Tappe Fondamentali dello Sviluppo dei Laser in Italia Orazio Svelto - - PowerPoint PPT Presentation

Dipartimento di Fisica del Politecnico di Milano Accademia Nazionale dei Lincei

Orazio Svelto

Tappe Fondamentali dello Sviluppo dei Laser in Italia

I Primi Lavori

• 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)

• O. Svelto

Pumping Power Considerations on an Optical Maser Applied Optics 1, 745 (April 1962)

• G. Toraldo di Francia

On the Theory of Optical Resonators

• Proc. Symp. on Optical Masers, Pol. Inst. Brooklyn (April 1963)

I Primi Laser (1962-1963)

Laser a He-Ne

(CISE, Ottobre 1962) F. T. Arecchi e A. Sona

Laser a Rubino

(Fondazione Bordoni, Giugno 1962), M. Bertolotti e D. Sette

Laser a Rubino

(Centro Microonde, Politecnico di Milano, CISE)

La Impresa Maser-Laser del CNR (1963-1968)

Gruppi partecipanti

CISE (F. T. Arecchi) Politecnico di Milano (O. Svelto) Centro Microonde (G. Toraldo di Francia) Fondazione Bordoni (M: Bertolotti)

Gruppo Promotore:

Daniele Sette, Emilio Gatti e Giuliano Toraldo di Francia

La Seconda Ondata (1965-1970)

1965 Primo laser ad Ar+ (CISE, A. Sona ) Primo Laser a CO2 (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)

Le Ricerche sui Laser (1965-1970)

Gruppo di Firenze (Toraldo di Francia)

Laser a molti elementi (Pratesi, Burlamacchi) Risonatori ottici (Checcacci, Scheggi) Teoria del laser multimodale (Bambini, Burlamacchi)

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)

Le Ricerche sui Laser (1965-1970)

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

Gruppo CISE (Arecchi e Sona)

Proprietà statistiche di laser a singolo modo e paragone con luce termica

La Ristrutturazione del CNR

Istituto di Elettronica Quantistica (FI, 1970) Centro Ricerche sulle Microonde ⇒ Istituto di

Ricerca sulle Onde Elettromagnetiche (FI, 1970)

Centro di Elettronica Quantistica e Strumentazione

Elettronica (MI, 1975)

Gruppo Nazionale di Elettronica Quantistica e Plasmi

I Progetti Finalizzati del CNR

Tecnologie Elettroottiche (A.M. Scheggi, 1989-1994) Laser di Potenza (A. Sona, 1978-1983) Materiali e Dispositivi per l’Elettronica a Stato Solido,

MADESS I (1987-1992) e II (1997-2002)

L’Inizio della Crisi del CNR

La creazione dell’Istituto Nazionale di Fisica della

Materia (1994-2005)

Scomparsa dei Gruppi Nazionali del CNR (metà

anni ’90)

La ristrutturazione del INFM nel CNR (2005- )

Dipartimento di Fisica del Politecnico di Milano Accademia Nazionale dei Lincei

Orazio Svelto

Ultrafast Laser Pulses: from Femtosecond to Attosecond

Ultrafast Optical Science

Communicating by fast optical signals Generating faster and faster optical signals Studying the dynamics of natural events

Stroboscopy

Microsecond Optical Pulses

Electrical flashes of light ∼ 1 μs

Harold Edgerton (≈1850)

Nanosecond Optical Pulses

Generation by a Spark Measuremente by a Kerr Cell

Abram and Lemoigne (1899)

Generation of Short Generation of Short Laser Laser Pulse Pulse

■ Dye lasers: 10 ps down to

27 fs

■ Solid state lasers: 10 ps (Nd:glass )

down to ∼ 6 fs (Ti:Sapphire, hundreds of pJ)

1965 1970 1975 1980 1985 1990 1995 2000

Year

Ti:sapphire Compression Solid-State Laser Dye Laser

10 ps 1 ps 100 fs 10 fs 1 fs 10

• 14

10

• 13

10

• 12

10

• 11

10

• 15

Pulse duration (s)

