High Spatial Frequency Research Articles

Speckle Noise-Free Interconnective Holographic Projection

Generally, speckle noise is regarded as unavoidable in holographic projection, and it results from unexpected high spatial frequency components of diffracted light at the sharp edge of pixel openings in a spatial light modulator. Speckle noise typically reduces image contrast and degrades the image quality of the holographic projection. In this study, we propose a novel holographic optical interconnection method free of speckle noise in holographic projection. This optical interconnection is achieved by using a holographic optical element (HOE). The HOE is designed to reconstruct Gaussian beams with low divergence. These Gaussian beams become points which form target images at desired depths. Since the Gaussian beam from the HOE does not share the same position with other Gaussian beams, there is no interference at the projection image. Therefore, the image is composed of the points from the Gaussian beams and there is no reason for unexpected high spatial frequency noise to appear on the image. In this paper, we fabricate the HOE, produced with our specially manufactured hologram printer, where the directions of two Gaussian beams with low divergence are controlled by goniometers. We experimentally demonstrated a speckle noise-free interconnective holographic projection. Two images are successfully formed at different depths by optically connecting two points in pairs.

Shock Boundary Layer Interaction and Aero-Optical Effects in a Transonic Flow over Hemisphere-on-Cylinder Turrets

Hemisphere-on-cylinder turrets are the main airborne optical platform structure. However, an unsteady shock boundary layer interaction (SBLI) would act on flow separation and turbulent wake, which causes serious aero-optical effects with high spatial and temporal frequency characteristics. In this paper, the SBLI phenomenon of a hemisphere-on-cylinder turret is recorded in a wind tunnel at Ma = 0.7 using shadowing and Mach-Zehnder interferometer measurements. Its wavefront distortion is measured using the Shack-Hartmann measurement. The detached eddy simulation (DES) based on SST k - ω turbulence model and ray-tracing methods are used to reproduce the transonic flow and optical aberration. Experiments and simulations suggest that the SBLI causes the flow to separate earlier relative to a subsonic flow over the turret. The time-averaged root-mean-square of optical path difference (OPD) over the beam aperture is 0.56 λ∼0.59 λ with λ as the wavelength, while the root-mean-square of the time-averaged OPD is about 0.45 λ. The local shock and wavefront distortion have dual peak frequencies at S t D = f D / U ∞ = 0.24 and 0.34, different from the single-peak-frequency phenomenon of a subsonic flow over turrets. Fast model decomposition of wavefront can be performed by proper orthogonal decomposition (POD) of its Zernike coefficients. The first two modes contain the shock’s reciprocating motion.

Predicting atmospheric background number concentration of ice-nucleating particles in the Arctic

Abstract. Mixed-phase clouds (MPCs) can have a net warming or cooling radiative effect on Earth's climate influenced by the phase and concentration of cloud particles. They have received considerable attention due to high spatial coverage and occurrence frequency in the Arctic. To initiate ice formation in MPCs at temperatures above −38 ∘C, ice-nucleating particles (INPs) are required, which therefore have important implications on the radiative properties of MPCs by altering the ice-to-liquid ratio of hydrometeors. As a result, constraining ambient INP concentrations could promote accurate representation of cloud microphysical processes and reduce the uncertainties in estimating the cloud-phase-related climate feedback in climate models. Currently, INP parameterizations are lacking for remote Arctic environments. Here we present INP number concentrations and their variability measured in Ny-Ålesund (Svalbard) at temperatures between 0 and −30 ∘C. No distinguishable seasonal difference was observed from 12 weeks of field measurements during October and November 2019 and March and April 2020. Compared to existing studies, the absence of a seasonal difference is not surprising, as most seasonal differences are reported for summer versus winter time INP concentrations. In addition, correlating INP concentrations to aerosol physical properties was not successful. Therefore, we propose a lognormal-distribution-based parameterization to predict Arctic INP concentration solely as a function of temperature, specifically for the transition seasons autumn and spring to fill in the data gap in the literature pertaining to these seasons. In practice, the parameterized variables allow for (i) the prediction of the most likely INP concentrations and (ii) the retrieval of the governing distribution of INP concentrations at given temperatures in the Arctic.

