Spatial Coherence Research Papers - Academia.edu (original) (raw)

2025, Scientific reports

Reciprocity is when wave or quantum scattering satisfies a symmetry property, connecting a scattering process with the reversed one. While reciprocity involves the interchange of source and detector, it is fundamentally different from rotational invariance, and is a generalization of time reversal invariance, occurring in absorptive media as well. Due to its presence at diverse areas of physics, it admits a wide variety of applications. For polarization dependent scatterings, reciprocity is often violated, but violation in the phase of the scattering amplitude is much harder to experimentally observe than violation in magnitude. Enabled by the advantageous properties of nuclear resonance scattering of synchrotron radiation, we have measured maximal, i.e., 180-degree, reciprocity violation in the phase. For accessing phase information, we introduced a new version of stroboscopic detection. The scattering setting was devised based on a generalized reciprocity theorem that opens the wa...

2025, Science World Journal

Temperature extremes have been linked to adverse pregnancy outcomes globally. This study investigated the influence of extreme temperature on adverse pregnancy outcomes in Kaduna State, Nigeria. Daily minimum and maximum temperature data of Kaduna State (2015-2023) were downloaded from NASA Power Access. Monthly records of three adverse pregnancy outcomes which include Pre-Term (PT), Low Birth Weight (LBW) and Still Birth (SB) for the period 2015 to 2023 were retrieved from the database of Barau Dikko Specialist Teaching Hospital, Kaduna State. RClimdex was employed to compute four percentile-based extreme temperature indices (TX10p; TX90p; TN10p; and TN90p). Pearson correlation coefficient and linear regression were used to examine the association and extent of the relationship between extreme temperature indices and adverse pregnancy outcomes in Kaduna State, Nigeria. Results of the correlation analysis revealed that correlation coefficient between TN10p and LBW, PT and SB were 0.237, 0.142 and-0.006, among which only LBW had a significant relationship. The correlation coefficient between TN90p and LBW, PT and SB were-0.190,-0.301, and-0.335, with PT and SB exhibiting significant relationship. The correlation coefficient between TX10p and PT, LBW and SB were 0.491, 0.440 and 0.361 respectively. All the correlation were statistically significant. Lastly, TX90p had moderate negative relationship with PT and SB, but a weak negative significant relationship with LBW, with correlation coefficients of-0.408,-0.449 and-0.397 respectively. From the regression analysis, it can be concluded that both cold and warm temperature extremes significantly influence adverse pregnancy outcomes in the study area. Also, daytime extremes exhibit stronger influence on adverse pregnancy outcomes compared to nighttime extremes. Therefore, this study recommends that pregnant women should be educated on the significance of avoiding extreme temperatures, as well as how to avoid health problems caused by heat or cold.

2025, Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)

The beam size at the low emittance configuration of the Photon Factory was measured by the use of the SR interferometer. The spatial coherence of the visible SR beam was measured for both of the vertical and horizontal directions with the wavelengths at 500nm and 633nm. From the measured spatial coherence of the SR beam, the beam size measurements of 87.3µm in the vertical and 261.2 µm in the horizontal were obtained. The observed horizontal beam size agreed with the designed beam size.

2025, arXiv (Cornell University)

The present article is devoted to the radiation from an electron bunch with modulated density passes through the stack consisting of two plates with different thicknesses and electrodynamic properties. The new elegant expression for the frequency -angular distribution of transition radiation is obtained. Using the existence of resonant frequency at which the longitudinal form-factor of bunch not suppresses radiation coherence and choosing parameters for the stack of plates, one can also avoid suppression of the radiation coherence by transverse form-factor of bunch. The radiation fro m a bunch with modulated density in the process SASE FEL can be part ially coherent at a resonant frequency. Then the intense sub monochromat ic beam of X-ray photons is formed. On the other hand one can define an important parameter of density modulation depth of bunch which is unknown to this day.

2025

Monthly distributions of surface latent heat flux and solar irradiance in the tropical Pacific were computed from observations of the Scanning Multichannel Microwave Radiometer on Nimbus-7 and the Visible Infrared Spin Scan Radiometer on GOES-W. They are the dominant variable components of the surface heat flux, the sum of which gives the approximate thermal forcing on the ocean.

