue shaded region indicates the 495 - 570 nm operating range where Ravg < 0.2% per surface. Performance outside of this region is provided for reference only and is not guaranteed.
1064 nm Zoom Beam Expander Reflectance
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Click Here for Raw Data
The reflectance per surface of the AR coating applied to the optics used in the ZBEx1 UVFS zoom beam expanders. The blue shaded region indicates the 980 - 1130 nm operating range where Ravg < 0.2% per surface. Performance outside of this region is provided for reference only and is not guaranteed.
Zoom Beam Expander Interference
The interference fringes produced by the SI100 Shearing Interferometer (with a mounted SIVS Viewing Screen) remain parallel to the reference line as the size of the beam changes by adjusting the magnification of the zoom beam expander (Item # ZBE22). For more information on how a shearing interferometer works, please see our full presentation here.

Collimation

Thorlabs' Shearing Interferometers can be used to determine if a coherent beam of light is collimated. The design consists of a wedged optical flat mounted at 45° and a diffuser plate with a ruled reference line down the middle. These interferometers are designed to provide qualitative analysis of a beam's collimation.

The diffuser plate is used to view the interference fringes created by Fresnel reflections from the front and back surfaces of the optical flat. If the beam is collimated, the resulting fringe pattern will be parallel to the ruled reference line. In addition to the degree of collimation, the fringes will also be sensitive to spherical aberration, coma, and astigmatism.

The video to the right shows the output of a shearing interferometer (Item # SI100) with the Magnified View Screen System (Item # SIVS) as the magnification is adjusted on a Zoom Beam Expander (Item # ZBE22). The fringes remain parallel to the reference line, meaning that the beam remains collimated as the size of the beam is adjusted (see images below for a reference).

Collimated
Collimated Light
Converging or Diverging
Converging Light Diverging Light
Examples of collimated versus converging or diverging light. For collimated light, the fringes remain parallel to the reference line as the size of the beam is adjusted.

 

Pointing Stability

The lenses in these Zoom Beam Expanders slide within the housings rather than rotating, which results in superior pointing stability of <1 mrad during magnification adjustments.

 

Adjustment

Thorlabs' Zoom Beam Expanders provide a variable magnification between 0.5X - 2.5X (ZBE1x) or 1X - 4X (ZBE2x) while maintaining the collimation of the output beam. In addition, the divergence of the collimated beam can be finely adjusted, or the beam can be focused between ±0.7 m (ZBE1x) or ±2 m (ZBE2x) measured from the mounting plane of the front thread of the housing.

The image to the right illustrates the two ways to adjust the zoom beam expander. To adjust the focusing distance, rotate the red section of the housing farthest from the input side. This will effectively alter the focus of the beam. To adjust the magnification, rotate the red section closest to the input side. This will effectively alter the size of the beam. The focusing ring has tick marks engraved to denote the focus distance in meters, and the zoom ring is engraved with a scale for the magnification.

Each adjustment ring can be locked in place by tightening a setscrew with the included 0.05" hex key.

 

Zoom Beam Expander Imaging

Imaging and Projection Applications

Thorlabs’ Zoom Beam Expanders are also excellent for any imaging or projection application where a small field of view needs to be enlarged with minimal aberration. The video to the right shows light from an M530L4 530 nm LED light source collimated using an ACL2520U-A molded asphere passing through an R1DS1N USAF target. This is imaged into infinity by an AC254-100-A 100 mm achromat before entering the ZBE12 Zoom Beam Expander. The Zoom Beam Expander images the USAF target onto an EDU-VS1 screen that is placed ~1 m from its output. The video shows the magnification being varied through the entire range (0.5X to 2.5X) and back. The focus plane remains constant, always producing a sharp image of the USAF target, throughout this adjustment. A schematic of the full setup is shown below.

Please note that the ratio of the output to the input angle for an off-axis ray will be equal to the inverted engraved magnification. Therefore, a projected image will be larger for the magnification of 0.5X and smaller for the engraved magnification of 2.5X.