• A first pump pulse (at λ=λ1) triggers a dynamical process.
• A second, delayed, probe pulse (at λ=λ2), detects pump-induced

transmission, or fluorescence, changes in the target

τ

The “pump-probe” technique

λ1 λ2

target

Pump-probe Experimental Setup

Beam splitter Translation stage Chopper

τ

Probe Pump

Sample

Slow detector (photodiode)

Lock-in 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

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

Femtosecond Molecular Dynamics

■ Ahmed H. Zewail, Nobel Prize for Chemistry 1999 (Femtochemistry)

NaI E2(R)⇒Na+ + I- (ionic) E3(R)⇒Na(2PJ) + I Fluorescence [Na(2PJ) → Na(2S1/2)]

From From Femtosecond Femtosecond to to Attosecond Attosecond

Hollow fiber

□ Pulse compression:

• 6 fs (1987) nJ
• 4.5 fs (1997) ∼1mJ

1965 1970 1975 1980 1985 1990 1995 2000

Year

Ti:sapphire Compression Solid-State Laser Dye Laser

10 ps 1 ps 100 fs 10 fs 1 fs 10

• 14

10

• 13

10

• 12

10

• 11

10

• 15

Pulse duration (s)

Compression of Light Pulses 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

F requency Intensity trailing edge

t I, ω

Self Self-

• phase Modulation

phase Modulation

Optical Kerr effect: n(r,t) = n0 + n2 I(r,t)

l ) t ( n k t ) t (

0 −

ω = ϕ l dt ) t ( I d n k dt d ) t (

2 0 −

ω = ϕ = ω

Phase Modulator φ(t)

linear chirp

Uniform Spectral Broadening Uniform Spectral Broadening

Solution Solution

Kerr effect in a guiding nonlinear medium

• 1974, Ippen et al.: SPM in a multimode optical fiber filled

with liquid CS2

• 1978, Stolen and Lin: SPM in single-mode silica core fibers

non uniform SPM vs r I(r,t) Δω= ω-ω0 = -k0n2[∂ I(r,t)/∂t] l Δω(r,t)

High Energy Pulse Compression 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 χ3 (electronic origin) ⇒ medium with high damage threshold and high critical power for self-focusing

Solution Solution

SPM in hollow fiber filled with noble gases

SPM by Hollow SPM by Hollow-

• Fiber

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

Pulse Compression by the Hollow Fiber

Only way to produce powerful (sub TW) pulses in the sub-6-fs regime

hollow waveguide 25 fs 5 fs 0.11 TW Chirped-mirror compressor 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

• 20
• 10

10 20 2 4 6 8

τ = 5 fs SH Intensity (a.u.) Delay (fs)

• M. Nisoli et al., Appl. Phys. Lett. 68, 2793 (1996)
• M. Nisoli et al., Opt. Lett. 22, 522 (1997)

Hollow Fiber Modulator Hollow Fiber Modulator

Hollow Fiber Output Beam

Fundamental mode with the lowest

attenuation: EH11 (hybrid mode)

radial intensity distribution (a bore radius)

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ∝ a r 405 . 2 J ) r ( I

2

Measured beam profile

Truncated zero order Bessel function

Chirped Chirped-

• mirror Compressor

mirror Compressor

⇒ Tailoring of dispersion compensation ⇒ ultra-broadband dispersion control with low losses ⇒ high intensity handling

Thickness (nm) Wavelenght (nm)

Applications of Few-cycle Laser Pulses

Coherent dynamical vibrations in F-centers Electron dynamics of electrons in molecules Extreme Nonlinear Optics and attosecond pulse generation

Coherent Dynamics in Coherent Dynamics in KBr KBr F F-

• c

centers enters

• M. Nisoli et al., Phys. Rev. Lett. 77, 3463 (1996).