2025

Three-dimensional animation sequences are often represented by a discrete set of compatible triangle meshes. In order to create the illusion of a smooth motion, a sequence usually consists of a large number of frames. We propose a pre-processing algorithm that considerably reduces the number of frames required to describe the whole animation. Our method is based on Batch Neural Gas , a new clustering and classification approach that can be used to automatically find the most relevant frames from the sequence. The meshes from the original sequence can then be expressed as linear combinations of these few key-frames with small approximation error. The key-frames can finally be compressed with any state-of-the-art compression scheme. Overall, this leads to improved compression rates as the number of key-frames is significantly smaller than the number of original frames and the storage overhead for the reconstruction weights is marginal.

2025, HAL (Le Centre pour la Communication Scientifique Directe)

In the context of random environment, time-domain simulations of structural responses are often necessary when the structure is nonlinear, but not only : when the structure is linear and the excitation modelled as a non-stationnary non-Gaussian process, Monte Carlo approaches are necessary to identify the probabilistic distribution of the output. It is for example the case in seismic analysis. In this paper we use a stochastic model developped earlier by the authors for non-stationnary and non-Gaussian random processes. It is based on an empirical Karhunen-Loève expansion of the process constructed from an available data basis. In a first part we study the particular case of linear structures. The Monte Carlo becomes particularely simple: one needs only to consider the construction of a low number of responses, corresponding to the deterministic eigen functions of the Karhunen-Loève expansion. The KL expansion of the response is then obtained directly. In a second part we study the case of nonlinear structures. We propose here to construct the Karhunen Loève model of the response, using the experimental input data basis for constructing a data basis for the response.

2025

International audienceIn the context of random environment, time-domain simulations of structural responses are often necessary when the structure is nonlinear, but not only : when the structure is linear and the excitation modelled as a non-stationnary non- Gaussian process, Monte Carlo approaches are necessary to identify the probabilistic distribution of the output. It is for example the case in seismic analysis. In this paper we use a stochastic model developped earlier by the authors for non- stationnary and non-Gaussian random processes. It is based on an empirical Karhunen-Lo`eve expansion of the process constructed from an available data basis.In a first part we study the particular case of linear structures. The Monte Carlo becomes particularely simple: one needs only to consider the construction of a low number of responses, corresponding to the deterministic eigen functions of the Karhunen-Lo`eve expansion. The KL expansion of the response is then obtained directly. In a ...

2025, Cerebral Cortex

Brain field potentials (FPs) can reach far from their sources, making difficult to know which waves come from where. We show that modern algorithms efficiently segregate the local and remote contributions to cortical FPs by recovering the generatorspecific spatial voltage profiles. We investigated experimentally and numerically the local and remote origin of FPs in different cortical areas in anesthetized rats. All cortices examined show significant state, layer, and region dependent contribution of remote activity, while the voltage profiles help identify their subcortical or remote cortical origin. Co-activation of different cortical modules can be discriminated by the distinctive spatial features of the corresponding profiles. All frequency bands contain remote activity, thus influencing the FP time course, in cases drastically. The reach of different FP patterns is boosted by spatial coherence and curved geometry of the sources. For instance, slow cortical oscillations reached the entire brain, while hippocampal theta reached only some portions of the cortex. In anterior cortices, most alpha oscillations have a remote origin, while in the visual cortex the remote theta and gamma even surpass the local contribution. The quantitative approach to local and distant FP contributions helps to refine functional connectivity among cortical regions, and their relation to behavior.

2025, arXiv: Atomic Physics

Superradiant decay is accompanied by two kinds of collective lineshifts, an induced shift and the spontaneous "collective Lamb shift." Both form as sum of dipole-dipole interaction-induced level shifts between atoms in the system. We have developed a procedure to obtain numerical results on this model that self-consistently incorporates the shifts. The induced shift displays large non-zero values early in the system evolution. In addition, its effect on the superradiant system is studied: there is only a very small dephasing effect on the decay rate. While the induced shift is largely absent in not-too strongly driven systems, this parameter region might provide a good experimental regime for measuring the collective Lamb shift. These results can have important consequences for highly sensitive systems, such as quantum information science or atomic clocks.

