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Optical scattering poses a significant challenge to high-resolution microscopy within deep tissue. To accurately predict the performance of various microscopy techniques in thick samples, we present a computational model that efficiently solves Maxwell’s equation in highly scattering media. This toolkit simulates the deterioration of the laser beam point spread function (PSF) without making a paraxial approximation, enabling accurate modeling of high-numerical-aperture (NA) objective lenses commonly employed in experiments. Moreover, this framework is applicable to a broad range of scanning microscopy techniques including confocal microscopy, stimulated emission depletion (STED) microscopy, and ground-state depletion microscopy. Notably, the proposed method requires only readily obtainable macroscopic tissue parameters. As a practical demonstration, we investigate the performance of Laguerre–Gaussian (LG) versus Hermite–Gaussian (HG) depletion beams in STED microscopy. 

In nonlinear spectroscopies, the detected spectrum is determined by the response of the system to the particular excitation pulses, which can vary as excitation energy and pulse duration are tuned. Here, we analytically show that, under reasonable assumptions, the nested integrals that describe the light-matter interaction of the system can be simplified by application of the Fourier convolution and shift theorems, resulting in an expression for the nonlinear spectrum that is a product of the impulsive system response and the interaction laser spectra. The impulsive response can then be obtained by linearly dividing the laser spectrum from the detected signal. We demonstrate our normalization scheme by recovering the impulsive response from two different material systems, highlighting removal of distinct spectral artifacts. 

We propose the braiding of optical vortices in a laser beam with more than $2\mathrm{\pi <\#comment/>}$rotation by superposing Bessel modes with a plane wave. We experimentally demonstrate this by using a Bessel–Gaussian beam and a coaxial Gaussian, and we present measurements of three complete braids. The amount of braiding is fundamentally limited only by the numerical aperture of the system, and we discuss how braiding can be controlled experimentally for any number of vortices. 

As optical two-dimensional coherent spectroscopy (2DCS) is extended to a broader range of applications, it is critical to improve the detection sensitivity of optical 2DCS. We developed a fast phase-cycling scheme in a non-collinear optical 2DCS implementation by using liquid crystal phase retarders to modulate the phases of two excitation pulses. The background in the signal can be eliminated by combining either two or four interferograms measured with a proper phase configuration. The effectiveness of this method was validated in optical 2DCS measurements of an atomic vapor. This fast phase-cycling scheme will enable optical 2DCS in novel emerging applications that require enhanced detection sensitivity. 

There are two established methods for measuring rotational Doppler shift: (1) heterodyne and (2) fringe. We identify a key distinction, that only the heterodyne method is sensitive to the rotating object’s phase, which results in significant differences in the signal-to-noise ratio (SNR) when measuring multiple rotating particles. When used to measure randomly distributed rotating particles, the fringe method produces its strongest SNR when a single particle is present and its SNR tends to zero as the number of particles increases, whereas the heterodyne method’s SNR increases proportionally to the number of particles in the beam.