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TECHSPEC® components are designed, specified, or manufactured by Edmund Optics. Learn More

75mm Sq., 4mm Thick, VIS-NIR Coated λ/4 N-BK7 Window

Stock #37-072 Other Coating Options
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Qty 6+
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Abbe Number (vd):
Protective as needed
Clear Aperture (%):
Clear Aperture CA (mm):
67.50 x 67.50
Dimensions (mm):
75.00 x 75.00
Thickness (mm):
4.00 ±0.20
VIS-NIR (400-1000nm)
Coating Specification:
Rabs≤0.25% @ 880nm
Ravg ≤1.25% @ 400 - 870 nm
Ravg ≤1.25% @ 890 - 1000nm
Coefficient of Thermal Expansion CTE (10-6/°C):
7.1 (-30 to +70°C)
8.3 (+20 to +300°C)
Density (g/cm3):
Fine Ground
Index of Refraction nd:
Knoop Hardness (kg/mm2):
Parallelism (arcmin):
Poisson's Ratio:
Substrate: Many glass manufacturers offer the same material characteristics under different trade names. Learn More
Surface Flatness (P-V):
Surface Quality:
Protective Window
Typical Energy Density Limit:
5 J/cm2 @ 532nm, 10ns
Wavelength Range (nm):
400 - 1000
Young's Modulus (GPa):
Length (mm):
Width (mm):
Damage Threshold, By Design: Damage threshold for optical components varies by substrate material and coating. Click here to learn more about this specification.
5 J/cm2 @ 532nm, 10ns

Regulatory Compliance

RoHS 2015:
Reach 224:
Certificate of Conformance:

Product Family Description

  • Circular and Square Sizes from 5mm to 150mm
  • 6 Broadband Anti-Reflection Coating Options Available
  • World's Largest selection of Standard N-Bk7 Windows
  • Also Available with Laser Line V-Coats

TECHSPEC® λ/4 N-BK7 Precision Windows are ideally suited for industrial and low power laser applications. The high tolerance design yields minimal beam distortion and scatter. Broadband coating options extend the range of these precision windows through the visible and near-infrared spectra.

Note: New additions to this product family may be specified with a transmitted wavefront distortion (TWD) specification instead of a surface flatness. For more information on the difference between these two specifications, see our application note on Understanding Optical Windows

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