Vacuum optical compressor:Tentative ideas, layout, size …

Mikhail Martyanov, CERN

AWAKE TB and PEB meeting 11-12 December 2014

Optical stretching and compression

Short pulse =1/0

Stretcher introduces +GDD

Thus pulse is stretched in time and chirped

Compressor introduces –GDD

Thus pulse is compressed back to short

“-1” order, AOI < Littrov

Arrangement #1

“-1” order, AOI > Littrov

Arrangement #2

sin(Littrov) = /2d

E.Treacy grating compressor (1969)

Input parameters (fixed for the given laser setup):Central wavelength = 780 nmSpectral “full” bandwidth = 40 nm (760nm -> 800nm)GDD introduced by stretcher = 6 ps2

The only parameters available for compressor:d – grating grooves pitch, nm - angle of incidence (AOI)H – gratings base (normal distance)

Target values:To introduce opposite sign GDD = -6 ps2

To maintain reasonable Gap ~ 10 cm!!! Watch out higher order spectral aberrations (third order at least)!!! Watch out tiny side-rays tilt due to focusing through a compressor!!! …

Designing a compressor …

Air-compressor in Munich, AMPLITUDEGratings 1500 lines / mm

GDD = - 5.9 ps2

Third dispersion 0.018 ps3

Courtesy of Joshua Moody and Patric Muggli

AOI = 30

Gratings base H ~ 60 cm

GapLittrov angle

Available gratings:Holographic sin-shape gold coated

HORIBA Jobin Yvon:1480 lines / mm “any” size1740 lines / mm “any” size

SPECTROGON:1480 max W x H = 140 x 1201500 max W x H = 120 x 1401600 max W x H = 120 x 1401700 max W x H = 120 x 1401740 max W x H = 120 x 1401800 max W x H = 120 x 140

Damage threshold in air almost the same.In vacuum ?

We n

eed m

in W x

H = 16

0 x 12

0

TM-polarisation meaning the electrical vector is perpendicular to the grating grooves corresponds to P-polarisation

TE-polarisation meaning the electrical vector is parallel to the grating grooves corresponds to S-polarisation

SPECTROGON (Sweden):1480 l/mm 120x140x20mm ~5.5 kEur1740 l/mm 120x140x20mm ~6 kEur

SPECTROGON: For ns pulses in the 800-1100 nm range, expected damage threshold is 0.9 J/cm² or 73 MW/cm². For fs pulses in the 800-1100 nm range, expected damage threshold is 0.25 J/cm².

SPECTROGON 1800 gr/mm grating

Efficiency 92%at 15 degrees deviation angle

Theoretical compressor efficiency= (0.92)4 = 72%

HORIBA Jobin Yvon (France or Germany ?):1480 l/mm 120x140x20mm ~ 7kEur1480 l/mm 120x140x20mm ~ 7kEur

HORIBA: Surface damage threshold fluence:0.4 J/cm2 in a nanosecond pulse range0.25 J/cm2 in a picosecond pulse range0.2 J/cm2 in a 500 femtosecond pulse range0.1 J/cm2 in a very short (30 femtosecond) pulse range

AOI < Littrov

Chamber 1200 mm

AOI > Littrov

Chamber 1500 mm

Grating 1480 grooves / mm

Grating 1740 grooves / mm

AOI < Littrov

Chamber 900 mm

Gap problem !

AOI > Littrov

Chamber 1000 mm

Laser beam profileand ray angles due to 40 meter focusing

Test value 80 arc.sec. for further calculation

NB! Different pulse properties after compression for different rays due to different angles

Gratinggr/mm

Gratings baseH, mm

AOI, grad

Deviation,|-|, grad

GratingsdistanceL, mm

~Chamber sizeL + 300, mm

Third dispersion,Ф3103 , ps3

FWHM pulse duration @ 80 arc.sec. tilt, fs

AOI < Littrov1480 690 29.5 12.0 921 1221 17.7 2231500 645 29.7 12.7 874 1174 18.4 2321600 430 30.5 17.3 640 940 23.0 294

AOI > Littrov1480 1040 40.0 9.2 1210 1510 13.5 1441500 1005 40.7 9.5 1175 1475 13.8 1451600 820 44.3 11.0 982 1282 14.9 1491700 670 48.2 12.7 823 1123 16.2 1511740 620 50.0 13.8 769 1069 16.7 1511800 550 52.5 14.9 695 995 17.7 152

Input parameters:Central wavelength = 780 nmSpectral “full” bandwidth = 40 nm (760nm -> 800nm)FWHM pulse width 100 fsGDD introduced by stretcher = 6 ps2 (third dispersion should be ~1810-3 ps3 )Gap = 10 cm

Comparison table for compressorsmade of different gratings in different arrangement

2-grating compressorGratings 1740 lines / mmLittrov angle 42.7 degSmall grating size WxH: 100 x 120 mmBig grating size WxH: 160 x 120 mm

Central wavelength 780 nmFull bandwidth 40 nmBeam size 50 mmGrating base 620 mmGrating distance 770 mmIncident angle 50 degGDD = -6 ps2

Compress FWHM: 167 ps to 100 fs

Shown circle diameter 1000 mmInputtop level

OutputTable level

Dia

gnos

ticTa

ble

leve

l

Mirror on the translatorTable level

Compressor preliminary layoutwith 1740 grooves / mm gratings, 1 meter

3D views from Amplitude

Positions of output ports do not conform with CERN layout

Laser integration at CERN

AMPLITUDE VOLUME STUDY 2

3.5 m

0.6 m

0.9m

0.51 m

1.5m

1 m

compresseur

The output beam must be closer to the wall in order to avoid crossing of tubes for “plasma” and “electron” laser beams

Laser integration at CERN

Handling railfor compressor maintenance

Lifting capacity 250 kg

A frame to support the lid during the maintenance is to be constructed

Proposed by

JL GRENARD