Near-infrared Light-emitting Diodes Research Articles

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Conventional gaze tracking systems are burdensome in that they require the user to gaze at several targets on the PC screen in the user-calibration process. The proposed calibration procedure requires the user to gaze at only one target. The implemented system consists of four camera-calibrated, wide-view video cameras arranged around the screen, with near-infrared light-emitting diode (LED) lights attached to each camera. The angle θ between the line of sight and the line connecting the center of the pupil and the camera (LED lights) is related to the vector from the center of the pupil to the corneal reflection detected from the video image. The user-calibration process makes it possible to determine three parameters, which can be achieved using three of the four cameras. Usually, the larger that angle θ is, the worse the gaze detection precision is. A weighted mean method is proposed to determine the final precise gaze point.

Yb3+ doped LaSi3N5 and YSi3N5 with low energy charge transfer for near-infrared light-emitting diode and solar cell application

Yb3+ doped LaSi3N5 phosphors have been prepared by solid-state synthesis in a high temperature furnace directly coupled to a glove box. The charge transfer (CT) band of Yb3+ in LaSi3N5 was observed at an unusually low energy of 3.1 eV. Excitation of this CT band results in f–f emission of Yb3+ at 1.2 eV, which could make Yb3+ doped LaSi3N5 suitable for application as a spectral conversion material for infrared light-emitting diodes or solar cells. Substitution of La3+ by the smaller Y3+ ion shifts the CT to higher energy (3.9 eV). A clear relation between the CT energy and the Yb3+ f–f emission intensity was found. With the help of a detailed energy level diagram that contains the position of the 4f and 5d levels of all divalent and trivalent ions with respect to the valence and conduction band, all hitherto observed luminescence properties of divalent and trivalent lanthanide dopants in LaSi3N5 are reviewed and explained.

Improved Cognitive Function After Transcranial, Light-Emitting Diode Treatments in Chronic, Traumatic Brain Injury: Two Case Reports

Two chronic, traumatic brain injury (TBI) cases, where cognition improved following treatment with red and near-infrared light-emitting diodes (LEDs), applied transcranially to forehead and scalp areas, are presented. Significant benefits have been reported following application of transcranial, low-level laser therapy (LLLT) to humans with acute stroke and mice with acute TBI. These are the first case reports documenting improved cognitive function in chronic, TBI patients treated with transcranial LED. Treatments were applied bilaterally and to midline sagittal areas using LED cluster heads [2.1″ diameter, 61 diodes (9 × 633 nm, 52 × 870 nm); 12-15 mW per diode; total power: 500 mW; 22.2 mW/cm(2); 13.3 J/cm(2) at scalp (estimated 0.4 J/cm(2) to cortex)]. Seven years after closed-head TBI from a motor vehicle accident, Patient 1 began transcranial LED treatments. Pre-LED, her ability for sustained attention (computer work) lasted 20 min. After eight weekly LED treatments, her sustained attention time increased to 3 h. The patient performs nightly home treatments (5 years); if she stops treating for more than 2 weeks, she regresses. Patient 2 had a history of closed-head trauma (sports/military, and recent fall), and magnetic resonance imaging showed frontoparietal atrophy. Pre-LED, she was on medical disability for 5 months. After 4 months of nightly LED treatments at home, medical disability discontinued; she returned to working full-time as an executive consultant with an international technology consulting firm. Neuropsychological testing after 9 months of transcranial LED indicated significant improvement (+1, +2SD) in executive function (inhibition, inhibition accuracy) and memory, as well as reduction in post-traumatic stress disorder. If she stops treating for more than 1 week, she regresses. At the time of this report, both patients are continuing treatment. Transcranial LED may improve cognition, reduce costs in TBI treatment, and be applied at home. Controlled studies are warranted.

