Systematic and quantitative comparison of lattice and Gaussian light-sheets

In the present paper, a scheme for generation of terahertz (THz) radiation in electron-neutral collisional plasma based on beating of two Gaussian laser array beams has been proposed. It is shown that the efficiency of THz radiation based on the Gaussian laser array beams can be enhanced drastically in comparison with the efficiency of THz radiation based on the Gaussian one. Furthermore, the producing THz radiation by the Gaussian laser array beams, which has an exclusive field profile, is affected by some array structure parameters. It can also be used to overcome the negative consequences of electron neutral collisions in plasma, which may be occurring in the THz radiation generation process. Optimizing the collisional plasma, laser beams and array structure parameters, THz radiation efficiency up to 0.07% can be obtained in our scheme which is about three times greater than the maximum efficiency obtained for standard (single) Gaussian laser beam. Also, considering the electrostatic energy channel in solving the THz wave equation, and reduction of THz radiation efficiency to 0.054%, in this assumption, the ratio between the efficiency of Gaussian laser array beams and standard Gaussian laser beam remained unchanged.

In this paper, by analyzing the main lobe of the Airy beam and its fitting Gaussian beam, we define the Rayleigh range of Airy beam based on the width of FEABs main lobe for scaling the propagation characteristic of the Airy beam. The similar diffraction-free distance of FEAB (here, the width of the main lobe expanding to times) can be scaled by Rayleigh range, but it is from infinite (Pure non-diffraction beam) to one Rayleigh range (the same with Gaussian beam) when decay factor is from 0 to 1. On the contrary, although the FEAB with smaller decay factor () can propagate more Rayleigh ranges keeping diffraction-free, the effective energy in the main lobe is low by studying the power in the bucket (PIB). If more energy needing in the main lobe, the FEAB need bigger decay factor () will become more similar with Gaussian beam which can propagate about one Rayleigh range.

Propagation of elegant higher-order Gaussian beams in turbulent atmosphere is studied in detail. Analytical propagation formulae of elegant higher-order Gaussian beams in turbulent atmosphere are derived based on extended Huygens-Fresnel integral. The intensity and spreading properties of elegant higher-order Gaussian beams and standard higher-order Gaussian beams in turbulent atmosphere are studied numerically and comparatively. It is found that the propagation properties of elegant higher-order Gaussian beams and standard higher-order Gaussian beams are much different from their properties in free space The standard higher-order Gaussian beams spread more rapidly than the elegant higher-order Gaussian beams in turbulent atmosphere.

Aberrations in optical microscopy reduce image resolution and contrast, and can limit imaging depth when focusing into biological samples. Static correction of aberrations may be achieved through appropriate lens design, but this approach does not offer the flexibility of simultaneously correcting aberrations for all imaging depths, nor the adaptability to correct for sample-specific aberrations for high-quality tomographic optical imaging. Incorporation of adaptive optics (AO) methods have demonstrated considerable improvement in optical image contrast and resolution in noninterferometric microscopy techniques, as well as in optical coherence tomography. Here we present a method to correct aberrations in a tomogram rather than the beam of a broadband optical interferometry system. Based on Fourier optics principles, we correct aberrations of a virtual pupil using Zernike polynomials. When used in conjunction with the computed imaging method interferometric synthetic aperture microscopy, this computational AO enables object reconstruction (within the single scattering limit) with ideal focal-plane resolution at all depths. Tomographic reconstructions of tissue phantoms containing subresolution titanium-dioxide particles and of ex vivo rat lung tissue demonstrate aberration correction in datasets acquired with a highly astigmatic illumination beam. These results also demonstrate that imaging with an aberrated astigmatic beam provides the advantage of a more uniform depth-dependent signal compared to imaging with a standard gaussian beam. With further work, computational AO could enable the replacement of complicated and expensive optical hardware components with algorithms implemented on a standard desktop computer, making high-resolution 3D interferometric tomography accessible to a wider group of users and nonspecialists.

The data acquisition speed of point scanning microscopy techniques at sub-cellular resolution limits imaging of large samples, as sample stability and focus drift are becoming an issue. Therefore, light sheet fluorescent microscopy (LSFM) has become the method of choice for imaging cleared samples. However, this method still suffers from a trade-off between imaging depth and resolution, due to diffraction of the illuminating beam limiting the achievable field of view. After improvement of the latter with non-diffracting Bessel beams, lattice light sheet microscopy has substantially reduced the illumination point-spread-function (PSF). Here, we propose further improvement by generation of structured light sheets via phased arrays implemented as silicon nitride photonic integrated circuits (PICs). Beam generation with PICs results in much higher power efficiency than beam forming with conventional liquid crystal based spatial phase modulators, as it does not require the use of narrow blocking apertures. Moreover, this approach enables increased control over the generated field profile. Modeling of concrete PIC concepts indicates that sub-cellular resolution with mm scale imaging depths can be concomitantly achieved. Maintaining a small PSF along the axis perpendicular to the direction of light propagation is sacrificed in order to maintain it over increased imaging depth along the beam propagation axis. Rapid lateral scanning of the illumination beam inside the plane of the light sheet is then obtained by scanning of the laser wavelength within the excitation spectrum of the target fluorescent protein, allowing for a wide bidirectional field-of-view with high resolution.

