Tappe Fondamentali dello Sviluppo dei Laser in Italia

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1 Tappe Fondamentali dello Sviluppo dei Laser in Italia Orazio Svelto Dipartimento di Fisica del Politecnico di Milano Accademia Nazionale dei Lincei

2 I Primi Lavori O. Svelto Pumping Power Considerations on an Optical Maser Applied Optics 1, 745 (April 1962) M. Bertolotti, L. Muzii, D. Sette Considerazioni sulla Costruzione e sul Funzionamento di un Laser a Rubino Alta Frequenza, XXXI, 560 (Sett. 1962) F. T. Arecchi, A. Sona He-Ne Optical Masers: Constructions and Measurements Alta Frequenza, XXXI, 718 (Nov. 1962) G. Toraldo di Francia On the Theory of Optical Resonators Proc. Symp. on Optical Masers, Pol. Inst. Brooklyn (April 1963)

3 I Primi Laser ( ) Laser a Rubino (Fondazione Bordoni, Giugno 1962), M. Bertolotti e D. Sette Laser a He-Ne (CISE, Ottobre 1962) F. T. Arecchi e A. Sona Laser a Rubino (Centro Microonde, Politecnico di Milano, CISE)

4 La Impresa Maser-Laser del CNR ( ) Gruppo Promotore: Daniele Sette, Emilio Gatti e Giuliano Toraldo di Francia Gruppi partecipanti CISE (F. T. Arecchi) Politecnico di Milano (O. Svelto) Centro Microonde (G. Toraldo di Francia) Fondazione Bordoni (M: Bertolotti)

5 La Seconda Ondata ( ) 1965 Primo laser ad Ar + (CISE, A. Sona ) Primo Laser a CO 2 (CISE, A. Sona) 1966 Primo laser a Nd:YAG CW (Politecnico) 1967 Primo laser a ML, rubino (Politecnico) (5 ps nel 1968) 1969 Primo laser a He-Cd (CISE)

6 Le Ricerche sui Laser ( ) Gruppo di Roma (Bertolotti e Sette) Proprietà di coerenza di laser a più modi, confronto fra le proprietà di coerenza e proprietà statistiche (Bertolotti, Sette) Gruppo di Firenze (Toraldo di Francia) Laser a molti elementi (Pratesi, Burlamacchi) Risonatori ottici (Checcacci, Scheggi) Teoria del laser multimodale (Bambini, Burlamacchi)

7 Le Ricerche sui Laser ( ) Gruppo CISE (Arecchi e Sona) Proprietà statistiche di laser a singolo modo e paragone con luce termica Gruppo del Politecnico (Svelto, Sacchi) Laser a stato solido con singolo modo trasversale Teoria del Mode-Locking ed effetti dovuti alla dispersione V. Daneu, S. Riva Sanseverino, G. Soncini

8 La Ristrutturazione del CNR Centro Ricerche sulle Microonde Istituto di Ricerca sulle Onde Elettromagnetiche (FI, 1970) Istituto di Elettronica Quantistica (FI, 1970) Centro di Elettronica Quantistica e Strumentazione Elettronica (MI, 1975) Gruppo Nazionale di Elettronica Quantistica e Plasmi

9 I Progetti Finalizzati del CNR Laser di Potenza (A. Sona, ) Tecnologie Elettroottiche (A.M. Scheggi, ) Materiali e Dispositivi per l Elettronica a Stato Solido, MADESS I ( ) e II ( )

10 L Inizio della Crisi del CNR Scomparsa dei Gruppi Nazionali del CNR (metà anni 90) La creazione dell Istituto Nazionale di Fisica della Materia ( ) La ristrutturazione del INFM nel CNR (2005- )

11 Ultrafast Laser Pulses: from Femtosecond to Attosecond Orazio Svelto Dipartimento di Fisica del Politecnico di Milano Accademia Nazionale dei Lincei

12 Ultrafast Optical Science Generating faster and faster optical signals Communicating by fast optical signals Studying the dynamics of natural events