Prophylactic low‐level light therapy for the treatment of hypertrophic scars and keloids: A case series

Hypertrophic and keloid scars result from alterations in the wound healing process. Treating abnormal scars remains an important challenge. The aim of this case series was to investigate the effectiveness of near infrared (NIR) light emitting diode (LED) treatment as a prophylactic method to alter the wound healing process in order to avoid or attenuate the formation of hypertrophic scars or keloids. Three patients (age 27-57) of phototypes I-III with hypertrophic scars or keloids due to acne or surgery participated in this case series. Following scar revision by surgery or CO(2) laser ablation on bilateral areas, one scar was treated daily by the patient at home with non-thermal, non-ablative NIR LED (805 nm at 30 mW/cm(2)) for 30 days. Efficacy assessments, conducted up to a year post-treatment, included the Vancouver Scar scale (VSS), clinical global assessment of digital photographs, and quantitative profilometry analysis using PRIMOS. Safety was documented by adverse effects monitoring. Significant improvements on the NIR-treated versus the control scar were seen in all efficacy measures. No significant treatment-related adverse effects were reported. Possible mechanisms involved are inhibition of TGF-beta I expression. Further studies in larger group of patients are needed to evaluate this promising technique.

Near‐Infrared Organic Compounds and Emerging Applications

This Focus Review describes the emerging class of near-infrared (NIR) organic compounds containing the conjugated polyene, polymethine, and donor-acceptor chromophores and exploration of their NIR-absorbing, NIR-fluorescence, and NIR-photosensitizing properties for potential applications in heat absorbers, solar cells, and NIR light-emitting diodes. Examples of NIR organic compounds are reviewed with emphasis on the molecular design, NIR absorption, and fluorescence and particular emerging applications. The donor-acceptor type of NIR chromophores are particularly introduced owing to some unique features, including the designer-made energy gaps, facile synthesis, good processability, and controllable morphology and properties in the solid state. Future directions in research and development of NIR organic materials and applications are then offered from a personal perspective.

SYNTHESIS AND CHARACTERIZATION OF NEAR-INFRARED ELECTROLUMINESCENT FLUORENE-BASED CONJUGATED COPOLYMERS

A series low band-gap conjugated copolymers(PFO-DTP) derived from 9,9-dioctylfluorene(DOF) and 5,7-dithien-2-ylthienopyrazine(DTP) is prepared by the palladium-catalyzed Suzuki coupling reaction with the feed ratios of DTP mole percents around 1%,5%,15%,30%.The resulted polymers are soluble in common organic solvents.There are two absorbance peak around 380 nm and 632 nm in the spectra of copolymers.The absorbance peak around 632 nm increased as the DTP contents increased.Maximum external quantum efficiency reaches 0.1% in devices of copolymers with the DTP content at 5 mol%.In comparison with its very well studied isomer copolymer poly(2,7-(9,9-dioctyl-fluorene)-co-4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole),the poly(2,7-(9,9-dioctylfluorene)-co-5,7-dithien-2-ylthienopyrazine)(PFO-DTP) shows a red shift of about 110 nm for photoluminescence(PL) and electroluminescence(EL) emissions,and the optical onset wavelength of the PFO-DTP is red shifted about 130 nm and their optical response is more matching the optical spectra of the solar terrestrial radiation.These copolymers are promising candidate materials for near-infrared light-emitting diodes and polymeric photovoltaic solar cell.