2025, Journal of Telecommunications and Information Technology

This paper deals with phase gratings working in the paraxial domain. The profile of the optimum-efficiency beam multiplier with an arbitrary number of output diffraction orders is derived in an analytic form by exploiting methods from the calculus of variation. The output beams may be equiintense or with arbitrary distribution of power. Numerical examples are given for different values of the number of output beams.

2025, Electronics Letters

2025, Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference

We present a high performance variant of the popular geodesic active contours which are used for splitting cell clusters in microscopy images. Previously, we implemented a linear pipelined version that incorporates as many cues as possible into developing a suitable level-set speed function so that an evolving contour exactly segments a cell/nuclei blob. We use image gradients, distance maps, multiple channel information and a shape model to drive the evolution. We also developed a dedicated seeding strategy that uses the spatial coherency of the data to generate an over complete set of seeds along with a quality metric which is further used to sort out which seed should be used for a given cell. However, the computational performance of any level-set methodology is quite poor when applied to thousands of 3D data-sets each containing thousands of cells. Those data-sets are common in confocal microscopy. In this work, we explore methods to stream the algorithm in shared memory, multi...

2025, Applied Optics

This work presents a very simple and comprehensive approach for classification of the combinational spatial frequencies of the superimposed periodic or quasi-periodic structures. The reciprocal vectors of the structures are used to express their respective spectral components, and a unique reciprocal vectors equation is introduced for presenting the corresponding combinational frequencies. By the aid of the reciprocal vectors equation we classify moiré patterns of combinational frequencies into four classes: the conventional moiré pattern, moiré fringes of higher-order harmonics, higher-order moiré patterns, and pseudo-moiré patterns. The difference between the moiré fringes of higher-order harmonics and higher-order moiré patterns is expressed in the formulas. By some typical examples, conditions for simultaneous formation of moiré patterns of different harmonics of the superimposed gratings are investigated. We show that in the superimposition of two gratings, where at least one has a varying period and another has a non-sinusoidal profile, different moiré patterns are formed over different parts of the superimposed area, where a distinct pair of spatial frequencies of the superimposed structures contributes to the formation of each of the patterns. We use the same procedure in the analysis of simultaneously produced defected moiré patterns in the superimposition of a linear grating and a zone plate, where one or both consist of some topological defects at specific locations and at least one of the gratings has a non-sinusoidal profile. The topological defects of resulting moiré fringes are similar to those appearing in the interference patterns of optical vortices. It is shown that the defect number of resulting moiré fringes depends on the defect numbers and order of frequency harmonics of the gratings. The dependency of the defect number of the moiré fringes and its sign to the defect numbers of the gratings and their contributed frequency harmonics is derived for both additive and subtractive terms of moiré fringes, and the results are verified with several examples based on computational simulations.

2025, Physical Review A

Temporal light modulation methods which are of great practical importance in optical technology, are emulated with matter waves. This includes generation and tailoring of matter-wave sidebands, using amplitude and phase modulation of an atomic beam. In the experiments atoms are Bragg diffracted at standing light fields, which are periodically modulated in intensity or frequency. This gives rise to a generalized Bragg situation under which the atomic matter waves are both diffracted and coherently shifted in their de Broglie frequency. In particular, we demonstrate creation of complex and non-Hermitian matter-wave modulations. One interesting case is a potential with a time-dependent complex helicity ͓Vϰexp(it)͔, which produces a purely lopsided energy transfer between the atoms and the photons, and thus violates the usual symmetry between absorption and stimulated emission of energy quanta. Possible applications range from atom cooling over advanced atomic interferometers to a new type of mass spectrometer.

