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Development and application of plasma-waveguide based soft x-ray lasers
Institute of Atomic and Molecular Sciences Academia Sinica, Taiwan
National Central University, Taiwan
Core members of the experimental group
Prof. Jyhpyng Wang (汪治平 ), Academia Sinica (Taiwan)Prof. Szu-yuan Chen (陳賜原 ), Academia Sinica (Taiwan)Prof. Jiunn-Yuan Lin (林俊元 ), National Chung-Cheng Univ.Prof. Hsu-Hsin Chu (朱旭新 ), National Central Univ.
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Outline
Introduction to soft x-ray lasers
Soft x-ray lasers pumped by optical-field ionization
Fabrication of transient plasma waveguides
Plasma-waveguide based soft x-ray lasers
Injection-seeding with high-harmonic generation
X-ray digital holographic microscopy
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Introduction to soft x-ray lasers
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X-ray lasers powered by nuclear bomb for “Star Wars”
1983
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2p
3p
3s
Ne-like ions: Ar8+, Ti12+, Fe16+
collisional excitation (~200 eV)
fast relaxation
lasing
lifetime = ~3 ps
Energy levels of soft x-ray lasers
He-Ne laser
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Early pumping scheme
line-focused high-power laser pulse
solid target
collisional excitation in hot plasma
solid target
x-ray lasing
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Pulse sequence for effective excitation
plasma generation
target
pump pulse
time delay to reduce plasma density gradient by diffusion
plasma heating
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Grazing-angle pumping scheme
plasma generating pulse
solid target solid target
J.J. Rocca et al. “Saturated 13.2 nm high-repetition-rate laser in nicke-llike cadmium” Opt. Lett. 30, 2581 (2005).
pumping at grazing angle
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Soft x-ray lasers pumped by optical-field ionization
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multiphotonionization
tunnelingionization
above-thresholdionization
Optical-field ionization
appearance intensity for 1+ ion (=1 m)Xe: 8.71013 W/cm2
He: 1.51015 W/cm2
above-thresholdionization heating
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electrons gain energy
electron-ioncollisional excitation
population inversionand lasing
tunneling ionization
above-threshold-ionization heating
time
laser fieldelec
tron
ve
loci
tyionization to
specific ion stage
Pumping by optical-field ionization
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Ionization of Xe as a function of intensity
When a laser pulse with appropriate laser intensity is incident into a gas jet, atoms in the jet can be ionized to specific ion species through optical-field-ionization.
0 1208040time (fs)
0.0
0.2
0.4
0.6
0.8
1.0
rela
tive
ion
pop
ula
tion
160
8+7+
1+2+
5+
4+
3+6+
laser inten
sity (10 W
/cm)
162
0
2
4
6
8
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Energy levels of soft x-ray lasers
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pump pulse
nozzle
grating
CCD
Longitudinally pumped optical-field-ionization x-ray lasers
gas jet
defocusing quickly reduces intensity
pump pulse lower refractive index
higher refractive index
advantages: high efficiency excellent beam profile no debris
problem: ionization defocusing
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mac
hini
ng-p
ulse
inte
nsity
Tomography of laser-plasma interaction
nanoseconds after
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focal spot: 20 m1.3 mm
function of the knife-edge: setting the interaction length
machining pulse
variable positionknife-edge
pump pulse
gas jetcylindrical lens pair
Setup of the machining beam for tomographic measurements
Phys. Rev. Lett. 96, 095001 (2006)
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Simulation shows the pump beam diverges quickly due to ionization defocusing. As a result, the x-ray output is limited by the absorption from the weakly pumped medium at the tail.
Tomography of x-ray lasing
0 1 2 3 4 5position (mm)
0
3
6
9
12
15
18
21
24 psi30 psi39 psi machining pulse: 30-mJ, 45-fs,
6-ns before pump pulse.
width of the line focus: 20 m6.61017 cm-3
8.31017 cm-3
1.11018 cm-
3
0
2
4
6
1
3
5
7
pump pulse: 240-mJ, 45-fs, focused to 10-m diameter.
