高次高調波発生とアト秒科学

Advanced Radiation Engineering 放射線応用工学E
Kenichi Ishikawa (石川顕一)
http://ishiken.free.fr/english/lecture.html
http://www.atto.t.u-tokyo.ac.jp
[email protected]
高次高調波発生と
アト秒科学
high-order harmonic generation
& attosecond science
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
High-harmonic generation 高次高調波発生
2015/10/8 No. 2
Quantum Beam Generation Engineering (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
References 参考文献
The lecture material is downloadable from: http://ishiken.free.fr/english/lecture.html M. Protopapas, C.H. Keitel and P.L. Knight, “Atomic physics
with super-high intensity lasers”, Rep. Prog. Phys. 60, 389–
486 (1997)
F. Krausz and M. Ivanov, “Attosecond Physics”, Rev. Mod.
Phys. 81, 163-234 (2009)
K. L. Ishikawa, High-harmonic generation, in Advances in
Solid-State Lasers, ed. by M. Grishin (INTEH, 2010), pp.
439-464
大森賢治編「アト秒科学: 1京分の1秒スケールの超高速現象
を光で観測・制御する」（化学同人、2015/8/10）
10/8
3
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高調波発生 (Harmonic generation)
結晶、ガス等(crystal, gas)
Linear optical effect
線形光学効果（弱い光）
ω
ω
Material response is linear in light intensity 物質の応答が、入射光強度に比例
非線形光学効果（強い光）€
€
ω
Nonlinear optical effect
Nonlinear material response
物質の応答が、入射光強度に非線形に依存
ω,3ω,5ω,!
波長変換 (frequency conversion)
D = ε0 E + P
€
P = ε0 [ χ E + χ E + χ E +!]
(1)
€
€
(2)
2
(3)
3
非線形分極 (nonlinear)
線形分極 linear polarization
€3ω：３次高調波(3rd harmonic)
5ω：５次高調波(5th harmonic)
€
反転対称な媒質では、 χ (2) = 0
for a medium with inversion symmetry €
2
∇ × ∇ × E = −µ 0
€
∂D
∂t 2
2015/10/8 No. 4
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
摂動論的高調波発生
(perturbative harmonic generation)
3rd harmonic
３次高調波
Ionization
電離
5th harmonic
５次高調波
Ionization
電離
仮想準位
Virtual level
!ω
Virtual level
仮想準位
!ω
!ω
€
€
€
!ω
€
€
3!ω
€
Ground state
基底状態 €
!ω
!ω
5!ω
!ω
€ !ω
Ground state
基底状態
€
次数が高くなるほど、発生効率は減少。
€
Harmonic order ↑
Efficiency ↓
2015/10/8 No. 5
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生
High-harmonic generation (HHG)
discovered in 1987
Intense femtosecond
laser pulse
3
High-order shortwavelength pulse
Phaser shift difference (rad)
2
1
0
-1
-2
gas jet
-3
-10
-5
0
5
-2
10
-1
0
1
Fundamental optical cycle
Highly nonlinear optical process in which the frequency of laser light is converted
into its integer multiples. Harmonics of very high orders are generated.
Pulse width (fs)
新しい極端紫外・軟エックス線光源として注目される。
New extreme ultraviolet (XUV) and soft X-ray source
2015/10/8 No. 6
2
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
How high orders?
Harmonic spectrum 高調波スペクトル
Wahlström et al., Phys. Rev. A 48, 4709 (1993)
041111-3
Takahashi et al.
Takahashi et al., Appl. Phys. Lett. 93, 041111 (2008)
Harmonic intensity (arb. unit)
1015 W/cm2
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
FIG. 4. !Color online" Experimentally obtained harmonic spectra in Ar. Red
and blue profile depict the spectra with #0 = 0.8 !m pump and #0 = 1.4 !m
pump, respectively. Both HH spectra are normalized to the peak intensity.
The laser focused intensity is adjusted to generate HH under a neutral condition for both wavelengths. The inset shows a measured two dimensional
harmonic spectrum image driven by 1.4 !m pump.
800 nm, 1.6×1014 W/cm2
Only odd orders
奇数次のみ
Simulation
0
10
20
30
Harmonic order
40
50
800÷31= 26
matching cond
propagation ax
the Ar harmon
cutoff energy w
spectrum drive
magnitudes low
measured HH
significant cuto
the 0.8 !m dr
field generate
higher energy
This photon en
predicted valu
In conclu
sources based
monic beams.
pulse width w
1.4 !m. Total
#45% conver
HH spectrum
extension exce
file is almost p
is attractive no
the kiloelectro
ergy scaling o
was raised up to 26 mJ, a maximal output energy exceeding
7 mJ was achieved at the signal wavelength near 1.4 !m.
Temporal characterization of amplified OPA pulses was
performed using a single-shot autocorrelation !AC" technique. A typical AC trace is shown in the inset of Fig. 2.
Assuming a Gaussian pulse shape, the pulse width of 1.4 !m
nmpulse
was evaluated to be 40 fs in full width at half maxi1
M. 7
Hentschel, R
2015/10/8 No.
mum !FWHM", the energy of which corresponds
to the red
T. Brabec, P. Co
filled circles in Fig. 3. The solid red line depicts the Fourier-
ture !London" 4
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Plateau（プラトー）- remarkable feature
of high-harmonic generation
plateau
cutoﬀ
1015 W/cm2
Harmonic intensity (arb. unit)
Wahlström et al., Phys. Rev. A 48, 4709 (1993)
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
800 nm, 1.6×1014 W/cm2
plateau
cutoﬀ
Simulation
0
10
20
30
Harmonic order
40
50
プラトー(plateau)：Eﬃciency does NOT decrease with
increasing harmonic order. 次数が上がっても強度が落ちない。
カットオフ(cutoﬀ)：Maximum energy of harmonic photons
e2 E02
2 2
14
Ec Ip + 3Up
Up (eV) =
=
9.3
10
I(W/cm
) (µm)
4m 2
ponderomotive energy
• 摂動論的には解釈できない(non-perturbative)
2015/10/8 No. 8
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生のメカニズム = 3 step model
Mechanism of HHG = 3 step model
摂動論的高調波
perturbative
電離 ionization
高次高調波（非摂動論的）
HHG(non-perturbative)
Laser field
レーザー電場 recombination
virtual state
仮想準位
再結合→
発光 photon emission (HHG)
!ω
!ω
€
€
€
!ω
€
3!ω
ground state
基底状態
electron 電子
トンネル
電離
tunneling ionization
電場中の古典
的運動
Semiclassical
electron motion
3-step model
Paul B. Corkum, Phys. Rev. Lett. 71, 1994 (1993)
2015/10/8 No. 9
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生のメカニズム = 3 step model
Mechanism of HHG = 3 step model
2015/10/8 No. 10
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生の３ステップモデル
3-step model of HHG
Paul B. Corkum, Phys. Rev. Lett. 71, 1994 (1993)
Ionization at
z=
ωt0 = φ0
E0
[(cos
2
!
