1. Vacuum optical compressor: Tentative ideas, layout, size … Mikhail Martyanov, CERN AWAKE TB and PEB meeting 11-12 December 2014

3. “-1” order, AOI < Littrov Arrangement #1 “-1” order, AOI > Littrov Arrangement #2 sin(Littrov) = /2d E.Treacy grating compressor (1969)

4. Input parameters (fixed for the given laser setup): Central wavelength = 780 nm Spectral “full” bandwidth = 40 nm (760nm -> 800nm) GDD introduced by stretcher = 6 ps 2 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 ps 2 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 …

5. Air-compressor in Munich, AMPLITUDE Gratings 1500 lines / mm GDD = - 5.9 ps 2 Third dispersion 0.018 ps 3 Courtesy of Joshua Moody and Patric Muggli AOI  = 30  Gratings base H ~ 60 cm Gap Littrov angle

6. Available gratings: Holographic sin-shape gold coated HORIBA Jobin Yvon: 1480 lines / mm“any” size 1740 lines / mm“any” size SPECTROGON: 1480max W x H = 140 x 120 1500max W x H = 120 x 140 1600max W x H = 120 x 140 1700max W x H = 120 x 140 1740max W x H = 120 x 140 1800max W x H = 120 x 140 Damage threshold in air almost the same. In vacuum ? We need min W x H = 160 x 120

7. 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 kEur 1740 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.

8. SPECTROGON 1800 gr/mm grating Efficiency 92% at 15 degrees deviation angle Theoretical compressor efficiency = (0.92) 4 = 72%

9. HORIBA Jobin Yvon (France or Germany ?): 1480 l/mm 120x140x20mm~ 7kEur HORIBA: Surface damage threshold fluence: 0.4 J/cm2 in a nanosecond pulse range 0.25 J/cm2 in a picosecond pulse range 0.2 J/cm2 in a 500 femtosecond pulse range 0.1 J/cm2 in a very short (30 femtosecond) pulse range

10. AOI < Littrov Chamber  1200 mm AOI > Littrov Chamber  1500 mm Grating 1480 grooves / mm

11. Grating 1740 grooves / mm AOI < Littrov Chamber  900 mm Gap problem ! AOI > Littrov Chamber  1000 mm

12. Laser beam profile and 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

13. Grating gr/mm Gratings base H, mm AOI , grad Deviation, |  -  |, grad Gratings distance L, mm ~Chamber size L + 300, mm Third dispersion, Ф 3  10 3, ps 3 FWHM pulse duration @ 80 arc.sec. tilt, fs AOI < Littrov 148069029.512.0921122117.7223 150064529.712.7874117418.4232 160043030.517.364094023.0294 AOI > Littrov 1480104040.09.21210151013.5144 1500100540.79.51175147513.8145 160082044.311.0982128214.9149 170067048.212.7823112316.2151 174062050.013.8769106916.7151 180055052.514.969599517.7152 Input parameters: Central wavelength = 780 nm Spectral “full” bandwidth = 40 nm (760nm -> 800nm) FWHM pulse width 100 fs GDD introduced by stretcher = 6 ps 2 (third dispersion should be ~18  10 -3 ps 3 ) Gap = 10 cm Comparison table for compressors made of different gratings in different arrangement

14. 2-grating compressor Gratings 1740 lines / mm Littrov angle 42.7 deg Small grating size WxH: 100 x 120 mm Big grating size WxH: 160 x 120 mm Central wavelength 780 nm Full bandwidth 40 nm Beam size  50 mm Grating base 620 mm Grating distance 770 mm Incident angle 50 deg GDD = -6 ps 2 Compress FWHM: 167 ps to 100 fs Shown circle diameter 1000 mm Input top level Output Table level Diagnostic Table level Mirror on the translator Table level Compressor preliminary layout with 1740 grooves / mm gratings,  1 meter

15. 3D views from Amplitude Positions of output ports do not conform with CERN layout

16. 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

17. Laser integration at CERN

18. Handling rail for compressor maintenance Lifting capacity 250 kg A frame to support the lid during the maintenance is to be constructed Proposed by JL GRENARD