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Journal Club
Jan 2012
Hollow-fibre – coupling
Different modes propagate in the fibreEH11 EH12
EH13 EH14
Nisoli, M. et al; Selected Topics in Quantum Electronics, IEEE Journal of. 1998, 4, 414-420.
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
Hollow fibre – design considerations
i. P limited by self-focusingii. ionizaton limits minimal core radiusiii. 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
Heamin (Ar) = 1.6 amin (Ne) = 1.8 amin (He)
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
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.
Flexible fibers – what is this?
ID/OD = 250µm / 360µm
ID/OD = 320µm / 440µm
Flexible hollow fibers – setup
HF: hollow fiberGT: glass tubeVC: vacuum-tight cement
OR: O-ringCR: clamping ringVT: vacuum tubing
“After curing, the fiber is cut within the glued regions by a diamond tool.”
Flexible fibers – Results input: 1.1mJ, 70fs, 780nm
42%1m250µmAr 300 mbarstatic fillF=9.2
64%3m320µmAr 200 mbarstatic fillF = 9.7
F = Δωout/Δωin
evacuated!!(=useless)
close to evacuated
a lot less then withno 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 seeCan you get better transmission with 1m?
Flexible fibers – Results
36%1m250µmAr 500 mbarstatic fill
“The ultimate spectral broadening with still regular spectral shape and acceptable spatial homogeneity”
48%3m320µmAr 500 mbarstatic fill
Flexible fibers – Results
48%3m320µmAr 500 mbar
FROG says: 4.5 fs
with 12µm (θ = 30.8°) BBO!!
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?