13 Microsecond Optical Pulses Harold Edgerton ( 1850) Stroboscopy Electrical flashes of light 1 μs

14 Nanosecond Optical Pulses Generation by a Spark Measuremente by a Kerr Cell Abram and Lemoigne (1899)

15 Generation of Short Laser Pulse ps Solid-State Laser Pulse duration (s) ps 100 fs 10 fs Dye Laser Ti:sapphire fs Compression Year Dye lasers: 10 ps down to 27 fs Solid state lasers: 10 ps (Nd:glass ) down to 6 fs (Ti:Sapphire, hundreds of pj)

16 The pump-probe technique τ λ 1 λ 2 target A first pump pulse (at λ=λ 1 ) triggers a dynamical process. A second, delayed, probe pulse (at λ=λ 2 ), detects pump-induced transmission, or fluorescence, changes in the target

17 Pump-probe Experimental Setup Beam splitter Pump Chopper Probe τ Sample Translation stage Lock-in Slow detector (photodiode) Typical sensitivity: ΔT/T =10-4 (for 1 khz repetition rate) to 10-6 (for 100 MHz repetition rate) Temporal resolution: 10 to 100 fs

18 Impulsive Coherent Vibrational Spectroscopy Eigenstate description: the short pulse excites, in phase, many vibrational eigenstates a wavepacket is formed on the excited state potential energy surface

19 Femtosecond Molecular Dynamics Ahmed H. Zewail, Nobel Prize for Chemistry 1999 (Femtochemistry) E 2 (R) Na + + I - (ionic) E 3 (R) Na( 2 P J ) + I NaI Fluorescence [Na( 2 P J ) Na( 2 S 1/2 )]

20 From Femtosecond to Attosecond ps Solid-State Laser Pulse duration (s) ps 100 fs 10 fs Dye Laser Ti:sapphire Pulse compression: 6 fs (1987) nj Hollow fiber 4.5 fs (1997) 1mJ fs Compression Year

21 Compression of Light Pulses General scheme Phase Modulator φ(t) Delay line T(ω) Phase Modulator: generation of extra-frequency band Delay line: re-phasing of the new frequency components

22 Self-phase Modulation Optical Kerr effect: n(r,t) = n 0 + n 2 I(r,t) Phase Modulator φ(t) ϕ( t) = ω 0 t k 0 n(t) l dϕ ω( t) = = ω 0 k 0n 2 dt di(t) l dt I, ω Intensity trailing edge t Frequency linear chirp

23 Uniform Spectral Broadening I(r,t) Δω= ω-ω 0 = -k 0 n 2 [ I(r,t)/ t] l Δω(r,t) non uniform SPM vs r Solution Kerr effect in a guiding nonlinear medium 1974, Ippen et al.: SPM in a multimode optical fiber filled with liquid CS , Stolen and Lin: SPM in single-mode silica core fibers

24 High Energy Pulse Compression Requirements for uniform spectral broadening of high energy pulses guiding medium of large transverse dimensions single transverse mode medium with fast and high χ 3 (electronic origin) medium with high damage threshold and high critical power for self-focusing Solution SPM in hollow fiber filled with noble gases

25 SPM by Hollow-Fiber Dielectric waveguide Noble gas Advantages of hollow-fiber large bore diameter (high energy) losses caused by multiple reflections inside the fiber greatly discriminate against higher order modes Advantages of noble gases purely electronic third-order nonlinear susceptibility (instantaneous response) control of nonlinearity strength by changing gas type and pressure

26 Pulse Compression by the Hollow Fiber Only way to produce powerful (sub TW) pulses in the sub-6-fs regime 25 fs hollow waveguide Argon p=0.5 bar Guiding medium with a large diameter mode, fast nonlinearity and high damage threshold Ultrabroad-band dispersion control by chirped-mirrors 5 fs 0.11 TW Chirped-mirror compressor M. Nisoli et al., Appl. Phys. Lett. 68, 2793 (1996) M. Nisoli et al., Opt. Lett. 22, 522 (1997) SH Intensity (a.u.) τ = 5 fs Delay (fs)

