Supercontinuum Generation in 1-decanol

TL;DR

The paper addresses the challenge of generating robust octave-spanning supercontinua using a non-toxic, high-boiling liquid medium. It employs ultrafast $100~\mathrm{fs}$ pulses in 1-decanol and quantifies nonlinear indices via z-scan, revealing a significant fifth-order term $n_4$ in addition to the Kerr coefficient $n_2$, with $n_2 = 1.87\times10^{-20}$ m$^2$/W and $n_4 = 7.22\times10^{-35}$ m$^4$/W$^2$. The experiment demonstrates a SC spanning ~450–950 nm driven by self-focusing/filamentation, with Raman loss observed near $-2984~\mathrm{cm}^{-1}$, and reports stability of the spectrum for at least 30 minutes. Overall, 1-decanol provides a safer, long-lasting medium whose nonlinear response is competitive with CS$_2$ at high intensities, enabling extended studies of strong-field optics and Kerr-instability amplification in liquids.

Abstract

Although solids have been recently used in ultrafast experiments for spectral broadening due to their relatively high nonlinearity, their sensitivity to damage limits their long-term stability. Liquids are a possible alternative to solids as a nonlinear medium because of their comparable nonlinearity and resistance to permanent damage. We generate a supercontinuum in 1-decanol that spans more than an octave from the visible to the near-infrared regime. We measure the nonlinear index of refraction of 1-decanol and find a significant $n_4$ contribution. This contribution leads to a nonlinearity comparable to CS$_2$ (a frequent reference for nonlinear optics) in high-intensity regimes while being significantly less volatile and toxic. We find this supercontinuum spectrum to be stable for at least 30 minutes.

Figures (5)

• Figure 1: (a) Experimental setup used for supercontinuum generation in 1-decanol. The beam travels from left to right passing through a half-wave plate ($\lambda/2$), followed by a polarizer (Pol.), a 200$~$mm focal length lens, and finally into a cuvette which sits on an automated translation stage. Not shown is the spectrometer that measures the spectrum of the output beam. (b) An image of the radial beam profile is shown. The beam waist is measured to be 26 µ m at the focus.
• Figure 2: (a) Low-intensity regime. The points are measured data while the solid lines are the corresponding curve fits. T is the transmittance, which is a function of normalized length $\zeta=\frac{z}{z_0}$ where $z$ is the direction of beam propagation and $z_0$ is the Rayleigh rangeStephen_2022. (b) High-intensity regime, showing deviation from the z-scan fit. (c) Plotting $n_2(I)$ in order to calculate the fifth-order nonlinear index of refraction,$n_4$.
• Figure 3: (a) As the cuvette passes through the focus ($\zeta = 0$ mm), the spectrum rapidly broadens and comprises frequencies across more than an octave. (b) A lineout of the spectrum at the focus ($\zeta=0$) and far from the focus ($\zeta=5$). Colours indicate the bandwidth of each optical filter used in the measurement; arrow indicates position of the Raman loss.
• Figure 4: The broad spectrum produced in 1-decanol as a function of radial angle from the center of the output beam. The visible portion exhibits a large divergence, indicative of the tight spatial confinement in the supercontinuum generation process.
• Figure 5: The temporal stability of the most intense portion of the spectrum over 30 minutes, demonstrating little variation in the supercontinuum.