Time-resolved inline digital holography for the study of noncollinear degenerate phase modulation

Investigation of Nonlinear Optical Properties of Quantum Dots Deposited onto a Sample Glass Using Time-Resolved Inline Digital Holography

We report on the application of time-resolved inline digital holography in the study of the nonlinear optical properties of quantum dots deposited onto sample glass. The Fresnel diffraction patterns of the probe pulse due to noncollinear degenerate phase modulation induced by a femtosecond pump pulse were extracted from the set of inline digital holograms and analyzed. The absolute values of the nonlinear refractive index of both the sample glass substrate and the deposited layer of quantum dots were evaluated using the proposed technique. To characterize the inhomogeneous distribution of the samples’ nonlinear optical properties, we proposed plotting an optical nonlinearity map calculated as a local standard deviation of the diffraction pattern intensities induced by noncollinear degenerate phase modulation.

FFT-based simulation of the hologram-recording process for light-in-flight recording by holography

We propose a numerical simulation method of the hologram-recording process for light-in-flight recording by holography (LIF holography) based on fast Fourier transform (FFT) to improve the efficiency of the simulation. Because it is crucial to consider the difference in the optical-path length between the object and reference light pulses, we modify a point-spread function by considering the optical-path lengths of the object and reference light pulses and whether both pulses interfere with each other in LIF holography. The computational time was shortened by 5.5×10⁵ times for the 4,096×4,096 resolution of the hologram using the proposed method. We evaluate the proposed method by calculating the root mean square error (RMSE) of the reconstructed holographic images. The RMSEs were relatively small considering the effect of speckle noise; these results effectively demonstrate the validity of the proposed method. Moreover, we reconstruct the moving pictures of light pulse propagation from the hologram generated by the proposed method. We compare the simulation and experimental results, and succeed in qualitatively demonstrating the validity of the proposed method.

Noncollinear degenerate phase modulation in samples with inhomogeneous optical nonlinear properties [Invited]

Digital inline pump-probe holography can be applied to estimate parameters of samples' optical nonlinear properties. Here we propose a mathematical model to describe noncollinear degenerate phase modulation in samples with inhomogeneities of nonlinear refractive index over all three dimensions, namely, two-layered samples and samples with local impurities. The impact of sample parameters in the considered configurations is analyzed. We show that analysis of inline digital holograms obtained by time-resolved inline digital holography can be successfully used for rapid detection and characterization of various types of nonlinear refractive index inhomogeneities.

Effect of object thickness on ultrashort pulse diffraction

When calculated in the spectral domain, the propagation of an ultrashort optical pulse may suffer from inaccuracy due to the finite thickness of the object it diffracts on. Unlike monochromatic radiation, ultrashort pulse interaction with an object in the time domain depends on the pulse longitudinal coordinate. Here, we propose an algorithm to study the effect of the object thickness on ultrashort pulse diffraction on amplitude, phase, and three-dimensional highly scattering objects. The algorithm comprises a stepwise approach to simulating the diffraction of ultrashort pulses on apertures or scatterers having a finite thickness. We confirm the applicability of the approach and convergence of the result upon reducing the simulation step. We compare the simulation results obtained with traditionally calculated wavefields and the updated results obtained with the proposed approach. We reveal a discrepancy of about 7% for pulsed radiation with λ=800nm on a 1 mm thick object. Then, we demonstrate the dependence of this mismatch on the object thickness and show that for non-Gaussian vortex beams, this effect is even more pronounced. We reveal that spatiotemporal coupling effects depend on the pulse-object interaction simulation approach as well. The obtained results demonstrate that applicability of the single-layer representation of the simulated object strongly depends on its specific features, and inaccuracy of such an approach strongly depends on individual characteristics of the object.

Single-shot ultrafast sequential holographic imaging with high temporal resolution and a large field of view

A compact system for single-shot sequential holographic imaging (SSSHI) with high temporal resolution and a large field of view is proposed. In this system, a specially designed sequence pulse train generator with a group of diffractive gratings inserted is adopted to simultaneously generate the probe pulse train and the reference pulse train required for recording a single-shot spatial frequency division multiplexing hologram. The system successfully overcomes the walk-off effect of the ultrashort pulse laser in SSSHI and, hence, effectively avoids the influence of the short coherence of ultrashort pulses on the spatial resolution (or field of view) of SSSHI; the complexity of the system and the difficulty in the precise synchronous alignment of the probe and the reference pulses also can be greatly reduced. An experimental setup of the system was constructed, and a SSSHI of dynamical air plasmas induced by a femtosecond pulse laser is successfully realized.

Multimodal Optical Diagnostics of Glycated Biological Tissues

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by the disruption of carbohydrate, lipid, and proteins metabolism and development of long-term microvascular, macrovascular, and neuropathic changes. This review presents the results of spectroscopic studies on the glycation of tissues and cell proteins in organisms with naturally developing and model diabetes and in vitro glycated samples in a wide range of electromagnetic waves, from visible light to terahertz radiation. Experiments on the refractometric measurements of glycated and oxygenated hemoglobin in broad wavelength and temperature ranges using digital holographic microscopy and diffraction tomography are discussed, as well as possible application of these methods in the diabetes diagnostics. It is shown that the development and implementation of multimodal approaches based on a combination of phase diagnostics with other methods is another promising direction in the diabetes diagnostics. The possibilities of using optical clearing agents for monitoring the diffusion of substances in the glycated tissues and blood flow dynamics in the pancreas of animals with induced diabetes have also been analyzed.