27 Hollow Fiber Modulator

28 Hollow Fiber Output Beam Fundamental mode with the lowest attenuation: EH 11 (hybrid mode) radial intensity distribution (a bore radius) I(r) J r a Truncated zero order Bessel function Measured beam profile

29 Chirped-mirror Compressor Tailoring of dispersion compensation ultra-broadband dispersion control with low losses high intensity handling Wavelenght (nm) Thickness (nm)

30 Applications of Few-cycle Laser Pulses Coherent dynamical vibrations in F-centers Extreme Nonlinear Optics and attosecond pulse generation Electron dynamics of electrons in molecules

31 Coherent Dynamics in KBr F-centers M. Nisoli et al., Phys. Rev. Lett. 77, 3463 (1996).

32 Extreme Nonlinear Optics : Influence of Carrier-Envelop Phase E(t)=A(t)cos(ωt+ϕ) ϕ = carrier-envelope offset (CEO) phase ϕ = 0 ϕ = π/2 ϕ = π

33 Extreme Nonlinear Optics Nonlinear optical effects which depend of the carrierenvelope phase Examples of extreme nonlinear optics High-harmonic and single attosecond pulse generation Electron dynamics in D 2+ molecule

34 High-order Harmonic Generation 1000 Red light (1.6 ev) Gas jet 0 Harmonics Intensity (arb. units) Intensity (arb. units) Photon energy (ev) Photon energy (ev) Odd harmonics of the red light are generated up to the soft X ray region

35 High Order Harmonic Generation Set-up laser gas jet 0 z Grazing incidence toroidal mirror and spherical varied-line-spacing grating Acquisition: micro-channel plate with output on phosphor screen, optically coupled to a CCD camera with single shot acquisition capability

36 Harmonic Generation Process ε(t) ( Photon Energy ) = E IP 17 U p max + 3.

37 Harmonic Generation by Few-cycle Laser Pulses Computed temporal evolution of 5-fs-laser driven 90-eV harmonic emission Electric field strength ϕ = 0 Electric field strength ϕ = π/ Time (fs) Time (fs) X-ray intensity 0.6 fs X-ray intensity Time (fs) Time (fs)

38 Phase Stabilized Laser System Q:switched pump laser Ti:Sa oscillator Multipass Ti:Sa amplifier Hollow-fiber compressor 5 fs, 0,4 mj, 1 khz cw pump laser AOM Locking electronics 1 st f-to-2f interferometer 2 nd f-to-2f 3 interferometer CEP drift (rad) Phaselocked pulses!! -2 Phase drift < 80 mrad (rms)!! Time (s)

39 Temporal characterization Intensity (a.u.) τ = 130 as Phase (rad) Time (as) -5 New world record G. Sansone et al., Science 314, 443 (2006)

40 Femtosecond and Attosecond Laboratories Phase-stabilised fewcycle laser system Grazing incidence spectrometer interaction chamber Attosecond Laboratory first torus Pump-probe interaction point

41 Electron Dynamics in Molecules Controlling the motion of an electron bound to a molecule (D 2+ ) ϕ = π ϕ = 0 E The driving field ionizes the D 2 molecule to the 1sσ + g state and then freed electron, upon recollision, promotes the D 2+ molecule to the 2p σ + u state The phase of the driving pulse controls which of the two nuclei the remaining electron eventually sticks to M. Kling et al., Science 392, 246 (2006)

42 From Femtosecond to Attosecond 4 fs 130 as

43 Attoscience New frontiers of Physics: Control of the electronic motion on the length and time scale of atoms New frontiers of chemistry (attochemistry): Steering of chemical / biochemical reactions by controlling electronic motion on molecular orbitals New frontiers of electronics: Control of electronic motion on small semiconductor nanostructures and molecular systems

44 Coworkers Enrico Benedetti, Giuseppe Sansone, Salvatore Stagira, Caterina Vozzi, Sandro De Silvestri, Mauro Nisoli Department of Physics, Politecnico of Milan (Italy) National Laboratory for Ultrafast and Ultraintense Optical Science (ULTRAS) European Facility Centre for Ultrafast Science and Biomedical Optics (CUSBO) C U S B O