Time-resolved interferometry of femtosecond-laser-induced processes under tight focusing and close-to-optical breakdown inside borosilicate glass

Abstract

We use an interferometric time-resolved observation of a femtosecond-laser pulse (800 nm/45 fs) interaction with glass from 100 fs to 10 ns at spatial lateral resolution down to the wavelength of the pulse. The phase and amplitude images reveal sequence of events after the irradiation of a single ultra-short laser pulse at close-to-threshold intensity when permanent refractive index changes occur. The proposed method is applicable to characterization of the processes induced by tightly focused fs-laser pulses during three-dimensional structuring of glasses and crystals for fundamental studies and optical applications. Generation of carriers, thermal expansion, generation and propagation of shockwaves, and formation of refractive index changes are experimentally observed and resolved in time and space with the highest resolution. Quantitative estimations of the threshold energies of different processes are achieved. The threshold energy of carrier generation is found the same as that of shockwave generation while the threshold energy of refractive index changes was by 40% higher. Application potential of the method is discussed.

In situ Micro-Raman Investigation of Spatio-Temporal Evolution of Heat in Ultrafast Laser Microprocessing of Glass

“…[1][2][3][4] Substantial efforts have been devoted to clarify the abovementioned fast processes by femtosecond time-resolved imaging techniques. [5][6][7][8][9][10][11] On the other hand, there have been few reports on the experimental investigation of temperature dynamics, which is supposed to have considerable effects on the characteristics of processed glass materials. For example, the heat accumulation effect caused by high repetition rate pulses is widely utilized because it allows us to smooth out the shape of processed region and to increase processing speed.…”

Control of multiphoton and avalanche ionization using an ultraviolet-infrared pulse train in femtosecond laser micro/nano-machining of fused silica

“…The interaction between femtosecond laser pulses and dielectric materials involves complicated processes, such as free electron excitation and decay, exciton generation, plasma absorption, energy transfer from electrons to lattices, hydrodynamics, shockwave propagation, damage formation, etc [1][2][3][4][5][6][7][8][9][10][11][12]. Understanding these processes is of great importance for potential application of femtosecond lasers in optical storage, micro-/nano-fluidics, opto-electronics and nanomachining [13][14][15][16][17].…”

Direct holographic imaging of ultrafast laser damage process in thin films

“…This is associated with a decrease of the free-electron density and a relaxation of intensity drop in transmission. Ringtype modulations in refractive index start to occur at a time delay of 100 ps that could be attributed to fast growth of the internal pressure [16] and the birth of the shockwaves both in the sample [9,17] and air [10]. The quantitative results of obtained pictures are summarized in Fig.…”

“…In contrast with these observations, melting effects were also observed in dielectric coatings [4], thus indicating that liquid phase exists in fs damage formation at fluencies close to damage threshold. Time-resolved images of nanosecond [5] and femtosecond [6][7][8][9][10] damage formation were taken in the surface and bulk of bare materials and liquids. Despite the fact there has been several attempts to study nonlinear effects in thin films [11], imaging of fs damage formation was never studied on dielectric coatings with both temporal and spatial resolution, including phase and amplitude contrast at the same time.…”