Behavioral signatures of Y-like neuronal responses in human vision

Retinal ganglion cells initiating the magnocellular/Y-cell visual pathways respond nonlinearly to high spatial frequencies (SFs) and temporal frequencies (TFs). This nonlinearity is implicated in the processing of contrast modulation (CM) stimuli in cats and monkeys, but its contribution to human visual perception is not well understood. Here, we evaluate human psychophysical performance for CM stimuli, consisting of a high SF grating carrier whose contrast is modulated by a low SF sinewave envelope. Subjects reported the direction of motion of CM envelopes or luminance modulation (LM) gratings at different eccentricities. The performance on SF (for LMs) or carrier SF (for CMs) was measured for different TFs (LMs) or carrier TFs (CMs). The best performance for LMs was at lower TFs and SFs, decreasing systematically with eccentricity. However, performance with CMs was bandpass with carrier SF, largely independent of carrier TF, and at the highest carrier TF (20 Hz) decreased minimally with eccentricity. Since the nonlinear subunits of Y-cells respond better at higher TFs compared to the linear response components and respond best at higher SFs that are relatively independent of eccentricity, these results suggest that behavioral tasks employing CM stimuli might reveal nonlinear contributions of retinal Y-like cells to human perception.

Precise phase retrieval for propagation-based images using discrete mathematics

The ill-posed problem of phase retrieval in optics, using one or more intensity measurements, has a multitude of applications using electromagnetic or matter waves. Many phase retrieval algorithms are computed on pixel arrays using discrete Fourier transforms due to their high computational efficiency. However, the mathematics underpinning these algorithms is typically formulated using continuous mathematics, which can result in a loss of spatial resolution in the reconstructed images. Herein we investigate how phase retrieval algorithms for propagation-based phase-contrast X-ray imaging can be rederived using discrete mathematics and result in more precise retrieval for single- and multi-material objects and for spectral image decomposition. We validate this theory through experimental measurements of spatial resolution using computed tomography (CT) reconstructions of plastic phantoms and biological tissues, using detectors with a range of imaging system point spread functions (PSFs). We demonstrate that if the PSF substantially suppresses high spatial frequencies, the potential improvement from utilising the discrete derivation is limited. However, with detectors characterised by a single pixel PSF (e.g. direct, photon-counting X-ray detectors), a significant improvement in spatial resolution can be obtained, demonstrated here at up to 17%.

Visual experience has opposing influences on the quality of stimulus representation in adult primary visual cortex.

Transient dark exposure, typically 7-10 days in duration, followed by light reintroduction is an emerging treatment for improving the restoration of vision in amblyopic subjects whose occlusion is removed in adulthood. Dark exposure initiates homeostatic mechanisms that together with light-induced changes in cellular signaling pathways result in the re-engagement of juvenile-like plasticity in the adult such that previously deprived inputs can gain cortical territory. It is possible that dark exposure itself degrades visual responses, and this could place constraints on the optimal duration of dark exposure treatment. To determine whether eight days of dark exposure has a lasting negative impact on responses to classic grating stimuli, neural activity was recorded before and after dark exposure in awake head-fixed mice using two-photon calcium imaging. Neural discriminability, assessed using classifiers, was transiently reduced following dark exposure; a decrease in response reliability across a broad range of spatial frequencies likely contributed to the disruption. Both discriminability and reliability recovered. Fixed classifiers were used to demonstrate that stimulus representation rebounded to the original, pre-deprivation state, thus dark exposure did not appear to have a lasting negative impact on visual processing. Unexpectedly, we found that dark exposure significantly stabilized orientation preference and signal correlation. Our results reveal that natural vision exerts a disrupting influence on the stability of stimulus preference for classic grating stimuli and, at the same time, improves neural discriminability for both low and high-spatial frequency stimuli.

Both low and high spatial frequencies drive the early posterior negativity in response to snake stimuli

Previous event-related potential (ERP) studies have shown that snake pictures elicit greater early posterior negativity (EPN) compared to other animal pictures. The EPN reflects early selective visual processing of emotionally significant stimuli. Evidence for the role that high and low spatial frequencies play in the early detection of snakes is still inconsistent. The current study aims to clarify this by studying the effect of high and low spatial frequencies on the elevated EPN for snakes separately. Using a rapid serial visual presentation paradigm, participants viewed images of snakes, spiders and birds in three different conditions of filtered spatial frequencies: high spatial frequency, low spatial frequency, and full spatial frequency (the original image). P1 and mean EPN activity in a time window of 225–300 ms after stimulus onset were measured at the occipital cluster (O1, O2, Oz). The results show smaller P1 amplitudes and shorter P1 latencies in response to full-spectrum snake pictures compared to full-spectrum spider and bird pictures, and an increased EPN in response to snake pictures compared to spider and bird pictures in all three filtering conditions. The EPN in response to full-spectrum snake pictures was larger than the EPN in response to filtered snake images. No difference in EPN was found between the snake pictures in the high and low spatial frequency conditions. The results suggest that the roles of high and low spatial frequencies in early automatic attention to snakes are equally important.