cos
0)
+(
0 ) sin
0]
Ekin = 2Up (sin φ − sin φ0 )2
Recombination at φ = φret (φ0 ) , which satisfies z = 0
Laser field
E(t) = E0 cos ωt
レーザー電場 recombination
Phase of recombination (phi_r)
350
300
250
再結合→
発光 photon emission (HHG)
200
150
100
electron 電子
50
0
0
50
100
Phase of electron release (phi0)
150
トンネル
電離
tunneling ionization
電場中の古典
的運動
Semiclassical
electron motion
2015/10/8 No. 11
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生の３ステップモデル
3-step model of HHG
Paul B. Corkum, Phys. Rev. Lett. 71, 1994 (1993)
2015/10/8 No. 12
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
高次高調波発生の３ステップモデル
3-step model of HHG
Field (in E0)
1
field
0
recombination
ionization
-1
3
There is the maximum kinetic energy
which is classically allowed.
Ec = Ip + 3.17Up
1
0
0
90
180
long
short
short
2
long
Electron kinetic energy (in Up)
Simple explanation of the cutoff law
カットオフ則のシンプルな説明
270
360
Phase (degrees)
There are two pairs of ionization and
recombination times which contribute to
the same harmonic energy.
Short and long trajectories
2015/10/8 No. 13
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Even up to 1.6 keV, > 5000 orders
(almost) x-ray!
Popmintchev et al., Science 336, 1287 (2012)
a new type of laser-based radiation source
レーザーをベースにした新しいタイプの放射線源
2015/10/8 No. 14
the retrieved pulse duration was 88 as.
e I ωL and I 2ωL
,)2;#0 <+=4#22>, 4+;# #?-+/3)', 3' /"%## 03$#',3)', +'0 ()$1-/#0 )./+3'#0 *%
%+03+/3)' )* /"#
,/%)'&2650%3;#'
+/)$3(
031)2#,
-,3'& +of
&#'#%+25
/+2 #%%)%K ,
Advanced Radiation Application (Kenichi ISHIKAWA)
for
internal use
only
(Univ.
Tokyo)
Both PROOF and FROG-CRAB /"#
assume
only
3@+/3)'
)* /"# ?-+'/-$ that
/%#+/$#'/ )* %#*:
8A: !"#,# ,3$-2+/3)', 63#20 /"# ;3,3.2#
, ωL , and twice
+ BCD5+, 75%+6 1-2,# '#+% /"# 1%)1+&+/3)' +=3, 3' /"# *+% E#20 43/"3' #=1#%3$#'
+ B5#F ,1#(/%+2
%+'&# '#+%streaking
GD #F H*-22 23'# 3' I3&: JKL +(()$1+'3#0 .6 /"# (+%%3#%
photoelectrons
emitted
in
a
small
angle
in the
delay between
+ *#4 ,$+22 ,+/#223/# 1-2,#,: !"# +11#+%+'(# )* ,+/#223/#, ,#1+%+/#0 .6 ,#()'0 1%#
What happens if the fundamental
laser
!! MN *%)$ /"# (#'/%+2 1-2,# 2#+0, /) + ,1#(/%+2 $)0-2+/3)' 43/" + )* /"# 4+;
photoelectron
1#%3)0 )* /43(# /"# 2+,#% 1")/)' #'#%&6L +, %#;#+2#0 .6 /"# (+2(-2+/#0 +$123/-0#
,1#(/%-$ H*-22 23'#K 3' /"# 3',#/ )* I3&: J: !"# 0#1/" )* /"3, 3'& /"# #;
nformation
of
$)0-2+/3)' 1%);30#, + ,#',3/3;# $#+,-%# )* ,+/#223/# ()'/#'/: !"# +//),#()'0
pulse
is very short? では、超短パルスレーザ
$#+,-%#0 ,1#(/%-$ )* /"# "+%$)'3( 75%+6 1-2,# %#O#(/#0 .6 )-% *#45(6(2# 0
<)MP3 $-2/32+6#% H0)//#0 23'# 3' /"# 3',#/ )* I3&: JK ,#/, + ,+*# -11#% "3&"5"+%$
ncoded in I ωL ,
23T#
Hentschel et al. (2001) H$)%#
ーによる高次高調波はどんな感じ？
)/"#% /"+'
se are guessed
*%+(/3)' )*
8
6
86
4
90
Energy (eV)
94
τx = 530 as
2
0
–6
–4
–2
0
Time (fs)
2
4
6
Laser electric field (arbitrary units)
X-ray intensity (arbitrary units)
D
2%'3"- 5 P'($3('%#+ .'&<E#(+8 1#'&<'Q*2 %#7"-&'( *1%#12*%; "&-E(# -. ' 2-.%<@<&'; "3(2#4
5,# @<&'; "3(2# *2 "&-+3$#+ *1 ' G<77<(-16 IDD<7>'& 1#-1 6'2 =-(37# >; ' B<.28 BCD<
17 6'322*'1 ('2#& "3(2# )*%, '1 -1<'Q*2 "#'J *1%#12*%; -. L " FDF0 H $7!I4 R-& %,#
#(#$%&*$ E#(+ -. %,# ('2#& "3(2#8 %9# : ! #Q"9!# IS%IT :$-29&D# U !: )*%, ! O D 9$-2*1# "3(2#:8
),#&# %T *2 %,# "3(2# +3&'%*-18 &D *2 %,# '163('& $'&&*#& .&#?3#1$; '1+ ! *2 %,# V'>2-(3%#W
",'2#4 5,# +'2,#+ (*1# 2,-)2 %,# -1<'Q*2 #(#$%&*$ E#(+ -. %,# ('2#& "3(2# (#'=*16 %,#
*1%#&'$%*-1 &#6*-14 5,# $'($3('%#+ @<&'; &'+*'%*-1 *2 2#(#$%#+ )*%,*1 ' C<#M 2"#$%&'( &'16#
1#'& LD #M4 N12#%8 $'($3('%#+ 9.3(( (*1#: '1+ 7#'23&#+ 9+-%%#+ (*1#: @<&'; "3(2# 2"#$%&37
2#(#$%#+ >; %,# X-S!* &#Y#$%-&8 2,-)*16 %,'% '>-3% LDZ -. %,# %-%'( Y3#1$# *2 )*%,*1 '
C<#M &'16# '&-31+ LD #M4
Zhao et al.
