Carmen Bao | University of Santiago de Compostela (original) (raw)

Papers by Carmen Bao

Epj Web of Conferences, 2022

Novel cell culture platforms, with more physiological surface roughness, require different techno... more Novel cell culture platforms, with more physiological surface roughness, require different technologies capable of precisely micropattern substrates. 3D printing offers a considerable accuracy and user-friendly procedures. For its part, pulsed laser ablation proves to be a versatile technology to perform detailed surface micropatterning. In this work, both technologies were combined to easily fabricate a versatile PDMS multi-well platform for performing cellular studies on a micropatterned biocompatible surface.

Cornell University - arXiv, Dec 18, 2022

The visual perception of the natural night sky in many places of the world is strongly disturbed ... more The visual perception of the natural night sky in many places of the world is strongly disturbed by anthropogenic light. Part of this artificial light is scattered in the atmosphere and propagates towards the observer, adding to the natural brightness and producing a light polluted sky. However, atmospheric scattering is not the only mechanism contributing to increase the visual skyglow. The rich and diverse biological media forming the human eye also scatter light very efficiently and contribute, in some cases to a big extent, to the total sky brightness detected by the retinal photoreceptors. In this paper we quantify this effect and assess its relevance when the eye pupil is illuminated by light sources within the visual field. Our results show that intraocular scattering constitutes a significant part of the perceived sky brightness at short distances from streetlights. These results provide quantitative support to the everyday experience that substantial gains in naked-eye star limiting magnitudes can be achieved by blocking the direct light from the lamps that reaches the eye pupil.

Journal of Quantitative Spectroscopy and Radiative Transfer

Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye... more Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye or any other physical detector does not come (exclusively) from high in the sky. The detected brightness is built up from the scattered radiance contributed by all elementary atmospheric volumes along the line of sight, starting from the very first millimeter from the eye cornea or the entrance aperture of the measuring instrument. In artificially lit environments, nearby light sources may be responsible for a large share of the total perceived sky radiance. We present in this paper a quantitative analytical model for the sky radiance in the vicinity of outdoor light sources, free from singularities at the origin, which provides useful insights for the correct design or urban dark sky places. It is found that the artificial zenith sky brightness produced by a small ground-level source detected by a ground-level observer at short distances (from the typical dimension of the source up to several hundred meters) decays with the inverse of the distance to the source. This amounts to a reduction of 2.5 mag/arcsec 2 in sky brightness for every log10 unit increase of the distance. The effects of screening by obstacles are also discussed.

Cornell University - arXiv, Jul 14, 2022

Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide area... more Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42°33′23″N, 8°59′32″ W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km 2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public streetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources' spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated.

Journal of Quantitative Spectroscopy and Radiative Transfer

Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide area... more Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42°33′23″N, 8°59′32″ W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km 2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public streetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources' spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated.

EPJ Web of Conferences

Synchronization control of complex systems is a field that emerged with huge interest and aims to... more Synchronization control of complex systems is a field that emerged with huge interest and aims to study new possible routes to synchronization in networks of non-locally coupled chemical oscillators. Light can be used to stimulate these systems and to be able to synchronize the different micro-reactors involved in the complex system. To this end, transparent reactors with good optical qualities are needed. Glass is the most appropriated material to be used for fabricating the micro-reactors. Subaquatic indirect Laser-Induced Plasma-Assisted Ablation is presented as a laser technique that combines underwater ablation with shock waves as a potential technique for fabricating these micro-reactors by using a Nd:YVO4 laser.

Optics Express

Subaquatic indirect Laser-Induced Plasma-Assisted Ablation (SLIPAA) is proposed as a laser-based ... more Subaquatic indirect Laser-Induced Plasma-Assisted Ablation (SLIPAA) is proposed as a laser-based technique for glass processing. In this configuration, a water layer is added between a metallic target and a soda-lime glass substrate, so the processing of the glass is due to a combination of the ablation mechanism, the shock waves, and the cavitation bubbles. Thus, this method makes it possible to produce higher depth structures than those performed up to now by other standard laser techniques based on ablation, achieving structures in glass with rectangular cross-sectional profiles. Channels of 1 mm width are fabricated, reaching an average maximal depth value of almost 1400 µm at 30 passes of the laser beam while keeping the focal position fixed. Furthermore, the difference between processing the material with and without the addition of the water layer is presented. The influence of the processing parameters on the shape and quality of the fabricated structures is studied by optic...

