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).
Reference:
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".
| Part No. | Description | Aperture | Thickness | Price | Availability | Add to Cart |
Basic Properties of Quartz Crystal:
| Transparency Range: 200 - 2300 nm |
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| 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 |
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| Damage Threshold ( 10 ns, 10 Hz) ~ 1GW/cm2 at 1064 nm ~ 500 MW/cm2 at 532 nm |
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| 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 |
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| Linear Absorption Coefficients: α<0.01 cm-1 from 300 to 2300 nm | ||||
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Sellmeier Equations: (λ in µm) : |
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| Wavelength (nm) | no | ne | Birefringence (Δn=ne-no) |
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° |
Specifications:
| 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 |
| Perpendicularity: Flatness: |
< 10 arc min < λ/8 @ 632.8 nm (for T>=1.0 mm) |
| Transmission Wavefront Distortion: | < λ/8 @632.8 nm |
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AR-coating: |
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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