Low-cost Laser Diode Research Articles

Singlet fission photovoltaic cells as dual-wavelength laser power converters compatible with highly efficient solar cells

I applied photovoltaic cells equipped with singlet fission (SF) of molecular systems to dual-wavelength laser power converters (DW-LPCs) that efficiently convert two laser lights of different wavelengths to electricity. When the SF-DW-LPC is illuminated by eye-safe laser light of 1470 nm wavelength emitted from a laser diode, a single photon is converted to a single carrier. On the other hand, a single high-energy photon emitted from a high-power and low-cost laser diode of 808 nm is converted to two carriers by SF owing to its endothermic feature, even though the photon energy is slightly lower than twice the fundamental energy gap. Furthermore, the SF-DW-LPC operates as a highly efficient solar cell. These functions are required for optical wireless power transmission to moving objects including electric vehicles and flying drones. I modeled the photovoltaic process with SF and evaluated the limiting conversion efficiencies by detailed-balance calculations. Conversion efficiencies of the SF-DW-LPC for these two laser lights are competitive with those of the conventional single-junction LPCs dedicated to these wavelengths, respectively. The efficiency under solar light is close to that of the optimally designed SF solar cell. Furthermore, the SF-DW-LPC outperforms other types of DW-LPCs designed on the basis of intermediate band, triplet–triplet annihilation, and multiple exciton generation solar cells. Endothermic SF and carrier/energy extraction into the neighboring acceptors have already been demonstrated. However, molecular systems that apply to 1470 nm have not yet been realized, which is the top-priority issue to be solved to realize highly efficient SF-DW-LPCs.

Autonomous diode laser weeding mobile robot in cotton field using deep learning, visual servoing and finite state machine

Small autonomous robotic platforms can be utilized in agricultural environments to target weeds in their early stages of growth and eliminate them. Autonomous solutions reduce the need for labor, cut costs, and enhance productivity. To eliminate the need for chemicals in weeding, and other solutions that can interfere with the crop’s growth, lasers have emerged as a viable alternative. Lasers can precisely target weed stems, effectively eliminating or stunting their growth. In this study an autonomous robot that employs a diode laser for weed elimination was developed and its performance in removing weeds in a cotton field was evaluated. The robot utilized a combination of visual servoing for motion control, the Robotic operating system (ROS) finite state machine implementation (SMACH) to manage its states, actions, and transitions. Furthermore, the robot utilized deep learning for weed detection, as well as navigation when combined with GPS and dynamic window approach path planning algorithm. Employing its 2D cartesian arm, the robot positioned the laser diode attached to a rotating pan-and-tilt mechanism for precise weed targeting. In a cotton field, without weed tracking, the robot achieved an overall weed elimination rate of 47% in a single pass, with a 9.5 second cycle time per weed treatment when the laser diode was positioned parallel to the ground. When the diode was placed at a 10°downward angle from the horizontal axis, the robot achieved a 63% overall elimination rate on a single pass with 8 seconds cycle time per weed treatment. With the implementation of weed tracking using DeepSORT tracking algorithm, the robot achieved an overall weed elimination rate of 72.35% at 8 seconds cycle time per weed treatment. With a strong potential for generalizing to other crops, these results provide strong evidence of the feasibility of autonomous weed elimination using low-cost diode lasers and small robotic platforms.

Laser Exposure Systems for Multiwell Plate Photodynamic Therapy (PDT) Treatments: Reactive Oxygen Species Generation and Photocytotoxicity

SignificanceThe study demonstrated the development of two low-cost custom laser diode exposure systems for early-stage PDT studies that provide homogenous output power at the target regions at specific wavelengths, during the duration of treatment. ApproachTwo custom laser diode exposure systems were built and optimized for high-throughput PDT applications. The power output for tested laser diodes was quantified and the photosensitizer induced photochemistry was evaluated using a cell-free and an in-vitro assay. ResultsThe experimental results showed that the laser exposure system was suitable for PDT experiments up to 10mW/cm2. The laser power was homogenous for the 4- and 6-well illumination with variable irradiation exposure time. The photoactivation of photosensitizers showed consistent results with the cell-free SOSG and in-vitro NRU assay. ConclusionsThe laser diode systems developed by the authors for use in high throughput PDT experiments, provided uniform and stable output up to 10mW/cm2. Variation between the output power was less than 10%The results obtained using the cell-free SOSG and in-vitro NRU assay were consistent and in agreement with the literature.

