Welcome To Ultrafast Optics - Brown University

Welcome to Ultrafast OpticsWho am I:Daniel Mittleman(office hours: to be determined)When, where:Tues / Thurs @ 9amWeb page:see canvasPrerequisites:Quantum mechanics and E&M at an undergraduatelevel, or permission of instructor. Come talk to me ifyou are uncertain.Grading:Lecture attendance (mandatory)Problem sets (occasional)Research presentations (everybody)

TextbooksNo required text! But if you will be working in this field,you will want to own some of these Recommended reading - lasers and nonlinear optics: Lasers, by A. Siegman(University Science Books, 1986) Fundamentals of Photonics, by Saleh and Teich(Wiley, 1991) The Principles of Nonlinear Optics, by Y. R. Shen(Wiley, 1984) Nonlinear Optics, by R. Boyd(Academic Press, 1992) Optics, by Eugene Hecht(Addison-Wesley, 1987)Recommended reading - ultrafast phenomena: Ultrashort laser pulse phenomena, by J.-C. Diels and W. Rudolph(Second Edition, Academic Press, 2006) Ultrafast Optics, by Andrew Weiner(Wiley, 2009)

Topics to be covered Basic optical physics Pulse propagation 2nd and 3rd-ordernon-linearities Mode-locking}How do they do this?(and why)Other topics pending www.chem.rug.nl/spectro/projects/laser.html

How big and how small?Prefixes:BigKilo (k)Mega (M)Giga (G)Tera (T)Peta (P)Exa (E)Zetta (Z)Yotta (Y)Small10-310-610-910-1210-1510-1810-2110-24Milli (m)Micro (µ)Nano (n)Pico (p)Femto (f)Atto (a)Zepto (z)Yocto (y)10 310 610 910 1210 1510 1810 2110 24OneComputer Cameramonth Age ofclock cycle flashpyramids10 fs light pulse1 minute10-1410-910-4110610Time (seconds)1110Human existenceAge of universe1610

Ultrafast Phenomena - The Evolution of SpeedSpeed 97019801990Year20002010currently:factor of 106

A brief history of time resolutionLelandStanfordThe "Trotting Horse" ControversyEadweardMuybridgePalo Alto, CA 1872Time Resolution:1/60th of a second

'Doc' Edgerton - Strobe PhotographyHarold Edgerton1942MIT Research Laboratory for Electronics“How to Make Apple sauce at MIT”H. Edgerton, 1964Time Resolution: a few microseconds“Splash on aGlass”Curtis HurleyJunior HighSchool student1996

It all started with the laser(Theodore Maiman (Hughes Research Lab),inventor of the laser, holding his invention (1960)

Shortest Pulse Duration (femtoseconds)The Laser - Mode LockingCurrent record(visible light):3.4 fsecYamane, et al. Nov. 2003Active mode locking1000Passive mode locking100Colliding pulsemode locking10Extra-cavity apphire laserIntra-cavity pulsecompression'90'95

Generating ultrashort pulses:mode locking

Long vs. Short light pulsesThe uncertainty principle says that the product of thetemporal and spectral pulse widths is greater than 1.Irradiance vs. timeSpectrumtimefrequencytimefrequencyLong pulseShort pulseTo make a short pulse, you need a lot of spectral bandwidth.

A typical pulseConsider a pulse:duration 100 femtosecondswavelength 800 nanometers2.6 fsecfrequency domain:E(ω)time domain:E(t)Fouriertransform780800820wavelength (nanometers)-2000200time (femtoseconds)number of cycles (duration of one cycle) / (duration of pulse)

The Shortest Pulses at Different WavelengthsWavelength3 mm3 µm3 nm-11Pulse Duration (seconds)10-1210-1310current record:80 attoseconds(x-rays)-1410One optical cycle-1510111012101310New in 2001New in 2006New10in 2008101010Newin 2003Frequency(Hz)1415161718101910

4Amplitude (arb. units)Amplitude (arb. units)The Shortest Pulses at Long Wavelengths20-20500 1000 1500 2000Delay (femtoseconds)1086420012Frequency (THz)3

Short Pulses at Short Wavelengths90 degree relativistic Thompson scatteringLawrence Berkeley National Laboratory

Breaking the attosecond barrierF. Krausz and co-workers, TU Vienna, 2001A cross-correlation of a 650 attosecond x-ray pulsewith a 7.5 femtosecond infrared pulseλ 13.8 nmmeasured signal: spectral width of a photoelectron spectrumRequired infrared pulse intensity: 5 1013 W/cm2

The shortest pulses ever (so far)measuredphotoelectronspectrumGoulielmakis, et al., Science, June 2008reconstructedattosecond pulse

Ultrafast set-ups can be very sophisticated.