(2012)
Light emission takes place
only once.
)*+
!"#$%&' (%
V3/" 3/, 0%+6 1-2,#
#;)2-/3)'
3',/+'/+'#
;3,3.2# 23&"
,3'-,)30+2
!"# 0)/, 3'
$+''#%L %#
!9BD '$
"+;# /) %#$
)'# &#'#%+
(+2(-2+/#0
75%+6 ,)-%
!"# $#+
2+%&#% /"+'
/3;#26 /"# 1
/"+/ /"# ).
© 2001 Macmillan Magazine
-18 sec) pulse
Attosecond
Fig. 3. (Color online) Characterization
of a 67 as(10
XUV pulse.
光の放出は１回だけ
(a) Streaked photoelectron spectrogram obtained experimenアト秒パルス
trace (left) from the spectrogram in
tally. (b) Filtered I
ωL
/3)' /) /"#
0%3;#% 13$1%);# /"
$#'/,:
spec(a) and the retrieved I ωL trace (right). (c) Photoelectron2015/10/8 No.
15
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
From femtosecond to attosecond
10-15 sec
10-18 sec
5
Molecular
rotation
5
10
10
FWHM 5 fs
(λ=800 nm)
44
Pulse
(fs)
Pulseduration
width (fs)
Molecular
Electronic vibration
dynamics
10
10
3
3
10
10
22
10
10
11
10
10
Single cycle at 800 nm
00
-6
10
10
-4
-2
0
2
4
6
fs
-1
-1
10
10
-2
-2
10
10
1960
1960
1970
1970
1980
1980
Year
1990
1990
Year
2000
2000
2010
FWHM 500 as
(λ=13 nm)
c = 3 ×108 m/s
dt = 1 as = 10−18 sec
c dt = 0.3 nm
2015/10/8 No. 16
How to generate IAP
17
K. L. Ishikawa
80
70
60
50
40
30
86
4
90
Energy (eV)
94
2
–4
–2
0
Time (fs)
2
0.6
)*+
2
0.4
80 as
-300
60
τx = 530 as
50
40
30
4
6
-200
-100
1
0
100
Time (as)
200
300
Attosecond (10
3'& /"# #;)2-/3)
+//),#()'0 /3$3'
*#45(6(2# 0%3;#%
"3&"5"+%$)'3(
H$)%# 23T#26K /)
)/"#% /"+' /"# )
*%+(/3)' )* +22 2+
/3)' /) /"# 0#/#
0%3;#% 1-2,#, 4
3$1%);# /"# 0+/
$#'/,:
!"#$%&' (%')*+,
V3/" 3/, 0-%+/3)
%+6 1-2,# (+' '
#;)2-/3)' )* /"#
3',/+'/+'#)-, (
;3,3.2# 23&"/ 1,3'-,)30+2 ),(322
!"# 0)/, 3' I3&: 9
0 %#;#+23'
2
$+''#%L
Delay
(fs)
!9BD '$
/) ,)$
"+;# /) %#$#$.
)'# &#'#%+/3'& /
(+2(-2+/#0 *%#?75%+6 ,)-%(#:
!"# $#+,-%#0
2+%&#% /"+' 1%#0
/3;#26 /"# 1%#03(
/"+/ /"# ).,#%;#0
−2 5 P'($3('%#+
0 .'&<E#(+8
2 1#'&<'Q*2 4
−4
−2
2%'3"%#7"-&'( *1%#12*%; "&-E(# -. ' 2-.%<@<&';
"3(2#4
Delay
5,# @<&';
"3(2# (fs)
*2 "&-+3$#+ *1 ' G<77<(-16 IDD<7>'& 1#-1 6'2 =-(37# >; ' B<.28 BCD<
17 6'322*'1 ('2#& "3(2# )*%, '1 -1<'Q*2 "#'J *1%#12*%; -. L " FDF0 H $7!I4 R-& %,#
#(#$%&*$ E#(+ -. %,# ('2#& "3(2#8 %9# : ! #Q"9!# IS%IT :$-29&D# U !: )*%, ! O D 9$-2*1# "3(2#:8
1.0
),#&# %T *2 %,# "3(2# +3&'%*-18 &D *2 %,# '163('& $'&&*#& .&#?3#1$; '1+ ! *2 %,# V'>2-(3%#W
",'2#4 5,# +'2,#+ (*1# 2,-)2 %,# -1<'Q*2 #(#$%&*$
4 E#(+ -. %,# ('2#& "3(2# (#'=*16 %,#
*1%#&'$%*-1 &#6*-14 5,# $'($3('%#+ @<&'; &'+*'%*-1 *2 2#(#$%#+ )*%,*1 ' C<#M 2"#$%&'( &'16#
0.8
1#'& LD #M4 N12#%8 $'($3('%#+ 9.3(( (*1#: '1+ 7#'23&#+ 9+-%%#+ (*1#: @<&'; "3(2# 2"#$%&37
τx2#(#$%#+
= 80 ±>;
5 %,#
as X-S!* &#Y#$%-&8 2,-)*16 %,'% '>-3% LDZ -. %,# %-%'( Y3#1$# *2 )*%,*1 '
3
C<#M &'16# '&-31+ LD #M4
Ne
0.8
B
70
XUV spectral intensity (arb.u.)
C
0.2
Light emission takes place
only once.
6
phase (rad)
5 fs
XUV intensity (arb.u.)
1.0
90
80
530
as
8
0
–6
−4
Photoelectron energy ( eV)
A
X-ray intensity (arbitrary units)
Photoelectron energy ( eV)
Baltuska et al. Nature 421, 611 (2003)
90
,1#(/%-$ H*-22 23'#K 3' /"# 3',#/ )* I3&: J: !"# 0#1/" )* /"3,
$)0-2+/3)' 1%);30#, + ,#',3/3;# $#+,-%# )* ,+/#223/# ()'/#'/: !"#
$#+,-%#0 ,1#(/%-$ )* /"# "+%$)'3( 75%+6 1-2,# %#O#(/#0 .6 )-%
<)MP3
$-2/32+6#% H0)//#0
23'# Nature
3' /"# 3',#/ )*414,
I3&: JK ,#/,
+ ,+*#
-11#%
Hentschel
et al.
