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Prem , Siva and Basudev Physics, I. I. T. Madras, CHENNAI
The Noble Prize for Physics 2018 Groundbreaking inventions in Laser Physics Prem , Siva and Basudev Physics, I. I. T. Madras, CHENNAI “The Nobel Prize in Physics 2018 was awarded "for groundbreaking inventions in the field of laser physics" with one half to Arthur Ashkin "for the optical tweezers and their application to biological systems", the other half jointly to Gérard Mourou and Donna Strickland "for their method of generating high-intensity, ultra-short optical pulses." IITM: Light dispersed by a grating Physics Colloquium IIT Madras, Oct. 10, 2018
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Physics World, May 2010, p. 15 50 years of lasers, Oct. 30th, 2010
How the present development at IITM can lead to wonders by chipping in with the new generation. ms 10-3 s 10-6 s ns 10-9 s ps 10-12 s fs 10-15 s as 10-18 s 50 years of lasers, Oct. 30th, 2010 Physics Colloquium IIT Madras, Oct. 10, 2018
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Notable Nobel Prizes for Laser related work
1964: Townes, Basov and Prokhorov for the MASER-LASER principle. 1971 Gabor for the basic ideas of the holographic method . 1981: Nicolaas Bloembergen and Arthur Schawlow for laser spectroscopy. 1997: Claude Cohen-Tannoudji , Steven Chu and William Phillips for development of methods to cool and trap atoms with laser light. 1999: Ahmed Zewail Ultrafast laser techniques 2000: Zhores Alferov and Herbert Kroemer for developing semiconductor heterostructures for CW semiconductor diode lasers. 2001: Eric Cornell, Wolfgang Ketterle, and Carl E. Wieman for Bose-Einstein condensation. 2005: Theodor Hansch, John Hall for development of laser-based precision spectroscopy, (optical frequency comb technique). 2009:Charles K. Kao: Father of Fiber Optic Communications 2012 Serge Haroche and David J. Wineland (photons in high Q cavity), 2014 Isamu Akasaki, Hiroshi Amano and Shuji Nakamura (Blue LED) 2018 Ashkin, Mourou and Strickland (Optical tweezers and CPA) Physics Colloquium IIT Madras, Oct. 10, 2018
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Nobel Prize 2018 Ashkin (US), Mourou (France) and Strickland (Canada)
Physics Colloquium IIT Madras, Oct. 10, 2018
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Physics ‘Noble by Women’
Marie Curie (1903) for radioactivity 60 years later Maria Göppert Mayer (1963) proposing the nuclear shell model of the atomic nucleus. [1GM=10-50 cm4s] 55 years later Donna Strickland (2018) for CPA Physics Colloquium IIT Madras, Oct. 10, 2018
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> 4700 citation 1985: The year I started research with pico second lasers with D D Pant at NainiTal Physics Colloquium IIT Madras, Oct. 10, 2018
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APL 1969 Physics Colloquium IIT Madras, Oct. 10, 2018
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SUN & the LASER Sun: nm, Brightness = 107 W/m2/St. Spectral Brightness = 2.5 x 104 W/m2/St./nm He-Ne Laser: 1 mW, nm, 1mm dia. , 1mSt: Spectral Brightness = 3.18 x 108 W/m2/St./nm दिवि सूर्य सहस्त्रस्य, भावेद्युग-पदुद्तिथा| यदि भाः सदृशी सा स्याद्भासस्तस्य महात्मनः || १२|| Divi surya sahastraya, bhawed-yug-pad-utitha: Yadi bha: sadrishi sa, syad-bhasas-tasya mahatmanah. 11-12: भगवतगीता: If you see it once, you can never see it again Physics Colloquium IIT Madras, Oct. 10, 2018
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Comparison of powers (i). 1 W CW laser = 1 W Power
(ii). 1 W pulsed laser with 10 fs duration, 1 kHz rep. rate Energy per pulse = Peak power of the pulse~ Pulsed lasers have high peak powers Physics Colloquium IIT Madras, Oct. 10, 2018
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need NOT be monochromatic !
Can we say that LASERS need NOT be monochromatic ! Physics Colloquium IIT Madras, Oct. 10, 2018
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Ultrafast pulses are obtained from mode-locked lasers.