Phys. Rev. A 74, 023804 (2006)
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How to make an all-optical plasma waveguide?
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creating seed electrons
heating up and generating more electrons
shock expansion & collisional ionization
forming a plasma waveguide
Plasma-waveguide formation from a line focus
Phys. Plasmas 11, L21 (2004)
heater ignitor
axicon
line focus
line focus
ignitor
heater
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length > 1.2 cm
- 4 0 - 2 0 0 2 0 4 0
0 . 0
0 . 5
1 . 0
1 . 5
2 . 0
2 . 5
3 . 0
r a d iu s ( m )
ele
ctr
on
de
ns
ity
(1
0 c
m)
1
9-3
ignitor: 15 mJ, 55 fs
heater: 85 mJ, 80 ps (1.1 ns delay)
probe: 1.2 ns after heater
density variation < 20%
electron density profile
Phys. of Plasma 11, L21 (2004)
Laser-drilled plasma waveguide
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pump pulse: 45 fs, 235 mJ
ignitor: 45 fs, 45 mJ
heater: 80 ps, 225 mJ
ignitor-heater separation: 200 ps
hearer-pump delay: 2.5 ns
atom density: 1.6×1019 cm-3
radial electron density profile
A uniform pure-Kr plasma waveguide of 9-mm length is produced with the axicon-ignitor-heater scheme. The guided beam size is smaller than 15 m.
(1)
(2)
(1)
(2)
ignitor + heater pulses
pump pulse in waveguide
Unexpected immunity to ionization defocusing
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Plasma-waveguide based soft x-ray lasers
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without waveguidepump pulse: 45 fs, 235 mJfocal position: 2.75 mmpump polarization: circular
pure Kr waveguidepump pulse: 45 fs, 235 mJpump polarization: circularfocal position: 500 mignitor: 45 fs, 45 mJheater: 80 ps, 225 mJignitor-heater separation: 200 psheater-pump delay: 2.5 ns
trade-off between larger gain coefficient and more severe ionization defocusing
linear growth (reaching saturation)
exponential growth
Phys. Rev. Lett. 99, 063904 (2007)
400-fold enhancement by waveguide
Atom-density dependence for Ni-like Kr lasing at 32.8 nm
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100 150 200 250108
109
1010
1011
Num
ber
of p
hoto
ns
Pump energy (mJ)
pure Kr waveguidepump pulse: 45 fs, 235 mJpump polarization: circularfocal position: 500 mignitor: 45 fs, 45 mJheater: 80 ps, 225 mJignitor-heater separation: 200 psheater-pump delay: 2.5 ns
Phys. Rev. Lett. 99, 063904 (2007)
linear growth (reaching saturation)
exponential growth
Pump-power dependence for Ni-like Kr lasing at 32.8 nm
optimized lasing without waveguide pump energy (m
J)
num
ber
of p
hoto
n/pu
lse
400 folds
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Phys. Rev. Lett. 99, 063904 (2007)
Reduced divergence
without waveguide
with waveguide
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energy diagram of Ne-like Arraw image recorded by x-ray spectrometer
46.9 nm46.5 nm
45.1 nm
46.9 nm
46.5 nm
45.1 nm
Phys. Rev. A 76, 053817 (2007)
Multi-line lasing for Ne-like Arin
tens
ity (a
rb. u
nits
)
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Kr/Ar mixed-gas waveguidepump pulse: 45 fs, 240 mJ pump polarization: circular ignitor: 45 fs, 45 mJheater: 160 ps, 220 mJ Kr atom density: 9.1×1018 cm-3
Ar atom density: 1.2×1019 cm-3
ignitor-heater separation: 200 ps hearer-pump delay: 1.5 ns
raw image recorded by flat-field spectrometer
Phys. Rev. A 76, 053817 (2007)
gas mixture Kr : Ar = 0.9 : 1.2
Multi-species parallel x-ray lasing
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Injection-seeding with high-harmonic generation
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Experimental set-up
x-ray mirror
parabolic mirror
axicon
bored lens
parabolic mirror
pump for high harmonic generation
high harmonic seed
x-ray laser pump
Ar jet
Kr jet amplified x-ray
pulses for waveguide fabrication (ignitor & heater)
pulse timing diagram
time
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Spectrum of the soft x-ray lasers
gas: argonatom density: 7.1×1018 cm-3
pump energy: 3.8 mJpump duration: 360 fsfocal position: 1250 m
gas: kryptonatom density: 1.6×1019 cm-3
pump pulse: 38 fs, 235 mJignitor: 38 fs, 45 mJheater: 160 ps, 270 mJignitor-heater separation: 200 psheater-pump delay: 2.5 ns
parameters of HHG seed:
parameters of x-ray amplifier:
seed-amplifier pump delay: 2 ps
Maximizing the 25th HHG output is achieved by adjusting the pump beam size, pump energy, focal position, and atom density.
