attosecond laser pulse

Transcription

1 Kenichi Ishikawa ( ) ishiken@atto.t.u-tokyo.ac.jp Advanced Plasma and Laser Science E attosecond laser pulse 1

2 attosecond pulse train (APT) isolated attosecond pulse (IAP) 2

3 High-order harmonics are generated as attosecond bursts repeated each half cycle of the fundamental laser (attosecond pulse train) Paul et al., Science 292, 1689 (2001) Nabekawa et al., Phys. Rev. Lett. 97, (2006) time [fs] Optical cycle(2.7 fs) Only one burst Isolated attosecond pulse (IAP) 3

4 Isolated attosecond pulse generation by a few-cycle laser pulse Baltuska et al. Nature 421, 611 (2003) Hentschel et al. Nature 414, 509 (2001) X-ray intensity (arbitrary units) Energy (ev) Time (fs) 530 as τ x = 530 as Laser electric field (arbitrary units) 5fs Light emission takes place only once. Zhao et al. (2012) Attosecond (10-18 sec) pulse 4

5 10-15 sec sec Molecular rotation Molecular vibration Electronic dynamics Pulse duration (fs) Year increase in intensity Single cycle at 800 nm (courtesy of Prof. J. Itatani) 5

6 0.1attosecond! 0.1 6

7 How to generate IAP 7

8 Isolated attosecond pulse generation by a few-cycle laser pulse Baltuska et al. Nature 421, 611 (2003) Hentschel et al. Nature 414, 509 (2001) X-ray intensity (arbitrary units) Energy (ev) Time (fs) 530 as τ x = 530 as Laser electric field (arbitrary units) 5fs XUV intensity (arb.u.) Ne C 80 as τ x = 80 ±5 as phase (rad) Goulielmakis et al. Science 320, 1614 (2008) Light emission takes place only once. Fig Time (as) A Attosecond (10-18 sec) pulse 8

9 IONIZATION SHUTTER domain, and the autocorrelation functions were then calculated. HHG is suppressed when neutral atoms are depleted density of neutral Ar atoms 9th harmonic (of 400 nm) = 27.9 ev fundamental field envelope (400 nm) 9 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 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 950 as from 8.3 fs 1.3 fs from 12 fs Isolated sub-fs pulse generation from a ~10 fs pulse Ar Sekikawa et al., Nature 432, 605 (2004) 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 cm cross-sectio the pulse du were was set to e electrons pe efficiencies, Methods Driving laser Blue laser pulses pulses to obtain the laser pulse, b spectrum comp pulse energies o durations were system. The opt configuration fo tilt and phase m coherence of th pulses. The puls and were found Autocorrelatio In the present produced by sp conventional a

10 POLARIZATION GATING (PG) FOCUS REVIEW ARTICLE HHG is suppressed when circular polarization is used counter-rotating circularly polarized pulses with a delay b Circularly polarized laser field Linearly polarized laser field EUV intensity Ar 130 as Phase (rad) L = 0.8 µm Contributing subcycle Time (as) Sansone et al., Science 314, 443 (2006) 5 = 0.8 µm 10

11 e information of encoded in I ωl, pulse are guessed DOUBLE OPTICAL GATING (DOG) Polarization gating + two-color gating PRL 100, (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 (2008) e gas cell is 1 mm. tra and spectral phases from Mashiko PROOFet(solid) Zhao etprofiles al., Opt. Lett (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) (dashed). respectively. The driving field is shown as theand red line. FROG-CRAB The two 11 IAP generation from a ~10 fs pulse vertical lines represent the gate width. Here, the filled curves are

12 GENERALIZED DOUBLE OPTICAL GATING (GDOG) = 0.8 µm L Elliptical instead of circular polarization c Laser field Bi-colour field with shaped polarization L HHG bursts = 0.8 µm Single HHG burst EUV intensity 1.0 Ar as Time (as) Phase (rad) L = 0.8 µm IAP generation from a v > 20 fs pulse without L = c initial need E L of carrierenvelope E L final stabilization initial E X-ray Gilbertson et al., PRL 105, (2010) final Gilbertson et al., PRA 81, (2010) E X-ray v X-ray = c L = 2.0 µm 12

13 2 INFRARED TWO-COLOR SYNTHESIS mix [arb. units] nm nm two-color driving field 800 nm 800 nm nm (a) ( 10 3 a. ( 10 3 a.u.) autocorrelation trace Xe 500 as 29 ev Time [fs] Δt (fs) Takahashi et al., PRL 104, (2010) Takahashi et al., Nat. e 3 Measured AC traces of an IAP obtained from the side peak of N þ Commun. 4, 2691 (2013) ion signals. The time resolutio 8 and 28 as, respectively. The error bars show the s.d. of each data point. The grey solid profiles are AC tr High-energy (1.3 micro J), high-power (2.6 GW) IAP more than 100 times more energetic than previously reported NATURE COMMUNICATIONS 4:2691 DOI: /nco & 2013 Macmillan 13 Publishers Limited. All rights K. reserved. L. Ishikawa

14 FROM FEMTOSECOND TO ATTOSECOND Molecular rotation Molecular vibration Electronic dynamics Pulse duration (fs) Year increase in intensity Single cycle at 800 nm (courtesy of Prof. J. Itatani) 14

15 Quest for higher photon energy (shorter wavelength) cutoff E c = I p +3.17U p U p (ev) = e2 E 2 0 4m 2 = I(W/cm 2 ) 2 (µm) Longer fundamental wavelength is advantageous Optical parametric chirped-pulse amplification (OPCPA) 15

16 WATER-WINDOW HHG spectral range between the K-absorption edges of C (284 ev) and O (543 ev) absorbed by biological samples but not by water attractive for high-contrast biological imaging 0 =1.55 µm I = W/cm µm He HHG [arb. units] He Space Carbon K edge Photon energy Transmission of Mylar filter Photon energy [ev] Takahashi et al., PRL 101, (2008)

17 kev HHG almost x-ray! 0 =3.9 µm Popmintchev et al., Science 336, 1287 (2012) a new type of laser- based radiation source 17

18 ATTOSECOND SCIENCE atomic unit of time = 24 attoseconds Orbital period of the Bohr electron mω 2 r = 1 4πϵ 0 e 2 r 2 T = 2! =2 r 4 0 mr 3 e 2 = 152 as = 2 a.u. real-time observation and time-domain control of atomic-scale electron dynamics 18