Introduction to Laser Material Introduction to Laser Material - - PowerPoint PPT Presentation

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Introduction to Laser Material Introduction to Laser Material Processing ME 677: Laser Material Processing Instructor: Ramesh Singh 1 Outline Contact details Course objectives Introductory remarks Grading policy Grading policy

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SLIDE 1

Introduction to Laser Material

ME 677: Laser Material Processing Instructor: Ramesh Singh

Introduction to Laser Material Processing

1

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SLIDE 2

Outline

  • Contact details
  • Course objectives
  • Introductory remarks

Grading policy

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • Grading policy
  • Intro to laser material processing

2

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SLIDE 3

Contact Details

  • Mr. Ramesh Singh

– Room: Machine Tools lab – E-mail:

  • ramesh@me.iitb.ac.in
  • rsingh@iitb.ac.in

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • rsingh@iitb.ac.in

– Tel: 7507 – Off. Hrs.: Fridays 2-5 p.m. – Also by appointment – Class website: http://www.me.iitb.ac.in/~ramesh/ME667/

3

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SLIDE 4

Focus and Objectives of Course

  • Introduction to the practical applications of lasers.
  • Developing insight into the physical phenomenon of laser-matter

interaction.

  • Development of first order mathematical descriptions for select laser

processes.

  • Understand the capabilities and limitations of various laser processes.
  • Apply this knowledge to process selection, design for manufacturing

and quality control.

ME 677: Laser Material Processing Instructor: Ramesh Singh

and quality control.

  • Encourage teamwork and group activity via group assignments and

Project.

4

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SLIDE 5

Introductory Remarks

  • See second page of syllabus

– Homework – Exams – Honor code

ME 677: Laser Material Processing Instructor: Ramesh Singh

– Honor code

5

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SLIDE 6

Grading Policy

  • Group Assignments (5)

15%

  • Quizzes

10%

  • Midterm

25% Project 20%

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • Project

20%

  • End semester exam

30

  • Total

100 %

6

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SLIDE 7

Course Summary

  • Focus on:

– Physical principles and analysis of process – Process Capabilities

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • Teamwork will be encouraged

– Homework – Project

7

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SLIDE 8

Introduction to Lasers

  • Lasers are everywhere!
  • Some applications

– Cutting – Welding

ME 677: Laser Material Processing Instructor: Ramesh Singh

– Welding – Bending – Hardening – Cladding – Laser Shows Yes!

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SLIDE 9

Laser

  • Laser-

Light Amplification by Stimulated Emission of Radiation

ME 677: Laser Material Processing Instructor: Ramesh Singh

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SLIDE 10

Operating Principle

  • Stimulation

– Source of input power for pumping – Mechanical, chemical, electrical or light sources

  • Flash Lamp
  • Electric arc
  • Amplification

ME 677: Laser Material Processing Instructor: Ramesh Singh

Amplification

– Optical Resonator Construction

  • two, parallel planar (or concave) mirrors
  • Couples part of the optical power back in the active medium
  • Positive feedback -> self-excitation -> oscillation
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SLIDE 11

Optical Resonance

  • Optical Resonator Function

Photons not aligned are not redirected

ME 677: Laser Material Processing Instructor: Ramesh Singh

– Photons not aligned are not redirected – Amplification occurs only for photons with proper orientation – Coherent beam is obtained

  • Population Inversion

– Under equilibrium conditions Boltzmann Equation gives the population at two states:

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SLIDE 12

Optical Resonance (Contd.)

  • Under normal condition there are fewer electrons at

higher energy states

  • −

−

=

KT E E

e N N

1 2

2

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • Population inversion

– Non equilibrium state where high energy electrons are more to provide stimulated emission

N1

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SLIDE 13

Properties of Laser

  • Small divergence

– Parallel, collimated beam

  • High power

– In continuous (CW) mode: tens, hundreds of watts (e.g., CO2), Few KW (Fiber) – Q-switched mode: instantaneous power is enormous (GW) Large spatial power density due to small divergence

ME 677: Laser Material Processing Instructor: Ramesh Singh

– Large spatial power density due to small divergence

  • Small spectral width

– “Monochrome” – Large spectral power density

  • Polarized
  • Possibility of very short pulses

– ps, fs

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SLIDE 14

Gillette

ME 677: Laser Material Processing Instructor: Ramesh Singh

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SLIDE 15

Cutting/Hardening

ME 677: Laser Material Processing Instructor: Ramesh Singh

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SLIDE 16

Laser Net Shaping (Sandia)

ME 677: Laser Material Processing Instructor: Ramesh Singh

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SLIDE 17

LASIK

ME 677: Laser Material Processing Instructor: Ramesh Singh

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SLIDE 18

Laser-Summary

  • What is needed for laser operation?

– Stimulated emission – Population inversion – Pumping

ME 677: Laser Material Processing Instructor: Ramesh Singh

– Pumping – Optical resonance

  • What are the main properties of laser light?

– Monochromatic – Coherent – Large optical power

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SLIDE 19

Introduction to Laser Material

ME 677: Laser Material Processing Instructor: Ramesh Singh

Introduction to Laser Material Processing

1

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SLIDE 20

Outline

  • Brief History
  • Design of Laser cavity
  • Stability

Types of Lasers

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • Types of Lasers

2

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SLIDE 21

Laser History

  • 1917 - Albert Einstein: Theoretical prediction of stimulated emission
  • 1946 - G. Meyer-Schwickerather: first eye surgery with light
  • 1950 - Arthur Schawlow and Charles Townes: Emitted photons may

be in the visible range

  • 1954 - N.G. Basow, A.M. Prochorow, and C. Townes: ammonia

maser

ME 677: Laser Material Processing Instructor: Ramesh Singh

maser

  • 1960 - Theodore Maiman: first laser (ruby laser)
  • 1964 - Basow, Prochorow, Townes (Nobel prize): quantum

electronics

  • 1970 - Arthur Ashkin: laser tweezers
  • 1971 - Dénes Gábor (Nobel prize): holography
  • 1997 - S. Chu, W.D. Phillips and C. Cohen-Tanoudji (Nobel prize):

Atom cooling with laser

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SLIDE 22

ME 677: Laser Material Processing Instructor: Ramesh Singh

Steen, 3rd Edition

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SLIDE 23

Optical Cavity Design

  • Basic designs components

– Totally reflecting mirror – Partially reflecting mirror – Mirror materials

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • ZnSe, GaAs and CdTe for C02 lasers
  • BK7 fused Silica

– Key parameters

  • R1, R2, L

– Multiple configurations

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SLIDE 24

Stability of Laser Cavity

  • Laser cavity could have two configurations:

– Stable – Unstable

  • If the cavity is unstable, the beam size will grow without

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • If the cavity is unstable, the beam size will grow without

limit, eventually growing larger than the size of the cavity mirrors and being lost

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SLIDE 25

Stability analysis for Optical Cavity

  • Ray transfer matrix analysis
  • ≤
  • −
  • −

≤

2 1

1 1 1 R L R L

ME 677: Laser Material Processing Instructor: Ramesh Singh

  • −

=

  • −

=

2 2 1 1

1 1 R L g R L g