The Noble Prize for Physics 2018 Groundbreaking inventions in Laser Physics

1. The Noble Prize for Physics 2018Groundbreaking inventions in Laser Physics “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." Prem , Siva and BasudevPhysics, I. I. T. Madras, CHENNAI IITM: Light dispersed by a grating IIT Madras, Oct. 10, 2018

2. Physics World, May 2010, p. 15 How the present development at IITM can lead to wonders by chipping in with the new generation. IIT Madras, Oct. 10, 2018 50 years of lasers, Oct. 30th, 2010

3. 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) IIT Madras, Oct. 10, 2018

4. Nobel Prize 2018 Ashkin (US), Mourou (France) and Strickland (Canada) IIT Madras, Oct. 10, 2018

5. 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 IIT Madras, Oct. 10, 2018

6. > 4700 citation 1985: The year I started research with pico second lasers with D D Pant at NainiTal IIT Madras, Oct. 10, 2018

7. APL 1969 IIT Madras, Oct. 10, 2018

8. Sun:400-700 nm, Brightness = 107 W/m2/St. Spectral Brightness = 2.5 x 104 W/m2/St./nm He-Ne Laser: 1 mW, 0.001 nm, 1mm dia. , 1mSt: Spectral Brightness = 3.18 x 108W/m2/St./nm SUN & the LASER 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 IIT Madras, Oct. 10, 2018

9. 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 IIT Madras, Oct. 10, 2018

10. Can we say that LASERS need NOT be monochromatic ! IIT Madras, Oct. 10, 2018

11. In phase RANDOM phase for all the laser modes LOCKED phases for all the laser modes Out of phase Out of phase Irradiance vs. Time Out of phase Time Time Concepts of Ultrafast pulses Ultrafast pulses are obtained from mode-locked lasers. Some matter of the slide is taken from http://www.dmphotonics.com/ Modes with same phase are only allowed to oscillate IIT Madras, Oct. 10, 2018

12. DnDt = const. Basic principles of ultrafast lasers Bandwidth vs Pulsewidth broadest spectrum broader spectrum narrow spectrum Dn bandwidth Dt continuous wave (CW) Dt duration pulses (mode-locked) shortest pulses Some matter of the slide is taken from http://www.dmphotonics.com/ Visible region: 2 fs duration IIT Madras, Oct. 10, 2018

13. 30 nm; [for 500 nm~ 2 fs] 755 nm 785 nm IIT Madras, Oct. 10, 2018

14. Why do we need “chirped pulsed” amplification (CPA)? Separate BOX: Prepared, synchronized states High peak power pulses Amplifier Amplifier Peak power must be reduced for amplification IIT Madras, Oct. 10, 2018

15. 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 IIT Madras, Oct. 10, 2018

16. F = -kx e- Simple harmonic oscillator IIT Madras, Oct. 10, 2018

17. Virtual level * Virtual level w1 (2) w1 w3 2 w3 1 w2 w2 3 SUMFREQENCY DIFFERENCE FREQENCY Signal Second harmonic Pump Idler (Pump generates two photons one of them is used in Optical parametric amplification (OPA) IIT Madras, Oct. 10, 2018

18. Optical parametric amplifiers (OPA) Difference frequency generation Ti:sapphire M2 800nm A1 L1 White light continuum BS Sapphire L2 BBO M3 WLC Pump 400 nm BBO M1 A2 Amplified pulse IIT Madras, Oct. 10, 2018

19. IITM THIRD ORDER NONLINEAR OPTICAL SUSCEPTIBILITY, c(3) Applications Longitudinal and transverse effects IIT Madras, Oct. 10, 2018

20. Lens (Transverse Kerr effect) High-intensity ultrashort pulse Focused pulse Longitudinal Kerr effect gives rise to Pulse chirping Kerr medium (n = n0 + n2I) Low-intensity beam Kerr lens modelocking of fs pulses, Other applications IIT Madras, Oct. 10, 2018

21. 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

22. n Wavelength/ nm Velocity of light in a medium = c / n Blue is slower than the red wavelength IIT Madras

23. Diffraction 1st Order Compressed pulse Ultrashort pulse Incident beam Chirped pulse Introducing “extra” chirp: Stretching the pulses Chirped pulse θ2 Blue Blue -1st Order Red Diffraction grating pair mλ= d (sinθ1+sinθ2) Red Grating pair provides positive dispersion Grating pair provides negative dispersion θ1 Pulse Stretching Compression Optical fibers or Prism-pairs are also used IIT Madras, Oct. 10, 2018

24. Stretched pulse Compressed pulse D. Strickland and G. Mourou, “Compression of Amplified Chirped Optical Pulses,”Optics Comm. 56, 219 (1985). IIT Madras, Oct. 10, 2018

25. Amplification of the chirped pulse IIT Madras, Oct. 10, 2018