Ruben Ramos-Garcia

Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) | INAOE · Optics Coordination

Colloidal crystal plays a major role in novel optical devices such as waveguides, photonic crystals, and colloidal crystal lasers, among others. It has been known that colloidal crystals may self-assemble due to optical, electric, or chemical potentials, and light-induced thermal effects, such as thermophoresis and convective currents. In this work...

The capacity to capture images using RGB silicon-based sensors in the visible (VIS) can be limited in outdoor environmental conditions. Due to illumination variations of the scene or scattering effects caused by the interaction of light with micrometer-size particles in the rain, fog, or smoke, limiting the depth of visibility and the level of cont...

In recent years, it had been an evolution in the sensors used by vision systems. Different technologies from RGB cameras, IR cameras, LIDAR, RADAR, or sensor combinations can work in different spectrum bands. A new alternative to the vision system is the single-pixel camera (SPC), an architecture based on the compressive sensing theory for 2D recon...

The captured images in scattering scenarios are a challenge to solve for the vision systems for Unmanned Flight Vehicles (UFVs). Currently, research has been conducted on the use of sensors in the near-infrared (NIR) part of the spectra as an option for the RGB camera in scenarios with higher scattering (fog or rain), because to the diameter of wat...

The captured images in scattering scenarios are a challenge to solve for the vision systems for Unmanned Flight Vehicles (UFVs). Currently, research has been conducted on the use of sensors in the near-infrared (NIR) part of the spectra as an option for the RGB camera in scenarios with higher scattering (fog or rain), because to the diameter of wat...

In the last decade, the vision systems have improved their capabilities to capture 3D images in bad weather scenarios. Currently, there exist several techniques for image acquisition in foggy or rainy scenarios that use infrared (IR) sensors. Due to the reduced light scattering at the IR spectra it is possible to discriminate the objects in a scene...

1,4-Dioxane is a pervasive and persistent contaminant in numerous aquifers. Although the median concentration in most contaminant plumes is in the microgram per liter range, a subset of sites have contamination in the milligram per liter range. Most prior studies that have examined 1,4-dioxane concentrations in the hundreds of milligrams per liter...

Single-pixel imaging is a technique that can reconstruct an image of a scene by projecting a series of spatial patterns on an object and capturing the reflected light by a single photodetector. Since the introduction of the compressed sensing method, it has been possible to use random spatial patterns and reduce its number below the Nyquist-Shannon...

In this work, we perform drilling of micro-holes and formation of microbubbles in titanium thin films. All these processes occur due the high titanium absorption at near infrared wavelength, the superheating of titanium produce high quality micro-holes which can be create simultaneously with different laser beam spots. Otherwise, when titanium inte...

The detection scheme based on phase detection of SPR response was developed. We show that the proposed biosensing scheme can detect SARS-CoV-2 genetic material with high specificity, low detection limit and short detection time.

In this paper, we propose a method for single-pixel 2D/3D imaging to be applied in hyperspectral camerasoperating in outdoor applications in unmanned aerial vehicles (UAVs). In rain rich environments, if camerasystems operating in the visible range are used, alongside the atmospheric absorption that inevitably takesplace, additional interactions oc...

We present a method to improve the quality of 2D/3D single-pixel reconstructed images using active illumination in the near-infrared (NIR) part of the spectra for outdoor applications in presence or rain. The proposed solution is based on an array of NIR LEDs emitting active illumination patterns in the wavelength 1550 nm to be detected by an InGaA...

In this article, we propose a method to be used for the reconstruction of single-pixel near-infrared (SPI-NIR) low-resolution 2D images using active illumination with a peak wavelength on 1550 nm, that is based on Batch Orthogonal Matching (Batch-OMP) processing algorithms and a region definition in the projection sequence of Hadamard illumination...

In this Letter, we show 3D steady-state trapping and manipulation of vapor bubbles in liquids employing a low-power continuous-wave laser using the Marangoni effect. Light absorption from photodeposited silver nanoparticles on the distal end of a multi-mode optical fiber is used to produce bubbles of different diameters. The thermal effects produce...

In recent years, 3D reconstruction has become a challenging task for navigation systems. Therefore, different technologies such as RGB cameras, LIDARs, or RADAR can capture information from the environment and perform 3D reconstruction. In an environment of high dispersion and low illumination, it is necessary to have a robust solution that operate...

Organic light emitting diodes (OLEDs) are very attractive light sources because they are large area emitters and, can in principle, deposited on flexible substrates. These features make them suitable for ambulatory photodynamic therapy (PDT), in fact there are a few reports of in vitro or in vivo OLED based PDT studies for cancer or microbial inhib...

