Effect of lens tilt on SCE and filamentation characteristics of femtosecond pulses in air

We present the evolution of SCE associated with filaments due to the tilt of focusing lens under tight focusing geometries. Transform limited femtosecond (fs) pulses (800 nm, 45 fs, 1 kHz repetition rate) were focused in ambient air using three different focusing geometries f/#6, f/#7.5, and f/#12 corresponding to numerical apertures (NA) of 0.08, 0.06, and 0.04, respectively. The focusing lens was tilted from zero up to 20 degrees. The filaments decayed into two shorter parts through tilting of the lens and the separation between shorter filaments increased with increasing lens tilt, in tune with earlier reports [Kamali et al., Opt. Commun. 282, 950-954 (2009)]. The separation between the filaments matched well with the predicted distances due to astigmatism induced in loose focusing geometries. However the deviation increased as we moved to the tighter focusing geometries. The SCE spectrum demonstrated an anomalous behaviour. The SCE spectrum was suppressed at larger tilt angles of 12 - 20°. However at lower tilt angles, up to 8°, the SCE was observed to be same to that measured without any tilt of the focusing lens. This behaviour is predominant with tighter focusing geometries of f/#6 and f/#7.5, wherein the SCE was observed to be higher at 4° and 8° in comparison with that observed at an angle of 0°. Systematic study of the focusing lens tilt on anomalous SCE spectra and filament characteristics in the tight focusing geometry are presented.

[1]  Robert R. Alfano,et al.  The Supercontinuum Laser Source: Fundamentals with Updated References , 2006 .

[2]  V. Tikhonchuk,et al.  Conical forward THz emission from femtosecond-laser-beam filamentation in air. , 2007, Physical review letters.

[3]  D. Gordon,et al.  Conductivity Measurements of Femtosecond Laser–Plasma Filaments , 2007, IEEE Transactions on Plasma Science.

[4]  Gadi Fibich,et al.  Control of multiple filamentation in air. , 2004, Optics letters.

[5]  Ecole Nationale,et al.  Generation of intense, carrier-envelope phase-locked few-cycle laser pulses through filamentation , 2004 .

[6]  G. Kumar,et al.  Focal dynamics of multiple filaments: Microscopic imaging and reconstruction , 2010 .

[7]  Gadi Fibich,et al.  Control of the filamentation distance and pattern in long-range atmospheric propagation. , 2007, Optics express.

[8]  A. Couairon,et al.  Femtosecond filamentation in transparent media , 2007 .

[9]  P. Prem Kiran,et al.  Supercontinuum emission from tightly focused femtosecond pulses in air: beyond intensity clamping , 2010, Photonics Europe.

[10]  B. Stein,et al.  Remote sensing of the atmosphere using ultrashort laser pulses , 2000 .

[11]  F. Salin,et al.  Conical emission from self-guided femtosecond pulses in air. , 1996, Optics letters.

[12]  H Schroeder,et al.  From random to controlled small-scale filamentation in water. , 2004, Optics express.

[13]  J. Daigle,et al.  Lens tilting effect on filamentation and filament-induced fluorescence , 2009 .

[14]  Jin Yu,et al.  Long-distance remote laser-induced breakdown spectroscopy using filamentation in air , 2004 .

[15]  B Hafizi,et al.  Stimulated Raman scattering of intense laser pulses in air. , 2003, Physical review. E, Statistical, nonlinear, and soft matter physics.

[16]  Prem Kiran P.,et al.  Focusing of ultrashort sub-TW laser pulses in air: supercontinuum emission , 2011, International Conference on Fiber Optics and Photonics.

[17]  See Leang Chin,et al.  Femtosecond Laser Filamentation , 2009 .

[18]  J V Moloney,et al.  Dynamic spatial replenishment of femtosecond pulses propagating in air , 1998, Technical Digest. Summaries of Papers Presented at the International Quantum Electronics Conference. Conference Edition. 1998 Technical Digest Series, Vol.7 (IEEE Cat. No.98CH36236).

[19]  Zhi‐zhan Xu,et al.  Impressive laser intensity increase at the trailing stage of femtosecond laser filamentation in air. , 2012, Optics express.

[20]  Jean-Claude Diels,et al.  Lightning Control with Lasers , 1997 .

[21]  G. Kumar,et al.  Filamentation without intensity clamping. , 2010, Optics express.