Near-infrared Light Source Research Articles

Noninvasive in vivo characterization of erythrocyte motion in human retinal capillaries using high-speed adaptive optics near-confocal imaging.

The flow of erythrocytes in parafoveal capillaries was imaged in the living human eye with an adaptive optics near-confocal ophthalmoscope at a frame rate of 800 Hz with a low coherence near-infrared (NIR) light source. Spatiotemporal traces of the erythrocyte movement were extracted from consecutive images. Erythrocyte velocity was measured using custom software based on the Radon transform. The impact of imaging speed on velocity measurement was estimated using images of frame rates of 200, 400, and 800 Hz. The NIR light allowed for long imaging periods without visually stimulating the retina and disturbing the natural rheological state. High speed near-confocal imaging enabled direct and accurate measurement of erythrocyte velocity, and revealed a distinctively cardiac-dependent pulsatile velocity waveform of the erythrocyte flow in retinal capillaries, disclosed the impact of the leukocytes on erythrocyte motion, and provided new metrics for precise assessment of erythrocyte movement. The approach may facilitate new investigations on the pathophysiology of retinal microcirculation with applications for ocular and systemic diseases.

Exploiting Singlet Fission in Organic Light-Emitting Diodes.

Harvesting of both triplets and singlets yields electroluminescence quantum efficiencies of nearly 100% in organic light-emitting diodes (OLEDs), but the production efficiency of excitons that can undergo radiative decay is theoretically limited to 100% of the electron-hole pairs. Here, breaking of this limit by exploiting singlet fission in an OLED is reported. Based on the dependence of electroluminescence intensity on an applied magnetic field, it is confirmed that triplets produced by singlet fission in a rubrene host matrix are emitted as near-infrared (NIR) electroluminescence by erbium(III) tris(8-hydroxyquinoline) (ErQ3 ) after excitonic energy transfer from the "dark" triplet state of rubrene to an "emissive" state of ErQ3 , leading to NIR electroluminescence with an overall exciton production efficiency of 100.8%. This demonstration clearly indicates that the harvesting of triplets produced by singlet fission as electroluminescence is possible even under electrical excitation, leading to an enhancement of the quantum efficiency of the OLEDs. Electroluminescence employing singlet fission provides a route toward developing high-intensity NIR light sources, which are of particular interest for sensing, optical communications, and medical applications.

Temperature dependent Cr3+ photoluminescence in garnets of the type X3Sc2Ga3O12 (X = Lu, Y, Gd, La)

Broad band near-infrared (NIR) light sources have great potential, e.g., in optical communication and non-invasive medical imaging. Here we report the optical properties of X3Sc2Ga3O12 (X = Lu, Y, Gd, La) garnets doped with Cr3+ showing efficient 4T2 → 4A2 broad band NIR emission between 600 and 1000 nm. The chromium-doped garnets were investigated in view of their capability for blue to NIR conversion in high power phosphor converted LEDs (pcLEDs). Typical high power (In,Ga)N LEDs reach junction temperatures up to 450 K. Hence, the photoluminescence (PL) quenching temperature is a crucial parameter for on-chip phosphors. The Cr3+-doped garnets reveal very high quenching temperatures for the broad band NIR emission, ~ 700 K for Lu3Sc2Ga3O12, Y3Sc2Ga3O12, Gd3Sc2Ga3O12, and 450 K for La3Sc2Ga3O12. The high quenching temperatures are in line with a small Stokes shift (~ 2400 cm−1) and weak electron-phonon coupling. To gain further insight in the luminescence properties, low temperature photoluminescence measurements were done. The optical properties of Cr3+ ions in garnets were analyzed in terms of the crystal field strength, Racah parameters, and phonon coupling parameters. The suitability for application in pcLEDs for high power broad band NIR sources was confirmed by emission measurements of ceramic pellets upon blue LED excitation.

Near-infrared light-guided miniaturized indirect ophthalmoscopy for nonmydriatic wide-field fundus photography.