ZBE12 Application Shot
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View Imperial Product List
Item #QtyDescription
Imperial Product List
M530L41530 nm, 370 mW (Min) Mounted LED, 1000 mA
DC410014-Channel LED Driver, 1 Modulation Input, 1 A, 5 V
SM1RC2Slip Ring for SM1 Lens Tubes and C-Mount Extension Tubes,
8-32 Tap
SM1L101SM1 Lens Tube, 1.00" Thread Depth, One Retaining Ring Included
SM1L201SM1 Lens Tube, 2.00" Thread Depth, One Retaining Ring Included
SM1M301SM1 Lens Tube Without External Threads, 3" Long, Two Retaining Rings Included
SM1T21SM1 (1.035"-40) Coupler, External Threads, 0.5" Long, Two Locking Rings
SM1RR1SM1 Retaining Ring for Ø1" Lens Tubes and Mounts
ACL2520U-A1Aspheric Condenser Lens, Ø25 mm, f=20.1 mm, NA=0.60 ARC: 350-700 nm
AC254-100-A1f = 100 mm, Ø1" Achromatic Doublet, ARC: 400 - 700 nm
R1DS1N1Negative 1951 USAF Test Target, Ø1"
PF20-03-P011Ø2" Protected Silver Mirror
POLARIS-K2S11Polaris® Low Drift Ø2" Mirror Mount, 2 Adjuster Knobs
RS2P8E1Ø1" Pedestal Pillar Post, 8-32 Taps, L = 2"
RS2.5P8E2Ø1" Pedestal Pillar Post, 8-32 Taps, L = 2.5"
CF1753Clamping Fork, 1.75" Counterbored Slot, Universal
SH25S06311/4"-20 Stainless Steel Cap Screw, 5/8" Long, 25 Pack
UPH21Ø1/2" Universal Post Holder, Spring Loaded Locking Thumbscrew, L = 2"
SH25S07511/4"-20 Stainless Steel Cap Screw, 3/4" Long, 25 Pack
TR11Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 1"
SS8S03818-32 Stainless Steel Setscrew, 3/8" Long, 50 Pack
ZBE1210.5X - 2.5X UVFS Zoom Beam Expander, 495 - 570 nm V Coating
EDU-VS11Post-Mountable White Polystyrene Viewing Screen, 5.91" x 5.91"
View Metric Product List
Item #QtyDescription
Metric Product List
M530L41530 nm, 370 mW (Min) Mounted LED, 1000 mA
DC410014-Channel LED Driver, 1 Modulation Input, 1 A, 5 V
SM1RC/M2Slip Ring for SM1 Lens Tubes and C-Mount Extension Tubes,
M4 Tap
SM1L101SM1 Lens Tube, 1.00" Thread Depth, One Retaining Ring Included
SM1L201SM1 Lens Tube, 2.00" Thread Depth, One Retaining Ring Included
SM1M301SM1 Lens Tube Without External Threads, 3" Long, Two Retaining Rings Included
SM1T21SM1 (1.035"-40) Coupler, External Threads, 0.5" Long, Two Locking Rings
SM1RR1SM1 Retaining Ring for Ø1" Lens Tubes and Mounts
ACL2520U-A1Aspheric Condenser Lens, Ø25 mm, f=20.1 mm, NA=0.60 ARC: 350-700 nm
AC254-100-A1f = 100 mm, Ø1" Achromatic Doublet, ARC: 400 - 700 nm
R1DS1N1Negative 1951 USAF Test Target, Ø1"
PF20-03-P011Ø2" Protected Silver Mirror
POLARIS-K2S11Polaris® Low Drift Ø2" Mirror Mount, 2 Adjuster Knobs
RS2P4M1Ø25.0 mm Pedestal Pillar Post, M4 Taps, L = 50 mm
RS2.5P4M2Ø25.0 mm Pedestal Pillar Post, M4 Taps, L = 65 mm
CF1753Clamping Fork, 1.75" Counterbored Slot, Universal
SH6MS161M6 x 1.0 Stainless Steel Cap Screw, 16 mm Long, 25 Pack
UPH50/M1Ø12.7 mm Universal Post Holder, Spring-Loaded Locking Thumbscrew, L = 50 mm
SH6MS201M6 x 1.0 Stainless Steel Cap Screw, 20 mm Long, 25 Pack
TR30/M1Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 30 mm
SS4MS101M4 x 0.7 Stainless Steel Setscrew, 10 mm Long, 50 Pack
ZBE1210.5X - 2.5X UVFS Zoom Beam Expander, 495 - 570 nm V Coating
EDU-VS1/M1Post-Mountable White Polystyrene Viewing Screen, 150 mm x 150 mm
USAF target projected on an EDU-VS1 Screen Using a ZBE12 Zoom Beam Expander
Damage Threshold Specifications
Item # Suffix Damage Threshold
UVB 5.0 J/cm2 (355 nm, 10 ns Pulse, 20 Hz, Ø0.342 mm)
3 10.0 J/cm2 (355 nm, 10 ns Pulse, 10 Hz, Ø0.406 mm)
2 15.0 J/cm2 (532 nm, 10 ns Pulse, 20 Hz, Ø0.213 mm)
1 20.0 J/cm2 (1064 nm, 10 ns Pulse, 20 Hz, Ø0.395 mm)