Atmospheric Pollution Research

Light pollution can be rigorously described in terms of the volume concentration of anthropogenic... more Light pollution can be rigorously described in terms of the volume concentration of anthropogenic photons (light quanta) in the terrestrial atmosphere. This formulation, consistent with the basic physics of the emission, scattering and absorption of light, allows one to express light pollution levels in terms of particle volume concentrations, in a completely analogous way as it is currently done with other classical pollutants, like particulate matter or molecular contaminants. In this work we provide the explicit conversion equations between the photon volume concentration and the traditional light photometry quantities. This equivalent description of the light pollution levels provides some relevant insights that help to identify artificial light at night as a standard pollutant. It also enables a complementary way of expressing artificial light exposures for environmental and public health research and regulatory purposes.

Optica Pura y Aplicada, 2021

Optica Pura y Aplicada, 2010

Optica Pura y Aplicada, 2003

Trends and Opportunities of Rapid Prototyping Technologies, 2022

Internal channels are one of the most interesting structures to implement in microfluidics device... more Internal channels are one of the most interesting structures to implement in microfluidics devices. Unfortunately, the optical technologies typically used in microfluidics, such as photolithography or reactive ion etching, are unable to generate these structures by only allowing surface structuring. Stereolithographic 3D printing has emerged as a very promising technology in internal microchannel manufacturing, by allowing a layer-by-layer structuring in volume performed by a laser that photopolymerises a liquid resin. Recent advances in laser technologies have reached resolutions of tens of micrometres. The high resolution of this type of printer, which a priori would allow the fabrication of channels of the same dimensions, may pose a problem by impeding the evacuation of uncured resin. In this chapter, the compromise between size and resin evacuation will be evaluated to find the optimal diameter range in which unobstructed and accurate microchannels can be obtained.

Optics and Lasers in Engineering, 2018

Phosphate coated zinc commercial plates (Anthra-Zinc®) have been processed by laser ablation in t... more Phosphate coated zinc commercial plates (Anthra-Zinc®) have been processed by laser ablation in the nanosecond pulsed regime varying the repetition rate at 10, 20 and 50 kHz. Phosphate coating was completely characterized. By monitoring the fluence it was possible to define three different processing regimes: phosphate ablation (up to 116 J/cm2), zinc ablation (up to 288 J/cm2) and zinc melting (at 375 J/cm2). 3D profilometry was used to assess both the roughness and depth parameters corresponding to each regime. The brightness was estimated from 450 to 800 nm by reflectance studies. Consequently, a long-lasting grey scale was attained envisaging in- and outdoor decorative uses.

Lasers and Applications, 2005

Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at... more Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at 355 nm, was used to study the potential of a laser backwriting process for the fabrication of optical waveguides via an index of refraction change. Metal foils of stainless steel, aluminum, copper, brass and gold have been used as blanks and irradiated by focusing the laser beam through a cylindrical lens under continuous movement in a direction perpendicular to the irradiation. An horizontal setup was found suitable to improve the effect of the plume in the sample. Results were obtained for two different configurations. Transversal profiles were analysed using a contact profilometer, comparing results obtained for the different configurations, traverse speeds and metal targets used. Two ablation regimes were identified, which are related to a critical laser fluence value of 2.7 J/cm 2. Surface micrographs obtained by scanning electron microscopy are discussed, together with the characteristics of the structures attained, taking into account the optical and thermal properties of the ablated metal blanks.

Journal of the Optical Society of America B, 2016

Tri-dimensional structures were internally mechanized into polymeric plates of polycarbonate (PC)... more Tri-dimensional structures were internally mechanized into polymeric plates of polycarbonate (PC) and polyethyleneterefthalate (PET) by a laser backwriting process performed with plates submerged in water. A Nd:YVO4 laser emitting at fundamental wavelength (1064 nm) in nanopulsed regime was employed. Keywordspolymeric plates; internal laser beam machining; 3D structures; informative panels; LED illumination

The Science of the total environment, 2020

A novel approach based on the direct pulsed irradiation of UV-C light onto ibuprofen (IBP) soluti... more A novel approach based on the direct pulsed irradiation of UV-C light onto ibuprofen (IBP) solutions was evaluated in this work, as proof of concept for the direct removal of micropollutants. The experiments confirmed that laser irradiation is able to completely degrade IBP in 15 min in distilled water, with a DOC depletion of ca. 25% and with transformation products (TPs) remaining in solution and estimated to represent ca. 10% of the initial IBP concentration. In wastewater spiked samples, removal efficiency is slightly lower but still significant (ca. 5% IBP remaining after 15 min). Hence, this work suggests that low power solid state pulsed lasers, emitting at 266 nm wavelength, show promise for the removal of these type of micropollutants from water. These results open new opportunities towards the development of chemical-free water treatment methods based on direct, selective irradiation using state of the art, miniaturized laser devices.

