Birefringent Filter Plates

Birefringent Filter Plates
Birefringent Filter Plates Birefringent Filter Plates

The birefringent filter (Lyot filter) plate is a linear retarder made of a-cut (or 90o cut with the maximum birefringence) crystalline quartz and used intracavity to selectively tune a desired wavelength and create reflection losses at other wavelengths. In use, it is placed at Brewster’s angle, and then rotated about the axis perpendicular to the surface to achieve a full wave retardation at the wavelength of interest. The selected wavelength contains only a p-polarization component, and thus experience no reflection loss. Other wavelengths undergo a different retardation, and have some amount of s-polarization, leading to reflection losses.

A birefringent filter used in a short-pulse laser cavity can be a single quartz plate. A birefringent filter for a narrow linewidth CW laser can contain a stack of 2–4 quartz  plates, each plate being half the thickness of the previous one. The thickest plate sets the bandwidth and the thinnest the free spectral range (FSR).


Birefringent filter for laser tuning: theory and design

On this page are A-cut filter plates with a thickness of multiples of T (T=0.5 mm). Some 25-deg cut plates for some specific applications are also included on this page.  More quartz plates/blocks with various apertures, thicknesses and coatings are on the page for the general "Quartz Crystals".

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Part No. Description Aperture Thickness Price Availability Add to Cart

Basic Properties of Quartz Crystal:

Transparency Range: 200 - 2300 nm

material-cq.GIF (10904 bytes)

Transmission Curve

Crystal Symmetry: Hexagonal, P3121
Lattice Constants: a=b=4.9133A, c=5.4053A
Density:  2.65 g/cm3
Thermo-Optic Coefficients:
dno/dT= -0.52 x 10-6 /oC @ 530 nm
dne/dT= -0.63 x 10-6/oC  @ 530 nm
Damage Threshold ( 10 ns, 10 Hz)
~ 1GW/cm2 at 1064 nm
~ 500 MW/cm2 at 532 nm
Optical Homogeneity: Δn < 10-6/cm
Mohs Hardness:  7
Thermal Expansion Coefficients:   αa = 14 x 10-6/K
  αc = 7.6 x 10-6/K
Linear Absorption Coefficients: α<0.01 cm-1 from 300 to 2300 nm

Sellmeier Equations: (λ in µm) :

 Wavelength (nm) no ne Birefringence
Walk-off Angle
 at 45°
1064 1.5341 1.5428 0.00872 -0.325°
800 1.5384 1.5473 0.00891 -0.331°
632.8 1.5427 1.5517 0.00906 -0.336°
532 1.5469 1.5561 0.00920 -0.340°
400 1.5577 1.5673 0.00957 -0.351°
355 1.5646 1.5744 0.00982 -0.358°
266 1.5916 1.6024 0.01077 -0.386°




Cut Orientation: a-cut +/-5 arc min with the optical axis (c-axis) in the plane surface
Diameter Tolerance: +0, -0.25 mm
Thickness Tolerance: +/-0.05 mm for T=<5mm, +/-0.1 mm for T>5mm 
Surface Quality: 10/5 Scratch and Dig
Parallelism: < 3 arc sec
< 10 arc min
< λ/8 @ 632.8 nm (for T>=1.0 mm)
Transmission Wavefront Distortion: < λ/8 @632.8 nm


R < 0.2% at the central wavelength is available upon request


Cut orientation (a-cut):

 * The optical axis (c-axis) is in the circular plane and perpendicular to the flat cut edge. 

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