Damage Threshold Data for Thorlabs' Zoom Beam Expanders

The specifications to the right are the damage thresholds for Thorlabs' zoom beam expanders.

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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.


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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
Mid-Infrared,
Sliding Lens
Zoom,
Sliding Lens
Zoom Achromatic,
Sliding Lens
Expansions Available 2X, 3X, 5X, 10X, 20Xa 2X, 3X, 5X, 10X,
15X, 20X
2X, 5X, 10X 0.5X - 2.5X, 1X - 4X 0.5X - 2.5X, 1X - 4X,
2X - 8X, 4X - 16X
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)
400 - 650 nm (A)
650 - 1050 nm (B)
1050 - 1650 nm (C)
Mirror Coating (Range) N/A
Reflectance (per Surface) Ravg < 0.2%
(RMax < 1.5% for -UVB)
RMax < 0.5% Ravg < 1.0% Ravg < 0.2%
(RMax < 1.5% for UVB)
RMax < 0.5%
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
0.5X - 2.5X: 10.9 to 8.0 mm
1X - 4X: 10.9 to 8.8 mm
2X - 8X: 6.0 to 4.4 mm
4X - 16X: 6.0 to 2.7 mm
Wavefront Error <λ/4 (Peak to Valley)
Surface Quality 10-5 Scratch-Dig 20-10 Scratch-Dig 80-50 Scratch-Dig 10-5 Scratch-Dig 20-10 Scratch-Dig
  • These 20X beam expanders are only available with V coatings for 355 nm, 532 nm, or 1064 nm.

Beam Expander
Description
Variable Magnification,
Rotating Lens
Variable Magnification,
Sliding Lens
Reflective Beam Expander
Fixed Magnification
Expansions Available 2X - 5X 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) Ravg < 0.5% Ravg < 0.5% Ravg > 96%
Max Input Beam Diameter 2X - 5X: 4.0 mm 0.5X - 2X: 6.0 mm to 3.0 mm 3 mm
Wavefront Error <λ/4 <λ/10a (RMS)
Surface Quality 20-10 Scratch-Dig 40-20 Scratch-Dig
  • For a Ø1.5 mm Input Beam at 2X magnification, Ø1.0 mm Input Beam at 4X magnification, or Ø0.5 mm Input Beam at 6X magnification.

UV Fused Silica Zoom Beam Expanders, Broadband AR Coated: 240 - 360 nm

Item # Expansion Max Input
Beam Diameter
Diffraction-Limited Input
Beam Diametera
Input Thread Output Thread
(External)
AR Coating
Max Reflectanceb
Typical
Transmission
Damage Thresholdc
ZBE1UVB 0.5X - 2.5X 10.9 mm @ 0.5X
8.0 mm @ 2.5X
10.0 mm @ 0.5X
7.0 mm @ 2.5X
Internal: SM05
External: SM1
SM1 <1.5% (240 - 360 nm) >89% @ 248 nm
>92% @ 266 nm
>90% @ 355 nm
5.0 J/cm² (355 nm,
10 ns Pulse, 20 Hz,
Ø0.342 mm)
ZBE2UVB 1X - 4X 10.9 mm @ 1X
8.8 mm @ 4X
10.0 mm @ 1X
7.0 mm @ 4X
M43 x 0.5d
  • Maximum input beam diameter for output Peak-to-Valley Wavefront Error (WFE) <λ/4 at 633 nm.
  • Per surface.
  • The maximum power that the beam expander can accept is limited by the AR Coating Damage Threshold.
  • The SM2A30 thread adapter can be used to integrate these beam expanders with our SM2-Threaded Lens Tubes and 60 mm Cage System.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ZBE1UVB Support Documentation
ZBE1UVB0.5X - 2.5X UVFS Zoom Beam Expander, AR Coated: 240 - 360 nm
$1,430.00
Today
ZBE2UVB Support Documentation
ZBE2UVB1X - 4X UVFS Zoom Beam Expander, AR Coated: 240 - 360 nm
$1,500.00
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UV Fused Silica Zoom Beam Expanders, 330 - 370 nm V Coating