Effect of near-infrared light-emitting diodes on nerve regeneration

BackgroundPhotobiomodulation by red to near-infrared light-emitting diodes (LEDs) has been reported to accelerate wound healing, attenuate degeneration of an injured optic nerve, and promote tissue growth. The purpose of this study was to investigate the effect of LEDs on nerve regeneration. A histological study as well as a measurement of antioxidation levels in the nerve regeneration chamber fluid was performed. MethodsFor the histological study, the bilateral sciatic nerves were transected, and the left proximal stump and the right distal stump were inserted into the opposite ends of a silicone chamber, leaving a 10-mm gap. Light from an LED device (660 nm, 7.5 mW/cm2) was irradiated for 1 h per day. At 3 weeks after surgery, regenerated tissue was fixed and examined by light microscopy. For the antioxidation assay of chamber fluid, the left sciatic nerve and a 2-mm piece of nerve from the proximal stump were transected and inserted into opposite sides of a silicone chamber leaving a 10-mm gap. LEDs were irradiated using the same parameters as those described in the histological study. At 1, 3, and 7 days after surgery, antioxidation of the chamber fluid was measured using an OXY absorbent test. ResultsNerve regeneration was promoted in the LED group. Antioxidation of the chamber fluid significantly decreased from 3 days to 7 days in the control group. In the LED group, antioxidation levels did not decrease until 7 days. ConclusionsChamber fluid is produced from nerve stumps after nerve injury. This fluid contains neurotrophic factors that may accelerate axonal growth. Red to near-infrared LEDs have been shown to promote mitochondrial oxidative metabolism. In this study, LED irradiation improved nerve regeneration and increased antioxidation levels in the chamber fluid. Therefore, we propose that antioxidation induced by LEDs may be conducive to nerve regeneration.

Low-frequency wide-field fluorescence lifetime imaging using a high-power near-infrared light-emitting diode light source.

Fluorescence lifetime imaging (FLi) could potentially improve exogenous near-infrared (NIR) fluorescence imaging, because it offers the capability of discriminating a signal of interest from background, provides real-time monitoring of a chemical environment, and permits the use of several different fluorescent dyes having the same emission wavelength. We present a high-power, LED-based, NIR light source for the clinical translation of wide-field (larger than 5 cm in diameter) FLi at frequencies up to 35 MHz. Lifetime imaging of indocyanine green (ICG), IRDye 800-CW, and 3,3(')-diethylthiatricarbocyanine iodide (DTTCI) was performed over a large field of view (10 cm by 7.5 cm) using the LED light source. For comparison, a laser diode light source was employed as a gold standard. Experiments were performed both on the bench by diluting the fluorescent dyes in various chemical environments in Eppendorf tubes, and in vivo by injecting the fluorescent dyes mixed in Matrigel subcutaneously into CD-1 mice. Last, measured fluorescence lifetimes obtained using the LED and the laser diode sources were compared with those obtained using a state-of-the-art time-domain imaging system and with those previously described in the literature. On average, lifetime values obtained using the LED and the laser diode light sources were consistent, exhibiting a mean difference of 3% from the expected values and a coefficient of variation of 12%. Taken together, our study offers an alternative to laser diodes for clinical translation of FLi and explores the use of relatively low frequency modulation for in vivo imaging.

A study to determine the effect of combination blue (415 nm) and near-infrared (830 nm) light-emitting diode (LED) therapy for moderate acne vulgaris

Background and objective: Acne vulgaris remains a major problem in dermatological practice. Phototherapy for acne with blue (415 nm) and red (633 nm) light-emitting diode (LED) arrays has recently attracted attention. This pilot study assessed the efficacy of the combination of 415 nm and near-infrared (IR) LED therapy for moderate acne. Methods: Seventeen individuals were recruited: 13 females and four males. Skin types ranged from type II to type VI, and the acne grades at baseline ranged from Burton grade 1 to 5. Patients underwent twice-weekly 20-minute sessions of LED therapy for 4 weeks, alternating between the blue (415 nm) and near-IR (830 nm) heads. No other treatment was allowed. Results were assessed and compared with the baseline values at 1, 4 and 8 weeks post-treatment. Results: Six individuals failed to complete the study. Eleven individuals showed improvement ranging from 0% to 83.3%. A downward shift in the Burton grade was seen overall. Non-inflammatory lesion counts increased in four patients, but improved in the other seven by an average of 48.8%. No adverse effects were reported. Conclusions: The combination therapy for acne produced results which were less effective in the reduction of inflammatory lesions than those achieved with the previously reported blue/red combination. Further study with a much larger patient population is warranted.