2025

Climate variability over Senegal and its relationships with global climate is examined for the period 1971-1998. Monthly observed rainfall for 20 stations over Senegal, monthly mean temperature for 12 stations and monthly average CMAP data were averaged for the months of June July, August and September, to generate seasonal rainfall totals for the wet season and climate indices averaged over the study period. The monthly SST data is the NOAA Extended Reconstructed SST data (ERSST) provided by the NOAA-CIRES Climate Diagnostics Center in Boulder, Colorado. The monthly, seasonal and annual temperature and precipitation distributions are mapped analyzed using ArcGIS Spatial Analyst. Rainfall distribution over Senegal is dominated by a N-S gradient, and temperature distribution by an E-W gradient.

2025, Lecture Notes in Computer Science

We propose a new model for probabilistic image segmentation with spatial coherence through a Markov Random Field prior. Our model is based on a generalized information measure between discrete probability distribution (β-Measure). This model generalizes the quadratic Markov measure field models (QMMF). In our proposal, the entropy control is achieved trough the likelihood energy. This entropy control mechanism makes appropriate our method for being used in tasks that require of the simultaneous estimation of the segmentation and the model parameters.

2025, Applied Surface Science

2025, Journal of Geophysical Research

A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with nearcomplete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

2025

Nearby grid cells have been observed to express a remarkable degree of long-range order, which is often idealized as extending potentially to infinity. Yet their strict periodic firing and ensemble coherence are theoretically possible only in flat environments, much unlike the burrows which rodents usually live in. Are the symmetrical, coherent grid maps inferred in the lab relevant to chart their way in their natural habitat? We consider spheres as simple models of curved environments and, waiting for the appropriate experiments to be performed, we use our adaptation model to predict what grid maps would emerge in a network with the same type of recurrent connections, which on the plane produce coherence among the units. We find that on the sphere such connections distort the maps that single grid units would express on their own, and aggregate them into clusters. When remapping to a different spherical environment, units in each cluster maintain only partial coherence, similar to ...

2025

Many aspects of reanalysis data are of high quality over regions with sufficiently dense data, but the accuracy is uncertain over areas with sparse observations. NCEP-NCAR reanalysis (NNR) and ECMWF 15/40-Yr Re-Analysis (ERA-15 and ERA-40) variables are compared to two independent rawinsonde datasets from the periphery of the Arctic Ocean during the late 1980s and early 1990s: the Coordinated Eastern Arctic Research Experiment (CEAREX) and the Lead Experiment (LeadEx). The study is prompted by J. A. Francis who found that the NNR and ERA-15 upper-level winds are very different from those observed during these two field experiments. All three reanalyses display large biases in comparisons of the wind components and wind speeds with CEAREX observations, particularly above the 500-hPa level, but exhibit smaller discrepancies with respect to the LeadEx data, generally consistent with the previous findings of J. A. Francis. However, all three reanalyses well capture the wind variability during both experiment periods. For the geopotential height, temperature, and moisture fields, the reanalyses demonstrate close agreement with the CEAREX rawinsonde observations. From comparisons with surrounding fixed rawinsonde stations and examination of the average vertical wind speed shear, it is concluded that the CEAREX upper-level wind speeds (especially above the 500-hPa level) are erroneous and average about half of the actual values. Thus, this evaluation suggests that the three reanalyses perform reliably for tropospheric-state variables from the edge of the Arctic Ocean during the modern satellite era.

2025, Applied Optics

A unified mathematical formulation for designing and analyzing even the most general optical processor is presented. It exploits the Wigner distribution function to characterize the illumination, the input, the inherent filter, and the output results. To characterize the propagation of the light through the optical processor setup, we exploit the Wigner matrix formalism, which is appealing because it allows simple geometric analysis. The Wigner distribution function was extended to include illumination of arbitrary coherence so that processors using either coherent light or partially coherent light can be designed and analyzed with the same Wigner formalism. The basic principles, design, and analysis of the imaging and Fourier-transform operations and use of the Wigner formalism to evaluate the performance and tolerances of optical processors are presented.