509
(2001)
Laser electric field (arbitrary units)
Isolated attosecond pulse
generation by a few-cycle
laser pulse
rad). (C to E) Spectra measured at the CE phase setting closest to the
~11° (
*#4 ,$+22 ,+/#223/# 1-2,#,: !"# +11#+%+'(# )* ,+/#223/#, ,#1+%+/#0 .6 ,#()'0 1%#(3,3)'
Fig. 1A. The zero+!!
ofMNthe
CE phase scale in (A) was set to yield the best agreement
*%)$ /"# (#'/%+2 1-2,# 2#+0, /) + ,1#(/%+2 $)0-2+/3)' 43/" + )* /"# 4+;# H0#
D
spectra in (B). 1#%3)0 )* /43(# /"# 2+,#% 1")/)' #'#%&6L +, %#;#+2#0 .6 /"# (+2(-2+/#0 +$123/-0# #';#2
D
0.6
Goulielmakis
etMagazines Ltd
© 2001 Macmillan
al. 0.4
Science 320,
1614 (2008)
0.2
φ″=(1.5 ± 0.2)×1
40
50
60
70 80 90
Photon energ
sec) pulse
Fig. 3. Sub-100-as XUV pulse retrieval. (A)
Measured ATR spectrogram compiled
-18
spectra of photoelectrons launched by an XUV pulse with a bandwidth of ~28 eV (FW
at delay settings increased in steps of 80 as. Here, a positive delay corresponds
arriving before the NIR pulse. The high flux of the XUV source allows this spectrogr
within ~30 min. (B) ATR spectrogram reconstructed after ~103 iterations of the FRO
(C) Retrieved temporal intensity profile and spectral phase of the XUV pulse. The in
18 XUV emission (Fig. 4B) is almost fully compensated by a 300-nm-thick
Zr foil introd
K. L. Ishikawa
model17. The ninth-harmonic pulse driven by an 8-fs pulse evolves
steeply with the highly nonlinear response of the dipole moment in
the rising edge of a driving pulse. When the optical electric field
becomes high enough to ionize the interacting atoms18, high
harmonic generation is shut off because of the small dipole moment
of the ions. In this case, a driving laser with a shorter pulse duration
is also preferred.
With the foregoing as a basis, modifications could be made by
taking account of the spatial intensity distribution in the driving
laser beam and the propagation of harmonics. For example,
harmonic pulses would be generated at different times at different
positions, but the phase-matching effect would not preserve the
difference19. However, two-dimensional or three-dimensional
fundamental
field
simulations
harmonic
that the harmodensityofofhigh
neutral
Argeneration
atoms indicate
nic pulses still retain the features of the single atom
in the cut-off
envelope
(400 nm)
tion traces were 1.3 ^ 0.1 and 1.8 ^ 0.1 fs, resulting in pulse
durations of 950 ^ 90 as and 1.3 ^ 0.1 fs, respectively.
In the 950-as pulse, however, bumps appeared around the main
peak and the gaussian function does not seem to be appropriate to
describe the pulse shape. To check the validity of the experimental
results, the spectra of the ninth harmonic (Fig. 3c) were Fouriertransformed with an assumption of a flat phase in the frequency
domain, and the autocorrelation functions were then calculated.
The results are shown by the blue lines in Fig 3a, b. Both the
autocorrelation trace of the 1.3-fs pulse and that of 8.3-fs pulse are
reproduced well. The bumps are therefore attributable to the
spectrum shape. Consequently, no other pulses were observed
within the scanned time range of 20 fs, showing the isolated single
IONIZATION SHUTTER
HHG is suppressed when neutral atoms are depleted
Ar
950 as from 8.3 fs
1.3 fs
from 12 fs
The spec
Ti:sapphire
around 800
amplifier of
with two pea
duration, al
spectra are m
For furth
use of a mu
generate hig
earlier than
duration. H
attosecond p
duration is
the tempor
(650 as). Th
to induce no
Finally, w
two-photon
volume V
( ¼ 1011 cm
cross-sectio
the pulse du
were 7.8 £ 1
was set to 10
1.6 £ 1023 e
electrons pe
efficiencies,
Methods
Driving laser
Figure 1 High harmonic pulse generation in the adiabatic picture. The red line is the ninth
harmonic pulse of the 8-fs driving pulse with a peak intensity of 5.5 £ 1014 W cm22
(dashed line). The blue line is the density of the neutral Ar atoms radiating high harmonics
calculated by using a tunnelling ionization theory18. The generation of high harmonics
ceases with the ionization of neutral atoms.
9th harmonic (of 400 nm) = 27.9 eV
606
Blue laser pulses
pulses to obtain
Figure 2 Two-photon above-threshold-ionization (ATI) autocorrelator. a, Experimentalthe laser pulse, b
spectrum comp
setup for the autocorrelation measurement of the ninth harmonic (9q) of the blue laser. To
pulse energies o
improve the spectral resolution of the photoelectron spectrometer, an electrostatic field
durations were
was applied to the time-of-flight (TOF) tube and the photoelectrons were decelerated system. The opt
configuration fo
inside the tube. b, The photoelectron spectrum. c, Diagram of the two-photon ATI tilt and phase m
coherence of th
process. The area in red in b indicates the photoelectrons ejected from He atoms by the
pulses. The puls
process shown in c.
and were found
Isolated sub-fs pulse generation from a ~10 fs pulse
©2004 Nature Publishing Group
NATURE | VOL 432 | 2 DECEMBER 2004 | www.nature.com/nature
Autocorrelatio
Sekikawa et al., Nature 432, 605 (2004)
19
K. L.
In the present
produced by sp
Ishikawa
conventional a
POLARIZATION
GATING
(PG)
FOCUS | REVIEW ARTICLE
2010.256
HHG is suppressed when circular polarization is used
counter-rotating
circularly polarized pulses with a delay
b
Linearly
polarized
laser field
EUV intensity
1.0
4
3
2
1
L = 0.8 µm
10
0.6
0.8
5
130 as
0.4
0
0.2
0
Contributing
subcycle
4
Phase (rad)
fs)
Ar
–300 –150
0
150
Time (as)
300
Phase (rad)
Circularly
polarized
laser field
–5
Sansone et al., Science 314, 443 (2006)
200
d
20
Experiment
1
K. L. Ishikawa
e information of
encoded in I ωL ,
pulse are guessed
DOUBLE OPTICAL GATING
(DOG)
Polarization gating + two-color gating
PRL 100, 103906 (2008)
week ending
14 MARCH 2008
PHYSICAL REVIEW LETTERS
2
2
Egate "t# $ E0 "e'2ln2&"t%Td =2'T0 =4# ="! (
2
2
' e'2ln2&"t'Td =2'T0 =4# ="! ( #sin"!0 t % ’CE #; (2)
where E0 is the amplitude of the circularly polarized
fundamental laser field with carrier frequency !0 (period
T0 ), pulse duration "! , and CE phase ’CE . Td is the time
delay between the two circular pulses. The delay, T0 =4,
between the gating and the driving fields is introduced by
the quarter-wave plate. #!;2! is the relative phase between
the fundamental and second harmonic pulses. The duration
of the SH pulse is "2! . Finally, a represents the strength of
the second harmonic field relative to the fundamental field.