The problem of reflection of a TE-polarised Gaussian light beam from a layered structure under conditions of resonance excitation of waveguide modes using a total internal reflection prism is considered. Using the spectral approach we have derived the analytic expressions for the mode propagation lengths, widths and depths of -lines (sharp and narrow dips in the angular dependence of the specular reflection coefficient), depending on the structure parameters. It is shown that in the case of weak coupling, when the propagation lengths of the waveguide modes are mainly determined by the extinction coefficient in the film, the depth of -lines grows with the mode number . In the case of strong coupling, when is determined mainly by the radiation of modes into the prism, the depth of -lines decreases with increasing . The change in the TE-polarised Gaussian beam shape after its reflection from the layered structure is studied, which is determined by the energy transfer from the incident beam into waveguide modes that propagate along the structure by the distance , are radiated in the direction of specular reflection and interfere with a part of the beam reflected from the working face of the prism. It is shown that this interference can lead to the field intensity oscillations near -lines. The analysis of different methods for determining the parameters of thin-film structures is presented, including the measurement of mode angles and the reflected beam shape. The methods are based on simultaneous excitation of a few waveguide modes in the film with a strongly focused monochromatic Gaussian beam, the waist width of which is much smaller than the propagation length of the modes. As an example of using these methods, the refractive index and the thickness of silicon monoxide film on silica substrate at the wavelength are determined.

Benefiting from the earlier derivations for the Gaussian beam, we formulate beam wander for dark hollow (DH) and flat-topped (FT) beams, also covering the annular Gaussian (AG) beam as a special case. Via graphical illustrations, beam wander variations of these beams are analyzed and compared among themselves and to the fundamental Gaussian beam against changes in propagation length, amplitude factor, source size, wavelength of operation, inner and outer scales of turbulence. These comparisons show that in relation to the fundamental Gaussian beam, DH and FT beams will exhibit less beam wander, particularly at small primary beam source sizes, lower amplitude factors of the secondary beam and higher beam orders. Furthermore, DH and FT beams will continue to preserve this advantageous position all throughout the considered range of wavelengths, inner and outer scales of turbulence. FT beams, in particular, are observed to have the smallest beam wander values among all, up to certain source sizes.

Underwater optical communication channels can provide access to GHz speed communications between assets located within a few hundred meters range of each other. However, channel phenomena such as turbulence, scattering layers, and propagation through density gradients (pycnoclines) even in the clearest of natural waters, can significantly degrade channel performance. Here, the role of the spatiotemporal structure of the optical resource is considered as a mechanism for improving performance of a surface-to-subsea downlink scenario through a typical pycnocline in clear, oceanic waters. A 3D+1 numerical solver was developed to incorporate experimentally collected CTD measurements of a pycnocline in the upper 80 m of the mixed layer in order to evaluate and compare the propagation of semi non-diffracting Bessel-Gauss beams and standard Gaussian beams through Jerlov Case 1 waters. In certain link environments with certain initial beam parameters, we find that utilizing nonstandard optical resources can provide system performance advantages.

Free-space optical communication systems are vulnerable to phase distortions and amplitude fluctuations caused by atmospheric turbulence, which degrade signal coherence and impair overall performance. Instead of correcting these distortions in real time, we propose an approach based on adaptive-waist modes statistically matched to the turbulence, assuming the transmitter has access to turbulence statistics but not to instantaneous atmospheric conditions. A fundamental Gaussian adaptive-waist mode maximizes power efficiency, while distributing power across multiple adaptive modes enhances link reliability by mitigating turbulence-induced fading. This tradeoff is quantitatively evaluated under varying turbulence conditions, demonstrating significant performance gains over standard Gaussian beams without requiring wavefront correction.

Ionizable lipid-containing lipid nanoparticles (LNPs) are regarded as promising nonviral vectors for gene therapy delivery systems. Rationale design of the ionizable lipid structure based on initial screening of ionizable lipid molecule libraries combined with systematic comparison and analysis on the physical chemical parameters related to delivery efficiency greatly accelerated the discovery of novel LNP candidates for delivering various nucleic acid therapeutics like mRNAs (mRNAs). Based on the copper-catalyzed azide-alkyne click reaction, which is highly efficient and biocompatible, we were able to obtain the lipid molecule library containing a common triazole moiety between different lipid tails and various substituents as hydrophilic head groups. Herein, we systematically investigated the change of pKa values of different ionizable lipid molecules with different substituents as head groups in the click-based lipid library, mapping the pKa value change to different steps in the process of the LNP assembly and mRNA delivery. Systematic analyses on the data including the pKa value of the ionized lipids and the encapsulation and delivery efficiency of mRNA in LNPs with these ionized lipids provided the possibility of rational design on the head and tail structure for the triazole containing ionized lipids to realize highly efficient delivery of different mRNAs.

