arXiv subjects

Nathaniel Hermosa

Publications and source records attributed to Nathaniel Hermosa.

15 recordsLinked to original sources

arXiv2025

The role of angular slit number and angular slit width on the OAM spectrum

The uncertainty principle sets the limit for simultaneous measurements of position and momentum, and its angular analogue is realized through angular diffraction. When a beam is spatially confined by angular slits, the uncertainty in its orbital angular momentum (OAM) increases, leading to the generation of OAM sidebands. Both the angular slit number and the angular slit width shapes the spatial confinement of the beam. In this study, we investigate this dependence of the OAM sidebands by obstructing a Gaussian beam with $N$ number of evenly spaced angular slits with angular separation $\Delta\theta_{sep}$. The power distribution among the OAM sidebands exhibits oscillatory behavior as a function of $\Delta\theta_{sep}$. We find that the number of oscillations over the full range $0 \leq \Delta\theta_{sep} \leq 2\pi/N$ is given by the ratio $\frac{|l|}{N}$. Furthermore, each OAM sideband acquires power only when $\frac{|l|}{N}$ takes an integer value, thereby demonstrating the role of the angular slit geometry to the structure of the OAM sidebands.

physics.optics↗

arXiv2025

Astrometric detection of exoplanets in face-on orbits using vortex filters

We propose a method to detect exoplanets based on their host star's intensity centroid after it passes thru a vortex filter. Based on our calculations with planets in face-on orbits, exoplanets with relative proximity to their host stars and with low mass ratios ($m_p/m_s$) can have discernible signals that can be amplified by the topological charge $\ell$ of the vortex filter. For exoplanets that have higher mass ratios and are far from their host stars, a clear signal can also be obtained but these are not affected by the value of $\ell$ and other planet detection methods may be more suitable. We present a simple table-top optical experiment to support our calculations. Our proposed method adds to the arsenal of techniques for astrometric exoplanet detection.

astro-ph.IM↗

arXiv2021

3D Fourier ghost imaging via semi-calibrated photometric stereo

We achieved three-dimensional (3D) computational ghost imaging with multiple photoresistors serving as single-pixel detectors using semi-calibrated lighting approach. We performed imaging in the spatial frequency domain by having each photoresistor obtain the Fourier spectrum of the scene at a low spectral coverage ratio of 5%. To retrieve a depth map of a scene, we inverted, apodized, and applied semi-calibrated photometric stereo (SCPS) to the spectra. At least 93.5% accuracy was achieved for the 3D results of the apodized set of images applied with SCPS in comparison with the ground truth. Furthermore, intensity error map statistics obtained at least 97.0% accuracy for the estimated surface normals using our method. Our system does not need special calibration objects or any additional optical components to perform accurate 3D imaging, making it easily adaptable. Our method can be applied in current imaging systems where multiple detectors operating at any wavelength are used for two-dimensional (2D) imaging, such as imaging cosmological objects. Employing the idea of changing light patterns to illuminate a target scene and having stored information about these patterns, the data retrieved by one detector will give the 2D information while the multiple-detector system can be used to get a 3D profile.

physics.optics↗

arXiv2021

Folded transit photometry

Transit photometry is perhaps the most successful method for detecting exoplanets to date. However, a substantial amount of signal processing is needed since the dip in the signal detected, an indication that there is a planet in transit, is minuscule compared to the overall background signal due mainly to its host star. In this paper, we put forth a doable and straightforward method to enhance the signal and reduce noise. We discuss how to achieve higher planetary signals by subtracting equal halves of the host star - a folded detection. This results in a light curve with a double peak-to-peak signal, 2R_p^2/R_s^2, compared to the usual transit. We derive an expression of the light curve and investigate the effect of two common noises: the white Gaussian background noise and the noise due to the occurrences of sunspots. We show that in both simulation and analytical expression, the folded transit reduces the effective noise by a factor of 1/sqrt(2). This reduction and the doubling of the signal enables (1) less number of transit measurements to get a definitive transiting planet signal and (2) detection of smaller planetary radii with the usual transit with the same number of transit data. Furthermore, we show that in the presence of multiple sunspots, the estimation of planetary parameters is more accurate. While our calculations may be very simple, it covers the basic concept of planetary transits.

