Babinet Compensator

Model: HO-ED-P-08

A Soleil-Babinet Compensator is a continuously variable zero-order retarder (wave plate) that can be used over a broad spectral range.The variable retardance is achieved by adjusting the position of a long birefringent wedge with respect to a short fixed birefringent wedge.The wedge angle and fast axis orientation is the same for both wedges so that the retardance is uniform across the entire clear aperture of the Soleil-Babinet compensator.

A compensator plate is attached to the fixed wedge, with its fast axis orthogonal to both the fast axis of the wedges and the propagation direction of the light. When the long birefringent wedge is positioned such that the total thickness of the two stacked wedges is equal to the thickness of the compensator plate, the net retardance of light passing through the Soleil-Babinet compensator will be zero. The position of the long wedge can then be adjusted with a precision micrometer in order to create a retardance transmitted beam of light.

Experiment Examples

To calibrate the Babinet compensator with monochromatic light.

The refractive index of the solid prism using the formula,

n    =    sin  ( (α+β) / 2 )   /   sin (α/2)

Where α is angle of the prism & β is angle of minimum deviation.

Measurement of the sample birefringence

Dispersive power,

ω = (n2- n1) / (n - 1)

where,

n1 and n2 are the refractive indices of the prism for any two colours, and n = (n1 + n2 ) / 2

Experiment procedure

Determine precisely the Babinet compensator interfringe at the wavelength of the green line of mercury. This is about 2.4 mm. The polarizers are spaced apart with their polarization axis rotated 90° to each other so that no light is transmitted. At this point the polarizers are crossed. Insert compensator in between the two polarizers. Adjust the tip/tilt so that the compensator is perpendicular to the optical beam. Turn the Babinet compensator to find the extinction. Fringes of high contrast should appear. Using micrometer, record the reading between two null position of the fringe.

Specifications

Wavelength range    :    380- 650 nm

Aperture    :    10 mm

Rotation    :    360°
Measurement of the sample birefringence

Using Babinet compensator, ordinary and extra-ordinary rays of light are produced. These light rays interfere and the interference fringes are observed. By introducing the sample sheet in between the incident ray and Babinet compensator, shift in the fringe pattern is produced. The fringe shift is measured and the differences in the refractive indices of the ordinary and extraordinary rays are calculated.

Calibration of the Babinet compensator with monochromatic light

A schematic diagram of the experimental setup

Related Topics

Wavelength

Polarization

Babinet compensator

Birefringence
Scope of Supply

Optical Rail

Model No: ED-P-08-OR
Length
:
500mm
Material
:
Black anodized Aluminum alloy
Quantity
:
1 no.

Babinet compensator with mount

Model No: ED-P-08-BCM
Material
:
Quartz Crystal
Surface Quality
:
40 - 20 (Scratch-dig)
:
0 - 2π (full wave)
Rotation
:
360° continuous
Quantity
:
1 no.

Polarizer with mount

Model No: ED-P-08-PRM
Material
:
Sheet Polarizer
Rotation
:
360 degree
Resolution
:
1 degree
Quantity
:
1 no.

Analyzer with mount

Model No: ED-P-08-ARM
Material
:
Sheet Polarizer
Rotation
:
360 degree
Resolution
:
1 degree
Quantity
:
1 no.

Diode laser with power supply

Model No: ED-P-08-DLPR
Wave length
:
650 nm
Optical power
:
3 mW
Quantity
:
1 no.

Detector with output measurement unit

Model No: ED-P-08-DOMU
Sensor Type
:
Photo Transistor
Display
:
7 segment, 3 ½ digit
Range
:
0 - 199 milli / micro amperes
Quantity
:
1 no.

Sample with mount

Model No: ED-P-08-SM
Quantity
:
1 no.