Figure 2(a) shows harmonic spectra of argon for onecolor (linearly polarized fundamental field only, Td $ 0,
a $ 0), two-color (a second harmonic field added to a
fundamental field polarized in the same direction, Td $
0), conventional PG (a $ 0), and DOG fields. Notice that
+2
Ne
with secondharmonic field
Fig. 3. (Color online) Characterization of a 67 as XUV pulse.
(a) Streaked photoelectron spectrogram obtained experimentally. (b) Filtered I ωL trace (left) from the spectrogram in
(a) and the retrieved I ωL trace (right). (c) Photoelectron specnerated by DOG in
trum obtained experimentally (thick solid) and retrieved specal., PRL and
2008,FROG-CRAB
103906 (2008)
e gas cell is 1 mm.
tra and spectral phases from Mashiko
PROOFet(solid)
Zhao etprofiles
al., Opt. Lett.
3891 (2012)
polarization gate is FIG. 1 (color).
(dashed).
(d)
Retrieved
temporal
and 37,
phases
from
The driving filed
components
for PG correspond to (a) without and (b) with the second harmonic field,
PROOF
(solid)
and
(dashed).
respectively.
The driving field
is shown as the
red line. FROG-CRAB
The two 21
K. L. Ishikawa
IAP generation from
a ~10 fs pulse
vertical lines represent the gate width. Here, the filled curves are
Elec
40
20
GENERALIZED DOUBLE
OPTICAL GATING (GDOG)
0
2
4
Ne
4
0.8
0.4
3
80 as
2
1
0.2
L = 0.8 µm
Elliptical instead of circular polarization
0
–200
0
Time (as)
200
d
c
Laser field
HHG bursts
L = 0.8 µm
Experimen
IAP generation from a
v =c
> 20 fs pulse without
E
need
of carrierTime dela
envelope
stabilization Theory,
E
L
Bi-colour field
with shaped
polarization Single HHG
burst
e
4
163 as
0
Phase (rad)
1.0 Ar
0.8
0.6
0.4
0.2
0
–200
EUV intensity
L = 0.8 µm
initial
L
30
20
10
0
initial
EX-ray
isolated pu
30
Gilbertson et al., PRL 105, 093902 (2010)
20
final
E
Gilbertson et
al., PRA 81, 043810 (2010)
X-ray
vX-ray = c
10
0
22
2
final
L
–4
0 200 400
Time (as)
Photoelectron
energy (eV)
0.6
Contributing
subcycle
Time delay (fs)
Photoelectron
energy (eV)
Contributing
subcycle
EUV intensity
1.0
–2
Phase (rad)
L = 0.8 µm
–4
1
Time dela
L = 2.0 µm
He
2
K. L. Ishikawa
–60
Ionization probability
0.8
(×10–3 a.u.)
(×10–3 a
central peak is markedly suppressed [see Fig. 1(a)]. Here,
the intensity ratio (# ¼ E21 =E20 ) and the phases (!CE , !1 )
–50
are
fixed
at
0.15
and
0
rad,
respectively.
The
intensity
ratio
INFRARED
TWO-COLOR
SYNTHESIS
between the central
peak
and
the
highest
side
peak
is
0.8,
–40
which is800
almost
same as
of a 5 fs pulse
at field
800 nm
nm the
+ 1300
nmthat
two-color
driving
–5.32most intense
–2.66
0.00 appears
2.66
(red line). Note that–7.98
the second
peak
autocorrelation trace
800 nm 800 nm + 1300 nm
0
Xe
500
as
10
(a)
(b)
–70
1.0
29 eV
4
[arb. units]
nee
E)
of
P
er
e
5.3
2
mix
2
-1
0.6
m
10
0.4
–50
4
o0.2
2
n
–40
-2
0.0
10
0
5
10
15
y
10
20
30
40
–7.0
–6.0
–1.0
0.0
1.0
6.0
Pulse
duration
[fs]
Time
[fs]
or
!t (fs)
Takahashi et al., PRL 104, 233901 (2010)
n
Takahashi
et al., Nat.
Commun. 4, 2691 (2013)
2
þ
re 3 | Measured
traces of (a)
an IAP
obtained
from the(E
side
peak of N ion signals. The time resolutio
FIG. 1 AC
(color).
Field
amplitude
mix ) of an 800 nm, 5 fs
d
48 and 28
as,
respectively.
Theand
error
show
theJ),s.d.
of eachline).
data point.
The
grey
solid profiles
are AC t
High-energy
(1.3abarsmicro
high-power
(2.6
GW)
IAP
pulse
(red line)
TC
field
(green
The
TC
field
is
As
generated by an 800 nm,more
30 than
fs pulse
mixed
a 1300
nm,| 4:2691
40reported
fs| DOI: 10.1038/nco
100 times
more with
energetic
than previously
NATURE
COMMUNICATIONS
is
pulse. The intensity ratio (#) and the phases (! , ! ) are fixed
23
CE Limited.
1
L. Ishikawa
& 2013 Macmillan
Publishers
All rights K.reserved.
FROM FEMTOSECOND TO ATTOSECOND
5
Molecular
rotation
5
10
10
FWHM 5 fs
(λ=800 nm)
44
Pulse
(fs)
Pulseduration
width (fs)
Molecular
Electronic vibration
dynamics
10
10
3
3
10
10
22
10
10
11
10
10
Single cycle at 800 nm
00
-6
10
10
-4
-2
0
2
4
6
fs
-1
-1
10
10
-2
-2
10
10
1960
1960
1970
1970
1980
1980
Year
1990
1990
Year
2000
2000
2010
FWHM 500 as
(λ=13 nm)
c = 3 ×108 m/s
dt = 1 as = 10−18 sec
c dt = 0.3 nm
24
K. L. Ishikawa
Quest for higher photon energy
(shorter wavelength)
cutoff
Ec = Ip + 3.17Up
e2 E02
Up (eV) =
= 9.3
4m 2
10
14
2
I(W/cm )
2
(µm)
Longer fundamental wavelength is advantageous
Optical parametric chirped-pulse amplification
(OPCPA)
25
K. L. Ishikawa
roximately 20 atm with a
matching is substantially satisfied along the propagation
By using the configuration
axis of the pump pulse. Moreover, this 2D image ensures
get [29], the effective gas
that our coherent water window source will be useful for
gion is estimated to be apacquiring 2D diffraction images.