ϕ = π/2 ϕ = 0 ϕ = π

Extreme Nonlinear Optics : Influence of Carrier-Envelop Phase

E(t)=A(t)cos(ωt+ϕ) ϕ = carrier-envelope offset (CEO) phase

Extreme Nonlinear Optics

Nonlinear optical effects which depend of the carrier-

envelope phase

Examples of extreme nonlinear optics

High-harmonic and single attosecond pulse generation Electron dynamics in D2

+ molecule

80 100 120 140 160

Intensity (arb. units) Photon energy (eV)

140 150 160 170 180 190

10 100 1000

Photon energy (eV) Intensity (arb. units)

Red light (1.6 eV)

Gas jet

Harmonics

• Odd harmonics of the red light are generated up to

the soft X ray region

High-order Harmonic Generation

High Order Harmonic Generation Set-up

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

gas jet laser z

Harmonic Generation Process

( )

p IP

U E Energy Photon 17 . 3

max

+ =

ε(t)

→

Harmonic Generation by Few-cycle Laser Pulses

• Computed temporal evolution of 5-fs-laser driven 90-eV harmonic emission
• 8
• 6
• 4
• 2

2 4 6 8

0.6 fs X-ray intensity Time (fs)

• 8
• 6
• 4
• 2

2 4 6 8

X-ray intensity Time (fs)

• 8
• 6
• 4
• 2

2 4 6 8

Electric field strength Time (fs)

ϕ = π/2

• 8
• 6
• 4
• 2

2 4 6 8

Electric field strength Time (fs)

ϕ = 0

Phase Stabilized Laser System Phase Stabilized Laser System

2nd f-to-2f interferometer

Phase- locked pulses !!

cw pump laser Ti:Sa oscillator Multipass Ti:Sa amplifier Q:switched pump laser Hollow-fiber compressor

AOM

1st f-to-2f interferometer Locking electronics

20 40 60 80 10

• 3
• 2
• 1

1 2 3

CEP drift (rad) Time (s)

Phase drift < 80 mrad (rms) !!

5 fs, 0,4 mJ, 1 kHz

Temporal characterization Temporal characterization

• 300
• 150

150 300 0.0 0.2 0.4 0.6 0.8 1.0

• 5

5 10

Intensity (a.u.) Time (as)

τ = 130 as

Phase (rad)

• New world record
• G. Sansone et al., Science 314, 443 (2006)

• Phase-stabilised few-

cycle laser system

interaction chamber first torus Pump-probe interaction point Grazing incidence spectrometer

• Attosecond Laboratory

Femtosecond and Attosecond Laboratories

Electron Dynamics in Molecules Electron Dynamics in Molecules

• Controlling the motion of an electron bound to a molecule (D2

+)

• M. Kling et al., Science 392, 246 (2006)
• The driving field ionizes the D2 molecule to the 1sσg

+ state

and then freed electron, upon recollision, promotes the D2

+ molecule to the 2p σu + state

• The phase of the driving pulse controls which of the two

nuclei the remaining electron eventually sticks to

E

ϕ = 0 ϕ = π

From From Femtosecond Femtosecond to to Attosecond Attosecond

130 as 4 fs

Attoscience Attoscience

■ New frontiers of chemistry (attochemistry):

Steering of chemical / biochemical reactions by controlling electronic motion on molecular orbitals

■ New frontiers of Physics:

Control of the electronic motion on the length and time scale of atoms

■ New frontiers of electronics:

Control of electronic motion on small semiconductor nanostructures and molecular systems

Coworkers Coworkers

■ Enrico Benedetti, Giuseppe Sansone, Salvatore Stagira, Caterina Vozzi, Sandro De Silvestri, Mauro Nisoli

C U S B O

National Laboratory for Ultrafast and Ultraintense Optical Science (ULTRAS) European Facility “Centre for Ultrafast Science and Biomedical Optics (CUSBO)” Department

• f Physics,

Politecnico

• f Milan (Italy)