Formation dynamics of ultra-short laser induced micro-dots in the bulk of transparent materials

In this paper, we study the formation dynamics of ultra-short laser-induced micro dots under the surface of transparent materials. Laser-induced micro dots find their application in direct part marking, to address full life cycle traceability. We first demonstrate the possibility of direct laser part marking into the cladding of an optical fiber. Then, we monitor the laser affected zone with the help of a time-resolved phase contrast microscopy setup in a fused silica substrate. We show that the transient energy relaxation processes affect the host material over a region that exceeds the micro dot size by several micrometers

Cold ablation driven by localized forces in alkali halides

Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ∼1 J cm-2 in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400 nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play

Finestructure, hyperfine structure and isotope shift of 4f

The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-1) assigned to the configuration $4f^{12}6s7s$ in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge. We performed a fine structure analysis in the SL-coupling scheme of the single configuration $4f^{12}6s7s$, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions of the $4f^{12}$ core and the (6s+7s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for 167Er were fitted to the experimental data by a least squares fit procedure: 0pt[0pt] MHz, 0pt[0pt] MHz, 0pt[0pt] MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained the following results for the CSO parameters for the isotope pairs 170-168Er: $d_{6s7s}=-740(30)$ MHz, $z_{4f}= 0(5)$ MHz, $(g_{3,6s}(f, 6s)+g_{3, 7s}(f, 7s))= -24(15)$ MHz and for 170-166Er: $d_{6s7s}=-1500(50)$ MHz, $z_{4f}=0(10)$ MHz, $(g_{3,6s}(f,6s)+g_{3,7s}(f+7s))=-50(29)$ MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion

ISOTOPE SHIFTS FOR THE 5D(5)6S7S AND 5D(5)6S6D CONFIGURATIONS OF RE-I

The isotope shift and hyperfine structure in a rhenium hollow cathode discharge was studied for transitions of the type 5d(5)6s7s --> 5d(5)6s6p and 5d(5)6s6d --> 5d(5)6s6p through Doppler-free saturation absorption laserspectroscopy and high resolution interferometry. Taking configuration mixing in the lower levels of 5d(5)6s6p under consideration, we obtain average configuration isotope shift values for 5d(5)6s7s of -1760(100) MHz and for 5d(5)6s6d of -1930(200) MHz. These experimental values compare extremely well with the theoretically predicted configuration isotope shifts in rhenium, based on pseudo-relativistic Hartree-Fock calculations, of -1710 MHz and -1940 MHz, resp. In addition hyperfine structure constants for rhenium levels of 5d(5)6s6d are reported here for the first time