Document

Tappe Fondamentali
dello Sviluppo dei Laser in Italia
Orazio Svelto
Dipartimento di Fisica del Politecnico di Milano
Accademia Nazionale dei Lincei
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)
I Primi Laser (1962-1963)
„ 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)
La Impresa Maser-Laser del CNR
(1963-1968)
„ 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)
La Seconda Ondata
(1965-1970)
1965 Primo laser ad Ar+
Primo Laser a CO2
(CISE, A. Sona )
(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 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)
Le Ricerche sui Laser
(1965-1970)
„ 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
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
I Progetti Finalizzati del CNR
„ Laser di Potenza (A. Sona, 1978-1983)
„ Tecnologie Elettroottiche (A.M. Scheggi, 1989-1994)
„ Materiali e Dispositivi per l’Elettronica a Stato Solido,
MADESS I (1987-1992) e II (1997-2002)
L’Inizio della Crisi del CNR
„ Scomparsa dei Gruppi Nazionali del CNR (metà
anni ’90)
„ La creazione dell’Istituto Nazionale di Fisica della
Materia (1994-2005)
„ La ristrutturazione del INFM nel CNR (2005- )
Ultrafast Laser Pulses:
from Femtosecond to Attosecond
Orazio Svelto
Dipartimento di Fisica del Politecnico di Milano
Accademia Nazionale dei Lincei
Ultrafast Optical Science
„ Generating faster and faster optical signals
„ Communicating by fast optical signals
„ Studying the dynamics of natural events
Microsecond Optical Pulses
Harold Edgerton (≈1850)
Electrical flashes of light ∼ 1 μs
Stroboscopy
Nanosecond Optical Pulses
Abram and Lemoigne (1899)
„ Generation by a Spark
„ Measuremente by a Kerr Cell
Pulse duration (s)
Generation of Short Laser Pulse
10
-11
10
-12
Ti:sapphire
100 fs
-14
10 fs
-15
1 fs
10
Solid-State Laser
1 ps
-13
10
10
10 ps
1965
Dye Laser
Compression
1970
1975
1980
1985
1990
1995
2000
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)
The “pump-probe” technique
τ
λ1
λ2
target
•
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
Pump-probe Experimental Setup
Beam
splitter
Pump
Probe
Chopper
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
Impulsive Coherent Vibrational Spectroscopy
¾Eigenstate 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)
E2(R)⇒Na+ + I- (ionic)
E3(R)⇒Na(2PJ) + I
NaI
Fluorescence [Na(2PJ) → Na(2S1/2)]
Pulse duration (s)
From Femtosecond to Attosecond
10
-11
10
-12
□ Pulse compression:
Ti:sapphire
100 fs
-14
10 fs
-15
1 fs
10
Solid-State Laser
1 ps
-13
10
10
10 ps
1965
Î
Hollow fiber
Dye Laser
Î
Compression
1970
1975
6 fs (1987) nJ
1980
1985
Year
1990
1995
2000
4.5 fs (1997) ∼1mJ
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
Self-phase Modulation
„
Optical Kerr effect: n(r,t) = n0 + n2 I(r,t)
Phase Modulator
φ(t)
ϕ ( t ) = ω 0 t − k 0 n( t ) l
dϕ
d I( t )
ω( t ) =
= ω0 − k 0 n2
l
dt
dt
I, ω
In te n s ity
tra ilin g e d g e
t
F re q u e n c y
linear chirp
Uniform Spectral Broadening
I(r,t)
Δω(r,t)
Δω=
ω-ω0 = -k0n2[∂ I(r,t)/∂t] l
non uniform SPM vs r
Solution
„ Kerr effect in a guiding nonlinear medium
Î
1974, Ippen et al.: SPM in a multimode optical fiber filled
with liquid CS2
Î
1978, Stolen and Lin: SPM in single-mode silica core fibers
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
„ SPM in hollow fiber filled with noble gases
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
Pulse Compression by the Hollow Fiber
Only way to produce powerful (sub TW) pulses in the
sub-6-fs regime
25 fs
hollow waveguide
Î Guiding medium with a large
diameter mode, fast nonlinearity
and high damage threshold
Î Ultrabroad-band dispersion control
by chirped-mirrors
Argon p=0.5 bar
8
Chirped-mirror
compressor
M. Nisoli et al., Appl. Phys. Lett. 68, 2793 (1996)
M. Nisoli et al., Opt. Lett. 22, 522 (1997)
τ = 5 fs
SH Intensity (a.u.)
