Single Attosecond Pulses
and XUV Supercontinuum
Shambhu Ghimire, Bing Shan, and Zenghu Chang
J. R. Macdonald Laboratory
Kansas State University
Applications of Attosecond Pulses
zs
10-21 s
as
fs
ps
10-18 s
10-15 s
10-12 s
Time
Generation of attosecond pulses
High harmonic generation
U(x,t)
Step1: Ionization
Step2: Acceleration
Step3: Recombination
Ion
x-ray
laser field
Ip
electron
electron
Previous work
Attosecond pulse at cutoff
85 eV
Attosecond pulse train
A. BALTU KA et.al, Nature 421, 611( 2003)
135 ev
Single as pulse
Attosecond pulse train
Elaser
Electron
trajectory
t (fs)
IHHG
-1 0 1
t (fs)
Discrete harmonic orders in the plateau
-Spatial analogy of pulse train interference
Discrete pattern at plateau analogy to multi-slit diffraction
Single slit
Double slit
Multi slit
Diffraction patterns
(spatial frequency)
Our goal
• The drawbacks of previous work
– Attosecond pulse train in the plateau
– Single attosecond pulse only at the cutoff
– Harmonic intensity is low at the cutoff
– Covers a narrow spectrum range
• We intend to generate single
attosecond pulses in the plateau range
Generation of single attosecond
pulse in the plateau
• Approach 1- Half cycle laser pulse
Reduce laser pulse to half of a cycle.
Very hard to do.
• Approach 2- Polarization gating
The laser pulse can have a few cycles.
Polarization gating
•Laser is linearly polarized

E
HHG emission
•Laser is circularly polarized
Ey
No HHG emission
Ex
•Polarization gating: linear portion is less than half of a cycle
t (fs)
Generation of ellipticity- depended pulse
-with birefringence optics
Optics axis
Time
delay
Laser
field
Time
delay
e-ray
o-ray
L
e-ray
o-ray
Optic axis
Quartz plate
¼ waveplate
R
Generation of ellipticity-depended pulse
Ey
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
t(fs)
Time (fs)
Ex
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
t(fs)
Time (fs)
Pulse duration measurement
Frequency-resolved optical gating
wavelength
Compensating plate
I(t)
time
BBO Crystal
I(t)
BS
Time Delay Stage
Computer
lens
Spectrometer and cold CCD
Pulse duration measurement
Hollow-core fiber output
26
24
Pulse duration (fs)
22
20
18
16
14
12
10
8
0
1
2
3
4
5
Compensating plate Thickness (mm)
6
Attosecond pulse generation
experimental setup
KLS
4 mJ, 25fs
0.8 mm
Hollow-core fiber
0.5 mJ, 8fs
Gas nozzle
CCD
Grating
Filter
MCP &
Phosphor
¼ waveplate
HHG Spectrum
Quartz plate
Spectra broadening for shorter pulse
19
21
23
25
27
With a linear, 25 fs pulses (~10 laser cycle)
( the interference of 20 as pulses)
19
21
23
25
27
With two circular ~12 fs pulses, linear portion ~3 fs (1 cycle)
( the interference of 2 as pulses)
The effect of polarization gating
With two pulses >9.2fs, 1.7fs linear polarization
Single Attosecond Pulses
and XUV Super continuum
~45 nm
~20 nm
With two pulses ~8 fs
Intensity (Arb. u.)
Simulated spectrum of HHG
Without polarization gating
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-9
1E-10
1E-11
1E-12
1E-13
1E-14
1E-15
1E-16
1E-17
1E-18
1E-19
1E-20
Ar
t=5 fs
14
2
I=6x10 W/cm
0
10
20
30
40
50
60
Harmonic order
70
80
90
Simulated spectrum of HHG
With polarization gating
Intensity (Arb. u.)
Continuum at plateau
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-9
1E-10
1E-11
1E-12
1E-13
1E-14
1E-15
1E-16
1E-17
1E-18
1E-19
1E-20
Ar
ellipticity chirped pulses,
t=5 fs
14
2
I=3x10 W/cm
0
10
20
30
40
50
Harmonic order
60
70
80
Summary
• Single attosecond pulse at plateau for the first
time.
• Birefringence optics was used to produce the
ellipticity-dependent laser pulse.
• The single attosecond over a broader spectrum
range.
• The attosecond at the plateau is more intense
than that at the cutoff.