A portable fundus imager is essential for emerging telemedicine screening and point-of-care examination of eye diseases. However, existing portable fundus cameras have limited field of view (FOV) and frequently require pupillary dilation. We report here a miniaturized indirect ophthalmoscopy-based nonmydriatic fundus camera with a snapshot FOV up to 67° external angle, which corresponds to a 101° eye angle. The wide-field fundus camera consists of a near-infrared light source (LS) for retinal guidance and a white LS for color retinal imaging. By incorporating digital image registration and glare elimination methods, a dual-image acquisition approach was used to achieve reflection artifact-free fundus photography.

A Colloidal-Quantum-Dot-Based Self-Charging System via the Near-Infrared Band.

A novel self-charging platform is proposed using colloidal-quantum-dot (CQD) photovoltaics (PVs) via the near-infrared (NIR) band for low-power electronics. Low-bandgap CQDs can convert invisible NIR light sources to electrical energy more efficiently than wider spectra because of reduced thermalization loss. This energy-conversion strategy via NIR photons ensures an enhanced photostability of the CQD devices. Furthermore, the NIR wireless charging system can be concealed using various colored and NIR-transparent fabric or films, providing aesthetic freedom. Finally, an NIR-driven wireless charging system is demonstrated for a wearable healthcare bracelet by integrating a CQD PVs receiver with a flexible lithium-ion battery and entirely embedding them into a flexible strap, enabling permanent self-charging without detachment.

Noncontinuous Super-Diffusive Dynamics of a Light-Activated Nanobottle Motor.

We report a carbonaceous nanobottle (CNB) motor for near infrared (NIR) light-driven jet propulsion. The bottle structure of the CNB motor is fabricated by soft-template-based polymerization. Upon illumination with NIR light, the photothermal effect of the CNB motor carbon shell causes a rapid increase in the temperature of the water inside the nanobottle and thus the ejection of the heated fluid from the open neck, which propels the CNB motor. The occurrence of an explosion, the on/off motion, and the swing behavior of the CNB motor can be modulated by adjusting the NIR light source. Moreover, we simulated the physical field distribution (temperature, fluid velocity, and pressure) of the CNB motor to demonstrate the mechanism of NIR light-driven jet propulsion. This NIR light-powered CNB motor exhibits fuel-free propulsion and control of the swimming velocity by external light and has great potential for future biomedical applications.

Noncontinuous Super‐Diffusive Dynamics of a Light‐Activated Nanobottle Motor

AbstractWe report a carbonaceous nanobottle (CNB) motor for near infrared (NIR) light‐driven jet propulsion. The bottle structure of the CNB motor is fabricated by soft‐template‐based polymerization. Upon illumination with NIR light, the photothermal effect of the CNB motor carbon shell causes a rapid increase in the temperature of the water inside the nanobottle and thus the ejection of the heated fluid from the open neck, which propels the CNB motor. The occurrence of an explosion, the on/off motion, and the swing behavior of the CNB motor can be modulated by adjusting the NIR light source. Moreover, we simulated the physical field distribution (temperature, fluid velocity, and pressure) of the CNB motor to demonstrate the mechanism of NIR light‐driven jet propulsion. This NIR light‐powered CNB motor exhibits fuel‐free propulsion and control of the swimming velocity by external light and has great potential for future biomedical applications.

Replacing incandescent lamps with an LED panel for hydrogen production by photofermentation: Visible and NIR wavelength requirements

Hydrogen production by Rhodobacter capsulatus is a photobiological anaerobic process requiring light as energy source. In this study, the influence of visible and near-infrared (NIR) parts of light spectra from incandescent lamp and LED panels on hydrogen production was investigated. The results showed that the lack of the visible part of the incandescent lamp light spectrum (17% of the lamp light intensity) reduced hydrogen production by 50%. NIR wavelength only partially sustained photofermentation due to light limitation reached at low bacterial concentration. Hydrogen production with NIR light source was only 58% of hydrogen obtained with an incandescent lamp used at the same irradiance. To maximize hydrogen production and flow rate, visible and NIR wavelength should be used concomitantly as light source. Using an energy-efficient LED panel with light spectrum designed to promote photofermentation, hydrogen production and flow rate were equivalent to the ones reached with incandescent lamp as light source.

