1. Journal Club Jan 2012

2. Hollow-fibre – coupling Different modes propagate in the fibre EH 11 EH 12 EH 13 EH 14 Nisoli, M. et al; Selected Topics in Quantum Electronics, IEEE Journal of. 1998, 4, 414-420.

3. Hollow-fibre – mode discrimination / attenuation Different modesDifferent fibre radii small fibre radius => high intensity but low transmission long fibre => good mode discrimination but lower transmission

4. Hollow fibre – design considerations i.P limited by self-focusing ii.ionizaton limits minimal core radius iii.length of fiber is limited by propagation losses Vozzi, C. et al., 2005. Applied Physics B: Lasers and Optics, 80(3), pp.285-289 α ~ 0.45, β ~ 0.51 Hea min (Ar) = 1.6 a min (Ne) = 1.8 a min (He)

5. conventional Hollow fibre parameters L = 1 m ID = 250 µm Input: ~1 mJ with τ ~30 fs best compromise between transmission losses and broadening. L is limited by production and table. Transmission sensitive to radius (more bendy = less transmission) Nagy, T., Forster, M. & Simon, P., 2008 Appl. Opt., 47(18), pp.3264-3268. in principle: larger inner diameter and using a longer fiber to compensate for smaller intensity allows for better overall transmission

6. Flexible fiber – why? Nagy, T., Forster, M. & Simon, P., 2008 Appl. Opt., 47(18), pp.3264-3268. bending problem is eliminated by stretching the fibre on the ends.

7. Flexible fibers – what is this? ID/OD = 250µm / 360µm ID/OD = 320µm / 440µm

8. Flexible hollow fibers – setup HF: hollow fiber GT: glass tube VC: vacuum-tight cement OR: O-ring CR: clamping ring VT: vacuum tubing “After curing, the fiber is cut within the glued regions by a diamond tool.”

9. Flexible fibers – Results input: 1.1mJ, 70fs, 780nm 42% 1m 250µm Ar 300 mbar static fill F=9.2 64% 3m 320µm Ar 200 mbar static fill F = 9.7 F = Δω out /Δω in evacuated!! (=useless) close to evacuated a lot less then with no gas spot too small for 300 mbar of Argon? ionization at entrance? shifting of z-position? Obviously you put more effort into result you want to see Can you get better transmission with 1m?

10. Flexible fibers – Results 36% 1m 250µm Ar 500 mbar static fill “The ultimate spectral broadening with still regular spectral shape and acceptable spatial homogeneity” 48% 3m 320µm Ar 500 mbar static fill

11. Flexible fibers – Results 48% 3m 320µm Ar 500 mbar FROG says: 4.5 fs with 12µm (θ = 30.8°) BBO!!

12. Discussion Pros: easy to keep the fiber straight fibers don’t break that easily good transmission good beam profile after fiber Cons: increasing ID => longer tubes table size limited tiny fiber might be immediatly burnt at higher energies larger ID impractical for us?