Quantitative Fluorescent Lateral Flow Strip Sensor for Myocardial Infarction Using Purity-Color Upconversion Nanoparticles.

Acute myocardial infarction is a serious cardiovascular disease and poses significant risks to human health. Its early diagnosis and real-time detection are of great importance. Herein, we design a low-cost device that has a high sensitivity of cTnT and cTnI detection. Dual-color upconversion nanoparticles (UCNPs) are prepared as probes, which not only have high-purity red upconversion luminescence (UCL) under 980 or 808 nm excitation but also achieve good temperature sensing. Temperature-dependent multicolor emission excitation is obtained, and the color turns from white to orange and red with increasing temperature. In particular, the maximum SR and SA values based on nonthermally coupled levels are 4.76% K-1 and 8.6% K-1, which are higher than those based on thermally coupled levels. With the UCNPs-based lateral flow strip (LFS), the specific detection of cTnI and cTnT antigens in samples is achieved with a detection limit of 0.001 ng/mL, which is 1 order of magnitude lower than that of their clinical cutoff. The UCNPs-LFS device has a low-cost laser diode and a simplified laser and permits a mobile-phone camera to collect the results, which has an important influence on the field of biomarker sensing.

Continuous-wave second-harmonic generation in the far-UVC pumped by a blue laser diode

Far-UVC light in the wavelength range of 200–230 nm has attracted renewed interest because of its safety for human exposure and effectiveness in inactivating pathogens. Here we present a compact solid-state far-UVC laser source based on second-harmonic generation (SHG) using a low-cost commercially-available blue laser diode pump. Leveraging the high intensity of light in a nanophotonic waveguide and heterogeneous integration, our approach achieves Cherenkov phase-matching across a bonded interface consisting of a silicon nitride (SiN) waveguide and a beta barium borate (BBO) nonlinear crystal. Through systematic investigations of waveguide dimensions and pump power, we analyze the dependencies of Cherenkov emission angle, conversion efficiency, and output power. Experimental results confirm the feasibility of generating far-UVC, paving the way for mass production in a compact form factor. This solid-state far-UVC laser source shows significant potential for applications in human-safe disinfection, non-line-of-sight free-space communication, and deep-UV Raman spectroscopy.

Low-cost, interdigitated capacitive sensor using laser-written graphene foam for touch, proximity, and liquid level detection

Flexible capacitive sensors are gaining popularity in place of sophisticated optical sensing or bulky mechanical designs for specific applications such as proximity/gesture detection and liquid level sensing. So, here, we propose Laser Induced Graphene Foam (LIGF) based planar capacitive sensors, which are flexible, highly sensitive, energy-efficient, and cost-effective, making them accessible for various applications. The working of these sensors involves the interdigitated planar electrode configuration and the fringing effect, influencing capacitance when the permittivity or the electric charge of the surrounding medium changes. LIGF planar capacitive elements were produced on a commercially availed polymer polyimide by using direct laser writing technique employing a low-cost diode laser. The developed LIGF-based planar capacitive touch sensor showed an average touch response (|ΔC/Co|) of more than 49%; moreover, when used for proximity sensing, this sensor could detect the presence of human hand up to a maximum distance of 170 mm from the sensor surface. An extended design of the sensor has demonstrated liquid level sensing with an accuracy of 0.97 mm. As a result of its ability to sense dielectric materials, contactless operation, long-range sensing, cost-effectiveness, low-power consumption, and environmental friendliness, the LIGF electrode-based capacitive sensor can be incorporated into a variety of modern technology and devices.