astro-ph.EP↗

arXiv2019

Proper scaling for triangular aperture in OAM measurement

A standard triangular aperture for measuring the orbital angular momentum (OAM) of light by diffraction usually has a fixed and limited radius R. This possesses a crucial issue since for an increasing topological charge m of an OAM beam, the radius r of the beam also increases. Here, we prove experimentally our supposition. We use a dynamic triangular aperture that can be programmed to have different characteristic R to diffract beams of various OAM values. By analysing the diffraction patterns with 2d-correlation, we find a minimum bound for R. For a constant initial waist w in the spatial light modulator and a constant position z of the aperture system, we find that the radius of the aperture is unique for each m value. Interestingly, this R scales according to the literature-reported beam's rms radius. We also show that with larger aperture, a smearing effect can be seen in the diffraction patterns which becomes a setback on discerning fringes for the measurement of the topological charge value and thus of the OAM of light. Employing this limit is required if a precise measurement of the OAM of light is needed.

physics.optics↗

arXiv2019

A paraxial cloak with four lenses of different focal lengths

We demonstrate cloaking with four lenses of different focal lengths. To achieve this, we compute the separation distances between lenses such that the effective ABCD matrix is equal to just a propagation in free space. Previously, calculations using this method are restricted to 2 pairs of lenses with equal focal lengths. Our computations, on the other hand, had no such restrictions: we generalize even with an asymmetric case. We derive expressions that show the dependence of the distances on the lenses and their focal lengths. Furthermore, we propose a way to minimize the length of this cloak. Our equations reduce to the Rochester cloak when its restriction is imposed. A general paraxial cloak could be useful in advanced undergraduate experiments in optics because: 1) the limit imposed by the focal length has been lifted; and 2) there is a pedagogical benefit of doing experiments with lenses beyond the usual imaging experiments such as reinforcing concepts in Gaussian optics.

physics.optics↗

arXiv2018

Probing higher OAM of LG beams via diffraction through translated single slit

Laguerre-Gaussian (LG) beams carry orbital angular momentum (OAM) as a consequence of a singularity in their phase profile. In this work, we probe the OAM of LG beams using a movable single slit. We invoke the method of stationary phase to determine the resulting diffraction pattern for different topological charges, observe how these patterns changes when the slit is moved transversely and show that by looking at the resulting diffraction pattern for different slit positions, we can determine the orbital angular momentum of the incoming beam. Using a digital micromirror device (DMD) as a dynamic slit, we were able to access higher $\ell$ that were not possible in previous works involving slit diffraction. Our results are valuable in the study of OAM specially for beams where the current technology for detection is not yet mature, for example, beams whose wavelengths are in the terahertz regime or beams of higher energy such as, electron vortex beams.

physics.optics↗

arXiv2017

Response of QD to structured beams via convolution integrals

We propose a new expression for the response of a quadrant detector using convolution integrals. This expression is easier to evaluate by hand, exploiting the properties of the convolution. Computationally, it is also practicable to use since a large number of computer programs can right away evaluate convolutions. We use the new expression to obtain an analytical form of the response of a quadrant detector to a Gaussian beam and to Hermite-Gaussian beams in general. We compare this analytic expression for the response for the Gaussian beam with the approximations from previous studies and with a response obtained through simulations. From the response, we also obtained an analytical form for the sensitivity of the quadrant detector to a Gaussian beam. Lastly, we demonstrate the computational ease of using our new expression for the response calculating the sensitivity of the quadrant detector to the Bessel beam.

physics.ins-det↗

arXiv2017

OAM beams from incomplete computer generated holograms

We show that optical beams with orbital angular momentum (OAM) can be generated even with incomplete computer generated holograms (CGH). These holograms are made such that random portions of it do not contain any information. We observe that although the beams produced with these holograms are less intense, these beams maintain their shape and that their topological charges are not affected. Furthermore, we show that superposition of two or more beams can be created using separate incomplete CGHs interspersed together. Our result is significant especially since most method to generate beams with OAM for various applications rely on pixelated devices or optical elements with imperfections.

physics.optics↗

arXiv2015

Subluminal velocity of OAM-carrying beam

We report a consequence of the orbital angular momentum (OAM) of a beam to its group velocity. We calculate the group velocity $v_g$ of Laguerre-Gauss beam ($\emph{LG}$) with $\ell$ and at $p=0$. The $v_g$ reduction of $\emph{LG}$ beam even in free space is observed to have dependence on both orbital or winding number $\ell$ and the beam's divergence $θ_0$. We found that light possessing higher $\ell$ travels relatively slower than that with lower $\ell$ values. This suggests that light of different OAM separate in the temporal domain along propagation and it is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in light with OAM from astronomical sources and/or data transmission in free space.

