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412 PHYS

Lasers and their Applications

Department of Physics

Faculty of Science

Jazan University

KSA

laser applications

Lecture-10

Optical Alignment ----”Optical tooling”

Low-power lasers provide considerably higher radiance for tooling applications than conventional

light sources. They are easily visible in ambient lighting conditions even at distances of hundreds

of feet from the laser. Lasers have been specifically designed for tooling applications, and these

are sometimes called "tooling lasers."

Laser tooling involves the use of the unidirectional beam for such tasks as determining

displacement of objects from a line, determining angular alignment, establishing planes,

performing leveling, and establishing right angles. Both helium-neon and semiconductor diode

lasers have been used for this applications

Many practical alignment systems employ a laser and a centering detector that

automatically determines the location of the center of the beam.

Laser tooling requires only one person to set up and operate the equipment. The

measurement is made by reading linear displacement directly from a meter. The

readings compare well for different operators. This is in contrast to conventional

optical tooling, wherein a single operator may be able to obtain reproducible

readings, but different operators may arrive at different results.

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Angle Tracking

A laser source illuminates a target. Light reflected by the target is imaged on the

detector. Angular information about the target is derived from the known position

sensitivity of the detector as indicated in figure below.

The angle α between the incoming rays and the optical axis common to the objective

and the detector is given as

where y is the lateral displacement of the

image from the centerline of the detector

and f is the focal length of the lens. For

small values of a, less than 5o this may be

approximated by

Confocal setup for surface

metrology. The pinhole is replaced

by a micro-lens array to cover a

large field of view.

Laser Scanning Applications

Laser triangulation setup

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Dr. M Fadhali - Laser applications

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6/14/2015 Dr. M Fadhali - Laser applications

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6/14/2015 Dr. M Fadhali - Laser applications

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Laser Metrology - Interferometry Basic Interferometry and Optical Testing

1. Two-Beam Interference

2. Fizeau Interferometer

3. Twyman-Green Interferometer

4. Laser-Based Fizeau Interferometer

5. Mach-Zehnder Interferometer

Holography

An ordinary photograph represents a two-dimensional recording of a threedimensional

scene. The emulsion on the photographic plate is sensitive only to the

intensity variations, and hence while a photograph is recorded, the phase distribution

which prevailed at the plane of the photograph is lost. Since only the intensity

pattern has been recorded, the three-dimensional character (e.g., parallax) of the

object scene is lost.

It was in the year 1948 that Dennis Gabor conceived of an entirely new

idea and proposed a method of recording not only the amplitude but also

the phase of the wave

The principle behind the method is the following: During the recording

process, one superimposes on the wave (emanating from the object) another

coherent wave called the reference wave

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The two waves interfere in the plane of the recording medium and produce

interference fringes.

This is known as the recording process. The interference fringes are characteristic

of the object and the recording medium records the intensity distribution in the

interference pattern.

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This interference pattern has recorded in it not only the

amplitude distribution but also the plane of the object wave.

Reconstruction

Process

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Holography

eye

reconstructed

image

reconstruction

beam

diffracted

reference beam

hologram LASER

Hologram (photographic

plate)

reference beam

beam

expander

BS objec

t

illuminating

beam

photographic

plate

object

illuminating

beam

eye 2D representation of

image (no depth)

photograph

Photography - record electric field intensity of light scattered by object

Holography - record electric field intensity and phase

RECORDING READING / RECONSTRUCTING

Holographic One-Way Window

• Large hologram of a window display

masks the interior

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• Indoor environments have controllable optical environments

• Holography may provide a way to disguise or mislead intruders

Door With Edge

Illuminated Hologram

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Infrared Holography

• Infrared holography is appealing because viewing devices are much

less sophisticated than the human eye

• Color fidelity is much less important

• no such holograms exist nor do the materials to make them

Example

holography

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Laser Ring Gyroscopes

Lasers can be used to measure angular rotation with great accuracy and precision.

Commercially available laser based gyroscopes are currently used in both aircraft

and shipping with single or triple axis devices used for orientation and stabilization.

Laser gyroscopes have number of advantages over more conventional gyros such as :

· there are no moving parts

· simple design , generally less than 20 component parts

· very rugged , vibration g and g2 insensitive

· wide dynamic range (>109)

· output is inherently digital and TTL compatible

· fast update rate , less than 50ms to measure a rotation of 0.5o/hour

· long and reliable lifetime (>30,000 hours)

· low total cost of ownership , “fit and forget”, no maintenance

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It applies quite generally to any path with an

enclosed area A and perimeter S.

(This is often referred to as the Sagnac effect:

Sagnac successfully demonstrated a rotating

ring interferometer in 1913).

The basic equation used for angular rotation

rate measurement.

S

A

Sc

Af

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Applications: • Navigation

• Geophysics

• Relativity

• Symmetry testing

• Quantum Field Theory

Example: Frequency shift in a ring laser gyro

Let us calculate the frequency shift corresponding to a rotation rate of 0.1° h-1 in a

triangle with 0.1 m side length assuming l = 632.8 nm.

The area of the triangle is (√3 x 10-2)/4 m2

S

A

Sc

Af

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Sol.

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Laser-Induced Fusion

It is well known that the enormous energy released from the sun and the stars is

due to thermonuclear fusion reactions, and scientists have been working for over 40

years to devise methods to generate fusion energy in a controlled manner. Once this

is achieved, one will have an almost inexhaustible supply of relatively pollutionf-ree

energy.

A thermonuclear reactor based on laser-induced fusion offers great

promise for the future. With the tremendous effort being expended on fabrication

of extremely high-power lasers, the goal appears to be not too far away, and once

it is practically achieved, it would lead to the most important application of the

laser.

Consider a nuclear reaction in which the two deuterons react to form a tritium

nucleus and a proton:

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The basic principle of pulsed laser range finding is shown in Figure 1. A short laser

pulse is sent out from a source directed to the target. Coincident with the emission of

this pulse a clock is started and, when the pulse is reflected from the target and returned

to a detector, the clock is stopped. The time for the round trip journey may be used to

calculate the distance to the target given that the speed of light is a known constant :

Military Applications

Given that the ranging pulse travels at the speed of

light, high speed timing will be required and the

shorter the range, or the smaller the error tolerance,

the more accurate the timing circuitry will need to

be. As an example take a target 100km distant. The

time of flight of the pulse will be approximately,

Timing Measurements

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