Observing temporal variation in hemolysis through photoacoustics with a low cost LASER diode based system

Patients under hemolytic condition need continuous monitoring of lysis as depletion of Red Blood Cells (RBC) and the presence of antioxidant free hemoglobin (Hb) in excess amount due to hemolysis lead to severe deterioration of their health. Out of many modalities, Photoacoustics (PA) offers real time information noninvasively from deep lying blood vessels since Hb is the strongest chromophore in mammalian blood and the PA response of blood varies with the amount of Hb present. During hemolysis, total Hb content in blood however remains unchanged, thus, questions the use of PA in hemolysis detection. In this report, a hypothesis that the amplitude of the PA signal would not change with the amount of lysis is framed and tested by applying osmotic shock to the RBCs in hypotonic environment and the PA response is recorded over time using a low cost NIR based PA system. The experimental outcome indicates that PA amplitude falls off as lysis progresses in course of time consequently rejecting the hypothesis. The decaying PA response also carries the signature of RBC swelling during the early phase of lysis. The PA measurement can detect hemolysis as low as 1.7%. These findings further advocate transforming this NIR-PA system into a portable, noninvasive patient care device to monitor hemolysis in-vivo.

Laser diode photoacoustic point source detection: machine learning-based denoising and reconstruction.

A new development in photoacoustic (PA) imaging has been the use of compact, portable and low-cost laser diodes (LDs), but LD-based PA imaging suffers from low signal intensity recorded by the conventional transducers. A common method to improve signal strength is temporal averaging, which reduces frame rate and increases laser exposure to patients. To tackle this problem, we propose a deep learning method that will denoise point source PA radio-frequency (RF) data before beamforming with a very few frames, even one. We also present a deep learning method to automatically reconstruct point sources from noisy pre-beamformed data. Finally, we employ a strategy of combined denoising and reconstruction, which can supplement the reconstruction algorithm for very low signal-to-noise ratio inputs.

Cladding pumped bismuth-doped fiber amplifiers operating in O-, E-, and S-telecom bands.

Bismuth-doped fibers (BDFs) are considered nowadays as an essential part of the development of novel optical amplifiers, which can provide a significant upgrade to existing fiber optic telecommunication systems, securing multiband data transmission. In this paper, a series of BDF amplifiers (BDFAs) for O-, E-, and S-telecom bands based on a cladding pumping scheme using low-cost multimode semiconductor laser diodes at a wavelength of 0.7-0.8 µm were demonstrated for, it is understood, the first time. The developed BDFAs are characterized by a high peak gain of >25-30 dB in the corresponding telecom bands and a relatively low noise figure of 5-6 dB. Comparative analysis shows that most of the parameters of cladding pumped BDFAs are close to those of the best core pumped ones. This research opens up new opportunities for utilizing Bi-doped fibers as a key element of cost-effective and ready-to-work BDFAs for various practical applications.

A tabletop experiment for speed of light measurement using a Red Pitaya STEMlab board

The speed of light is an important fundamental constant in physics, and so determining its value is a common undergraduate laboratory experiment. Methods to measure the light speed can help students practice their experimental skills and become familiar with the concepts of modern precision measurement techniques. In this paper, we demonstrate that a tabletop optical setup, comprised of an affordable Red Pitaya STEMlab board and a low-cost laser diode module, can be used to accurately determine the speed of light by measuring the frequency response of the phase shift between intensity-modulated light beams reflected by two end mirrors separated by 50 cm. By using the STEMlab built-in Bode analyzer to automatically scan the modulation frequency over the range from 10 to 40 MHz, the frequency response of phase is measured and recorded. These phase shift data are then used to calculate the speed of light with an uncertainty of less than 0.5%. With the help of the Red Pitaya board, the number of required electronic instruments for our setup is reduced. All of the required components are commercially available, and no electronic construction work is necessary so that teachers and students can implement the experiment in a plug-and-play manner.

Efficient high-power sub-50-fs gigahertz repetition rate diode-pumped solid-state laser.