physics.optics↗

arXiv2015

Propagation dynamics of vortices in Helico-Conical optical beams

We present the dynamics of optical vortices (OVs) that came from the propagation of helico-conical optical beam. This dynamics is investigated numerically by tracking the OVs at several distances using rigorous scalar diffraction theory. To ensure that our numerical calculations are correct, we compare the intensity profiles and their corresponding interferograms taken at different propagation distances between simulations and experiments. We observe that the peripheral isopolar vortices transport radially inward, toward the optical axis along the transverse spatial space as the beam propagates. When the beam has a central vortex, these vortices have significant induced angular rates of motion about the optical axis. These propagation dynamics of vortices influence the internal energy flow and the wave profile reconstruction of the beam, which can be important when deciding their applications.

physics.optics↗

arXiv2015

Frequency conversion of structured light

We demonstrate the coherent frequency conversion of structured light, optical beams in which the phase varies in each point of the transverse plane, from the near infrared (803nm) to the visible (527nm). The frequency conversion process makes use of sum-frequency generation in a periodically poled lithium niobate (ppLN) crystal with the help of a 1540-nm Gaussian pump beam. We perform far-field intensity measurements of the frequency-converted field, and verify the sought-after transformation of the characteristic intensity and phase profiles for various input modes. The coherence of the frequency-conversion process is confirmed using a mode-projection technique with a phase mask and a single-mode fiber. The presented results could be of great relevance to novel applications in high-resolution microscopy and quantum information processing.

physics.optics↗

arXiv2014

Direction-sensitive transverse velocity measurement by phase-modulated structured light beams

The use of structured light beams to detect the velocity of targets moving perpendicularly to the beam's propagation axis opens new avenues for remote sensing of moving objects. However, determining the direction of motion is still a challenge since detection is usually done by means of an interferometric setup which only provides an absolute value of the frequency shift. Here, we put forward a novel method that addresses this issue. It uses dynamic control of the phase in the transverse plane of the structured light beam so that the direction of the particles' movement can be deduced. This is done by noting the change in the magnitude of the frequency shift as the transverse phase of the structured light is moved appropriately. We demonstrate our method with rotating micro-particles that are illuminated by a Laguerre-Gaussian beam with a rotating phase about its propagation axis. Our method, which only requires a dynamically configurable optical beam generator, can easily be used with other types of motion by appropriate engineering and dynamic modulation of the phase of the light beam.

physics.optics↗

arXiv2014

Measuring the translational and rotational velocity of particles in helical motion using structured light

We measure the rotational and translational velocity components of particles moving in helical motion using the frequency shift they induced to the structured light beam illuminating them. Under Laguerre-Gaussian mode illumination, a particle with a helical motion reflects light that acquires an additional frequency shift proportional to the angular velocity of rotation in the transverse plane, on top of the usual frequency shift due to the longitudinal motion. We determined both the translational and rotational velocities of the particles by switching between two modes: by illuminating with a Gaussian beam, we can isolate the longitudinal frequency shift; and by using a Laguerre-Gaussian mode, the frequency shift due to the rotation can be determined. Our technique can be used to characterize the motility of microorganisms with a full three-dimensional movement.

physics.optics↗

arXiv2012

Weak interference in the high-signal regime

Weak amplification is a signal enhancement technique which is used to measure tiny changes that otherwise cannot be determined because of technical limitations. It is based on the existence of a special type of interaction which couples a property of a system, i.e., polarization or which-path information, with a separate degree of freedom, i.e., transverse position or frequency. Unfortunately, the weak amplification process is generally accompanied by severe losses of the detected signal, which limits the applicability of the weak amplification concept. However, we will show here that since the weak measurement concept is essentially an interference phenomena, it should be possible to use the degree of interference to get relevant information about the physical system under study in a more general scenario, where the signal is not severely depleted (high-signal regime). This can widen the range of systems where the weak measurement concept can be applied. In this scenario, which can be called generally weak interference, the idea of weak value does not convey any useful information.

quant-ph↗