Item # Expansion Max Input
Beam Diameter
Diffraction-Limited Input
Beam Diametera
Input Thread Output Thread
(External)
AR Coatingb Typical
Transmission
Damage Thresholdc
ZBE13 0.5X - 2.5X 10.9 mm @ 0.5X
8.0 mm @ 2.5X
10.0 mm @ 0.5X
7.0 mm @ 2.5X
Internal: SM05
External: SM1
SM1 Ravg < 0.2%
(330 - 370 nm)

Rmax < 0.7%
(325 - 380 nm)

Rmax < 0.2%
(335 - 362 nm)
>95% @ 355 nm 10.0 J/cm² (355 nm,
10 ns Pulse, 10 Hz,
Ø0.406 mm)
ZBE23 1X - 4X 10.9 mm @ 1X
8.8 mm @ 4X
10.0 mm @ 1X
7.0 mm @ 4X
M43 x 0.5d
  • Maximum input beam diameter for output Peak-to-Valley Wavefront Error (WFE) <λ/4 at 633 nm.
  • Per surface.
  • The maximum power that the beam expander can accept is limited by the AR Coating Damage Threshold.
  • The SM2A30 thread adapter can be used to integrate these beam expanders with our SM2-Threaded Lens Tubes and 60 mm Cage System.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ZBE13 Support Documentation
ZBE130.5X - 2.5X UVFS Zoom Beam Expander, 330 - 370 nm V Coating
$1,430.00
Today
ZBE23 Support Documentation
ZBE231X - 4X UVFS Zoom Beam Expander, 330 - 370 nm V Coating
$1,500.00
Today

UV Fused Silica Zoom Beam Expanders, 495 - 570 nm V Coating

Item # Expansion Max Input
Beam Diameter
Diffraction-Limited Input
Beam Diametera
Input Thread Output Thread
(External)
AR Coatingb Typical
Transmission
Damage Thresholdc
ZBE12 0.5X - 2.5X 10.9 mm @ 0.5X
8.0 mm @ 2.5X
10.0 mm @ 0.5X
7.0 mm @ 2.5X
Internal: SM05
External: SM1
SM1 Ravg < 0.2%
(495 - 570 nm)

Rmax < 0.7%
(488 - 580 nm)

Rmax < 0.2%
(503 - 553 nm)
>96% @ 532 nm 15.0 J/cm² (532 nm,
10 ns Pulse, 20 Hz,
Ø0.213 mm)
ZBE22 1X - 4X 10.9 mm @ 1X
8.8 mm @ 4X
10.0 mm @ 1X
7.0 mm @ 4X
M43 x 0.5d
  • Maximum input beam diameter for output Peak-to-Valley Wavefront Error (WFE) <λ/4 at 633 nm.
  • Per surface.
  • The maximum power that the beam expander can accept is limited by the AR Coating Damage Threshold.
  • The SM2A30 thread adapter can be used to integrate these beam expanders with our SM2-Threaded Lens Tubes and 60 mm Cage System.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ZBE12 Support Documentation
ZBE120.5X - 2.5X UVFS Zoom Beam Expander, 495 - 570 nm V Coating
$1,430.00
Lead Time
ZBE22 Support Documentation
ZBE221X - 4X UVFS Zoom Beam Expander, 495 - 570 nm V Coating
$1,500.00
Lead Time