2025, Earth and Planetary Science Letters

Using a climatic calibration based on the scores of the plant functional types (PFTs) calculated for 1245 surface pollen spectra, the climate at 6 ka BP has been reconstructed for a set of 116 pollen spectra from the former Soviet Union and Mongolia. The results are presented as maps of climatic anomalies and maps of probability classes showing the significance of these differences from the modern climate. The reconstructed patterns are spatially coherent, but have confidence levels that vary from region to region, due to the often-large error ranges. At 6 ka, the winters were more than 2ºC warmer than today north of 50ºN, with a high significance east of the Urals. Summers were also more than 2ºC warmer than today with a high level of confidence north of the Polar Circle and in central Mongolia. In the mid-latitudes of Siberia, in northern Kazakhstan and around the Black and the Caspian seas, 6 ka summers were significantly cooler than today. The reconstructed moisture availability (ratio of actual to equilibrium evapotranspiration) was more than 10% higher than today in the Ukraine, southern Russia and northern Mongolia, and more than 10% lower than today in central Mongolia. This pattern corresponds partly with that of the water budget (annual precipitation minus evaporation) reconstructed from lake level records.

2025, Physical Review Letters

We study the coherence and density modulation of a non-equilibrium exciton-polariton condensate in a one-dimensional valley with disorder. By means of interferometric measurements we evidence a modulation of the first-order coherence function and we relate it to a disorder-induced modulation of the condensate density, that increases as the pump power is increased. The non-monotonous spatial coherence function is found to be the result of the strong non-equilibrium character of the one-dimensional system, in the presence of disorder.

2025, Physical Review B

Real-and momentum-space spectrally resolved images of microcavity polariton emission in the regime of condensation are investigated under nonresonant excitation using a laser source with reduced intensity fluctuations on the time scale of the exciton lifetime. We observe that the polariton emission consists of many macroscopically occupied modes. Lower-energy modes are strongly localized by the spatial polaritonic potential disorder on a scale of a few microns. Higher-energy modes have finite k vectors and are delocalized over 10-15 m. All the modes exhibit long-range spatial coherence comparable to their size. We provide a theoretical model describing the behavior of the system with the results of the simulations in good agreement with the experimental observations. We show that the multimode emission of the polariton condensate is a result of its nonequilibrium character, the interaction with the local polaritonic potential, and the reduced intensity fluctuations of the excitation laser.

2025, arXiv (Cornell University)

Context. In comparison to the radio and sub-millimetric domains, imaging with optical interferometry is still in its infancy. Due to the limited number of telescopes in existing arrays, image generation is a demanding process that relies on time-consuming reconfiguration of the interferometer array and super-synthesis. Aims. Using single mode optical fibres for the coherent transport of light from the collecting telescopes to the focal plane, a new generation of interferometers optimized for imaging can be designed. Methods. To support this claim, we report on the successful completion of the 'OHANA Iki project: an end-to-end, on-sky demonstration of a two-telescope interferometer, built around near-infrared single mode fibres, carried out as part of the 'OHANA project. Results. Having demonstrated that coherent transport by single-mode fibres is feasible, we explore the concepts, performances, and limitations of a new imaging facility with single mode fibres at its heart: Agile Guided Interferometer for Longbaseline Imaging Synthesis (AGILIS). Conclusions. AGILIS has the potential of becoming a next generation facility or a precursor to a much larger project like the Planet Formation Imager (PFI).

2025, Opto-Electronics Review

We present results on development and experimental implementation of a 1-kHz, coherent extreme ultraviolet (XUV) radia- tion source based on high-order harmonic generation of the femtosecond, near-infrared laser pulses produced by the titanium-doped sapphire laser system (35 fs, 1.2 mJ, 810 nm) at the Institute of Physics AS CR / PALS Centre. The source comprises a low-density static gas cell filled with a conversion medium, typically argon. The comprehensive optimization of the XUV harmonic source has been performed with respect to major parameters such as gas pressure in the cell, cell length, position of the focus of the driving laser field with respect to the gas cell position, size of the driving near-infrared laser beam, chirp of the femtosecond pulse, and the focal length of the lens deployed in the experimental setup. Harmonic spectra were recorded using an XUV transmission grating spectrometer developed specifically for this purpose. Detailed characterization of the XUV sou...