In this article we present a directly diode-pumped high-power Kerr-lens mode-locked Yb:CALGO bulk laser oscillator operating at 1-GHz repetition rate. We report on two laser configurations optimized for either highest average power or shortest pulse duration. In the first configuration optimized for high average power, the oscillator delivers up to 6.9 W of average power, which is the highest average power of any ultrafast laser oscillator operating at gigahertz repetition rate. The 93-fs pulses have a peak power of 64 kW, and the optical-to-optical efficiency amounts to 37%. In the second configuration optimized for short pulse duration, we demonstrate 48-fs pulses at 4.1 W of average power corresponding to a higher peak power of 74kW with 21% optical-to-optical efficiency. This is the shortest pulse duration and the highest peak power demonstrated by any GHz-class Yb-based laser oscillator. The compact laser setup is directly pumped by a low-cost multimode fiber-coupled laser diode and has a high potential as an economical yet powerful source for various applications.

Deep-Learning-Based Algorithm for the Removal of Electromagnetic Interference Noise in Photoacoustic Endoscopic Image Processing.

Despite all the expectations for photoacoustic endoscopy (PAE), there are still several technical issues that must be resolved before the technique can be successfully translated into clinics. Among these, electromagnetic interference (EMI) noise, in addition to the limited signal-to-noise ratio (SNR), have hindered the rapid development of related technologies. Unlike endoscopic ultrasound, in which the SNR can be increased by simply applying a higher pulsing voltage, there is a fundamental limitation in leveraging the SNR of PAE signals because they are mostly determined by the optical pulse energy applied, which must be within the safety limits. Moreover, a typical PAE hardware situation requires a wide separation between the ultrasonic sensor and the amplifier, meaning that it is not easy to build an ideal PAE system that would be unaffected by EMI noise. With the intention of expediting the progress of related research, in this study, we investigated the feasibility of deep-learning-based EMI noise removal involved in PAE image processing. In particular, we selected four fully convolutional neural network architectures, U-Net, Segnet, FCN-16s, and FCN-8s, and observed that a modified U-Net architecture outperformed the other architectures in the EMI noise removal. Classical filter methods were also compared to confirm the superiority of the deep-learning-based approach. Still, it was by the U-Net architecture that we were able to successfully produce a denoised 3D vasculature map that could even depict the mesh-like capillary networks distributed in the wall of a rat colorectum. As the development of a low-cost laser diode or LED-based photoacoustic tomography (PAT) system is now emerging as one of the important topics in PAT, we expect that the presented AI strategy for the removal of EMI noise could be broadly applicable to many areas of PAT, in which the ability to apply a hardware-based prevention method is limited and thus EMI noise appears more prominently due to poor SNR.

Highly photo-stable, kHz-repetition-rate, diode pumped circulation-free liquid dye laser with thermal lens management

Liquid dye lasers have long been considered as ideal tunable laser sources in the visible range but are bulky, expensive, and require a complex system for dye circulation. Here, we present a system that relies on a low-cost blue laser diode as the pump source and a sealed dye cell with no flowing circuitry, resulting in a device that combines the convenience and size of a solid-state device with the stability of a liquid organic laser. A very high photo-stability is obtained (up to 1.2 × 109 pulses or 12 days at 1 kHz), which is five orders of magnitude higher than a solid-state dye laser operated in similar conditions. The number of pulses obtainable at low repetition rates is found to be limited by molecular self-diffusion and, hence, related to the total cuvette volume. In contrast, the repetition rate is limited to a few kHz, which suggests that thermal effects play a bigger role than triplet population effects. Thermal effects participate in the suppression of lasing through the buildup of a strong negative thermal lens; correcting the non-aberrant part of this thermal lens by resonator design enables the repetition rate to be pushed up to 14 kHz with possible further optimization. This work shows a route for building off-the-shelf, compact, low-cost, and convenient tunable pulsed lasers in the visible range that have superior stability over organic solid-state lasers.

Cerebrovascular imaging in vivo by non-contact photoacoustic microscopy based on photoacoustic remote sensing with a laser diode for interrogation.