A study to determine the efficacy of a novel handheld light‐emitting diode device in the treatment of photoaged skin

The use of visible or near-infrared spectral light alone for the purpose of skin rejuvenation has been previously reported in the literature. These devices use large arrays of diodes to deliver light to the skin. In this study, a novel method of light-emitting diode (LED) photo rejuvenation incorporating a combination of these wavelengths delivered from a small handheld unit is proposed. Twenty-two subjects with facial rhytides received eight light therapy treatments over a course of 4 weeks, using the Omnilux handheld LED system. Assessment of global skin grading was evaluated at weeks 6, 9, and 12 by a dermatologist. Additional outcome measures included assessments of clinical photography and patient satisfaction scores. Seventy-four percent of the subjects reported a visible improvement in fine lines and wrinkles at 8 weeks posttreatment. Combination red and near-infrared LED therapy delivered from a small portable handheld unit represents an effective and acceptable method of photo rejuvenation. Further studies to optimize the parameters of treatment are required.

Investigation of Extracting Photonic Crystal Lattices for Guided Modes of GaAs-Based Heterostructures

The issue of extracting guided modes from a standard light-emitting heterostructure similar to those of visible or near-infrared light-emitting diodes is considered with respect to the role of lattices and of the amount of omnidirectionality in the extraction performances. Triangular lattices are first-order natural candidates. We examine first whether they can be made omnidirectional thanks to a grating + coupler combination initially proposed by Fehrembach et al (2001), whereby the short periodicity concentrates emission in few in-plane modes, and the double periodicity extracts it. We then examine lattices that directly extract, for a Ga(Al)As system on a GaAs substrate, with a specific 3-D mode decay calculation. We compare triangular and Archimedean lattices experimentally and point out the role of photonic strength also through a spectrally and angularly resolved experiment.

Imaging simulated smeared fingers with a sensor based on scattered-light detection

Fingerprint identification is susceptible to the surface conditions of a finger. We studied the effect of image degradations with our sensor technology based on scattered-light detection. To simulate a smeared finger, we printed small black dots on a transparent sheet and inserted it between a finger and our sensor. With a green light-emitting diode (LED) as its light source, the rate of successful identification decreased constantly as the number of black dots increased. With a near-infrared LED, the rate remained almost constant when the total area covered by the black dots was less than 1% of the input area. The infrared LED generated a clearer image for oily fingers than the green LED as well. We attribute these findings to the presence of an internal fingerprint pattern, which near-infrared light can probe better.

Imaging Characteristics and Quantum Efficiency: Key Properties for Pixelless Far-Infrared Semiconductor Upconversion Imaging Devices

Employing the concept of photon frequency upconversion, we have proposed two types of semiconductor upconverters to realize pixelless far-infrared (FIR) imaging. The upconverter consists of a GaAs FIR homojunction interfacial work-function internal photoemission detector integrated with a GaAs/AlGaAs near-infrared light-emitting diode (LED), or GaN/AlGaN mid-IR/FIR dual-band heterojunction detector with a GaN/AlGaN violet LED. We have studied in detail the dependences of the modulation transfer function and quantum efficiency of the upconverters on various device parameters. Through the application of resonant cavity to the GaAs-based upconverter, we can expect sharp and high-resolution image and improved quantum efficiency. In addition, due to the large light absorption in the GaN/AlGaN heterojunction detector, the quantum efficiency of the GaN-based upconverter is much higher than that of GaAs-based one.