5 fs
0.11 TW
6
4
2
0
-20
-10
0
Delay (fs)
10
20
Hollow Fiber Modulator
Hollow Fiber Output Beam
„ Fundamental mode with the lowest
attenuation: EH11 (hybrid mode)
Î
radial intensity distribution (a bore radius)
r⎞
⎛
I (r ) ∝ J02 ⎜ 2.405 ⎟
a⎠
⎝
Truncated zero order Bessel
function
Measured beam profile
⇒ Tailoring of dispersion
compensation
⇒ ultra-broadband dispersion
control with low losses
⇒ high intensity handling
Wavelenght (nm)
Chirped-mirror Compressor
Thickness (nm)
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
Coherent Dynamics in KBr F-centers
M. Nisoli et al., Phys. Rev. Lett. 77, 3463 (1996).
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
Extreme Nonlinear Optics
„ Nonlinear optical effects which depend of the carrier-
envelope phase
„ Examples of extreme nonlinear optics
Î High-harmonic and single attosecond pulse generation
Î Electron dynamics in D2+ molecule
High-order Harmonic Generation
Harmonics
Red light
(1.6 eV)
0
Intensity (arb. units)
Gas jet
Intensity (arb. units)
1000
10
140
80
Î
100
100
120
150
160
170
180
Photon energy (eV)
Photon energy (eV)
140
190
160
Odd harmonics of the red light are generated up to
the soft X ray region
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
‹
Harmonic Generation Process
ε→
(t)
(Photon
Energy
)max
= E IP + 3 .17 U p
Harmonic Generation by Few-cycle Laser
Pulses
Computed temporal evolution of 5-fs-laser driven 90-eV harmonic emission
-8
-6
-4
-2
0
2
Time (fs)
4
6
-6
-4
-2
0
2
Time (fs)
4
Electric field strength
8
0.6 fs
-8
ϕ = π/2
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
-2
0
2
4
6
8
Time (fs)
X-ray intensity
Electric field strength
ϕ=0
X-ray intensity
„
6
8
Time (fs)
Phase Stabilized Laser System
Q:switched
pump laser
Ti:Sa oscillator
Hollow-fiber
compressor
5 fs, 0,4 mJ,
1 kHz
AOM
1st f-to-2f
interferometer
2nd f-to-2f 3
interferometer
Phaselocked
pulses !!
2
Locking
electronics
CEP drift (rad)
cw pump
laser
Multipass
Ti:Sa amplifier
1
0
-1
-2
-3
Phase drift < 80 mrad (rms) !!
0
20
40
60
Time (s)
80
10
Temporal characterization
1.0
0.8
0.6
5
τ = 130 as
0.4
0
Phase (rad)
Intensity (a.u.)
10
0.2
0.0
-300
Î
-150
0
Time (as)
150
300
-5
New world record
G. Sansone et al., Science 314, 443 (2006)
Femtosecond and Attosecond Laboratories
„
Grazing incidence spectrometer
„
Phase-stabilised fewcycle laser system
interaction chamber
Attosecond Laboratory
first torus
Pump-probe interaction point
Electron Dynamics in Molecules
„
Controlling the motion of an electron bound to a molecule (D2+)
ϕ=π
ϕ=0
E
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
Î 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)
Î
From Femtosecond to Attosecond
4 fs
130 as
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
Coworkers
■ Enrico Benedetti, Giuseppe Sansone,
Salvatore Stagira, Caterina Vozzi,
Sandro De Silvestri, Mauro Nisoli
Î Department
of Physics,
Politecnico
of Milan (Italy)
Î National Laboratory
for Ultrafast and
Ultraintense Optical
Science (ULTRAS)
Î European Facility
“Centre for Ultrafast
Science and Biomedical
Optics (CUSBO)”
C
U
S
B
O