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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).

Reference:

Birefringent filter for laser tuning: theory and design

The birefringent filter plates in this page typically have a thickness of multiples of T (T=0.5 mm) with the diameter of 1" or 0.5".  More quartz plates/blocks with various apertures, thicknesses and coatings are available under the general "Quartz Crystals".

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Aperture:
Thickness:
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) :
no2=2.3573-0.01170λ2+0.01054/λ2+1.3414x10-44-4.4537x10-76+5.9236x10-88
ne2=2.3849-0.01259λ2+0.01079/λ2+1.6518x10-44-1.9474x10-66+9.3648x10-88

 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

AR-coating:

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

 


Cut orientation (a-cut):

 

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