2025, International Journal of Climatology

Trends in extreme daily temperature and rainfall have been analysed from 1961 to 1998 for Southeast Asia and the South Pacific. This 38-year period was chosen to optimize data availability across the region. Using high-quality data from 91 stations in 15 countries, significant increases were detected in the annual number of hot days and warm nights, with significant decreases in the annual number of cool days and cold nights. These trends in extreme temperatures showed considerable consistency across the region. Extreme rainfall trends were generally less spatially coherent than were those for extreme temperature. The number of rain days (with at least 2 mm of rain) has decreased significantly throughout Southeast Asia and the western and central South Pacific, but increased in the north of French Polynesia, in Fiji, and at some stations in Australia. The proportion of annual rainfall from extreme events has increased at a majority of stations. The frequency of extreme rainfall events has declined at most stations (but not significantly), although significant increases were detected in French Polynesia. Trends in the average intensity of the wettest rainfall events each year were generally weak and not significant.

2025

Experiments to produce and measure femtosecond electron bunches are described. A 2.6 MeV rf-gun with thermionic cathode is used at the SUNSHINE (Stanford University Short Intense Electron Source) facility in conjunction with an Î±-magnetic for bunch compression to produce f-sec electron bunches. Transition radiation generated by these bunches is analyzed in a Michelson interferometer to determine the bunch length. Limitations

2025, RevMexAA (Serie de …

Se encuentra una distribución log-normal con valor mediano de 27.0 m. La importancia de L 0 en la derivación del desempeño de la óptica adaptativa (OA) es analizada. Se demuestra que valores bajos de L 0 incrementan las habilidades... more

2025, Astronomy and Astrophysics

The first measurements of the spatial coherence outer scale at the Observatorio Astronómico Nacional at San Pedro Mártir (OAN-SPM) are reported along with long term seeing measurements. These parameters were measured with the Generalized Seeing Monitor and with a Differential Image Motion Monitor. An instrumented mast was also used to measure the structure constant of the refractive index C 2 n in the first 15 m. Log-normal statistics were found for the seeing and for the outer scale, with median values of 0.92 and 27.0 m, respectively. The distribution of the outer scale values is similar to that found in other observatories around the world, suggesting that the presence of trees in the OAN-SPM do not affect the outer scale values. Correlation studies suggest that large values of the seeing and the outer scale are likely to occur when the wind blows from the SSW. Further studies are recommended to confirm this tendency.

2025, Acta Geophysica

The analysis of weak variations in the energetic particle flux, as detected by neutron or muon monitors, can often be considerably improved by analysing data from monitor networks and thereby exploiting the spatial coherence of the flux. We present a statistical framework for carrying out such an analysis and discuss its physical interpretation. Two other applications are also presented: filling data gaps and removing trends. This study focuses on the method and its various uses.

2025, Journal of Optical Technology

An experimental and theoretical study has been carried out of the ablation of a solid insulator with a wide band gap (LiF) under the action of ultrashort laser pulses of the UV range, obtained in a free-electron laser (pulse width τ L = 0.3 ps, photon energy hω L = 20.2 eV), and the soft X-ray region, obtained in a silver-plasma laser (τ L = 7 ps, hω L = 89.3 eV). A comparison is made of the results obtained on the two laser systems. It is shown that the ablation threshold is about the same for both lasers. A theory is presented that explains the weak growth of the ablation mass with increasing surface energy density of the laser radiation (the fluence) in the case of X-ray lasers as a result of the transition from spallation close to the ablation threshold to evaporative ablation at high fluence values.

2025

The paper is devoted to experimental and theoretical studies of ablation of condensed matter by optical (OL), extreme ultraviolet (EUV) and X-ray lasers (XRL). Results obtained at two different XRL are compared. The first XRL is collision Ag-plasma laser with pulse duration τ L = 7 ps and energy of quanta hν=89.3 eV, while the second one is EUV free electron laser (EUV-FEL) and has parameters τ L = 0.3 ps and energy of quanta 20.2 eV. It is shown that ablation thresholds for these XRL at LiF dielectric are approximately the same. A theory is presented which explains slow growth of ablated mass with fluence in case of XRL as a result of transition from spallative ablation near threshold to evaporative ablation at high fluencies. It is found that the metal irradiated by short pulse of OL remains in elastic state even in high shear stresses. Material strength of aluminum at very high deformation rates V /V ∼ 10 9 s -1 is defined.

