Journal Club Jan 2012. Hollow-fibre – coupling Different modes propagate in the fibre EH 11 EH 12...

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?