EEE 6503 LASER T HEORY C HAPTER -7:: F AST P ULSE P RODUCTION C - - PowerPoint PPT Presentation

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EEE 6503 LASER T HEORY C HAPTER -7:: F AST P ULSE P RODUCTION C - - PowerPoint PPT Presentation

Sep 22, 2022 280 likes •774 views

EEE 6503 LASER T HEORY C HAPTER -7:: F AST P ULSE P RODUCTION C HAPTER -8:: N ONLINEAR O PTICS Presented by, 1 A.F.M. Saniul Haq ID# 0412062205 F AST P ULSE P RODUCTION 2 I NTRODUCTION LASERs are widely used for marking, cutting, drilling.

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EEE 6503 LASER THEORY CHAPTER-7:: FAST PULSE PRODUCTION CHAPTER-8:: NONLINEAR OPTICS

Presented by, A.F.M. Saniul Haq ID# 0412062205

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FAST PULSE PRODUCTION

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INTRODUCTION

LASERs are widely used for marking, cutting,

drilling.

Works on the principle of vaporizing material CW LASER tends to heat the surrounding area of

target and also can damage substrate. target and also can damage substrate.

Short pulses are best for controlled operation. Fast, powerful pulses tend to ablate material quickly

without heating.

For many operation, the shorter the pulse the better.

FAST PULSE PRODUCTION

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FAST-PULSE PRODUCTION

Simplest technique envisioned is to switch the gain

  • f the medium on and off.

Its done by switching pump energy on and off. The problem with the scheme: Delay for population inversion Delay for population inversion Sets limit in the pulse length and repetition time

Q-Switching Technique

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CONCEPT OF Q-SWITCHING

LASER output is controlled by switching loss in the

medium

Also called Loss Switching. Loss is inserted in the cavity and hence output is

spoiled. spoiled.

Q-switch can be thought of as an optical gate

blocking optical path

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INTRACAVITY SWITCHES

Rotating Mirror EO or AO switch Saturable dye switch

  • synchronization
  • Linear Q-value
  • controlled
  • Sharp Q-change
  • organic
  • Q varies with lifetime

Saturable dye switch • Q varies with lifetime

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ENERGY STORAGE

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POPULATION INVERSION

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PULSE POWER AND ENERGY

  • Lifetime of the photon in cavity

Lifetime of the photon in cavity

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PULSE POWER AND ENERGY

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PULSE POWER AND ENERGY

  • Integrating constant

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PULSE POWER AND ENERGY

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PULSE POWER AND ENERGY

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PULSE POWER AND ENERGY

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PULSE POWER AND ENERGY

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ELECTROOPTIC MODULATOR

EO modulators works on the principle of birefringence. Separates incident light ray into two rays that may

travel in different direction.

It is also called Double Refraction.

Calcite is natural crystal that exhibits birefringence.

Calcite is natural crystal that exhibits birefringence.

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ELECTROOPTIC MODULATOR

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ELECTROOPTIC EFFECT

  • Linear EO coefficient

Second order EO coefficient

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ELECTROOPTIC MODULATOR

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ELECTROOPTIC MODULATOR

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EO MODULATOR

Fastest Q-switch :: feature switching time 10ns. Large hold-of or extinction ratio :: as high as 1000:1 Suitable EO crystals :: very expensive

Driver circuitry :: very critical

High voltage capacitors required

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ACOUSTOOPTIC MODULATOR

Simplest modulator Acoustic wave originated from piezoelectric crystal

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ACOUSTOOPTIC MODULATOR

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DIFFRACTION

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RAMAN-NATH DIFFRACTION

Incoming beams are perpendicular to alternating

layers.

Act like parallel slits of transmission diffraction

grating.

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AO MODULATOR

Requires RF drive signal at 27 to 28 MHz and

minimum power of 10 W

Low hold-of ratio :: about 10% loss in the central

beam.

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CAVITY DUMPING

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MODELOCKING

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MODELOCKING IN FREQUENCY DOMAIN

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MODELOCKING IN FREQUENCY DOMAIN

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NON-LINEAR OPTICS

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LINEAR AND NONLINEAR PHENOMENA

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POLARIZATION

  • Linear coefficient

Non-linear coefficient

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POLARIZATION

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POLARIZATION

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SHG

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PHASE MATCHING

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PHASE MATCHING

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NON-LINEAR INTERACTION

Mixing of two lights beam sum or difference freq. Phase matching is required in crystal for this. Non-linear crystals are of 2 types: Type-I Type-II

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TYPE OF CRYSTAL

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  • EX. OF PHASE MATCHING

WHY?

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NON-LINEAR MATERIAL

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NON-LINEAR MATERIAL

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SHG EFFICIENCY

  • Length of crystal

Area of the beam

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OPTICAL MIXING

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HIGHER-ORDER NONLINEAR EFFECT

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OPTICAL PARAMETRIC OSCILAATION

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