Resonant-Cavity-Enhanced Far-Infrared Upconversion Imaging Devices

We have carried out a detailed investigation on the application of resonant cavities to the photon-frequency-upconversion-based far-infrared (FIR) semiconductor imaging devices. The employment of a bottom mirror (BM) enhances the FIR photon absorption efficiency and, therefore, increases the quantum efficiency of GaAs homojunction interfacial work- function internal photoemission (HIWIP) FIR detectors. Significant improvement of the extraction efficiency could be achieved in resonant cavity enhanced (RCE) GaAs-AlGaAs near-infrared (NIR) light-emitting diodes (LEDs) through redirecting as many NIR photons as possible into the escape cone. Under the optimal structural parameters, we have predicted that the upconversion quantum efficiency of the integrated HIWIP-BM-RCE-LED imaging device could be boosted to 5-6 times of the normal HIWIP-LED upconverter without any resonant cavities. As a consequence of few reincarnation cycles needed by NIR photons to escape in the photon recycling process, we can further expect sharp and high-resolution imaging in HIWIP-BM-RCE-LED

An economical wireless cavity-nest viewer

Inspection of cavity nests and nest boxes is often required during studies of cavity-nesting birds, and fiberscopes and pole-mounted video cameras are sometimes used for such inspection. However, the cost of these systems may be prohibitive for some potential users. We describe a user-built, wireless cavity viewer that can be used to access cavities as high as 15 m and with entrance diameters as small as 2.5 cm. System components include a wireless camera, boom with near-infrared lighting system, hand-held television, and telescoping pole. The unit can be assembled in about one day with commonly available tools, and the total cost was about $850 (US). Our cavity-viewing system was used to monitor the nests of Western Bluebirds (Sialia mexicana) and proved to be reliable and effective. During two field seasons, we attempted to check the status of nests 928 times and were able to determine the nesting stage 901 times (97%). For those willing to assemble their own units, our cavity viewer permits safe, direct examination of cavity nests or open nests for investigators with limited budgets. SINOPSIS. Aparato inhalambrico de bajo costo para observar nidos en cavidades Para examinar nidos en cavidades y cajas de anidamiento, muchas veces es necesario usar instrumentos de fibra ´ optica y cde videos montadas en postes. Sin embargo, el costo de estos sistemas pudiera ser muy elevado para algunos investigadores potenciales. Describimos un aparato inhalque puede ser utilizado para examinar cavidades de hasta 15 m de altura y de 2.5 cm de dien su entrada. Entre los componentes del sistema encontramos una cinhalun sistema de iluminaci´ on infrarojo, un monitor de televisi´ on manual y un poste telescEl sistema puede ser montado en un dia (si hay las herramientas necesarias) y su costo es de $850 dolares. Nuestro sistema fue utilizado para monitorear nidos de Sialia mexicana yp rov´ o ser confiable y efectivo. Durante dos temporadas de campo intentamos determinar el estatus de nidos en 928 ocasiones y pudimos determiner la etapa en que se encontraban en 901 (97%) de estas. Para aquellos que est´ en en la disposicide ensamblar sus propias unidades de monitoreo, nuestro equipo es adecuado y se presta para estudios con presupuesto limitado y le permite al investigador hacer observaciones directas con seguridad.

An instrument for measurement of water contamination in hydraulic fluids

This paper describes an optical instrument that uses the transmission and scattering properties of water droplets in hydraulic fluids to measure the water fraction in the fluid. The instrument consists of a small optical chamber that can be built into an active hydraulic system. Light is supplied via a near-infrared light-emitting diode and is collected via a simple system of lenses and two wavelength-matched detectors placed at 90° to the beam path and directly in the path of the transmitted light. A novel method of measuring the water contamination is utilized that greatly reduces the signal noise caused by dynamic changes in the system during operation.

