30
HRS Program FLS2010 Workshop March 4 th , 2010 HHG based Seed Generation for X-FELs Franz X. Kärtner, William S. Graves and David E. Moncton and WIFEL Team Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology Cambridge, MA, USA

HHG based Seed Generation for X-FELs

  • Upload
    akio

  • View
    39

  • Download
    0

Embed Size (px)

DESCRIPTION

HHG based Seed Generation for X-FELs. Franz X. Kärtner, William S. Graves and David E. Moncton and WIFEL Team Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology Cambridge, MA, USA. Acknowledgement. - PowerPoint PPT Presentation

Citation preview

Page 1: HHG based Seed Generation for X-FELs

HRS Program

FLS2010 WorkshopMarch 4th, 2010

HHG based Seed Generation for X-FELs

Franz X. Kärtner, William S. Graves and David E. Monctonand WIFEL Team

Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology

Cambridge, MA, USA

Page 2: HHG based Seed Generation for X-FELs

2

Acknowledgement

Students:

Ch.-J. Lai, A. Benedick, S.-W. Huang, S. BhardwajA. Siddiqui, V. GkortsasB. Putnam, Li-Jin Chen

Research Scientists: K.-H. Hong, J. Moses

Postdocs and Visitors:

G. Cirmi (Politecnico Milano, Rocca Foundation)

A. Gordon (Technion, Israel)O. Muecke (Techn. Univ. Vienna)E. Falcao (Pernambuco, Brazil)

Page 3: HHG based Seed Generation for X-FELs

3

Outline Required Seed Power Levels

Single Pass Efficiencies in High Harmonic Generation

Wavelength Scaling of HHG

Seed Generation for High Repetition Rate FELS

A High Average Power HHG Source for 13.5 nmpumped by 515 nm Lasers (SHG of 1030nm), where powerful Yb-doped lasers exist

Page 4: HHG based Seed Generation for X-FELs

4

Required Seed Power Levels

Direct Seeding: 100 kW (30fs) 3 nJ

Seeding for HGHG: 100 MW (30fs) 3 µJ

Push direct seed wavelength as short as possible. How does efficiency scale?

Repetition rate determines drive power:

Efficiency determines required drive pulse energy

Efficiency: 10-6 Pulse energy 3 mJ // 3 J

Rep. Rate 1kHz / 10MHz Power: 3W / 30kW // 3 kW / 30MW

Page 5: HHG based Seed Generation for X-FELs

5

High Harmonic Generation

21

2XUV pI mx

Corkum, 1993 Cutoff formula

ħωmax = Ip+3.17 Up

Ele

ctri

c F

ield

, P

osi

tio

n

Time

Ionization

Three-Step Model Trajectories

Page 6: HHG based Seed Generation for X-FELs

6

Wavelength Scaling of HHG Efficiency

20

max 23.17

4p

EI

1m e

Atomic units Field amplitude

Drive pulse frequency

0EIncrease intensity

Decrease frequency(increase wavelength)

Ionization potential

What is the impact on HHG conversion efficiency?

1.) Single-Atom Response

2.) Gas properties

3.) Phase matching

Page 7: HHG based Seed Generation for X-FELs

)(1)1(

1

)(

),(20236.0 0

2

4

)1(4

223/160

2250

cutoff

N

cutoffcutoff

recptbEw

NE

LkgaI

HHG efficiency for N-cycle flat top pulse

Cutoff

92/9250

50 ~~/ pcutoff UE

200 400 600 8001E-5

1E-4

1E-3

0.01

0.1

1

(a

.u.)

EnergyHHG

(eV)

He Ne Ar Kr Xe

200 400 600 800

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

a rec

EnergyHHG

(eV)

He Ne Ar Kr Xe

E. L. Falcão et al., Opt. Expr. 17, 11217 (June, 2009).

Page 8: HHG based Seed Generation for X-FELs

8

HHG Efficiency into Single Harmonic

800-nm (Xe)

400-nm driver (He)

• Conversion efficiency very sensitive to drive wavelength and interaction parameters

800-nm driver (He)

Page 9: HHG based Seed Generation for X-FELs

9

Experimental HHG Setup

800-nm Ti:S amplifier(1 kHz, 7 mJ)

HHG chamber

Telescope &Beam delivery

Beam input port

Beam transport

Pulsed nozzle

Soft-X-ray spectrometer

Page 10: HHG based Seed Generation for X-FELs

• Pulse energy of 0.94 mJ for all gases• Peak intensity: ~7.8x1014 W/cm2 (estimation)• Nozzle length: 2 mm