UV Fused Silica Zoom Beam Expanders, 980 - 1130 nm V Coating

Item # Expansion Max Input
Beam Diameter
Diffraction-Limited Input
Beam Diametera
Input Thread Output Thread
(External)
AR Coatingb Typical
Transmission
Damage Thresholdc
ZBE11 0.5X - 2.5X 10.9 mm @ 0.5X
8.0 mm @ 2.5X
10.0 mm @ 0.5X
7.0 mm @ 2.5X
Internal: SM05
External: SM1
SM1 Ravg < 0.2%
(980 - 1130 nm)

Rmax < 0.7%
(960 - 1160 nm)

Rmax < 0.2%
(1000 - 1100 nm)
>96% @ 1064 nm 20.0 J/cm² (1064 nm,
10 ns Pulse, 20 Hz,
Ø0.395 mm)
ZBE21 1X - 4X 10.9 mm @ 1X
8.8 mm @ 4X
10.0 mm @ 1X
7.0 mm @ 4X
M43 x 0.5cd
  • Maximum input beam diameter for output Peak-to-Valley Wavefront Error (WFE) <λ/4 at 633 nm.
  • Per surface.
  • The maximum power that the beam expander can accept is limited by the AR Coating Damage Threshold.
  • The SM2A30 thread adapter can be used to integrate these beam expanders with our SM2-Threaded Lens Tubes and 60 mm Cage System.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ZBE11 Support Documentation
ZBE11Customer Inspired! 0.5X - 2.5X UVFS Zoom Beam Expander, 980 - 1130 nm V Coating
$1,430.00
Lead Time
ZBE21 Support Documentation
ZBE211X - 4X UVFS Zoom Beam Expander, 980 - 1130 nm V Coating
$1,500.00
Lead Time

Mounting Accessories

Several mounting options for the UVFS Zoom Beam Expanders are provided in the table below. For our complete selection of thread adapters, see our Optical Component Thread Adapters selection guide.

Item # SM1RC(/M) SM1TC CP36 SM2A21 SM2A30
Photo
(Click to Enlarge)
SM1RC SM1TC CP36 SM2A21 SM2A30
Application Slip Ring for Post Mounting Clamp for Post Mounting 30 mm Cage Mount for
Ø1.2" Housing
Mount Zoom Beam Expander in
Ø2" or SM2-Threaded Optic Mounts
Integrate Zoom Beam Expander with
SM2-Threaded Components
Compatible UVFS Zoom Beam Expanders (Item # Prefix) ZBE1
ZBE2
ZBE1
ZBE2
ZBE1
ZBE2a
ZBE1
ZBE2
ZBE2
Internal Bore /
Threads
Ø1.2" Bore Ø1.2" Bore Ø1.2" Bore Ø1.2" Bore M43 x 0.5 Threads
External Threads / Outer Diameter - - - SM2 Threads and
Ø2" Smooth Surface
SM2 Threads
Mounting Holes 8-32 (M4) Tap #8 (M4) Counterbore Compatible with
30 mm Cage Systems
- -
  • The output of these beam expanders will not fit inside of a 30 mm cage system. The CP36 can be used to mount these beam expanders if they are being used at the termination of a section of cage system, i.e., the cage rods only extend over the Ø1.2" section of the housing. If the entire beam expander needs to be enclosed in the cage system, the SM2A21 adapter can be mounted in an LCP09 cage plate for integration into a 60 mm cage system.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Imperial Price Available
SM1RC Support Documentation
SM1RCSlip Ring for SM1 Lens Tubes and C-Mount Extension Tubes,
8-32 Tap
$25.73
Today
+1 Qty Docs Part Number - Universal Price Available
SM1TC Support Documentation
SM1TCClamp for SM1 Lens Tubes and C-Mount Extension Tubes
$46.86
Today
CP36 Support Documentation
CP3630 mm Cage Plate, Ø1.2" Double Bore for SM1 and C-Mount Lens Tubes
$22.62
7-10 Days
SM2A21 Support Documentation
SM2A21Externally SM2-Threaded Mounting Adapter with Ø1.20" (Ø30.5 mm) Bore and 2" Outer Diameter
$50.19
Today
SM2A30 Support Documentation
SM2A30Adapter with External SM2 Threads and Internal M43 x 0.5 Threads
$16.97
Today
+1 Qty Docs Part Number - Metric Price Available
SM1RC/M Support Documentation
SM1RC/MSlip Ring for SM1 Lens Tubes and C-Mount Extension Tubes,
M4 Tap
$25.73
Today