Measurement of shock roughness due to phase plate speckle imprinting relevant for x-ray diffraction experiments on 3rd and 4th generation light sources

Laser-shock compression experiments at 3rd and 4th generation light sources generally employ phase plates, which are inserted into the beamline to achieve a repeatable intensity distribution at the focal plane. Here, the laser intensity profile is characterized by a high-contrast, high-frequency laser speckle. Without sufficient smoothing, these laser non-uniformities can translate to a significant pressure distribution within the sample layer and can affect data interpretation in x-ray diffraction experiments. Here, we use a combination of one- and two-dimensional velocity interferometry to directly measure the extent to which spatial frequencies within the laser focal spot intensity pattern are smoothed out during propagation within the laser plasma and a polyimide ablator. We find that the use of thicker polyimide layers results in spatially smoother shock fronts, with the greatest degree of smoothing associated with the highest spatial frequencies. Focal spots with the smallest initial speckle separation produce the most rapid smoothing. Laser systems that employ smoothing by spectral dispersion techniques to rapidly modulate the focal plane intensity distribution are shown to be the most effective ones in producing a spatially smooth shock front. We show that a simple transport model combined with the known polyimide Hugoniot adequately describes the extent of shock smoothness as a function of polyimide thickness. Our results provide a description of spatial structure smoothing across a shock front, which can be used to design targets on x-ray free electron laser facilities.

Compact structured illumination microscopy with high spatial frequency diffractive lattice patterns.

Structured illumination microscopy (SIM) enables live-cell super-resolution imaging with wide field of view (FOV) and high imaging speed, but the illumination system is usually bulky. With the advantages of small structure and high efficiency, lattice patterns assisted by diffractive optical elements (DOEs) have been used for structured illumination in SIM. But it is still challenging to raise the spatial frequency of diffractive lattice patterns when using traditional DOE design method, and thus the super-resolution imaging performance is restricted. In this paper, we propose a novel design method for DOE to generate lattice patterns with spatial frequency close to the cut-off frequency. It is the first time to obtain a lattice pattern with such high spatial frequency by diffractive optics. Finally, the proposed SIM achieves a lateral resolution of 131 nm at 519 nm fluorescent light while maintaining an original size as a standard inverted fluorescence microscope by only inserting a single well-designed DOE in the illumination optical path, which may promote this compact SIM applied in super-resolution imaging field.

Suprathreshold Contrast Perception Is Altered by Long-term Adaptation to Habitual Optical Blur.

PurposeTo investigate whether visual experience with habitual blur alters the neural processing of suprathreshold contrast in emmetropic and highly aberrated eyes.MethodsA large stroke adaptive optics system was used to correct ocular aberrations. Contrast constancy was assessed psychophysically in emmetropic and keratoconic eyes using a contrast matching paradigm. Participants adjusted the contrasts of gratings at various spatial frequencies to match the contrast perception of a reference grating at 4 c/deg. Matching was done both with fully corrected and uncorrected ocular aberrations. Optical correction allowed keratoconus patients to perceive high spatial frequencies that they have not experienced for some time.ResultsEmmetropic observers exhibited contrast constancy both with their native aberrations and when their aberrations were corrected. Keratoconus patients exhibited contrast constancy with their uncorrected, native optics but they did not exhibit constancy during adaptive optics correction. Instead. they exhibited striking underconstancy: they required more contrast at high spatial frequencies than the contrast of the 4-c/deg stimulus to make them seem to have the same contrast.ConclusionsThe presence of contrast constancy in emmetropes and keratoconus patients viewing with their native optics suggests that they have learned to amplify neural signals to offset the effects of habitual optical aberrations. The fact that underconstancy was observed in keratoconus patients when their optics were corrected suggests that they were unable to learn the appropriate neural amplification because they did not have experience with fine spatial detail. These results show that even adults can learn neural amplification to counteract the effects of their own optical aberrations.

Evidence of Serial Dependence from Decoding of Visual Evoked Potentials.