Epj Web of Conferences, 2022

Novel cell culture platforms, with more physiological surface roughness, require different techno... more Novel cell culture platforms, with more physiological surface roughness, require different technologies capable of precisely micropattern substrates. 3D printing offers a considerable accuracy and user-friendly procedures. For its part, pulsed laser ablation proves to be a versatile technology to perform detailed surface micropatterning. In this work, both technologies were combined to easily fabricate a versatile PDMS multi-well platform for performing cellular studies on a micropatterned biocompatible surface.

Cornell University - arXiv, Dec 18, 2022

The visual perception of the natural night sky in many places of the world is strongly disturbed ... more The visual perception of the natural night sky in many places of the world is strongly disturbed by anthropogenic light. Part of this artificial light is scattered in the atmosphere and propagates towards the observer, adding to the natural brightness and producing a light polluted sky. However, atmospheric scattering is not the only mechanism contributing to increase the visual skyglow. The rich and diverse biological media forming the human eye also scatter light very efficiently and contribute, in some cases to a big extent, to the total sky brightness detected by the retinal photoreceptors. In this paper we quantify this effect and assess its relevance when the eye pupil is illuminated by light sources within the visual field. Our results show that intraocular scattering constitutes a significant part of the perceived sky brightness at short distances from streetlights. These results provide quantitative support to the everyday experience that substantial gains in naked-eye star limiting magnitudes can be achieved by blocking the direct light from the lamps that reaches the eye pupil.

Journal of Quantitative Spectroscopy and Radiative Transfer

Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye... more Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye or any other physical detector does not come (exclusively) from high in the sky. The detected brightness is built up from the scattered radiance contributed by all elementary atmospheric volumes along the line of sight, starting from the very first millimeter from the eye cornea or the entrance aperture of the measuring instrument. In artificially lit environments, nearby light sources may be responsible for a large share of the total perceived sky radiance. We present in this paper a quantitative analytical model for the sky radiance in the vicinity of outdoor light sources, free from singularities at the origin, which provides useful insights for the correct design or urban dark sky places. It is found that the artificial zenith sky brightness produced by a small ground-level source detected by a ground-level observer at short distances (from the typical dimension of the source up to several hundred meters) decays with the inverse of the distance to the source. This amounts to a reduction of 2.5 mag/arcsec 2 in sky brightness for every log10 unit increase of the distance. The effects of screening by obstacles are also discussed.

Cornell University - arXiv, Jul 14, 2022

Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide area... more Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42°33′23″N, 8°59′32″ W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km 2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public streetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources' spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated.

Journal of Quantitative Spectroscopy and Radiative Transfer

Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide area... more Low Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42°33′23″N, 8°59′32″ W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km 2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public streetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources' spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated.

EPJ Web of Conferences

Synchronization control of complex systems is a field that emerged with huge interest and aims to... more Synchronization control of complex systems is a field that emerged with huge interest and aims to study new possible routes to synchronization in networks of non-locally coupled chemical oscillators. Light can be used to stimulate these systems and to be able to synchronize the different micro-reactors involved in the complex system. To this end, transparent reactors with good optical qualities are needed. Glass is the most appropriated material to be used for fabricating the micro-reactors. Subaquatic indirect Laser-Induced Plasma-Assisted Ablation is presented as a laser technique that combines underwater ablation with shock waves as a potential technique for fabricating these micro-reactors by using a Nd:YVO4 laser.

Optics Express

Subaquatic indirect Laser-Induced Plasma-Assisted Ablation (SLIPAA) is proposed as a laser-based ... more Subaquatic indirect Laser-Induced Plasma-Assisted Ablation (SLIPAA) is proposed as a laser-based technique for glass processing. In this configuration, a water layer is added between a metallic target and a soda-lime glass substrate, so the processing of the glass is due to a combination of the ablation mechanism, the shock waves, and the cavitation bubbles. Thus, this method makes it possible to produce higher depth structures than those performed up to now by other standard laser techniques based on ablation, achieving structures in glass with rectangular cross-sectional profiles. Channels of 1 mm width are fabricated, reaching an average maximal depth value of almost 1400 µm at 30 passes of the laser beam while keeping the focal position fixed. Furthermore, the difference between processing the material with and without the addition of the water layer is presented. The influence of the processing parameters on the shape and quality of the fabricated structures is studied by optic...

