Chemical Formula

Be(Al_1-xCr_x)₂O₄

Crystal Lattice

Orthorhombic

Lattice Constant

a=5.476Å per ASTM 10-32

b=9.404 Å

c=4.427 Å

X-ray Density

3.7g/cm³

Melting Point

1870 °C

Thermal Expansion

∥a 5.9×10^-6 K^-1

∥b 6.1×10^-6 K^-1

∥c 6.7×10^-6 K^-1

Thermal Conductivity

0.23 Wcm^-1K^-1

Hardness（Vickers）

2000 kgmm^-2

Yang’s Modulus

469 GPa

Fracture Stress

0.457-0.948 GPa

Heat Shock Resistance

35-74W/cm

Diameter Tolerance

+.000”/-.002”

Clear Aperture

≥98%

Chamfer

0.005“± 0.003“@45°

Roll Finish

55±5 μinches

Perpendicularity

<5′

Parallelity

<30″

Flatness

λ/[email protected]

Surface Finish

10-5 scratch-dig per MIL-O-13830

Wavefront Distortion

Less than λ/2 per inch (measured in 1 micron)

End Coating

Single-layer MgF₂

Single wavelength, broadband

AR coating

Cr Doping

Reflection standard range: 0.10–0.17 at.%

Optimal chromium concentration: 0.83/d at.% (diameter in mm)

Chromium Concentration Range

0.01-0.2 at.%

Chromium Ion Concentration (0.1 at.%)

3.51×10cm^-3

Refractive Index (750 nm)

(Two-axis)

E ||a = 1.7367

E ||b = 1.7421

E ||c = 1.7346

Doping Position Symmetry

78% mirror (laser active)

22% inversion

Nonlinear Refractive Index，n₂

~10-13 esu

Findlay-Clay Insertion Loss

<0.3% cm^-1

Refractive Index Temperature Change

8×10-6 K^-1