Concepts of Ultrafast pulses Ultrafast pulses are obtained from mode-locked lasers. Some matter of the slide is taken from Out of phase In phase LOCKED phases for all the laser modes Out of phase RANDOM phase for all the laser modes Irradiance vs. Time Modes with same phase are only allowed to oscillate Time Physics Colloquium IIT Madras, Oct. 10, 2018
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Bandwidth vs Pulsewidth
Basic principles of ultrafast lasers Bandwidth vs Pulsewidth DnDt = const. broadest spectrum broader spectrum narrow spectrum bandwidth Dn continuous wave (CW) duration Dt Dt pulses (mode-locked) shortest pulses Some matter of the slide is taken from Visible region: 2 fs duration Physics Colloquium IIT Madras, Oct. 10, 2018
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755 nm 785 nm 30 nm; [for 500 nm~ 2 fs] Physics Colloquium
IIT Madras, Oct. 10, 2018
![755 nm 785 nm 30 nm; [for 500 nm~ 2 fs] Physics Colloquium](http://slideplayer.com/slide/15494733/93/images/13/755+nm+785+nm+30+nm%3B+%5Bfor+500+nm%7E+2+fs%5D+Physics+Colloquium.jpg "IIT Madras, Oct. 10,")
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Why do we need “chirped pulsed” amplification (CPA)?
Separate BOX: Prepared, synchronized states Amplifier High peak power pulses Amplifier Peak power must be reduced for amplification Physics Colloquium IIT Madras, Oct. 10, 2018
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Comparison of powers (i). 1 W CW laser = 1 W Power
(ii). 1 W pulsed laser with 10 fs duration, 1 kHz rep. rate Energy per pulse = Peak power of the pulse~ Want to reduce the peak power ?: -> Increase the pulse duration Physics Colloquium IIT Madras, Oct. 10, 2018
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Simple harmonic oscillator
F = -kx e- Physics Colloquium IIT Madras, Oct. 10, 2018
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(2) w1 w2 w3 SUM FREQENCY w1 w2 w3 * DIFFERENCE FREQENCY 2 3 1
Virtual level DIFFERENCE FREQENCY Virtual level 2 3 1 Signal Second harmonic Pump Idler (Pump generates two photons one of them is used in Optical parametric amplification (OPA) Physics Colloquium IIT Madras, Oct. 10, 2018
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Optical parametric amplifiers (OPA) Difference frequency generation
White light continuum 800nm Amplified pulse Pump Ti:sapphire L1 Sapphire L2 BBO A1 WLC M3 M1 M2 A2 BS 400 nm Physics Colloquium IIT Madras, Oct. 10, 2018
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THIRD ORDER NONLINEAR OPTICAL SUSCEPTIBILITY, c(3)
IITM Applications Longitudinal and transverse effects THIRD ORDER NONLINEAR OPTICAL SUSCEPTIBILITY, c(3) Physics Colloquium IIT Madras, Oct. 10, 2018
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Lens (Transverse Kerr effect)
Kerr medium (n = n0 + n2I) Low-intensity beam High-intensity ultrashort pulse Focused pulse Kerr lens modelocking of fs pulses, Other applications Longitudinal Kerr effect gives rise to Pulse chirping Physics Colloquium IIT Madras, Oct. 10, 2018
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Ultrafast broadening : Pulse chirping
I (w) Ultrafast pulse I (t) n(t) Non linear medium no I (w) Monochromatic pulses become polychromatic due to SPM, as additional frequency components are added up. (rising edge less, trailing edge more) IIT Madras
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Velocity of light in a medium = c / n
Wavelength/ nm n Velocity of light in a medium = c / n Blue is slower than the red wavelength IIT Madras
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Introducing “extra” chirp: Stretching the pulses
Incident beam Diffraction 1st Order -1st Order θ2 Diffraction grating pair mλ= d (sinθ1+sinθ2) θ1 Ultrashort pulse Red Blue Chirped Grating pair provides positive dispersion Pulse Stretching Red Blue Chirped pulse Compressed pulse Grating pair provides negative dispersion Compression Optical fibers or Prism-pairs are also used Physics Colloquium IIT Madras, Oct. 10, 2018
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Stretched pulse Compressed pulse
D. Strickland and G. Mourou, “Compression of Amplified Chirped Optical Pulses,” Optics Comm. 56, 219 (1985). Physics Colloquium IIT Madras, Oct. 10, 2018
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Amplification of the chirped pulse
Physics Colloquium IIT Madras, Oct. 10, 2018
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