670 nanometer light treatment attenuates dioxin toxicity in the developing chick embryo

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an acutely toxic anthropogenic chemical. Treatment with a red to near-infrared (630-1000 nm) light-emitting diode (LED) attenuates the toxicant-induced oxidative stress and energy deficit in neuronal cell culture. For this study, fertile chicken (Gallus gallus) eggs were injected once at the start of incubation with sunflower oil vehicle or 200 pg TCDD/g egg (200 parts per trillion), an environmentally relevant dose. Daily LED treatment after TCDD exposure reduced embryonic mortality by 47%. LED treatment of TCDD-exposed eggs also decreased the hepatic oxidized-to-reduced glutathione ratio by 88%. Activities of other hepatic indicators of oxidative stress, such as glutathione reductase and catalase, were increased after LED treatment of TCDD-exposed eggs. Our study demonstrates that 670 nm phototherapy can mitigate the oxidative stress and energy deficit resulting from developmental exposure to TCDD while reducing TCDD-induced embryo mortality. Moreover, LED treatment restores hepatic enzyme activities to control levels in TCDD-exposed embryos. The effective attenuation of TCDD-induced embryo toxicity by LED treatment could extend to mitigating the effects of other teratogens that induce oxidative and energy stress.

Development of a bidirectional transcutaneous optical data transmission system for artificial hearts allowing long-distance data communication with low electric power consumption

We have developed a wavelength division bidirectional transcutaneous optical data transmission system using amplitude shift keying (ASK) modulation. The bidirectional optical data transmission system consists of two kinds of light emitting diodes (LEDs) having different wavelengths and an ASK modulator and demodulator. Two narrow directional visible LEDs with a peak output wavelength of 590 nm were used to transmit data from inside the body to outside the body, and a narrow directional near-infrared LED with a peak output wavelength of 940 nm was used for transmission from outside the body to inside the body. The ASK modulator employs a carrier pulse signal (50 kHz) to support a maximum data transmission rate of 9600 bps. An in vitro experiment showed that the maximum tissue thickness of near-infrared optical data transmission without error was 45 mm; the figure was 20 mm for visible optical data transmission. There was no interference between the signals under full-duplex data transmission. Electric power consumption for the data transmission links was 122 mW for near-infrared light and 162 mW (81 mW x 2) for visible light. From the above results, a bidirectional transcutaneous optical data transmission system promises adequate performance for monitoring and control of an artificial heart.

Optimization of quantum-well infrared detectors integrated with light-emitting diodes

The optimization of diffraction gratings for pixelless thermal imagers based on the epitaxial integration of a 9-μm quantum-well infrared photodetector (QWIP) and a near-infrared light-emitting diode (LED) is reported. It is found that the thickness of the reflecting layer deposited onto the grating should be carefully controlled to reach a good tradeoff between high infrared responsivity of the QWIP and reasonable external efficiency of the LED. In addition, on a non-optimized device we demonstrated thermal images with a temperature sensitivity below 100 mK and a noise equivalent temperature difference of 57 mK.

Melatonin modulates the action of near infrared radiation on cell adhesion.

The adhesion of human cervical cancer (HeLa) cells to a glass matrix is evaluated following their irradiation in a suspension with a pulsed near-infrared (IR) light-emitting diode (wavelength 820 nm, pulse repetition frequency 10 Hz, irradiation dose 16-120 J/m2) when melatonin (4 x 10(-11) to 4 x 10(-5) m) is added to cell suspension immediately before or after the irradiation. Also, the dependence of visible-to-near-IR radiation (600-840 nm, 52 J/m2) on cell adhesion (action spectrum) is recorded in absence and presence of melatonin (4 x 10(-6) m). It is found that melatonin in pharmacological concentrations (but not in physiological range) inhibited cell adherence. Irradiation of cells before or after melatonin treatment normalizes cell adhesion to control level. Melatonin in pharmacological concentrations eliminates stimulation of cell attachment induced by irradiation. Pre-treatment (but not post-treatment) with melatonin in the physiological concentration eliminates cell adhesion stimulation induced by irradiation. Melatonin modifies the light action spectrum significantly in near IR region (760-840 nm only). Thus, the peak at 820-830 nm characteristic for the light action spectrum is fully reduced.