50 eV photon energy, Gouy
We further explored the generation of HH under a
"1
evaluated to be 360 cm
neutral-medium condition by changing the nonlinear me"1
pulse and 615 cm from
dium from Ne to He with the aim of obtaining a higher
Also, plasma
dispersion
is
spectral
range between
the K-absorption
of Cthe(284
eV) and
(543
eV)
photon
energy. Figureedges
3 shows
measured
HeOHH
spec-
WATER-WINDOW HHG
tra driven by a 1:55 !m pulse with a focusing intensity of
absorbed by5:5
biological
samples
not by water
2 , but
which
is obtained with a
! 1014 W=cm
0.8
2400
grooves=mm
grating.
The pump energy, beam diattractive for
high-contrast
biological
imaging
I = 5.5 ⇥ 10
Space
W/cm
0.2
300
350
400
0.0
rgy [eV]
onic spectra from neutral Ne
the reciprocal of imaginary
ine and the dashed blue line
e spectrum obtained with a
2
He
Carbon K edge
0.8
0.8
0.6
0.6
Photon energy
0.4
0.4
0.2
0.2
0.0
200
250
300
350
400
450
500
550
Transmission of Mylar filter
0.4
14
1.0
Space
= 1.55 µm
(1/f2 )2
0
1.55 µm He HHG [arb. units]
Int.
0.6
0.0
Photon energy [eV]
FIG. 3 (color).
Takahashi et al., PRL 101, 253901 (2008)
harmonic spectra from neutral He.K. L. Ishikawa
26
Measured
keV HHG
Even up to 1.6 keV, > 5000 orders
almost x-ray!
0
= 3.9 µm
Popmintchev et al., Science 336, 1287 (2012)
a new type of laser-based radiation source
27
K. L. Ishikawa
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Attosecond Science
アト秒科学
2015/10/8 No. 28
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
femtosecond, attosecond
ミリ
m
10-3
マイクロ
μ
10-6
ナノ
n
10-9
ピコ
p
10-12
フェムト
f
10-15
アト
a
10-18
Light propagates during 30 fs …
3 × 108 (m/s) × 30 × 10−15 (s) = 9 × 10−6 (m) = 9 µm
2015/10/8 No. 29
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Why so short pulses?
necessary shutter speed
snapping ultrafast motion
for
2015/10/8 No. 30
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Electrons moving around the
nucleus
Orbital period of
the electron
inside an atom
Electron
Nucleus
2π
T =
= 2π
ω
!
2
1
e
mω 2 r =
4πϵ0 r2
4πϵ0 mr3
−18
=
152
×
10
s = 152 as
2
e
Need for attosecond shutter
2015/10/8 No. 31
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Dynamics of the Auger eﬀect
オージェ効果のダイナミクス
A method to analyze ultrafast
processes with a laser ﬁeld.
2015/10/8 No. 32
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Auger eﬀect
Ejection of a core electron
オージェ効果
Photoelectron
光電子
Augerオージェ電子
electron
光電子
Photoelectron
内殻電子が電離（光電効果）
Instantaneous
Core-excited ion
内殻励起状態のイオン
~ a few fs
Ejection of a valence electron
特性Ｘ線を放出するかわり
に軌道電子を放出
Observation of the ejection of Auger electrons
→Ionizing X rays < a few fs →Attosecond pulse
2015/10/8 No. 33
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
How to measure the electron ejection time?
Pump（イオン化を引き起こす）
高調波(HHG)
Probe（電子の放出時刻を測る）
レーザー光（laser）
2015/10/8 No. 34
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
How to measure the electron ejection
time?
高調波とレーザー光を遅
延時間を持たせて照射
Irradiate an atom with
an attosecond pulse
and laser pulse with
delay
2015/10/8 No. 35
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
How to measure the electron ejection time?
E(t) = E0 (t) cos(ωt + φ)
dv
dp
=m
= −eE(t)
dt
dt
ionization at
t = tr で電離
Initial momentum 初速度（運動量）
!
p0 = 2m(h̄ωX − Ip )
p = p0 + ∆p
! ∞
"
eE0 (t)
∆p = −e
E(t)dt = −eA(tr ) ≈
sin(ωtr +φ) = 4mUp (tr ) sin(ωtr +φ)
ω
tr
検出器での運動量 Momentum at the detector
検出器での運動エネルギー Kinetic energy at the detector
p0 ∆p
W ≈ W0 +
= W0 +
m
!
8W0 Up (tr ) sin(ωtr + φ)
2015/10/8 No. 36
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
How to measure the electron ejection
time?
検出器での運動エネルギー
!
W ≈ W0 + 8W0 Up (tr ) sin(ωtr + φ)
Electron kinetic energy
Ejection time
光電子のエネルギーと
遅延時間の関係
2015/10/8 No. 37
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Life time of the Auger decay∼8 fs
Auger effect
光電子
オージェ電子
Auger
electron
光電子
Probe…Laser
750 nm
Photoelectron
Pump…HHG soft x rays
13 nm
10フェムト秒程度の超高速過程が見える！
Ultrafast process 10 fs
2015/10/8 No. 38
Advanced Radiation Application (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Delay in photoemission
光電効果には何アト秒かかるか？
2015/10/8 No. 39
online 29 October 2009 (10.1126/science.1178535).
tant addition to this field, which should evenAdvanced
Radiation
Application
tually lead to
a better understanding
of how
membrane proteins fold.
(Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
Downloaded from www.sciencemag.org on June 21, 2011
would require a translocon pore size with a
diameter of ~50 Å, which is consistent with
biochemical data (11) but which is too large
10.1126/science.1193065
PHYSICS
When Does
Photoemission
When
Does Begin?
Photoemission Begin?
Ultrafast spectroscopy and multielectron
calculations reveal complex electron dynamics
occurring just before an atom emits a
photoelectron.
H. W. van der Hart
T
The complex dynamics
of atomic
in the positive
ion, and as the electrons
adjust
The photoelectric
effect
is photousually
considered
instantaneous.
emission has a simple origin—the emission to their new energy levels, they release energy
he process of photoemission was one
of the effects that led to the formulation of quantum mechanics. If an
atom or surface absorbs sufficient energy
from incoming light, it can transfer that
energy to an electron, which is then emitted. Theories of photoemission mainly focus
on energetics—the temporal or dynamic
aspects are ignored—but complex electron
interactions occur that will create a slight
delay between light absorption and electron
emission. This time delay has been poorly
understood for a fundamental reason: We
cannot “see” an atom absorbing a photon.
At best, we can follow subsequent emission events and use them to establish a “time
zero” when the light was absorbed. A practical challenge has been that the time delay is
extremely short, and only recently have direct
experiments been feasible with the advent
of lasers that emit pulses on the attosecond
(as, 10 18 s) time scale. On page 1658 of this
issue (1), Schultze and co-workers present
measurements of time delays between different photoemission processes generated by the
same ultrashort light pulse. This finding not
only allows further studies of the timing of
photoemission but also provides a new way to
investigate electron interactions in atoms.