WearLight: Toward a Wearable, Configurable Functional NIR Spectroscopy System for Noninvasive Neuroimaging.

Functional near-infrared spectroscopy (fNIRS) has emerged as an effective brain monitoring technique to measure the hemodynamic response of the cortical surface. Its wide popularity and adoption in recent time attribute to its portability, ease of use, and flexibility in multimodal studies involving electroencephalography. While fNIRS is still emerging on various fronts including hardware, software, algorithm, and applications, it still requires overcoming several scientific challenges associated with brain monitoring in naturalistic environments where the human participants are allowed to move and required to perform various tasks stimulating brain behaviors. In response to these challenges and demands, we have developed a wearable fNIRS system, WearLight that was built upon an Internet-of-Things embedded architecture for onboard intelligence, configurability, and data transmission. In addition, we have pursued detailed research and comparative analysis on the design of the optodes encapsulating an near-infrared light source and a detector into 3-D printed material. We performed rigorous experimental studies on human participants to test reliability, signal-to-noise ratio, and configurability. Most importantly, we observed that WearLight has a capacity to measure hemodynamic responses in various setups including arterial occlusion on the forearm and frontal lobe brain activity during breathing exercises in a naturalistic environment. Our promising experimental results provide an evidence of preliminary clinical validation of WearLight. This encourages us to move toward intensive studies involving brain monitoring.

Minilaparoscopy vs Standard Laparoscopy for Sentinel Node Dissection: A Pilot Study

ObjectiveTo compare 3-mm minilaparoscopy and standard 5-mm laparoscopy for sentinel lymph node (SLN) detection in apparent early-stage endometrial cancer (EC). DesignRetrospective study (Canadian Task Force classification II-2). SettingTwo academic research centers. PatientsConsecutive women with apparent early-stage EC who underwent surgical staging with SLN detection between November 2015 and April 2016. InterventionsThe surgical approach was a total laparoscopic extrafascial hysterectomy plus bilateral salpingo-oophorectomy and SLN detection. Systematic lymphadenectomy was performed in selected cases. In all patients, SLN detection was performed with cervical injection of indocyanine green and the use of an optical camera with a near-infrared high-intensity light source for detection of fluorescence imaging. All patients who underwent a minilaparoscopic approach (using one 5-mm scope and three 3-mm ancillary trocars) have been enrolled at the University of Insubria, whereas at the San Gerardo Hospital, standard laparoscopy was performed with one 10-mm scope and three 5-mm ancillary trocars. Measurements ad Main ResultsA total of 38 patients were enrolled, including 15 (39.5%) in the 3-mm group and 23 (60.5%) in the 5-mm group. No between-group differences were found in terms of demographic and tumor characteristics. Bilateral SLNs were detected in 73.3% of the patients in the 3-mm group and in 73.9% in the 5-mm group. Operative time, blood loss, hemoglobin drop, hospital stay, and the incidence and severity of complications were similar in the 2 groups. One patient (4.3%) in the standard 5-mm group had a positive SLN result (a micrometastasis in the left external iliac SLN). No positive SLNs were detected in the 3-mm group. ConclusionMinilaparoscopic SLN biopsy appears to be a promising and feasible technique for EC staging. Further research is warranted to investigate the possible benefits of 3-mm instruments in this specific setting.

Preparation of SiC/Ge/graphene heterostructure on 4H-SiC(0001)

Due to the wide bandgap of SiC, SiC-based optoelectronic devices can not be operated by visible (VIS) and near-infrared (NIR) light sources. A promising way to solve this problem is to adopt a SiC/Ge/Graphene heterostructure. The Ge film can be used as VIS-NIR-absorbing layer. As a electrode, graphene also forms a Schottky junction with Ge on 4H-SiC. To form the SiC/Ge/graphene heterostructures, Ge film was prepared on 4H-SiC(0001) by chemical vapor deposition, and then graphene on Cu foil was wet transferred on Ge films. The Ge film on 4H-SiC(0001) has polycrystalline structure and consists of self-assembled submicron Ge islands. The monolayer graphene with a few cracks and wrinkles was transferred on the Ge rough surface. The SiC/Ge/graphene heterostructure with high light absorption in the 500–1200nm range was prepared on 4H-SiC successfully.

