Fabry - Perot Interferometer

(Projection based)

Model: HO-ED-INT-10

In Fabry - Perot interferometer, the distance between the partially reflecting mirrors are varied by using coarse and finely adjustable translation stage driven by micro-meters. One beam splitter is fixed and the other is mounted on the translation stage through a kinematic mount. This two axis kinematic mount is used to correct the parallelism between beamsplitters.

The Fabry - Perot design contains plane surfaces that are partially reflecting so that multiple rays of light are responsible for the creation of the observed interference patterns. For high resolution spectroscopy, where a resolution in the range of MHz to GHz is required, a Fabry - Perot interferometer (FP) is used. The FP consists of two plane mirrors mounted accurately parallel to each another, with an optical spacing of 'd' between them.

The enclosed air gap generally varies from several millimeters to centimeters, when the device is used interferometrically. If the gap can be mechanically varied by moving one of the beam splitters, then the device is referred to as an interferometer. It’s transmission spectrum as a function of wavelength exhibits peaks of transmission corresponding to resonances of the etalon. Fabry - Perot interferometers are widely used in telecommunication, lasers and spectroscopy for controlling and measuring the wavelength of light.

Experiment Examples

To find the wavelength of monochromatic light

The wavelength of laser is calculated by,

λ  =  ( 2d / N ) Δ

where ‘d’ is the change in position that occurs for ‘N’ fringes to pass and Δ is the calibration constant of the micrometer

To determine the spacing between the plates of fabry perot etalon from the fringe Pattern

The Spacing of the Etalon is given by,

t  =  nD2λ  /  χn2

where n is the order, ‘D ’ is the distance between the etalon and the screen, ‘λ’ is the wavelength of light used.

χn2  =  χm+n2  -  χm2

χm+n2 is the square of the radius of (m+n)th ring and χm2 that of mth ring.

To find the finesse and free spectral range (FSR) of etalon from the fringe calibration at different cavity thickness

The Free Spectral Range of the Etalon is given by,

FSR  =  c / 2t,

Where c is the speed of light in air and t is the spacing of the Etalon

The finesse is a measure of the interferometer's ability to resolve closely spaced spectral lines.

The finesse F is defined by the following equation.

F  =  π √R / ( 1-R )

Where, R is the reflectivity of surfaces

Fabry - Perot Interferometer – Spectral Range

If two wavelengths are very close, their fringe maxima may overlap

The two peaks will be distinguishable if the two wavelengths are too close

A separation of full width at half maximum (FWHM) corresponds to minimum separation between the wavelength components

Related Topics

Spectral range

Wavelength

Resolving power

Finesse of etalon

Interference
Features

Diode laser is used as the light source.

The mechanical assembly is made out of corrosion free materials.

All components and modules are mounted on rail by carriage system for easy adjustment.

The optics and mechanics used are of research quality.
Scope of Supply

Optical Rail

Model No: ED-INT-10-OR
Length
:
1000 mm
Material
:
Black anodized Aluminum alloy
Quantity
:
1 no.

Fabri-Perot Interferometer

Model No: ED-INT-10-FPI
Material
:
N-BK7
Diameter
:
25 mm
Coating
:
Aluminium
R / T
:
60 : 40
Spacing of plates
:
2 - 8mm variable
Least count of micrometer
:
0.01 mm
Quantity
:
1 no.

Kinematic Laser Mount

Model No: ED-INT-10-KLM
Material
:
Black anodized Aluminum alloy
:
:
+/-4 degrees
Quantity
:
1 no.

Plano Convex Lens with Mount Supply

Model No: ED-INT-10A-PCLM
Material
:
N-BK7
Diameter
:
20 mm
Effective Focal Length
:
26 mm
Quantity
:
1 no.

Diffuser Screen with Measurement unit

Model No: ED-INT-09-DSM
Material
:
Float
Size
:
150 x 138 x 3 mm
Quantity
:
1 no.

Diode Laser with Power supply (Red)

Model No: ED-INT-10-DLPR
Wave length
:
650 nm
Optical power
:
5 mW
Quantity
:
1 no.

Diode Laser with Power supply (Green)

Model No: ED-INT-10-DLPG
Wave length
:
532 nm
Optical power
:
5 mW
Quantity
:
1 no.

Accessories

Allen Key
User Manual

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