Self-focusing of few-cycle laser pulses at 1800 nm in air

Abstract

The self-focusing of few-cycle pulses at the wavelength of 1800 nm under different focusing conditions and polarization states is experimentally investigated. The critical power and nonlinear refractive index for linearly and circularly polarized few-cycle pulses are determined. The value of the critical power for few-cycle pulses is found much larger than that of multi-cycle pulses, which is consistent with the previous result on few-cycle pulses at 800 nm.

An Experimental Determination of Critical Power for Self-Focusing of Femtosecond Pulses in Air Using Focal-Spot Measurements

“…For instance, the approaches of P-scan, S-scan, and PMT fluorescence measurement typically exhibit higher sensitivity compared to the focal-shifting method [33,39,48]. Furthermore, the determination of the critical power for self-focusing is also influenced by experimental conditions, particularly the laser pulse duration and the external focusing conditions [29,30,39,[49][50][51].…”

“…Interestingly, in our recent work [48], we observed a similar transition of laser propagation regimes from self-focusing to filamentation, where we defined two critical powers: one for self-focusing and the other for mature filamentation. Hence, we contend that using just one critical power is inadequate for comprehensively studying the filamentation process in certain cases [33,35,36,48], and it is also reasonable to assign the crossover power as the self-focusing critical power at which the self-focusing effects become evident, which has been used in our recent work and other relevant studies [27,[30][31][32]34,39,48,49,52]. These experimental measurements of critical powers under various conditions by using different methods are of great importance in the field of femtosecond filamentation.…”

“…One crucial aspect to consider is whether the experimental measured crossover power is suitable to be regarded as the critical power for self-focusing of femtosecond pules [27,[29][30][31][32]34,39,48,49,52,53]. The theoretical definition of the critical power for selffocusing of a cw laser is well established.…”

Numerical simulation study on distinguishing nonlinear propagation regimes of femtosecond pulses in fused silica

“…Moreover, directly determining the exact nominal critical power in experiment can be challenging 26 . However, for the purpose of providing clear and referenceable measurements for experimental investigations and practical applications of femtosecond filamentation, in this study, we adopt the crossover power as the critical power for self-focusing, as done in our recent work and relevant literatures 10 , 11 , 20 , 21 , 24 , 28 , 29 .…”