Doped high-entropy glassy materials to create optical coherence from maximally disordered systems.

Control over excitation wavelengths, sample size, and doping concentrations in glassy materials with high levels of configuration entropy shows promises of efficient correlation between absorption and build-up of coherent emission of radiation.

Sensitivity of coherent anti-Stokes Raman lineshape to time asymmetry of laser pulses.

We show that coherent anti-Stokes Raman lineshapes do not follow known spectral profiles if the time asymmetry of realistic laser pulses is taken into account. Examples are given for nanosecond and picosecond laser pulses commonly employed in frequency-resolved coherent anti-Stokes Raman scattering. More remarkably, the analysis suggests an effect of line narrowing in comparison to the customary approach, based primarily on the Voigt lineshape.

Time-domain coherent anti-Stokes Raman scattering in terms of the time-delayed Yuratich equation.

We show that the increasingly popular nonlinear optical technique of time-domain coherent anti-Stokes Raman scattering (CARS), which is often viewed from the dynamical perspective of the semiclassical time-dependent third-order polarization, can also be studied by means of the time-delayed version of the Yuratich equation, so popular in traditional frequency-domain CARS. The method proves successful in explaining experimental results that are otherwise treated by means of numerical methods only.

Coherent anti-Stokes Raman scattering microscopy of samples probed with Gaussian volumes.

Coherent anti-Stokes Raman scattering (CARS) microscopy is becoming increasingly popular to characterize biochemical samples. Within this context, we show that theoretical analysis can still be accomplished under the simple assumption of Gaussian volumes instead of spatial shapes obtainable from diffraction necessary to describe the tight-focusing condition realized within the focus of microscopes with high numerical apertures. The assumption, common in other physical and chemical spectroscopic techniques based on microscopy (e.g., fluorescence correlation spectroscopy, photon counting histogram) and never applied to CARS, is here used to determine the expression of the anti-Stokes electric field. Contrary to the standard approach resorting to numerical methods, we find that either the field is analytical for certain shapes of the Raman scatterer or the numerical reconstruction is strongly limited. In addition, we examine tests against two typical problems found in the literature, namely, a description of CARS radiation patterns and CARS imaging. With regard to the latter, we remark that the loss of spatial symmetry, the treatment of which is onerous in standard CARS microscopy because of possible separations between the microscope focus and the Raman scatterer, can be handled with ease in the limit of Gaussian volumes. An example is considered for polystyrene beads that are usually employed as test model of a CARS response of relevant biochemical samples.

Two-photon excitation fluorescence correlation spectroscopy of diffusion for Gaussian-Lorentzian volumes.

Fluorescence correlation spectroscopy (FCS) is valuable in many scientific domains where diffusion plays a fundamental role. One important experimental realization is based on fluorescence induced by two-photon excitation (TPE). In comparison with one-photon excitation (OPE), TPE-FCS defines better the interrogation volume and the background noise is sensibly reduced. Within this context and for overfilled objective lenses, the three-dimensional Gaussian (3DG) approximation, according to which the spectroscopic interaction is spatially defined by Gaussian profiles only, guarantees a simple analytical data interpretation. By contrast, the volume illuminated by the laser beam focused with partially filled objective lenses follows a Gaussian-Lorentzian (GL) distribution that is taken into account by means of numerical methods only. Here we show that contrary to common belief, the assumption of a GL volume does not hamper analytical treatment of TPE-FCS. Differences and similarities in comparison with the 3DG approximation are discussed.

Geometric determination of saturation in fluorescence spectroscopy.

In laser spectroscopy, saturation of atomic or molecular transitions cannot be ignored, even at modest laser intensities. The saturation status is customarily diagnosed from measurements of saturation curves describing the dependence of spectroscopic signals on laser intensity. I propose an alternative method that relies on a geometric comparison of the spatial laser profile with images of the spectroscopic quantity under investigation. A single image can be used to determine the saturation status and its associated saturation laser intensity.

Fluorescence correlation spectroscopy: incorporation of probe volume effects into the three-dimensional Gaussian approximation.

Fluorescence correlation spectroscopy is a valuable tool in many scientific disciplines. In particular, such a spectroscopic technique has received a great deal of attention because of its remarkable potential for single-molecule detection. It is understood, however, that quantitative measurements can be considered reliable as long as molecular photophysics has been well characterized. To that end, molecular saturation and probe volume effects, which can worsen experimental accuracy, are treated here. These phenomena are adequately incorporated into the well-known three-dimensional Gaussian approximation by a novel method applied to interpret saturated fluorescence signals [Opt. Lett. 28, 2016 (2003)]. Comparisons with literature data are given to show the improvements of the suggested method compared with other approaches.

Spatial laser-wing suppression in saturated laser-induced fluorescence without spatial selection.

Spatial wings of laser beams are of great concern in saturated laser-induced fluorescence. Their contribution to fluorescence is customarily avoided by resolution of laser peaks in the interaction volume. An alternative and versatile approach is formulated, based on the derivative of fluorescence with respect to laser intensity. It turns out that wing-free data are possible, although they are obtained from wing-dependent fluorescence. The advantages of this approach are exact centerline detection and simplicity of the experimental setup and procedure.