The spreading of Gaussian array beams for two types of beam combination propagating through turbulent ocean is investigated. Analytical formulas for the Rayleigh range zR and turbulence distances zT and zTT are derived. Numerical results show that the spreading regions are influenced by the oceanic turbulence parameters and the source parameters. Moreover, the Rayleigh range of the coherent combination case tends to be more sensitive to parameters of the source and oceanic turbulence than that for the incoherent combination one, while in the case of turbulence distances, it is the reverse.

We investigate the enhancement of nonlinearity in one-dimensional (1D) photonic crystals (PCs) with Kerr nonlinearity by numerical Z-scan experiments based on the finite-difference time-domain technique. Focused Gaussian beams with well-defined waists and Rayleigh lengths necessary for Z-scan experiments are generated through a conjugated manipulation of the Gaussian beams propagating in free space. The Z-scan measurements used for bulk materials are naturally extended to 1D PCs after incorporating the frequency- and power-density-dependent reflections into their linear and nonlinear absorptions. The closed- and open-aperture Z-scan traces for the 1D PCs are obtained and a symmetric method is employed to modify the asymmetric closed-aperture traces. The nonlinearity enhancement factors at different frequencies in the first and second bands are derived numerically and analytically. A good agreement is found between the numerical and analytical results in the case of weak nonlinearity. Moreover, the dependences of the enhancement factor on the incident power density for different frequencies in the 1D PCs are extracted and they are found to be much different from those in bulk materials. It is revealed that the variation of the group velocity with increasing power density is responsible for the power-density dependence of the enhancement factor. It indicates that in practice one must deliberately choose the working frequency and power density of PC-based devices in order to achieve a maximum enhancement of nonlinearity.

Source Mask Optimization1 (SMO) is one of the most important techniques available for extending ArF immersion lithography. The combination of freeform source shape and complex mask pattern, determined by SMO, can extend the practical resolution of a lithography system. However, imaging with a small k1 factor (~0.3 or smaller) is very sensitive to many imaging parameters, such as illumination source shape error, lens aberration, process property, etc. As a result, the real source shape must be re-adjusted to realize the expected imaging performance as may be seen, for example, in an Optical Proximity Effect (OPE) curve. In this paper we present an illumination pupilgram re-adjustment method that can effectively control the various illumination parameters to get optimum imaging performance, which is required for the lithography process design. The modulation functions are called Zernike intensity/distortion modulations2. Since the pupilgram modulation is expressed by Zernike polynomials3, a high degree of pupilgram adjustment freedom is provided to the intelligent illuminator4 (freeform illumination) which can be effectively modeled in the optimization. Furthermore, the magnitude of each adjusting Zernike component can be restricted to prevent over modulation, which may affect imaging performance for various patterns on a mask. Furthermore, the linear impact of each term of Zernike modulation can allow us to use Zernike linear combination analysis to calculate imaging performance. Therefore, optimization using a large variety of illumination modulation terms may be possible with reasonable computation loads. The method is combined with an imaging simulator that includes resist models and optimization algorithms in pupilgram refinement software called OPE Master. The software can take into account the scanner signature and various constraints so that the result of the optimization can be accurately realized on the scanner. The optimization can be performed based on rigorous imaging simulation and Zernike linear combination analysis, which is based on a precalculated Zernike linear sensitivity table.

The scintillation index is formulated for modified Bessel-Gaussian beams propagating in weakly turbulent media. Numerical calculations applied directly to the derived triple integral show that, for off-axis positions, the modified Bessel-Gaussian beams of higher than zero order scintillate less than Gaussian beams at large input beam sizes and low beam orders with the increasing width parameter initially contributing positively to this phenomenon of less scintillation. As the beam order exceeds two, this advantage is diminished. The modified Bessel-Gaussian beam of order zero is a special case, however, exhibiting lowest scintillation at small input beam sizes. When considered against the propagation length, higher-order modified Bessel-Gaussian beams continue to offer less scintillation than those of order zero. At various radial positions, the scintillation index of modified Bessel-Gaussian beams with orders higher than zero attains small values toward the beam edges but rises sharply when approaching the beam axis. The effect of inner and outer scales of turbulence is also studied, and it is found that while increasing the inner scale of turbulence seems to cause increases in scintillation, the influence of the outer scale is hardly noticeable.

A 2-dimensional scalar aerial image model was used to computationally study i-line imaging with oblique illumination. Limited comparisons between developed photoresist images and aerial images were made. The effects on CD control, exposure latitude, and bias of varying annular and quadrupole geometry were mapped via simulation. Significant improvements in DOF of isolated lines was achieved with oblique illumination. Isolated line to dense line bias could be adjusted by changing the illumination type. Although oblique illumination improved the aerial image contrast at defocus, it caused degradation in the aerial image contrast at best focus. Long and short range proximity effects degraded the simulated CD control of optimized oblique illumination systems. This was observed in simulations of an SRAM gate cell. The imaging performance at .9 micrometers defocus, of an i-line system (NA .48) with oblique illumination, was judged to be worse than a KrF system (NA .42) with standard illumination. Quadrupole illumination was not found to measurably affect lens distortion.