In this paper, we present a novel mechanism for the generation of laser pulses based on the phenomenon of thermocavitation. Thermocavitation bubbles were generated within a glass cuvette filled with copper nitrate dissolved in water, where the tip of an optical fiber was placed very close to the bubble generation region. Once the bubble is generate...

An experimental and theoretical study on the 3D trapping and manipulation of microbubbles by means low power laser-induced temperature gradients induced in ethanol by bulk light absorption (λ = 1550 nm) is presented. Two optical fibers were used: One for bubble generation (OFG) and the other for both trapping and manipulation (OFT). Light from a Q-...

In this paper, a theoretical analysis of a vision system for 2D/3D single-pixel imaging using principles of compressed sensing and Indirect-Time-of-flight measurements is presented. The goal is to use this system for autonomous drone navigation in environments with adverse conditions where typical sensors used by RGB or RGB-Depth cameras typically...

In recent time there has been an increasing amount of interest in developing novel techniques for the generation of complex vector light beams. Amongst these, digital holography stands out as one of the most flexible and versatile with almost unlimited freedom in the generation of scalar and complex vector light fields featuring arbitrary polarisat...

The inclusion of thermal effects in optical manipulation has been explored in diverse experiments, increasing the possibilities for applications in diverse areas. In this Letter, the results of combined optical and thermal manipulation in the vicinity of a highly absorbent hydrogenated amorphous silicon layer, which induces both the generation of c...

We present a case study for a time-of-flight 3D imaging system using single-pixel imaging (SPI) accompanied by the Time-of-flight (ToF) principle for drone applications involving autonomous navigation. In present, an alternative work present a solution to conventional RGB or RGB-depth sensors , limited when working under poor visibility conditions,...

During the last decades the radio detecting and ranging (RADAR) technology underwent an evolution transiting from the linear-frequency-modulated (LFM) systems developed in the 1970s, up to the orthogonal frequency-division multiplexing (OFDM) systems developed in the early 2000s. In mid 2010s, systems were proposed that combined the radar principle...

The compressive sensing (CS) technique is a novel tool used to reconstruct images using fewer samples, normally sparse in the transform domain, than those required by conventional imaging systems. However, the methods applied for signal reconstruction within the CS approach still present some problems in the implementation, mainly due to their inte...

We present a case study for a time-of-flight (ToF) 3D imaging system using single-pixel imaging (SPI) approach based on compressive sensing (CS), accompanied by the Time-of-flight (ToF) principle applied to four reference points of the 2D image created and then mapped to the rest of the SPI generated virtual pixels. In this analysis we have develop...

The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pu...

In recent time there has been an increasing amount of interest in developing novel techniques for the generation of complex vector light beams. Amongst these, digital holography stands out as one of the most flexible and versatile with almost unlimited freedom to generate scalar and vector light beams with arbitrary polarisation distributions and s...

Numerical simulations using the Finite-Difference Time-Domain method were used to study the propagation of an acoustic wave within a truncated ellipsoidal cavity. Based in our simulations, a fluidic device was designed and fabricated using a 3D printer in order to focus an acoustic wave more efficiently and expel a liquid jet. The device consists o...

Background: We compared the effectiveness of a single irradiation vs repetitive irradiation of light, for in vitro photodynamic inactivation (PDI) of Candida albicans and Trichophyton mentagrophytes, by using methylene blue (MB) and rose bengal (RB) as photosensitizers (PS). Methods: MB from 5 to 60 μM and RB from 0.5 to 10 μM, with energy densi...

Visualization of blood vessels is a fundamental task in the evaluation of the health and biological integrity of tissue. Laser speckle contrast imaging (LSCI) is a non-invasive technique to determine the blood flow in superficial or exposed vasculature. However, the high scattering of biological tissue hinders the visualization of those structures....

To visualize blood vessels in Laser Speckle Imaging (LSI) is an important task since parameters such as blood pressure, relative blood flow and vessel size can be estimated through of them to then be used in medical diagnostics. LSI is the common method for visualizing blood vessels however, resulting images contain a high level of noise. For impro...

Pseudonocardia dioxanivorans strain BERK-1 grows aerobically with 1,4-dioxane as its sole substrate. Reported here is its draft genome sequence, with a size of 7.1 Mbp. Key genes are highlighted in this article. BERK-1 exhibits a reduced level of cell aggregation and adherence to surfaces compared to those ofP. dioxanivoransCB1190, giving it an app...

The generation and manipulation of microbubbles by means of temperature gradients induced by low power laser radiation is presented. A laser beam (λ = 1064 nm) is divided into two equal parts and coupled to two multimode optical fibers. The opposite ends of each fiber are aligned and separated a distance D within an ethanol solution. Previously, si...