HHG spectra generated by 400-nm driver

Ar: 0.05 mbarNe: 0.3 mbarHe: 1 bar

Page 11: HHG based Seed Generation for X-FELs

Ar: 0.05 barNe: 0.3 barHe: 1 bar

Total HHG efficiency from 400-nm driver

• Conversion efficiency of up to 2x10-4 from He over Al window• “Good” agreement to analytic theory [1]

E. L. Falcão-Filho et al., Opt. Express 17, 11217 (June, 2009).

Page 12: HHG based Seed Generation for X-FELs

Efficiency per harmonic from 400-nm driver

• 8x10-5 at ~35 eV and 1x10-5 at ~60 eV for He• 6x10-5 at ~27 eV for Ar

Page 13: HHG based Seed Generation for X-FELs

Peak intensity: ~1.6x1015 W/cm2

40 50 60 70 80 90 100 1100

20

40

60

80

100

HH

Inte

nsity

(A

rb. U

.)

Photon Energy (eV)

40 50 60 70 80 90 100 1100

100

200

300

HH

Int

ensi

ty (

Arb

. U

.)

Photon Energy (eV)

HHG spectra generated from 800-nm driver

He: 1 barEnergy: 2 mJ

Ne: 0.3 barEnergy: 2 mJ

Page 14: HHG based Seed Generation for X-FELs

Total HHG efficiency from 800-nm driver

• Conversion efficiency of up to 2x10-6 from He over Al and Zr window• Efficiency per harmonic is one-to-two-order-of-magnitudes lower.

Zr window(60-100 eV)

Al window(20-70 eV)

Page 15: HHG based Seed Generation for X-FELs

15

Comparison with previous results

800-nm driver (He)

400-nm driver (He)

• Conversion efficiency very sensitive to the driving wavelength • But predictable from our analytic theory that has shown a good agreement to experimental results studied by 400-nm and 800-nm drivers.

Page 16: HHG based Seed Generation for X-FELs

In final OPA stage:• Yb:YAG pump replaces Nd:YLF• BBO replaces MgO:PPSLT

2-µm drive laser based on cryo-Yb:YAG pump laser

MgO:PPLN

DFGMgO:PPLN

OPA 1 = 2.0 µm

140µJSi

2.5 mJ,30 fs

SuprasilMgO:PPSLT

OPA 2

30 mJ

BBO

OPA 3

1 mJ

800-nm OPCPA

seed 800-nm OPCPApump

Nd:YLF CPA systemCFBG, 2 YDFA, Nd:YLF regen amp + 2 Nd:YLF multipass amp, grating stretcher

12 ps, 4 mJ @1kHz

Ti:Sapphireoscillator

Yb:YAG CPA systemCFBG, YDFA, Yb:YAG regen amp +

Yb:YAG multipass amp, grating stretcher15 ps, 30 mJ @1kHz

= 1.0 µm

AOPDF

Page 17: HHG based Seed Generation for X-FELs

2.2-m drive wavelength extends HHG cutoff to 500 eV Conversion efficiency of 10-7-10-8

Best current water-window experimental result:

300 eV cutoff, ~ 5x10-8, using multi-mJ 1.6-m drive pulsesE. J. Takahashi et al., PRL 101, 253901 (2008).

Gaussian pulse, FWHM = 6 cycles

Ne gas, p = 3 bar, L = 2.5 mm, w0 = 50 m, E ~ 1 mJ

Theoretical Prediction

Simulation parameters:

Page 18: HHG based Seed Generation for X-FELs

High-flux, High Repetition Rate 13.5-nm

(~93 eV) EUV source

30 40 50 60 70 80 90 100 1100

2

4

6

8

10

Effi

cien

cy (

10-6)

Energy (eV)

0.6 0.7 0.8

1E-4

1E-3

0.01

0.1

1

10

Effi

cie

ncy

(10-6

)

Pump Energy (mJ)

515 nm 400 nm

• With 515-nm drive pulses generated from SGH of powerful 1µm lasers

Efficiency into single harmonic: ~ 10-5

Page 19: HHG based Seed Generation for X-FELs

19

High Intensity Femtosecond

Enhancement Cavities for

High Repetition Rate FELs

Use enhancement cavity to scale efficiency to ~ 10-2

Page 20: HHG based Seed Generation for X-FELs

High-Power Enhancement Cavity

20

Requirements: optical beam access, high-intensity in interaction region, and low loss

