Absolute measurement of the transient optical nonlinearity in N2, O2, N2O, and Ar

Abstract

The absolute time-dependent nonlinear response of O 2 , N 2 , N 2 O, and Ar to intense nonionizing, ultrashort optical pump pulses is measured with single-shot spectral interferometry. The instantaneous and delayed rotational responses are distinguished as a function of pump-pulse duration and probe central wavelength. Our measurements are central to the modeling and understanding of nonlinear propagation of intense ultrashort laser pulses in gases.

Nonlinear optical polarization response and plasma generation in noble gases: Comparison of metastable-electronic-state-approach models to experiments

“…The SSSI technique has been described in detail in several earlier publications [8][9][10][11][12]. The experimental setup here is substantially similar, except in the current experiment we extend the capability to measure probe phase shifts (x,y,t) in two space dimensions by transversely scanning the probe beam image across the entrance slit.…”

“…The total uncertainty in the absolute peak intensity has two sources. The largest source is the uncertainty in the n Ar 2 measurement [9], which was 12%. The other source of uncertainty (5%) arises from the fit used to find C. The total absolute uncertainty is thus 13%.…”

“…Here, x is a transverse spatial coordinate (to the pump and probe propagation direction) in the medium local to the pump interaction, and defined by the entrance slit of a spectrometer. When coupled with a well-characterized target, absolute measurements of the optical nonlinearity in gases can be performed [9,16]. While nonabsolute transient ionization in gases has been measured using SSSI [17,18], FIG.…”

“…The background-subtracted value p of each pixel is related to the (temporal, cycle-averaged) peak intensity by I peak (x,y) = Cp(x,y). To find the calibration constant C, we use the known n Ar 2 of argon [9] and the relation, (1) where peak (x,y) is the peak phase shift, k is the probe wave vector, and L eff is the effective interaction length of the gas target. The calibration constant C is found from the measured peak (x,y) and L eff at intensities below the appearance of ionization.…”

“…This is achieved here by restricting the propagation distance in a thin gas target [8,9]. The nonlinear phase shift in the gas is * kolesik@optics.arizona.edu measured by single-shot supercontinuum spectral interferometry (SSSI) [10][11][12].…”