Centre for Theoretical Atomic, Molecular, and Optical Physics,
School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK. E-mail: [email protected]
of a negatively charged electron changes the
neutral atom into a positive ion. The energy
levels of the remaining electrons are different
that is transferred to the outgoing electron.
The time needed for this transfer is the origin
of the small time delays.
e–
Ne
Ne
+
∆t2s
2p
Ne
2s
Short light pulse
Ne
Ne+
∆t2p
e–
Electron hesitation. Schematic diagram of a photoemission process for Ne. An incoming photon of an ultrashort light pulse is absorbed by either a 2s (top row) or a 2p (bottom row) electron. After photoabsorption, the
electron escapes, while the orbitals of the other electrons adjust to the new surroundings as the atom becomes
an ion. This adjustment leads to a time delay ∆t in the emission of the electron, which is longer for emission
of a 2p electron than for emission of a 2s electron.
www.sciencemag.org SCIENCE VOL 328 25 JUNE 2010
Published by AAAS
1645
2015/10/8 No. 40
the measured delay of ~20 as cannot be explained
by a delayed onset of streaking, which was the
dominant effect in (17). The streaking NIR
field may be significantly screened by bound
electrons at small distances from the nucleus.
After the absorption of an XUV photon, it takes
the positive-energy electron a finite time to leave
this screened volume, and this time interval may
be different for electrons originating from different orbitals. However, for an atom, this difference cannot exceed a few attoseconds. The
characteristic scales can be extracted from the
classical trajectories shown in Fig. 1B. If we assume that the 2s and 2p electrons are set in
motion at the same moment, their classical
distance of less than 1 Å from the
nucleus.
Further- parameters,
function cðeÞ
describes
properties
of
for allowing
us to track the history of
rent
experimental
thefully
small
devia- thetime
more, ifAdvanced
screening played
a dominant
role,
the
the
wave
packet.
In
this
representation,
a
delay
Dt
Radiation
Application
(Kenichi
ISHIKAWA)
for
useaccurately
only (Univ.
of
phenomena
(Fig. 1A)
tions between the electron’s exact motion and microscopicinternal
faster 2p electrons would be exposed to the in photoemission, shown as a shift of the electhat modeled via the CVA give rise to a 2-as calls for precise knowledge of the delay bestreaking field earlier than the slower 2s ones, tron’s trajectory in Fig. 1B, adds eℏ Dt to the phase
tween the XUV pulse and an outgoing electron
discrepancy in the relative delay.
whereas measurements and quantum simulations of cðeÞ. It is therefore meaningful to define the
wave
packet
Accepting
this
small
discrepancy,
manyshow that the slower electron is emitted first.
group delay of the outgoing electron
wave
pack-(henceforth, absolute delay). This
can
only
electron
models
were
applied
to
investigate
the
Now we turn our attention to the quantum- et, in accordance with earlier work (4, 5, 25),beas inferred from theory. For multidAs a first attempt,
systems, such as Ne, physical descripof electron
mechanical description. First effects
of all, we
need a correlation.
aðeÞ ¼ ℏ de
arg½cðeÞ%. Analyzingelectron
our simulaof the discrepancies
revealed by this work
thedelay.
multiconfigurational
Hartree-Fock
was the tion
definition for the photoemission
Consider tions,
we averagemethod
aðeÞover
bandwidth
of
proved
to created
evaluate
matrix
a photoelectron wave functionused
jyðtÞ〉
bytransition
the XUV
pulseelements
(29) andfrom
denote the
resulttoasbe
a. a challenge. The sensitive experstateofof Ne toAs
states
where
electron
an XUV pulse centered at t ¼the
0. ground
The motion
the first
andthe
most
importantimental
task, wetest
val-to which time-dependent manythe wave packet after photoionization
is conve- idate
the experimental
Intuitively,
models can now be subjected will benefit
wave asymptotically
propagated
along the methodology.
direc- electron
niently described in a basis oftion
continuum
states one
expects
thatfield.
a delay
in the formation
of a
their development.
of the streaking
NIR
electric
These
je〉, each of which has a well-defined energy e wave packet causes a corresponding temporal
and describes a wave that propagates in the di- shift of the streaking spectrogram. This holds true
Downloaded from www.sciencemag.org on June 21, 2011
The 2s electron appears to come out 21
attoseconds earlier than the 2p electron!
measure only re
Tokyo)
photoemission c
lute delays relies
tested time-dep
Presently, only tw
provide this de
photoionization
cause of low S/N
complex system
of the photoelect
streaking will
atomic photoion
sensitive tests, w
ually improving
predictions. Thes
understanding of
and will make t
atomic chronosc
References a
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Fig.
3. The relative delay
between
photoemission
from the 2p and 2s subshells of Ne atoms, induced by
Schultze et al.,sub–200-as,
Science
328,
1658
(2010)
near–100-eV XUV pulses. The depicted delays are extracted from measured attosecond
streaking spectrograms by fitting a spectrogram, within the strong-field approximation, with parameterized NIR and XUV fields. Our optimization procedure matches the first derivatives along the time delay
dimension of the measured and reconstructed spectrograms, thereby eliminating the influence of unstreaked background electrons [for details on the fitting algorithm, see (29)]. From the analysis of a set of
spectrograms, the measured delays and associated retrieval uncertainties are plotted against the amplitude
of the vector potential applied in the attosecond streak camera. Spectrograms measured in the presence of
a satellite attosecond pulse were found to exhibit a less accurate retrieval of the delay value. When a subset
of data (red diamonds) that represents scans with less than 3% satellite pulse content was evaluated, a
mean delay value of 21 as with a standard deviation of ~5 as was found. The green circles represent the
result of analyzing spectrograms recorded with an XUV pulse with narrower bandwidth in order to exclude
the potential influence of shakeup states contributing to the electron kinetic energy spectrum.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
H. Hertz, Annal
W. Hallwachs, A
A. Einstein, Ann
E. P. Wigner, P
C. A. A. de Carv
83 (2002).
A. F. Starace, in
(Springer, Berli
S. T. Manson, R
M. Y. Ivanov, J.
(2007).
A. Baltuška et a
R. Kienberger e
M. Nisoli, G. Sa
(2009).
G. Sansone et a
M. Schultze et a
E. Goulielmakis
M. Hentschel et
A. Borisov, D. S
Echenique, Che
A. L. Cavalieri e
A. K. Kazansky,
177401 (2009)
C. Lemell, B. So
A 79, 062901
J. C. Baggesen,
043602; and er
U. Becker, D. A
Photoionization
(Plenum, New Y
A. Rudenko et a
J. Mauritsson et
22.