The spectral overlap between HHG seed and amplifier is done by adjusting the chirp of HHG pump pulse.
high harmonic seed
unseeded laser
seeded laser
25th harmonic
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Angular distribution (with waveguide)
gas: argonatom density: 7.1×1018 cm-3
pump energy: 3.8 mJpump duration: 360 fsfocal position: 1250 m
gas: kryptonatom density: 1.6×1019 cm-3
pump pulse: 38 fs, 235 mJignitor: 38 fs, 45 mJheater: 160 ps, 270 mJignitor-heater separation: 200 psheater-pump delay: 2.5 ns
parameters of HHG seed:
parameters of x-ray amplifier:
seed-amplifier pump delay: 2 ps
fluctuations of beam pointing and angular distribution ~0.13 mrad
With seeding the divergence of the x-ray laser is greatly reduced from 4.5 mrad to 1.1 mrad, which is about the same as that of the HHG seed.
With the waveguide-based soft-x-ray amplifier, the HHG seed is amplified by a factor of 104.
unseeded laser
seeded laser
high harmonic seed
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Controlled polarization
detector
polarization analyzer (Is : Ip > 19)
x-ray laser
-90 45-45 0 90analyzer angle (degree)
inte
nsity
1234
0
p
s
-90 45-45 0 90
inte
nsity
1234
0
analyzer angle (degree)
p
s
-90 45-45 0 90analyzer angle (degree)
inte
nsity
1234
0
unseeded laser
seeded laser
high harmonic seed
The x-ray analyzer consists of two multilayer x-ray mirrors which are strongly polarization dependent.
The polarization of seeded soft-x-ray laser follows that of the HHG seed.
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spectral brightness (photon/sec/mm2/mrad2) for
NSRRC (Taiwan) x-ray laser (HHG seeding)
6.6101
4
9.81012
3.310267.91014
average spectral brightness at 32.8 nm
peak spectral brightness at 32.8 nm
repetition rate 106 Hz 10 Hz
wavelength tunable discrete set
pulse duration 100 ps 200 fs*
Comparing our x-ray laser with synchrotron radiation
* assuming the pulse duration is limited by bandwidth
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X-ray digital holographic microscopy
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Working principle
focused x-ray laser
object
focusing mirrorCCD camera
constructed images
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Experimental set-up
waveguide-basedx-ray laser
10-TWlaser system
x-rayconcave
mirror
gatevalve
vacuum chamber Alfilter
f=20 cm
f=30 cm
x-rayflat
mirror
x-ray CCD
Alfilter
objectAFM tip
Opt. Lett. 34, 623 (2009)
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resolution: 0.5 mSEM image
working distance: 20 cm
10 m
Image of an AFM tip
Opt. Lett. 34, 623 (2009)
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Thank you for your attention.