It is well known that recent sensory experience influences perception, recently demonstrated by a phenomenon termed "serial dependence." However, its underlying neural mechanisms are poorly understood. We measured ERP responses to pairs of stimuli presented randomly to the left or right hemifield. Seventeen male and female adults judged whether the upper or lower half of the grating had higher spatial frequency, independent of the horizontal position of the grating. This design allowed us to trace the memory signal modulating task performance and also the implicit memory signal associated with hemispheric position. Using classification techniques, we decoded the position of the current and previous stimuli and the response from voltage scalp distributions of the current trial. Classification of previous responses reached full significance only 700 ms after presentation of the current stimulus, consistent with retrieval of an activity-silent memory trace. Cross-condition classification accuracy of past responses (trained on current responses) correlated with the strength of serial dependence effects of individual participants. Overall, our data provide evidence for a silent memory signal that can be decoded from the EEG potential, which interacts with the neural processing of the current stimulus. This silent memory signal could be the physiological substrate subserving at least one type of serial dependence.SIGNIFICANCE STATEMENT The neurophysiological underpinnings of how past perceptual experience affects current perception are poorly understood. Here, we show that recent experience is reactivated when a new stimulus is presented and that the strength of this reactivation correlates with serial biases in individual participants, suggesting that serial dependence is established on the basis of a silent memory signal.

Compact integrated aberration-compensating module for a 9 kW Nd:YAG slab laser based on an off-axis stable-unstable resonator.

An integrated aberration-compensating module (IACM), consisting mainly of an adjustable slab-aberration compensator, a one-dimensional Shack-Hartmann wavefront sensor, and a data processor, which meet the urgent requirements of correcting the specific wavefront aberrations of a slab laser based on an off-axis stable-unstable resonator, is designed and experimentally demonstrated. Benefits include compactness, robustness, simplicity, automation, and cost-effectiveness. The particular wavefront aberrations of the 9 kW level quasi-continuous-wave Nd:YAG slab laser, which have characteristics of asymmetry, large amplitude and gradient, high spatial frequency, and low temporal frequency, were measured and theoretically analyzed. In the experiment, the wavefront aberrations of the slab laser were corrected by the IACM. At the average output power of 9 kW, the diffraction-limited factor β was improved from 20.3 times diffraction limit (DL) to 3.6 times DL. The peak-to-valley and root-mean-square values of aberrations were reduced from 9.6 to 0.85 µm and from 2.86 to 0.18 µm within five iterations of the IACM, respectively. Moreover, The IACM is capable of maintaining the compensating surface figure after power-off.

Hourly assimilation of different sources of observations including satellite radiances in a mesoscale convective system case during RELAMPAGO campaign

This paper evaluates the impact of assimilating high-resolution surface networks and satellite observations using the WRF-GSI-LETKF over central and north eastern Argentina where the surface and upper air observing networks are relatively coarse. A case study corresponding to a huge mesoscale convective system (MCS) that developed during November 22, 2018 was used. The accumulated precipitation associated with this MCS was quite high, exceeding 200 mm over northern Argentina and Paraguay. The MCS developed during the Intense Observing Period (IOP) of the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. The GSI-4DLETKF data assimilation package is used to produce analyses by assimilating observations every hour with 10-km horizontal grid spacing and a 60-member multiphysics ensemble. Four assimilation experiments are conducted using different sets of observations: CONV, consisting of conventional observations from NCEP’s prepBUFR files; AWS, combining CONV and dense automatic surface weather station networks (AWS), SATWND, combining AWS with satellite-derived winds, and RAD, including SATWND; and satellite radiances from different microwave and infrared sensors. The assimilation of observations with high temporal and spatial frequency generates an important impact on the PBL, primarily on the precipitable water content, that leads to the development of deep convection and heavy precipitation closer to the observed in this case study. The assimilation of radiance observations produces a better development of the convection mainly during the mature state of the MCS leading to an increase in the accumulated precipitation. Ensemble forecasts initialized from each experiment were also simulated to evaluate their skill to predict precipitation. The hourly assimilation of the observations in AWS, SATWND, and RAD helped to improve the precipitation forecast.