41
2015/10/8 No. 23.
plication of isolated attosecond pulses in 2002
(2). This demonstration was then followed by
other important experimental results in the field
of ultrafast atomic physics, such as the real-time
observation of electron tunneling (3) and the
measurement of temporal delays of the order of
a few tens of attoseconds in the photoemission
of electrons from different atomic orbitals of neon
(4) and argon (5). The unprecedented time resolution offered by attosecond pulses has also allowed quantum mechanical electron motion and
its degree of coherence to be measured in atoms
by using attosecond transient absorption spectroscopy (6). Attosecond techniques have been
applied in the field of ultrafast solid-state physics, with the measurement of delays in electron
photoemission from crystalline solids (7) and
the investigation of the ultrafast field-induced
insulator-to-conductor state transition in a dielectric (8). In the past few years, attosecond
pulses have also been used to measure ultrafast
electronic processes in simple molecules (9). Subfemtosecond electron localization after attosecond excitation has been observed in H2 and D2
produced
a doubly
charged for
molecular
fragment
ical reaction in a D2 molecule (13).
Although
Quantum
Beamthe
Generation
Engineering
(Kenichi ISHIKAWA)
internal use
only (Univ. of Tokyo)
by ejection of a second electron, and charge mistudy of more complex molecules is challenging,
gration manifested itself as a sub-4.5-fs oscillaa formative measurement of the amino acid
tion in the yield of this fragment as a function
phenylalanine has shown that ionization by a
フェニルアラニン
of pump-probe delay. Numerical simulations of
short APT leads to dynamics on a temporal scale
the temporal evolution of the electronic wave
of a few tens of femtoseconds. This has been inpacket created by the attosecond pulse strongly
terpreted as the possible signature of ultrafast
support the interpretation of the experimental
electron transfer inside the molecule (14).
data in terms of charge migration resulting from
The application of attosecond techniques to
ultrafast electron dynamics preceding nuclear
molecules offers the possibility of investigating
rearrangement.
primary relaxation processes, which involve elecamino
The a-amino acids consist
of a acid
central carbon
tronic and nuclear degrees of freedom and their
atom (a carbon) linked
to an amine (-NH2)
coupling. In the case of large molecules (e.g., biアミノ酸
ologically relevant molecules), prompt ionizagroup, a carboxylic group (-COOH), a hydrogen
Ultrafast electron dynamics in phenylalanine
initiated through ionization
by attosecond pulses
Calegari et al., Science 346, 336-339 (2014)
1
Fig. 1. Three-dimensional
structure of phenylalanine.
Molecular structure of the most
abundant conformer of the
aromatic amino acid phenylalanine.
Dark gray spheres represent
carbon atoms; light gray spheres,
hydrogen atoms; blue sphere,
nitrogen; and red spheres, oxygen.
The molecular geometry has
been optimized by using density
functional theory (DFT) with a
B3LYP functional.
N
O
biological effect of
ionizing radiation
Institute of Photonics and Nanotechnologies (IFN)–Consiglio
Nazionale delle Ricerche (CNR), Piazza Leonardo da
Vinci 32, 20133 Milano, Italy. 2Departamento de Química,
Modulo 13, Universidad Autónoma de Madrid, Cantoblanco
28049 Madrid, Spain. 3Department of Physics, Politecnico di
Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
4
Centre for Plasma Physics, School of Maths and Physics,
Queen’s University, Belfast BT7 1NN, UK. 5IFN-CNR, Via
Trasea 7, 35131 Padova, Italy. 6Dipartimento di Scienze
Chimiche e Farmaceutiche, Università di Trieste and
CNR–Istituto Officina dei Materiali, 34127 Trieste, Italy.
7
Instituto Madrileño de Estudios Avanzados en Nanociencia,
Cantoblanco, 28049 Madrid, Spain.
放射線の生物効果
*Corresponding author. E-mail: [email protected] (F.M.);
[email protected] (M.N.)
336
17 OCTOBER 2014 • VOL 346 ISSUE 6207
sciencemag.org SCIENCE
of attosecond techniques to
he possibility of investigating
processes, which involve elecdegrees of freedom and their
se of large molecules (e.g., bimolecules), prompt ioniza-
nsional
lalanine.
of the most
r of the
d phenylalanine.
epresent
gray spheres,
ue sphere,
pheres, oxygen.
metry has
using density
FT) with a
data in terms of charge migration resulting from
ultrafast electron dynamics preceding nuclear
rearrangement.
The a-amino acids consist of a central carbon
atom (a carbon) linked to an amine (-NH2)
group, a carboxylic group (-COOH), a hydrogen
N
O
Quantum Beam Generation Engineering (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
pump
sub-300 as XUV
15-35 eV
probe
4 fs VIS/NIR
1.77 eV / 700 nm
sciencemag.org SCIENCE
detect
++NH -CH-R dication
2
scale. The experimental data display a rise time of
10 T 2 fs and an exponential decay with time
constant of 25 T 2 fs [this longer relaxation time
constant is in agreement with earlier experi-
Quantum
Beam Generation
Engineering
(Kenichi ISHIKAWA)
for internal use 430
only (Univ.
of Tokyo)
K, only
the
be related
to nuclear
dynamics,
which usually
come into play on a longer temporal scale, ultimately leading to charge localization in a particular molecular fragment. Indeed, standard
dication yield oscillates with period ~ 4.3 fs
Fig. 2. Pump-probe measurements. (A) Yield of doubly charged immonium ion (mass/charge = 60) as
a function of pump-probe delay, measured with 3-fs temporal steps.The red line is a fitting curve with an
exponential rise time of 10 fs and an exponential relaxation time of 25 fs. (B) Yield of doubly charged
immonium ion versus pump-probe delay measured with 0.5-fs temporal steps, within the temporal
window shown as dotted box in (A). Error bars show the standard error of the results of four measure-
six
substantially presen
mentary materials, w
figuration shown in
To further investi
we also varied the
width of the attosec
an indium foil in th
XUV spectrum was
width at half maxim
15 eV, followed by
component extendi
doubly charged imm
ly visible, suggesting
involves relatively
cation. We have cal
gram with all the sta
alanine generated b
all the states of the
materials). A numbe
states of the cation
dication are possibl
tion of just a few VI
cannot be accessed
in the case of XUV
dium foil. In this c
states to the lowest
the less probable a
photons.
We also performe
describe the hole d
second pulse simila
ment. Details of the
supplementary ma
central frequency a
the pulse, a manifo
assigned to electron dynamics in the molecule
Quantum Beam Generation Engineering (Kenichi ISHIKAWA) for internal use only (Univ. of Tokyo)
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