2025, Contributions to Plasma Physics

Ultrashort X‐ray laser pulse acts onto electron subsystem of dielectrics such as LiF and transfers matter into a two‐temperature state with hot electrons excited by the pulse from valence to conduction band. Because of the small heat conduction, the hydrodynamic motion proceeds in adiabatic regime keeping the radiation attenuation depth Datt as the only scale of the spatial heat distribution. Hydrodynamic motion qualitatively changes with absorbed energy increase. At low fluences F ∼ 10mJ/cm2 a spallative removal of LiF remaining in solid state takes place. This is a reason for the low ablation threshold. The paper presents new experimental findings supporting this conclusion. For the first time these findings are obtained using ultrashort extreme vacuum ultraviolet‐free electron laser (EUV‐FEL). In the case of high fluence, also achieved in our experiments at EUV‐FEL, material removal happens as result of outflow of matter transferred into the gaseous state. This explains the slow ...

2025, Contributions to Plasma Physics

Laser-matter interaction is defined by an electronic band structure of condensed matter and frequency ωL of electromagnetic radiation. In the range of moderate fluences, the energy absorbed by electrons from radiation finally thermalizes in the ion thermal energy. The thermalization processes are different for optical as compared with X-ray quanta and for metals relative to semiconductors and dielectrics, since the light absorption and electron-electron, electron-ion dynamics are sensitive to the electron population in a conduction band and the width of a forbidden gap. Although the thermalization processes are different, the final state is simply a heated matter. Laser heating creates powerful stresses in a target if duration of a laser pulse τL is short in acoustic time scale. Nucleation and material removal take place under such stresses. Such way of removal is called here the spallative ablation. Thus the spallative ablation is an ablation mechanism universally important for qualitatively different materials and quanta.

2025, Applied Physics A

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration τ L is shorter than acoustic relaxation time t s is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation strongly depends on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse.

2025, Springer Series in Optical Sciences

At first, we summarize the properties of a transverse electromagnetic wave. This is followed by the discussion of the diffraction of light. We present the concept of coherence-temporal and spatial-and compare laser radiation with thermal light. After that, we treat the Gaussian beam and the higher transverse modes. An overview of typical laser parameters is given. Finally, we deal with the dangers of laser radiation. The total of all electromagnetic phenomena is governed by Maxwell's equations. They link the temporal and spatial derivatives of the electric and the magnetic field strength, Ẽ and H [1-5]. Starting from Maxwell's equations, J. C. Maxwell predicted the existence of electromagnetic waves that propagate with the speed of light. During the years 1887/88, H. Hertz succeeded in the generation and detection of electromagnetic waves. So, light was recognized as a special case of an electromagnetic wave. An overview of the investigated and mostly technically used frequency or wavelength spectrum of electromagnetic waves gives Fig. .1. The laser radiation-usually k = 0.1-10 lm-represents only a small part of the total spectrum. In the simplest case, a laser beam is represented by a plane harmonic wave that propagates in z-direction with Ẽ electric field strength vector, H magnetic field strength vector; Ẽ0 ; H0 amplitude, x angular frequency, k angular wave number and u 0 phase angle. The directions of the field strength vectors and the direction of propagation of that electromagnetic wave are shown in Fig. .2. Light is a

2025, Applied Optics

We propose a 3D imaging technique based on the combination of full-field swept-source optical coherence microscopy (FF-SSOCM) with low spatial coherence illumination and a special numerical processing that allows for numerically focused coherent-noise-free imaging without mechanical scanning in longitudinal or transversal directions. We show, both theoretically and experimentally, that the blurring effects arising in FF-SSOCM due to defocus can be corrected by appropriate numerical processing even when low spatial coherence illumination is used. A FF-SSOCM system was built for testing the performance of this technique. Coherent-noise-free imaging of a sample with longitudinal extent exceeding the optical depth of field is demonstrated without displacement of the sample or any optical element.