Dimensional X-Ray computed tomography: Apparent feature form error and its effect on measurement tasks

X-ray computed tomography (XCT) provides a unique set of dimensional measurement capabilities suitable for assessing complex geometry. However, due to the origins of XCT as a medical imaging method and qualitative non-destructive examination technique, only recently has XCT been rigorously investigated as a dimensional metrology tool. Although the data produced via XCT may be leveraged with conventional coordinate metrology techniques, the instrument physics and volumetric reconstruction methods which govern the accuracy and precision of the data are complex, workpiece-specific, and non-negligible. In particular, there is minimal prior work which has studied complex multi-step metrology tasks such as datum reference frame (DRF) construction and feature position measurement. In this work, a qualified artifact was used to evaluate the fitness of XCT for such a task. Multiple XCT systems were used, and multiple instrument magnification levels compared. The form error of planar and cylindrical features was evaluated. Further, the influence of individual feature reconstruction on the development of datums and upstream position measurements was studied. It was found that negative, i.e., bore-like, and positive, i.e., pin-like configurations of certain features were subject to distinct XCT artifact effects which caused upstream measurement errors when these features were used to construct a DRF. High magnification and X-ray scatter produced high spatial frequency noise in surface reconstruction while beam hardening and beam penetration distance variation produced gross apparent form error. The latter was associated with greater measurement errors in feature position measurement within an DRF.

Real-Time Integration Center of Mass (riCOM) Reconstruction for 4D STEM.

A real-time image reconstruction method for scanning transmission electron microscopy (STEM) is proposed. With an algorithm requiring only the center of mass of the diffraction pattern at one probe position at a time, it is able to update the resulting image each time a new probe position is visited without storing any intermediate diffraction patterns. The results show clear features at high spatial frequency, such as atomic column positions. It is also demonstrated that some common post-processing methods, such as band-pass filtering, can be directly integrated in the real-time processing flow. Compared with other reconstruction methods, the proposed method produces high-quality reconstructions with good noise robustness at extremely low memory and computational requirements. An efficient, interactive open source implementation of the concept is further presented, which is compatible with frame-based, as well as event-based camera/file types. This method provides the attractive feature of immediate feedback that microscope operators have become used to, for example, conventional high-angle annular dark field STEM imaging, allowing for rapid decision-making and fine-tuning to obtain the best possible images for beam-sensitive samples at the lowest possible dose.

Aberration-free synthetic aperture phase microscopy based on alternating direction method

Objective measurements of the morphology and dynamics of label-free cells and tissues can be achieved by quantitative phase with low phototoxicity and no photobleaching. Modern quantitative phase imaging is developing toward high throughput and a huge amount of data. The quantitative nature makes it susceptible to optical aberrations when high spatial-frequency content of the object spectrum is recorded by using synthetic aperture. We present an effective and straightforward global phase aberration-free synthetic-aperture phase microscopy (AF-SAPM). We introduce alternating direction method (ADM) in the variable splitting strategy. The optimization in optical fields is decomposed into two solutions with object terms and aberration terms. The inverse problem of aberration extraction is solved by imposing the sparsity regularization on the object and coefficients of polynomial bases. The background aberration in different angle of oblique illumination can be directly decomposed with the Zernike polynomials. Global phase aberration can be suppressed for faithful synthetic aperture reconstruction, which outperforms the existing solutions. We demonstrate the availability of the proposed method in quantitative monitoring of endocrine tumor with highly variable phases.

Flattening laser frequency comb spectra with a high dynamic range, broadband spectral shaper on-a-chip.

Spectral shaping is critical to many fields of science. In astronomy for example, the detection of exoplanets via the Doppler effect hinges on the ability to calibrate a high resolution spectrograph. Laser frequency combs can be used for this, but the wildly varying intensity across the spectrum can make it impossible to optimally utilize the entire comb, leading to a reduced overall precision of calibration. To circumvent this, astronomical applications of laser frequency combs rely on a bulk optic setup which can flatten the output spectrum before sending it to the spectrograph. Such flatteners require complex and expensive optical elements like spatial light modulators and have non-negligible bench top footprints. Here we present an alternative in the form of an all-photonic spectral shaper that can be used to flatten the spectrum of a laser frequency comb. The device consists of a circuit etched into a silicon nitride wafer that supports an arrayed-waveguide grating to disperse the light over hundreds of nanometers in wavelength, followed by Mach-Zehnder interferometers to control the amplitude of each channel, thermo-optic phase modulators to phase the channels and a second arrayed-waveguide grating to recombine the spectrum. The demonstrator device operates from 1400 to 1800 nm (covering the astronomical H band), with twenty 20 nm wide channels. The device allows for nearly 40 dBs of dynamic modulation of the spectrum via the Mach-Zehnders , which is greater than that offered by most spatial light modulators. With a smooth spectrum light source (superluminescent diode), we reduced the static spectral variation to ∼3 dB, limited by the properties of the components used in the circuit. On a laser frequency comb which had strong spectral modulations, and some at high spatial frequencies, we nevertheless managed to reduce the modulation to ∼5 dBs, sufficient for astronomical applications. The size of the device is of the order of a US quarter, significantly cheaper than their bulk optic counter parts and will be beneficial to any area of science that requires spectral shaping over a broad range, with high dynamic range, including exoplanet detection.