This is a study motivated by the need to develop a needle-free device for eliminating major global healthcare problems caused by needles. The generation of liquid jets by means of a continuous-wave laser, focused into a light absorbing solution, was studied with the aim of developing a portable and affordable jet injector. We designed and fabricate...

A high-velocity fluid stream ejected from an orifice or nozzle is a common mechanism to produce liquid jets in inkjet printers or to produce sprays among other applications. In the present research, we show the generation of liquid jets of controllable direction produced within a sessile water droplet by thermocavitation. The jets are driven by an...

Laser Speckle Imaging (LSI) is a non-invasive optical technique used to measure relative blood speed and visualize superficial blood vessels (limited to some hundreds of microns depth) due to the highly scattering nature of the tissue. In this work, digital image processing techniques are implemented to improve the visualization of deep blood vesse...

Visualization of deep blood vessels in speckle images is an important task as it is used to analyze the dynamics of the blood flow and the health status of biological tissue. Laser speckle imaging is a wide-field optical technique to measure relative blood flow speed based on the local speckle contrast analysis. However, it has been reported that t...

Intensity discrete structured light illumination systems project a series of projection patterns for the estimation of the absolute fringe order using only the temporal grey-level sequence at each pixel. This work proposes the use of error-correcting codes for pixel-wise correction of measurement errors. The use of an error correcting code is advan...

Structured light illumination (SLI) systems are well-established optical inspection techniques for noncontact 3D surface measurements. A common technique is multi-frequency sinusoidal SLI that obtains the phase map at various fringe periods in order to estimate the absolute phase, and hence, the 3D surface information. Nevertheless, multi-frequency...

We discuss a simple method to generate a configurable annular vortex beam (AVB) with the maximum possible peak intensity, employing a phase hologram whose transmittance is the phase of a Bessel beam. Due to its maximum intensity, the AVB provides the optimal density of the orbital angular moment. Another attribute of the generated AVB is the relati...

A model to characterize the response of a thin media that can exhibit more than one nonlocal nonlinear response when it is illuminated with a Gaussian beam in a z-scan experiment is proposed. The model considers that these nonlocal contributions can be treated as independent contributions in the refractive or absorptive nonlinear response. Numerica...

Background and objectives Antimicrobial photodynamic therapy (aPDT) is a technique that combines the photoactivation properties of an innocuous chromophore or photosensitizer (PS) and light, producing reactive oxygen molecules that trigger cell death processes. In this study the in-vitro application of aPDT to fight fungal infections was investigat...

We report the experimental measurement of the relationship between the size of particles being moved by optically patterned dielectrophoresis in an Optoelectronic Tweezers (OET) device and the force that they experience. The OET device turns an optical pattern into a pattern of electrical fields through the selective illumination of a photoconducti...

We designed and built a microfluidic device for the generation of liquid jets produced by thermocavitation. A continuous wave (CW) laser was focused inside a micro-chamber filled with a light-absorbing solution to create a rapidly expanding vapor bubble. The chamber is connected to a micro-channel which focuses and ejects the liquid jet through the...

The statistics of temporal integration of dynamically scattered light is commonly employed to calculate the correlation time of the light and related physical properties of the object that produce it, i.e. scatterer's speed. Recently, studying the statistics of time-averaged fluorescence intensity, it was reported that a small dead-time (1% of the...

In this work we demonstrate optical trapping and manipulation of microparticles suspended in water due to laser-induced convection currents. Convection currents are generated due to laser light absorption in an hydrogenated amorphous silicon (a:Si-H) thin film. The particles are dragged towards the beam's center by the convection currents (Stokes d...

The blood flow velocity optical monitoring techniques, such as laser speckle velocimetry, are attractive due its noninvasive character, but they are limited to superficial blood vessels. The visualization of deep blood vessel is difficult because of the highly scattering coefficient of the biological tissue. There are some techniques that allow the...

Optical imaging through highly scattering media such as biological tissue is limited by light scattering. Recently, it has been shown that wavefront shaping is a powerful tool to overcome this problem. In this work, wavefront shaping using spatial light modulators is used to compensate static scattering media (piece of translucent tape) to allow fo...

In this work, the simultaneous presence of saturable (SA) and two-photon absorption (TPA) in zinc nanoparticles (ZnNPs) photodeposited onto the core of an optical fiber was studied in the nanosecond regime with the P-scan method using a high gain pulsed erbium-doped fiber amplifier. An analysis based on Mie theory was carried out to demonstrate the...