2025, Journal of Atmospheric and Oceanic Technology

Simulations, made with the fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5), of the response of the marine atmospheric boundary layer (MABL) as air moves over a sharp SST front are compared with observations made during the Frontal Air-Sea Interaction Experiment (FASINEX) in the North Atlantic subtropical convergence zone. The purpose of undertaking these comparisons was to evaluate the performance of MM5 in the vicinity of an SST front and to determine which of the planetary boundary layer (PBL) parameterizations available best represents MABL processes. FASINEX provides an ideal dataset for this work in that it contains detailed measurements for scenarios at the two extremes: wind blowing from warm to cold water normal to a 2ЊC SST front and the converse, wind blowing from cold to warm water. For the wind blowing from warm to cold water, there is a pronounced modification of the near-surface wind field over the front, in both model results and aircraft observations. The decrease of near-surface wind speed and stress is due to a stable internal boundary layer (IBL) induced by the SST front, restricting exchange of mass and momentum between the surface and upper part of the MABL. For the cold-to-warm case, the relatively strong vertical mixing through the entire MABL over warm water dampens the response of the near-surface winds and surface stress to the SST front. The properties observed by the aircraft are simulated quite well in both cases, suggesting that MM5 captures the appropriate boundary layer physics at the mesoscale or regional scale.

2025, Physical Review Letters

On the basis of spectral-expansion Green's function theory, we theoretically describe the topography, polarization, and spatial-coherence properties of the second-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental frequency and SH local fields are very different, with highly enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-Rayleigh scattering, in agreement with recent experiments. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.

2025, Superlattices and Microstructures

The theoretical and experimental status of the Bose–Einstein Condensation (BEC) of trapped quantum well (QW) polaritons in a microcavity is presented. The results of recent experiments that have shown the possibility to create an in-plane harmonic potential trap for a two-dimensional (2D) exciton polaritons in a cavity are discussed. We report the theory of BEC and of the trapped QW

2025

The effects of interference and diffraction produced by a bidimensional structure composed of multiple and identical apertures are studied. The apertures have different shapes, sizes and spatial distribution. Such effects are competitive during the propagation, that is, in some planes the interference effects are more visible, while in others prevail the diffraction ones.

2025, Journal of Computational Electronics

A rigorous, truly two-dimensional method for threshold analysis of distributed feedback (DFB) lasers based on a coupled wave transfer matrix formalism is presented. The method makes it possible to systematically study the effect of the various structural and material properties parameters of the laser on the threshold gain and lasing frequency. Since the optical fields inside and outside the laser are very accurately represented in our analysis, the small differences in gain of pairs of longitudinal laser modes symmetrically located on both sides of the gap can be more accurately calculated than in any previous work. The analysis is applicable to gratings of any shape for both the TE and TM modes, but numerical results are given only for first-order gratings with rectangular and triangular tooth-shape. Reflectivities of the laser end facets have been calculated from first principles in some typical cases rather than treated as given parameters.

2025, Physical Review Letters

We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.

2025, APS Meeting …

The first realisation of a polariton condensate has been very recently achieved in a CdTe microcavity [Kasprzak et al., Nature 443, 409 (2006)]. The direct comparisons with theoretical calculations reveal crucial information about the... more

2024

2024, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

When characterizing an extreme ultraviolet (EUV) lithographic optical system, visible light interferometry is limited to measuring wave front aberration caused by surface figure error while failing to measure wave front errors induced by the multilayer coatings. This necessitates the development of interferometric techniques at an EUV camera’s operational wavelength (at-wavelength testing), which is typically around 13 nm. While a laser plasma source (LPS) is being developed as a lithography production source, it has generally been considered that only an undulator located at a synchrotron facility can provide the necessary laserlike point source brightness for EUV interferometry. Although an undulator-based approach has been successfully demonstrated, it would be advantageous to test a camera in its operational configuration with an LPS. We are developing the latter approach by utilizing extended source size schemes to provide usable flux throughput. A slit mounted at the source pl...