Far-field sub-diffraction optical imaging using near-field illumination by optoplasmonic hybrid materials

Here, we propose a method to fabricate large-scale optoplasmonic hybrid materials (OHMs) as a near-field illumination source for sub-diffraction imaging through a traditional optical microscope. An OHM is comprised of a metal/dielectric multilayer coated substrate and a microcylinder (MC) placed on top of the multilayer. Under the dark-field illumination of a traditional optical microscope, the photonic nanojet (PNJ) generated by the MC and the electric field produced on the substrate surface by the photonic–plasmonic interaction work as the near-field illumination source for an object placed on the substrate near the PNJ. High spatial frequencies of the object can be shifted to the passband of the optical microscope and weak scattering signals of the object can be enhanced upon the near-field illumination. Low-contrast objects, such as a 300-nm-diameter SiO2 nanoparticle array, two 100-nm-diameter polystyrene nanoparticles spaced ∼86 nm apart, and Escherichia coli can be resolved using the optical microscope. In addition, the field of view (FOV) is rectangular, the length of the FOV depends on the length of the MC, and the width relates to the diameter of the MC. The proposed method is wide-field, label-free, direct, noninvasive, and far-field, and it presents the potential of super-resolution imaging of unlabeled biological samples using a traditional optical microscope.

Surgical outcomes and observation in exotropia cerebral palsy children with cortical visual impairment

PurposeCortical visual impairment (CVI) is the common cause of pediatric visual impairment in cerebral palsy (CP) while exotropia is the most common strabismus associated with CP. We aim to observe the strabismic surgery outcomes in pediatric patients with CP and CVI.MethodOur medical records were collected from pediatric patients treated in our hospital from May 1, 2017 to Jan 1, 2022. With normal intelligence assessment and diagnosis of exotropia in children with CP and CVI, microsurgeries were performed under intravenous combined inhalation anesthesia. The strabismus was examined by the prism test under best vision correction and the contrast sensitivity testing (CST) was measured at five levels of spatial frequencies.ResultA total of 38 exotropia patients with CP and CVI were identified and included for analysis during the study period with age ranged from 5 to 12 years (mean 8.45 years) and mean follow up duration was 8.7 months (6–42 months). After bilateral lateral rectus recession (with/without medial rectus resection or inferior oblique transposition), the exotropia amount of participants were obviously revealed from − 30 ~ − 140 (median, IQR: − 50, 40) prism diopters (PD) preoperatively to 0 ~ − 15 (0, 5) PD postoperatively. Statistically significantly improvements were observed at all levels of spatial frequency on CST postoperatively, especially at high spatial frequency areas (p < 0.05).ConclusionOur results demonstrated that the effect of strabismus surgery on exotropia in children with CP and CVI were stable and monocular contrast sensitivity post- operation increased significantly at all spatial frequencies levels.

LIPSS for SERS: Metal Coated Direct Laser Written Periodic Nanostructures for Surface Enhanced Raman Spectroscopy

AbstractA novel method of fabricating large‐area, low‐cost surface‐enhanced Raman spectroscopy (SERS) substrates is introduced which yields densely nanostructured surfaces utilizing laser‐induced periodic surface structuring (LIPSS) of crystalline silicon (Si). Two different interaction regimes yield low spatial frequency (LSFL) and high spatial frequency (HSFL) LIPSS patterns. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50–70 nm thick Ag layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by LSFL and HSFL nature of the structure. The SERS substrates are found to be capable of detecting a Raman analyte down to 10−11 m. SERS performance of the Ag deposited substrates at 532, 660, and 785 nm excitation wavelengths is compared. Both LSFL and HSFL Si surfaces with 70 nm thick Ag are found to exhibit the strongest SERS under 660 nm excitation exhibiting Raman enhancement factors (EFs) as high as 109. The Raman EFs are calculated both by SERS spectra experimentally, and using finite‐elements method simulation of the electric field enhancement where a good agreement is found.