Efficient and Fast Implementation of Embedded Time-of-Flight Ranging System Based on FPGAs

Time-of-flight cameras perceive depth information about the surrounding environment with an amplitude-modulated near-infrared light source. The distance between the sensor and objects is calculated through measuring the time the light needs to travel. To be used in fast and embedded applications, such as 3-D reconstruction, visual SLAM, human-robot interactions, and object detection, the 3-D imaging must be performed at high frame rates and accuracy. Thus, this paper presents a real-time field programmable gate arrays platform that calculates the phase shift and then the distance. Experimental results shown that the platform can acquire ranging images at the maximum frame rate of 131fps with a fine measurement precision (appropriately 5.1mm range error at 1.2m distance with the proper integration time). Low resource utilization and power consumption of the proposed system make it very suitable for embedded applications.

11-5 遠隔注視点検出装置における近赤外光源の発光量自動調整による注視点検出のロバスト性向上(第11部門 ヒューマンインフォメーション(視覚特性および映像・画像評価))

11-5 遠隔注視点検出装置における近赤外光源の発光量自動調整による注視点検出のロバスト性向上(第11部門 ヒューマンインフォメーション(視覚特性および映像・画像評価))

Near-infrared photodynamic inactivation of S. pneumoniae and its interaction with RAW 264.7 macrophages.

Pneumonia is the main cause of children mortality worldwide, and its major treatment obstacle stems from the microorganisms increasing development of resistance to several antibiotics. Photodynamic therapy has been presenting, for the last decades, promising results for some subtypes of cancer and infections. In this work we aimed to develop a safe and efficient in vitro protocol for photodynamic inactivation of Streptococcus pneumoniae, one of the most commonly found bacteria in pneumonia cases, using two near-infrared light sources and indocyanine green, a FDA approved dye. Photodynamic inactivation experiments with bacteria alone allowed to determine the best parameters for microbial inactivation. Cytotoxicity assays with RAW 264.7 macrophages evaluated the safety of the PDI. To determine if the photodynamic inactivation had a positive or negative effect on the natural killing action of macrophages, we selected and tested fewer indocyanine green concentrations and 10 J/cm2 on macrophage-S. pneumoniae co-cultures. We concluded that ICG has potential as a photosensitizer for near-infrared photodynamic inactivation of S. pneumoniae, producing minimum negative impact on RAW 264.7 macrophages and having a positive interaction with the immune cell's microbicidal action.

Fast subsurface fingerprint imaging with full-field optical coherence tomography system equipped with a silicon camera.

Images recorded below the surface of a finger can have more details and be of higher quality than the conventional surface fingerprint images. This is particularly true when the quality of the surface fingerprints is compromised by, for example, moisture or surface damage. However, there is an unmet need for an inexpensive fingerprint sensor that is able to acquire high-quality images deep below the surface in short time. To this end, we report on a cost-effective full-field optical coherent tomography system comprised of a silicon camera and a powerful near-infrared LED light source. The system, for example, is able to record 1.7 cm×1.7 cmen face images in 0.12s with the spatial sampling rate of 2116 dots per inch and the sensitivity of 93dB. We show that the system can be used to image internal fingerprints and sweat ducts with good contrast. Finally, to demonstrate its biometric performance, we acquired subsurface fingerprint images from 240 individual fingers and estimated the equal-error-rate to be ∼0.8%. The developed instrument could also be used in other en face deep-tissue imaging applications because of its high sensitivity, such as in vivo skin imaging.

