Laser Beam Attenuators
 Neutral Density Attenuation of 29  34 dB
 UV Fused Silica Prism Design for up to 200 W Max Power
 30 mm Cage Compatible and Post Mountable
Back
Front
ATT30
Prism Attenuator,
Uncoated
T2 Port Transmission
(~510% Intensity)
Input Beam
(100% Intensity)
Reflected Output Beam
(~0.05% Intensity)
T1 Port Transmission
(~9095% Intensity)
Please Wait
Key Specs^{a}  

Input & Output Apertures  Ø19 mm  
Attenuation  29 to 34 dB  
Wavelength Range^{b} 
ATT30(/M)  200  2000 nm (Uncoated) 
ATT30(/M)UV  AR Coated for 245  400 nm  
ATT30(/M)A  AR Coated for 350  700 nm  
ATT30(/M)B  AR Coated for 650  1050 nm  
ATT30(/M)C  AR Coated for 1050  1700 nm  
ATT30(/M)YAG  AR Coated for 532 & 1064 nm  
Max Input Power  Uncoated: 200 W AR Coated: 50 W 

Polarization Insensitivity  ≤1° Azimuth, ≤1° Ellipticity 
Click to Enlarge
Mounting Features
Features
 Ideal for Attenuation Prior to Beam Characterization Applications:
 Beam Profiling: Beam Size, Beam Shape, and Beam Stability
 M^{2} Measurement: Beam Quality, and Waist Position
 Polarimetry: Ellipticity and Azimuth Angle
 Spectral Analysis
 UV Fused Silica Prism Substrate
 Uncoated or ARCoated Prisms (Coatings Applied to Second Surface Only)
 Compatible with 30 mm Cage Systems
 SM1Threaded Input, Output, and Beam Dump (T1/T2) Apertures
 1/4"20 (M6 x 1.0) Tap for Post Mounting
 Black Anodized Aluminum Housing
Thorlabs' ATT30 Series Beam Attenuators use a twofold reflection on two stacked prisms for attenuation of highpower beams up to 200 W (uncoated) or 50 W (AR coated). AR coatings are only applied to second surfaces for the purpose of reducing secondary beams at the output port caused by multiple reflections at the second surface each prism. The beam attenuation varies smoothly with wavelength (see the Graphs tab).
The two compensating reflections preserve the polarization, size, and shape of the beam, allowing these attenuators to be used with polarization instrumentation while minimizing the effects on the measurement. The prisms transmit up to 95% of the light through the transmission apertures (labeled T1 and T2 in the diagram above). Beam blocks or traps (not included) should be installed on the transmission ports of the ATT30 series attenuators to capture any high residual laser power.
For ease of integration with our 30 mm cage systems, the housings feature 440 mounting threads around the input port and Ø6 mm bores for cage rods around the output port. All ports feature SM1 (1.035"40) internal threads for mounting lens tubes or other SM1threaded optomechanics. These mounting features also allow tandem positioning to enhance the attenuation. To discuss potential custom AR coating wavelengths not available below, please contact Tech Support.
Common Specifications^{a}  

Optical Specs  
Prism Substrate  UV Fused Silica^{b} 
Input & Output Apertures  Ø19 mm 
Typical Attenuation^{c,d}  29  34 dB 
Polarization Insensitivity  ≤1° Azimuth ≤1° Ellipticity 
Surface Quality  2010 ScratchDig 
Surface Flatness  <λ/4 at 633 nm 
Exit Angle of Reflected Beam on each Prism 
90° ± 10° arcmin 
Mechanical Specs  
Input Aperture  Ø19 mm 
Dimensions  44.0 mm x 76.5 mm x 44.0 mm (1.73" x 3.01" x 1.73") 
Mass  0.303 kg (0.668 lbs) 
Operating Conditions  
Operating Temperature  0 to 40° C 
Storage Temperature  40 to 70° C 
Item #  AR Coating^{a}  Wavelength Range  Max Input Power  LIDT^{b} 

ATT30(/M)  Uncoated  200  2000 nm  200 W  10 kW/cm^{2} 15 J/cm^{2} 
ATT30(/M)UV  UV  245  400 nm  50 W  400 W/cm^{2} 2 J/cm^{2} 
ATT30(/M)A  Visible  350  700 nm  
ATT30(/M)B  NearIR  650  1050 nm  
ATT30(/M)C  NearIR  1050  1700 nm  
ATT30(/M)YAG  Nd:YAG  532 & 1064 nm 
Click to Enlarge
The graph above is a comparison of ATT30 series prism attenuators with our reflective and absorptive (visible and nearIR) neutral density (ND) filters with optical density (OD) = 3.0. Note that OD = (attenuation in decibels)/10.
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:  
Martin Redeby
(posted 20211008 05:21:14.107) I don't see a specified length of the beampath, please add (even though it is easy to calculate).
also a half size sm0.5 version would be awesome! nreusch
(posted 20211015 06:46:32.0) Thank you for your feedback and your suggestion, we will consider adding a 1/2’’ version in the future. The length of the beam path is 76.2 mm (3’’). 