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

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 • Intro to laser material processing ME 677: Laser Material Processing Instructor: Ramesh Singh 2

Contact Details • Mr. Ramesh Singh – Room: Machine Tools lab – E-mail: • ramesh@me.iitb.ac.in • rsingh@iitb.ac.in • 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/ ME 677: Laser Material Processing Instructor: Ramesh Singh 3

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. and quality control. • Encourage teamwork and group activity via group assignments and Project. ME 677: Laser Material Processing Instructor: Ramesh Singh 4

Introductory Remarks • See second page of syllabus – Homework – Exams – Honor code – Honor code ME 677: Laser Material Processing Instructor: Ramesh Singh 5

Grading Policy • Group Assignments (5) 15% • Quizzes 10% • Midterm 25% • Project Project 20% 20% • End semester exam 30 • Total 100 % ME 677: Laser Material Processing Instructor: Ramesh Singh 6

Course Summary • Focus on: – Physical principles and analysis of process – Process Capabilities • Teamwork will be encouraged – Homework – Project ME 677: Laser Material Processing Instructor: Ramesh Singh 7

Introduction to Lasers • Lasers are everywhere! • Some applications – Cutting – Welding – Welding – Bending – Hardening – Cladding – Laser Shows Yes! ME 677: Laser Material Processing Instructor: Ramesh Singh

Laser • Laser- L ight A mplification by S timulated E mission of R adiation ME 677: Laser Material Processing Instructor: Ramesh Singh

Operating Principle • Stimulation – Source of input power for pumping – Mechanical, chemical, electrical or light sources • Flash Lamp • Electric arc • Amplification 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 ME 677: Laser Material Processing Instructor: Ramesh Singh

Optical Resonance • Optical Resonator Function – Photons not aligned are not redirected 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: ME 677: Laser Material Processing Instructor: Ramesh Singh

Optical Resonance (Contd.) • Under normal condition there are fewer electrons at higher energy states � � E E − � � 2 1 N − � � KT 2 e = N N 1 • Population inversion – Non equilibrium state where high energy electrons are more to provide stimulated emission ME 677: Laser Material Processing Instructor: Ramesh Singh

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 Large spatial power density due to small divergence • Small spectral width – “Monochrome” – Large spectral power density Polarized • • Possibility of very short pulses – ps, fs ME 677: Laser Material Processing Instructor: Ramesh Singh

Gillette ME 677: Laser Material Processing Instructor: Ramesh Singh

Cutting/Hardening ME 677: Laser Material Processing Instructor: Ramesh Singh

Laser Net Shaping (Sandia) ME 677: Laser Material Processing Instructor: Ramesh Singh

LASIK ME 677: Laser Material Processing Instructor: Ramesh Singh

Laser-Summary • What is needed for laser operation? – Stimulated emission – Population inversion – Pumping – Pumping – Optical resonance • What are the main properties of laser light? – Monochromatic – Coherent – Large optical power ME 677: Laser Material Processing Instructor: Ramesh Singh

Introduction to Laser Material Introduction to Laser Material Processing ME 677: Laser Material Processing Instructor: Ramesh Singh 1

Outline • Brief History • Design of Laser cavity • Stability • Types of Lasers Types of Lasers ME 677: Laser Material Processing Instructor: Ramesh Singh 2

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 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 ME 677: Laser Material Processing Instructor: Ramesh Singh

Steen, 3 rd Edition ME 677: Laser Material Processing Instructor: Ramesh Singh

Optical Cavity Design • Basic designs components – Totally reflecting mirror – Partially reflecting mirror – Mirror materials • ZnSe, GaAs and CdTe for C0 2 lasers • BK7 fused Silica – Key parameters • R1, R2, L – Multiple configurations ME 677: Laser Material Processing Instructor: Ramesh Singh

Stability of Laser Cavity • Laser cavity could have two configurations: – Stable – Unstable • If the cavity is unstable, the beam size will grow without • 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 ME 677: Laser Material Processing Instructor: Ramesh Singh

Stability analysis for Optical Cavity • Ray transfer matrix analysis � − � � − � L L � � � � 0 1 1 1 � � � � ≤ ≤ � � � � R R 1 2 � � − � � L � � g 1 � � = 1 � � R 1 � − � L � � 1 g � � = 2 � � R 2 ME 677: Laser Material Processing Instructor: Ramesh Singh