Optics Lab: An overview

List of Experiments • Optical Activity

• Faraday’s Effect • Michelson Interferometer • Ellipsometery • Reflection, Transmission and Fresnel’s coefficients • Interference and Diffraction • Scanning Fabry Perot interferometer • Basic properties of Laser diode • Polarization • Debye Spear’s velocity of sound • Diffraction Grating • Frustrated Total Internal Reflection • Zeeman Effect • Optical Pumping

Reflection, Transmission and Fresnel’s coefficients

•Working with optical components •Investigation of polarization by reflection •Verification of Fresnel’s equations •Finding the Brewster’s angle •Finding the Refractive index of thin micro scope slide

• Drive Fresnel’s Coefficients, rs, ts, rp and tp

• Find the Brewster angle for p- polarized light • Find index of refraction • Predict the reflectance curves by Matlab simulations • Collect the data for Rp, Rs, R45 for all possible incident

angles • Plot data

Experiment

Results

Interference and Diffraction

•Superposition of waves •Interference condition •Fraunhoufer diffraction •Single slit and double slit diffraction patterns •Babinet’s principle: opposite of a slit

Experiment

• Predict the angular dependence of intensity of the diffracted light

where, , a is the slit width and θ is

the angle between the normal to the slit and the distance to the observation point.

• Measure the angular dependence of intensity of diffracted light for different slit widths

• Calculate the width of the central maximum • Do the same for double slit diffraction patterns • Analysis of interference pattern for double slit • Verification of Babinet’s principle

2

2

0)(sin

ββII =

)sin(2

2 θλπβ a

=

azx λ2

0 =∆

CCD/photodiode

θ x

z

sin( )θ =+

xx z2 2

CCD

HeNe

Slit

wid

th ‘a

’

θ

0

10

20

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90

100

1 21

41

61

81

101

121

141

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261

281

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321

341

361

381

401

421

441

461

481 0

20

40

60

80

100

120

1 19

37

55

73

91 1…

12

7 14

5 16

3 18

1 19

9 21

7 2…

2…

271 2…

3…

3…

3…

36

1 3…

3…

415 4…

Single slit diffraction pattern Diffraction pattern of my hair

0

50

100

150

200

250

300 0 18

36

54

72

9…

1…

1…

1…

1…

1…

1…

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2…

2…

3…

3…

3…

3…

3…

3…

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4…

4…

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6…

Interference and diffraction pattern of double slit

Single slit envelope Interference

pattern

Scanning Fabry Perot Interferometer

•To understand the basics of SFPI •To align the instrument to perfection •To investigate the longitudinal modes of HeNe

HeNe Laser

Plano convex lens

Fabry Perot interferometer

Control box

Free spectral range FSR = c/4nd = 1.5 GHz

FWHM=.44ms x calibration factor Finesse (the resolution of the instrument) = FSR/FWHM >150

Basic properties of Laser Diodes

• Laser diode collimation • Understand the concept of PI controller • Use PI controller for tuning of laser diode • Optical spectrum of laser diode

Temperature controller circuit

Current controller

PD LD

Set temperature

IRF540

PI controller

DAQ

TEC element

V

LD temperature

TCLDM9

Tuning of laser diode

Optical power tuning by changing the injection current

Characteristic of Laser diode

Wavelength tuning

Wavelength tuning

Optical power of laser diode reduces with temperature

References

• “Introduction to optics”; Frank L. Pedrotti • “Optics”; Eugene Hecht • www.thorlabs.com

To be continued…..