Efficient High-Power Ultrashort Pulse Compression in Self-Defocusing Bulk Media

Peak and average power scalability is the key feature of advancing femtosecond laser technology. Today, near-infrared light sources are capable of providing hundreds of Watts of average power. These sources, however, scarcely deliver pulses shorter than 100 fs which are, for instance, highly beneficial for frequency conversion to the extreme ultraviolet or to the mid- infrared. Therefore, the development of power scalable pulse compression schemes is still an ongoing quest. This article presents the compression of 90 W average power, 190 fs pulses to 70 W, 30 fs. An increase in peak power from 18 MW to 60 MW is achieved. The compression scheme is based on cascaded phase-mismatched quadratic nonlinearities in BBO crystals. In addition to the experimental results, simulations are presented which compare spatially resolved spectra of pulses spectrally broadened in self-focusing and self-defocusing media, respectively. It is demonstrated that balancing self- defocusing and Gaussian beam convergence results in an efficient, power-scalable spectral broadening mechanism in bulk material.

Ultra-small near-infrared multi-wavelength light source using a heterojunction photonic crystal waveguide and self-assembled InAs quantum dots

We herein propose and verify an ultra-small near-infrared (NIR) multi-wavelength light source using a heterojunction photonic crystal waveguide (PC-WG) and quantum dots (QDs). A heterojunction two-dimensional PC-WG, which consists of multiple PC-WGs with sequentially shifted structural parameters, is fabricated on a GaAs-slab including InAs QDs. Spontaneous emission (SE) from embedded InAs QDs was enhanced at multiple wavelengths resonating with slow-light regions of the PC-WG modes. The enhanced SE was propagated and detected through the heterojunction PC-WG. These results indicate the feasibility of the proposed light source.

Preparation and photothermal study of polystyrene coated with gold nanoshell composite particles

Polystyrene coated with gold nanoshell composite particles, with good photothermal properties, were prepared by electrostatic self-assembly. Firstly, polystyrene (PS) microspheres were synthesized by emulsifier-free emulsion polymerization, and it is determined that the PS microsphere has an average diameter of 165 nm, carboxyl on the surface, and its surface potential turned into +38.3 mV after modified by polyallylamine hydrochloride (PAH). Secondly, gold seeds, with an average diameter of 5.14 nm and surface potential of −10.7 mV, were prepared via sodium borohydride reducing chloroauric acid. Then, gold seeds were adsorbed on the surface of PS microspheres by electrostatic self-assembly and the composite particles were obtained after gold seeds grew multiple times. Finally, 0.3 mg/mL composite particles dispersion was irradiated with a near-infrared (NIR) light source and the temperature of the dispersion increased 13 °C after 5 min.

Photo-Induced Cell Damage Analysis for Single- and Multifocus Coherent Anti-Stokes Raman Scattering Microscopy

In this study, we investigated photo-induced damage to living cells during single- and multifocus excitations for coherent anti-Stokes Raman scattering (CARS) imaging. A near-infrared pulsed laser (709 nm) was used to induce cell damage. We compared the photo-induced cell damage in the single- and the multifocus excitation schemes with the condition to obtain the same CARS signal in the same frame rate. For the evaluation of cell viability, we employed 4′,6-diamidino-2-phenylindole (DAPI) fluorophores that predominantly stained the damaged cells. One- and two-photon fluorescence of DAPI fluorophores were, respectively, excited by an ultraviolet light source and the same near-infrared light source and were monitored to evaluate the cell viability during near-infrared pulsed laser irradiation. We found lower uptake of DAPI fluorophores into HeLa cells during the multifocus excitation compared with the single-focus excitation scheme in both the one- and the two-photon fluorescence examinations. This indicates a reduction of photo-induced cell damage in the multifocus excitation. Our findings suggested that the multifocus excitation scheme is expected to be suitable for CARS microscopy in terms of minimal invasiveness.

Growth of quantum three-dimensional structure of InGaAs emitting at ~1 µm applicable for a broadband near-infrared light source

We obtained a high-intensity and broadband emission centered at ~1µm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduced misfit dislocations. However, under certain growth conditions for the In concentration and growth temperature, the growth mode of the InGaAs layer can be transformed from two-dimensional to 3D growth. We found the optimal conditions to obtain a broadband emission from 3D structures with a high intensity and controlled center wavelength at ~1µm. This method offers an alternative approach for fabricating a broadband near-infrared light source for telecommunication and medical imaging systems such as for optical coherence tomography.