Advanced Optics Lab at San Jose State University

Ramen Bahuguna

Department of Physics

• We meet once a week for 4 hours. One hour lecture+3 hours of Lab

• There are about 6 labs and one project. The project takes about a month

• The prerequisite is Physics 158 Optics course using Pedrotti or Hecht’s book

We do the following experiments:

• Experiment (1) (Lecture on “Familiarity with optical techniques and optical components)

• Cleaning of Optics• Aligning a laser beam through a narrow glass tube with

two plane mirrors• Aligning a spatial filter for filtering an expanded laser beam• Collimating an expanded Laser beam using a wedged

plate shearing interferometer• Rotation of Polarization by two reflections• Use of wave plates• Use of Beam Splitters (cube as well as variable plate)• Optical isolator

• Experiment (2): (lecture on refraction in a prism)

• Measuring refractive index of a liquid placed in a hollow prism by minimum deviation method

• Experiment (3): (Lecture on Geometrical Optics-imaging with lens combinations)

• imaging with a single lens• imaging with concave and convex mirrors• imaging with lens combinations• real and virtual images• proper use of a doublet to collimate a beam

• Experiment (4): (Lecture on Interferometery)• (a)Alignment of a Michelson Interferometer using

three techniques• (b)Measurement of refractive index of air with a

Michelson Interferometer• Experiment (5): (Lecture on Holography and

diffraction Gratings)• (a)Fabrication of a Reflection Hologram• (b)Fabrication of a Holographic Diffraction

Grating and determining its diffraction efficiency

• Experiment (6): (Lecturer on Fourier transforming properties of lenses)

• (a)Abbe-Porter experiment in Fourier Optics.• (b) Different Fourier transforming configurations

using a lens: scaling properties• Experiment (7): (Lecture on Subjective and

Objective laser speckles)• (a) measurement of small translation of a diffuse

object by Laser Speckle Photography• (b) measurement of small rotation of a diffuse

object by laser Speckle Photography

• Experiment (8): (Lecture on Holographic Interferometry)

• Measurement of small rotations of a diffuse object by Holographic Interferometry

PROJECTS

• Student Grating Spectrometer• (a) building a collimator A variable slit is provided to the students. They are

supposed to select a doublet lens of the proper focal length from a catalog such that for a typical source the lens is substantially illuminated. This in turn will illuminate a substantial part of the grating which will result in higher resolution.

• (b) building a telescope The students select two doublet lenses for the telescope

keeping in mind the fact that they have to overfill the pupil of their eyes so that the spectrum does not disappear on moving one's head slightly. Over filling the pupil will result in loss of intensity.

• (c) Fabrication of a holographic diffraction grating

The students are asked to fabricate a holographic grating with 600 lines/mm. They calculate the angle between the two plane waves by the formula: d= λ/(2sinθ)

A laser beam is expanded, collimated and then split with a beam splitter and then combined with the help of mirrors on a holographic plate (PFG-01). Once fabricated, the grating constant is determined by diffracting a laser beam.

• (d) Mounting of the collimator, telescope and the grating on the turn table provided.

All the components are mounted on the turn table and aligned. Interaction with the mechanical shop is key to the success of the project. Finally the spectrometer is tested with a known spectrum.

Fingerprint Sensor

• In this project the students are asked to study a patent on Fingerprint sensor based on Total Internal Reflection. They are asked to select a prism from a catalog with parameters close to that mentioned in the patent. They are also provided with a CCD camera.

• (a) The Light Source. The students come up with several LEDs' as a source of uniform illumination of the finger.

• Image Capture. They calculate the viewing angle from the given formula. Viewing at this angle reduces the keystone image. They are also asked to derive the formula from the fundamentals.

finger

Camera l lens

LED source

image of fingerprint

Refractive Index measurement of a given liquid

• In this project the students measure the refractive index of several liquids. The principle is based on the well known "Apparent depth technique" but with better precision.

• (a) Expansion and collimation of the laser beam A He-Ne laser is used as a source of light. The laser light

is expanded by means of a microscopic objective. The beam is spatially filtered through a pin hole to remove diffraction artifacts. A hollow glass cell is placed in the path of the expanded beam. The expanded beam is collimated by a doublet mounted on a axial translational stage. The collimation is tested with a parallel plate shearing interferometer. The reading on the translational stage is recorded.

• (b) Testing Collimation after the cell is filled with the desired liquid

The glass cell is then filled with the given liquid. The collimation is obviously disturbed due to the apparent position of the laser point source. The lens is translated to get back the collimation using the interferometer and the new position of the stage recorded. From the two data one can easily calculate the refractive index of the liquid by the well known formula:

N= Real Depth/Apparent Depth

Laser point source

Liquid cell lens

Wedged plate

Interference bands on screen

Collimated beam