Atmospheric Pollution Research

Light pollution can be rigorously described in terms of the volume concentration of anthropogenic... more Light pollution can be rigorously described in terms of the volume concentration of anthropogenic photons (light quanta) in the terrestrial atmosphere. This formulation, consistent with the basic physics of the emission, scattering and absorption of light, allows one to express light pollution levels in terms of particle volume concentrations, in a completely analogous way as it is currently done with other classical pollutants, like particulate matter or molecular contaminants. In this work we provide the explicit conversion equations between the photon volume concentration and the traditional light photometry quantities. This equivalent description of the light pollution levels provides some relevant insights that help to identify artificial light at night as a standard pollutant. It also enables a complementary way of expressing artificial light exposures for environmental and public health research and regulatory purposes.

Optica Pura y Aplicada, 2021

Optica Pura y Aplicada, 2010

Optica Pura y Aplicada, 2003

Trends and Opportunities of Rapid Prototyping Technologies, 2022

Internal channels are one of the most interesting structures to implement in microfluidics device... more Internal channels are one of the most interesting structures to implement in microfluidics devices. Unfortunately, the optical technologies typically used in microfluidics, such as photolithography or reactive ion etching, are unable to generate these structures by only allowing surface structuring. Stereolithographic 3D printing has emerged as a very promising technology in internal microchannel manufacturing, by allowing a layer-by-layer structuring in volume performed by a laser that photopolymerises a liquid resin. Recent advances in laser technologies have reached resolutions of tens of micrometres. The high resolution of this type of printer, which a priori would allow the fabrication of channels of the same dimensions, may pose a problem by impeding the evacuation of uncured resin. In this chapter, the compromise between size and resin evacuation will be evaluated to find the optimal diameter range in which unobstructed and accurate microchannels can be obtained.

Optics and Lasers in Engineering, 2018

Phosphate coated zinc commercial plates (Anthra-Zinc®) have been processed by laser ablation in t... more Phosphate coated zinc commercial plates (Anthra-Zinc®) have been processed by laser ablation in the nanosecond pulsed regime varying the repetition rate at 10, 20 and 50 kHz. Phosphate coating was completely characterized. By monitoring the fluence it was possible to define three different processing regimes: phosphate ablation (up to 116 J/cm2), zinc ablation (up to 288 J/cm2) and zinc melting (at 375 J/cm2). 3D profilometry was used to assess both the roughness and depth parameters corresponding to each regime. The brightness was estimated from 450 to 800 nm by reflectance studies. Consequently, a long-lasting grey scale was attained envisaging in- and outdoor decorative uses.

Lasers and Applications, 2005

Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at... more Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at 355 nm, was used to study the potential of a laser backwriting process for the fabrication of optical waveguides via an index of refraction change. Metal foils of stainless steel, aluminum, copper, brass and gold have been used as blanks and irradiated by focusing the laser beam through a cylindrical lens under continuous movement in a direction perpendicular to the irradiation. An horizontal setup was found suitable to improve the effect of the plume in the sample. Results were obtained for two different configurations. Transversal profiles were analysed using a contact profilometer, comparing results obtained for the different configurations, traverse speeds and metal targets used. Two ablation regimes were identified, which are related to a critical laser fluence value of 2.7 J/cm 2. Surface micrographs obtained by scanning electron microscopy are discussed, together with the characteristics of the structures attained, taking into account the optical and thermal properties of the ablated metal blanks.

Journal of the Optical Society of America B, 2016

Tri-dimensional structures were internally mechanized into polymeric plates of polycarbonate (PC)... more Tri-dimensional structures were internally mechanized into polymeric plates of polycarbonate (PC) and polyethyleneterefthalate (PET) by a laser backwriting process performed with plates submerged in water. A Nd:YVO4 laser emitting at fundamental wavelength (1064 nm) in nanopulsed regime was employed. Keywordspolymeric plates; internal laser beam machining; 3D structures; informative panels; LED illumination

The Science of the total environment, 2020

A novel approach based on the direct pulsed irradiation of UV-C light onto ibuprofen (IBP) soluti... more A novel approach based on the direct pulsed irradiation of UV-C light onto ibuprofen (IBP) solutions was evaluated in this work, as proof of concept for the direct removal of micropollutants. The experiments confirmed that laser irradiation is able to completely degrade IBP in 15 min in distilled water, with a DOC depletion of ca. 25% and with transformation products (TPs) remaining in solution and estimated to represent ca. 10% of the initial IBP concentration. In wastewater spiked samples, removal efficiency is slightly lower but still significant (ca. 5% IBP remaining after 15 min). Hence, this work suggests that low power solid state pulsed lasers, emitting at 266 nm wavelength, show promise for the removal of these type of micropollutants from water. These results open new opportunities towards the development of chemical-free water treatment methods based on direct, selective irradiation using state of the art, miniaturized laser devices.