OPTI510R: Photonics Khanh Kieu College of Optical Sciences, University of Arizona kkieu@optics.arizona.edu Meinel building R.626
Announcements HW #5 due today April 11 th class will be at 2PM instead of 11AM, still in 307 Final exam May 2
Lasers Introduction Brief history Laser characteristics Laser types Laser modes of operation Laser market Fiber lasers Semiconductor lasers next lecture
Laser History Einstein predicts stimulated emission Townes invents and builds first MASER Schawlow and Townes propose LASER Maiman builds first (ruby) LASER Javan invents He-Ne laser Hall builds semiconductor laser 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Nakamura builds blue laser diode Alferov builds first heterostructure laser IBM builds first laser printer first fiber optic communication system (Chicago) CD player Spectra introduces Ti:Sapphire laser Faist builds quantum cascade laser
Time and frequency metrology, Precision spectroscopy, Calibration of Astro-spectrometers, Clock synchronization over large distance, Very large baseline interferometry, High harmonic generation, Atto-second pulses, Test of special and general relativity, Drift of fundamental constants... Frequency Comb
Blue light emitting diodes
Laser Nobel awards Nobel Prize in Physics awarded for contribution related to laser 1964: Townes, Basov and Prokhorov 1971: Gabor 1981: Bloembergen and Schawlow 1997: Chu, Cohen-Tannoudji and Phillips 2000: Alferov and Kroemer 2005: Hänsch an Hall 2014: Akasaki, Amano, Nakamura
T. H. Maiman The first laser paper!
Who invented the laser? Charles Hard Townes and Arthur Leonard Schawlow Gordon Gould N. Basov and A. Prokhorov Nico Blombergen
Who invented the laser?
Who invented the laser?
Who invented the laser?
A piece of history
Laser Characteristics spectrally broad divergent can t be focused tightly low efficiency, intensity incoherent What is needed? very monochromatic does not diverge as fast can be focused tightly can be extremely intense spatial coherence temporally coherent More generally: active medium pump (to create population inversion) feedback (resonator, mirrors)
Laser Threshold Above threshold, stimulated emission into dominant mode with lowest loss Below threshold, spontaneous emission in all directions
Longitudinal modes Allowed modes of the cavity are those where mirror separation is equal to multiple of half wavelength.,q is an integer Frequency separation: for L >> l L
Transverse modes Transverse modes are mode that are in a plane perpendicular (transverse) to direction of propagation (m,n). Profiles depend on the mirror shape. Lowest order mode TE 00 is the Gaussian beam. Circular symmetric modes Laguerre polynomials Rectangular symmetric modes Hermite polynomials mnq c L (1 m n) q cos 1 L (1 )(1 r 2 1 2 L r ) O. Svelto, Principles of Lasers
Laser types Solid state lasers (crystal based) Gas lasers Dye lasers Semiconductor lasers Fiber lasers
Laser types
Modes of operation CW Continuous wave Single-frequency lasers Q-switched lasers Q-switched (ns, us) Mode-locked lasers ML (ps, fs)
Laser beam characteristics Center wavelength, spectral bandwidth (OSA) Average power, peak power (power meter) Pulse energy, repetition rate (energy meter) Intensity Divergence, beam quality (M 2 measurement)
Laser market Laserfocusworld.com
Laser market Laserfocusworld.com
Laser market Laserfocusworld.com
Laser market Laserfocusworld.com
Communications & optical storage Includes all laser diodes used in telecommunications, data communications, and optical storage applications, including pumps for optical amplifiers.
Materials processing & lithography Includes lasers used for all types of metal processing (welding, cutting, annealing, drilling); semiconductor and microelectronics manufacturing (lithography, scribing, defect repair, via drilling); marking of all materials; and other materials processing (such as cutting and welding organics, rapid prototyping, micromachining, and grating manufacture). Also includes lasers for lithography.
Laser materials processing
Laser market Laserfocusworld.com
Laser market Current fiber lasers market share is ~ 20% (2013 data) Laserfocusworld.com
Why are people still doing research in lasers? The physics of laser operation is well understood. But there is always need for better and cheaper lasers. Also, there are still a lot of applications requirements that current technology can not satisfy. Requirements: New wavelength bands Maximum average output power Maximum peak output power Minimum output pulse duration Maximum power efficiency Minimum cost
Fiber lasers First laser was demonstrated in 1960 by T. Maiman First fiber laser was demonstrated in 1963 E. Snitzer
Advantages of fiber format Fiber format removes the strict requirement of heat management which is normally very critical in solid-state lasers But there are also disadvantages: Long gain media High nonlinearity Polarization stability High efficiency Air-cooled Direct diode pumping Compact Alignment free Reliable Low cost Performance
Fiber lasers
Laser design Linear cavity design Er-doped fiber WDM Output coupler Isolator Ring cavity design
Fiber laser performance
mj energy femtosecond fiber laser: > 1GW peak power! Tünnermann s group
What can fiber laser do?
Cladding pump technology http://www.rp-photonics.com/double_clad_fibers.html
Cladding pump technology (US patent # 5,864,644) (Goldberg, Opt. Lett. 1999) GTWave technology (credit: D. Payne)
Beam combination (credit: D. Payne)
Literature A. Siegman, Lasers O. Svelto, Principles of Lasers