Abstract
This study reports z-scan measurements in which high-repetition-rate and reduced repetition-rate (pulse-picked) laser beams were employed using a standard sample, carbon disulfide (CS2) contained in supposedly high damage-threshold spectroscopic-grade pristine fused-quartz cuvettes. The results suggest that at reduced repetition rates, the closed aperture z-scan profile for CS2 displays the expected configuration. However, at high repetition-rates the closed aperture z-scans are distinctly different resulting in unexpectedly large nonlinear refractive index of CS2 due to thermal effects that resulted in below-threshold laser-induced damage of the cuvettes. Normaski microscope images confirm the damage and open aperture z-scan study of the damaged fused-quartz cuvettes yielded about two orders of magnitude enhancement in the nonlinear absorption coefficient of silica. Based on these findings, the necessary criterion for recognizing below-threshold laser-induced damage in any high-repetition-rate laser z-scan measurement has been formulated in order to help avoid erroneous interpretation of the origin and strength of nonlinear response in such studies.
Highlights
The search for materials that have optical limiting properties for possible optoelectronic and optical limiting applications has recently become an active field of research in which several methods have been employed for studying the third-order optical susceptibility of such materials (Jafari, Zeynizadeh, & Darvishi, 2018; Smirnova, Rudenko, & Hryn, 2017; Dissanayake, Cifuentes, & Humphrey, 2018; Reyna et al, 2018; Gao & Kong, 2018)
This work reports on the study of the influence of high laser repetition-rate on nonlinear response of test materials as well as apparently high damage threshold fused-quartz cuvettes in which samples are contained during z-scan measurements
Contrary to the expected valley-peak closed aperture (CA) z-scan signature profile for CS2, Figure 2(a) rather depicts peak-valley configuration and the n2 was determined to be 1.1 x 10-12cm/W which shows an order of magnitude enhancement at 76MHz
Summary
The search for materials that have optical limiting properties for possible optoelectronic and optical limiting applications has recently become an active field of research in which several methods have been employed for studying the third-order optical susceptibility of such materials (Jafari, Zeynizadeh, & Darvishi, 2018; Smirnova, Rudenko, & Hryn, 2017; Dissanayake, Cifuentes, & Humphrey, 2018; Reyna et al, 2018; Gao & Kong, 2018). The nonlinear optical characterization technique of choice is usually the z-scan (Falconieri & Salvetti, 1999); a simple and sensitive single-beam method that uses the principle of spatial beam distortion to measure both the real and imaginary parts of complex indices of refraction and their signs This approach requires tight-focusing of the probe beam into the test material in order to induce the expected nonlinear response. Vol 11, No 2; 2019 the damage morphologies that suggest that that under certain experimental conditions, some of the supposedly high LID materials do experience below-threshold damage
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