1-MW intracavity power, 10 mJ, ~100 fs pulses circulating

Cavity Finesse > 3000

15 cm

2.6 mm

patterned dielectric mirror

Confocal cavity for high-intensity Bessel-Gauss beams – Cavity shown enables 1000 TW/cm2

1000 TW/cm2

0.1 TW/cm2

Page 21: HHG based Seed Generation for X-FELs

21

Preliminary Cavity Demonstration

Single-mode HeNe source

Beam Expander

Pellicle

CCD

Photodiode

Polarizerλ/2

R=91%R=99%

20μm Piezo2μm Piezo

LPF PI

42 kHz

Lock-in Amp

First demonstration of cavity operation is carried out with CW laser. Also, axicon coupling optics excluded. Instead, collimated beam is used allowing measurement of intrinsic suppression of higher modes.

Page 22: HHG based Seed Generation for X-FELs

22

Cavity Results With One Patterned Mirror

Pellicle (loss<1%)

CCD

R = 91% or 99%R = 99%

First cavity experiments done with single patterned mirror

Asymmetric modes seen, showing general structure of desired modes, but differing transverse profiles

Transverse profiles at cavity center

R=91%

R=99%

Page 23: HHG based Seed Generation for X-FELs

23

~30 modes with <1% loss

only 2 modes (superposition modes in each direction) with <1% loss, next

higher mode >5% loss

Cavity Results With One Patterned MirrorL

oss

Mode

One Patterned Mirror

Lo

ss

Mode

Two Patterned Mirrors

Page 24: HHG based Seed Generation for X-FELs

24

Thank You

Needs large average power Yb-doped Lasers!

Page 25: HHG based Seed Generation for X-FELs

25

Analytical Bessel-Gauss Form of ModesThe cavity modes have been analyzed numerically with custom paraxial wave optics software package. They can also be understood from an analytical perspective as Bessel-Gauss beams.

Bessel-Gauss beam is a superposition of tilted Gaussian beams with wavevectors lying along the surface of a cone,

Tilted Gaussian Beam

Page 26: HHG based Seed Generation for X-FELs

26

Analytical Bessel-Gauss Form of ModesBessel-Gauss beams traversing paraxial optical systems transform with an ABCD matrix similar to a Gaussian beam. Bessel-Gauss beams can then be shown to be modes of the confocal resonator, and the dominant modes of our special cavity.

Bessel-Gauss Modified Bessel-Gauss

Numerically computed mode

Analytical Bessel-Gauss mode

Field profile at focus: numerical versus analytical

solution

Page 27: HHG based Seed Generation for X-FELs

Pump laser upgrade > 50 mJ, 2 kHz, 10 ps

(c) Yb:YAG 4-pass amplifier

fs, Yb-fiber oscillator

CFBG stretcher

/4F1029

PBS

1 mW 400 ps

/4

/2

FI

Te

les

co

pe

30-mW Yb-fiber preamplifier (1030

nm)

>40 W

Yb:YAG crystal

PCTFP

(b) Yb:YAG regenerative amplifier

TFP

FI

seedRegen output5 mJ@2 kHz

Fiber-coupled LD

/4

Te

les

co

pe

(a) Fiber seed

>60 mJ@2 kHz

Telescope

10 ps, >50 mJ@2 kHz

(d) Multi-layer dielectric grating compressor

LN2 Dewar Yb:YAG crystals

Fiber-coupled pump laser

DM

/4

DML1 L2 L2 L1

TelescopeTFP

TFP

Telescope

27

Page 28: HHG based Seed Generation for X-FELs

28

SummarykW-class cryogenically cooled Yb:YAG ps-lasers are ideal for

Inverse Compton Scattering Sources (direct use) -> 2nd generation synchrotron like laboratory sources with exceptional beam properties

micron sized source ideal for phase contrast imaging

fs-pulse durations ideal for time resolved x-ray diffraction

Pumping of few cycle OPCPAs covering the visible to MID IR range

Analytic HHG efficiency formulas and wavelength scaling

Development of few-cycle 2-m OPCPA (200 J)

Initial results on 800 nm OPCPA

Page 29: HHG based Seed Generation for X-FELs

29

(a) For a 5-cycle-driver-pulse, k = 0, L = 5 mm at 1 bar.

(b) Same as (a) including plasma and neutral atom phase mismatching.

Page 30: HHG based Seed Generation for X-FELs

Efficiency Measurement using Calibrated XUV PhotodiodeAt 40eV, Al transmission = 30%,

photodiode response = 4 electrons/photon

19

40

30% 4 1.6 10 1000 30ph ph

HH

I eV I JE pulseA

photodiode response