A continuous-wave (cw) laser:irradianceWhy does ultrashort usually mean ultra-intense?timeaverage energy power/time joules per second WattsA pulsed laser:pulse duration 100 fspulse rate 100 MHzirradianceExample: 1 Watt at λ 800 nm is 4 1018 photons per second. So, in a100 fs window, we have only 4 105 photons.10 nstimeExample: 1 Watt at λ 800 nm is 4 1010 photons per pulse.Energy per pulse 4 1010 photons per pulse energy/photon 10 nJ/pulsePeak energy energy per pulse / pulse duration 105 WFocus this to a 10 µm diameter spot: Peak irradiance 1015 W/m2

Chirped pulse amplification

The Highest Intensities You Can Possibly Imagine0.2 TW 200,000,000,000 watts!1 kHz CPA system at the University of California, Santa Barbara

(used to be) The world’s biggest laserNova - Lawrence Livermore National Laboratory

(currently) The world’s biggest laserNational Ignition Facility(commissioned in 2009)192 shaped pulses1.8 MJ total energy

National Ignition FacilityIn 2012: generated a peak power of 500 terawatts (2 megajoulesin 4 nanoseconds)For that brief instant, NIF produced 1000 times as much poweras the entire US electrical grid.

Ultrafast Laser Spectroscopy: Why? Most events that occur in atoms and molecules occur on fs andps time scales. The length scales are very small, so very little timeis required for the relevant motion. Excited state decay via fluorescence occurs on a ns time scale,but competing non-radiative processes only speed things upbecause relaxation rates add:1τ ex 1τ fl 1τ nr Biologically important processes utilize excitation energy forpurposes other than fluorescence and hence must be very fast. Collisions in room-temperature liquids occur on a few-fs timescale, so nearly all processes in liquids are ultrafast. Semiconductor processes of technological interest arenecessarily ultrafast or we wouldn’t be interested.

The most common type of ultrafast measurementτ Strong pump pulse perturbs the sample at t 0. A time τ later, a weak probe pulse interrogates the sample. Measure the transmission of the probe pulse at each delay τ.transmittedpulse energyτ 0information about the dynamics!delay

PRESS RELEASE 12 OCTOBER 1999The Royal Swedish Academy of Sciences has awarded the 1999 Nobel Prize in Chemistry toProfessor Ahmed H. Zewail, California Institute of Technology, Pasadena, USAfor showing that it is possible with rapid laser technique to see how atoms in a molecule moveduring a chemical reaction.The Academy's citation:For his studies of the transition states ofchemical reactions using femtosecondspectroscopy.This year's laureate in Chemistry is beingrewarded for his pioneering investigation offundamental chemical reactions, using ultrashort laser flashes, on the time scale on whichthe reactions actually occur. Professor Zewail'scontributions have brought about a revolution inchemistry and adjacent sciences, since this typeof investigation allows us to understand andpredict important reactions.

What is "Femtochemistry"?Example:Pump-probe fluorescence ofiodine in the gas phaseZewail, et al., J. Chem. Phys., 106, 4353 (1997)

Ultrashort in time is also ultrashort in spacecw laser beama few mmlaserpulsed laser beamultrafastlasera few mm3 meters30 microns(for a 100 fs pulse)

Ultrashort in time is also ultrashort in space, part IIIn multi-photon imaging, we focus an ultrashort pulse tightly into anobject and observe the multi-photon signal light.F I2F Two-photonFluorescenceenergy

Ultrashort in time is also ultrashort in space, part IIIOne-photonfluorescence from abeam entering fromthe rightTwo-photonfluorescence froman identical beamentering from the leftImage from Chris Schaffer, UCSD

Ultrashort pulses interact with materials differentlygroove machined with nanosecond pulse and with femtosecond pulseClark MXR, Inc., Ann Arbor, MI

Ultrafast lasers make great scalpels!New eye surgery technique developed at CUOS(Center for Ultrafast Optical Sciences), at theUniversity of Michiganwww.intralase.com

Lightning protection usingamplified short pulsesguided andunguided lightningThe pulse induces a conducting path, dischargingthe cloud before lightning can occur.

Ultrafast lasers make great clocks! Temporal spacing of pulses translates to frequency spacing of the comb Temporal spacing can be stabilized to much better than one part in 1011

PRESS RELEASE 4 OCTOBER 2005The Royal Swedish Academy of Sciences has awarded the 2005 Nobel Prize in Physics for 2005with one half toRoy J. GlauberHarvard University, Cambridge, MA, USA"for his contribution to the quantum theory of optical coherence"and one half jointly toJohn L. HallNational Institute of Standards and Technology, Boulder, CO, USA andTheodor W. HänschMax-Planck-Institut für Quantenoptik,Garching, Germany"for their contributions to the development oflaser-based precision spectroscopy, including theoptical frequency comb technique".

How does it work?In order to understand the formation of femtosecondpulses, we need to know about: how a cw (continuous wave) laser works. how a short pulse propagates through materialsat low intensities, and at high intensities. mode locking.Our model system to learn all of this:Titanium-doped sapphire laser(Ti:sapphire)

The Ti:sapphire laserA typical optical layout, if you want to build your own:or you can buy one:

RemindersThis class has: mandatory lecture attendance no text book oral presentations by all students in March/April weekly office hours (Tuesday 1:00-2:30 in Brockman 351)

Recommended reading -lasers and nonlinear optics: Lasers, by A. Siegman (University Science Books, 1986) Fundamentals of Photonics, by Saleh and Teich (Wiley, 1991) The Principles of Nonlinear Optics, by Y. R. Shen (Wiley, 1984) Nonlinear Optics, by R. Boyd (Academic Press, 1992) Optics, by Eugene Hecht (Addison-Wesley, 1987)