Photoacoustic microscopy (PAM) is a unique tool for biomedical applications because it can visualize optical absorption contrast in vivo. Recently, non-contact PAM based on non-interferometric photoacoustic remote sensing (PARS), termed PARS microscopy, has shown promise for selected imaging applications. A variety of superluminescent diodes (SLDs) have been employed in the PARS microscopy system as the interrogation light source. Here, we investigate the use of a low-cost laser diode (LD) as the interrogation light source in PARS microscopy, termed PARS-LD. A side-by-side comparison of PARS-LD and a PARS microscopy system using an SLD was conducted that showed comparable performance in terms of resolution and signal-to-noise ratio. More importantly, for the first time to our knowledge, in vivo PAM imaging of mouse brain vessels was conducted in a non-contact manner, and the results show that PARS-LD provides great performance.

Low-cost laser diode pulse generator for quantum information applications

A simple short-pulse generator circuit based on electronic gates is designed for short electric pulse of about 12 ns at Full Width at Half Maximum (FWHM) and 3.6 Volt amplitude for driving a laser diode. Using our circuit with a 780 nm laser diode designed and fabricated for producing short light pulses. The circuit utilizes an AND gate, a XOR gate, and a common function generator, provides a repetition rate from DC up to 1 MHz. The laser pulses were generated and then detected via an avalanche photodiodes (APD). This finding can benefit the field of light-based quantum information including single photon experiments.

Waveguide Enhanced Raman Spectroscopy for Biosensing: A Review.

Waveguide enhanced Raman spectroscopy (WERS) utilizes simple, robust, high-index contrast dielectric waveguides to generate a strong evanescent field, through which laser light interacts with analytes residing on the surface of the waveguide. It offers a powerful tool for the direct identification and reproducible quantification of biochemical species and an alternative to surface enhanced Raman spectroscopy (SERS) without reliance on fragile noble metal nanostructures. The advent of low-cost laser diodes, compact spectrometers, and recent progress in material engineering, nanofabrication techniques, and software modeling tools have made realizing portable and cheap WERS Raman systems with high sensitivity a realistic possibility. This review highlights the latest progress in WERS technology and summarizes recent demonstrations and applications. Following an introduction to the fundamentals of WERS, the theoretical framework that underpins the WERS principles is presented. The main WERS design considerations are then discussed, and a review of the available approaches for the modification of waveguide surfaces for the attachment of different biorecognition elements is provided. The review concludes by discussing and contrasting the performance of recent WERS implementations, thereby providing a future roadmap of WERS technology where the key opportunities and challenges are highlighted.

Compact long-working-distance laser-diode-based photoacoustic microscopy with a reflective objective

Photoacoustic microscopy (PAM) has quickly developed into a noninvasive biomedical imaging technique to achieve detection, diagnosis, and monitoring. Compared with Q-switched neodymium-doped yttrium aluminum garnet or optical parametric oscillator lasers, a low-cost and small-size laser diode (LD) used as an alternative light source is conducive to achieving the miniaturization and integration for preclinical transformation. However, the LD’s low peak output power needs the high numerical aperture objective to attain tight focus, which limits the working distance (WD) of the system in only 2–3 mm, resulting in not achieving the backward coaxial confocal mode. Here, we present a compact visible LD-based PAM system with a reflective objective to achieve a 22 mm long WD and a 10 µm lateral resolution. Different depth subcutaneous microvascular networks in label-free mouse ears have successfully reappeared in vivo with a signal-to-noise ratio up to 14 dB by a confocal alignment. It will be a promising tool to develop into a handy tool for subcutaneous blood vessel imaging.

Optical properties of graphene oxide thin film reduced by low-cost diode laser

A non-toxic, fast, low-cost, single step and highly efficient reduction method is proposed in this research for the development of high-quality multilayer graphene film using laser diode. Graphene oxide film is irradiated with a diode laser (808 nm, 6 W) for different exposure times (1, 1.5, 2, 2.5, and 3 min.) to reduce it. Surface damage was observed on the graphene oxide (GO) film for exposure time greater than 3 min and at power 6 W. Different measurement techniques (Raman spectroscopy, Uv–visible absorption, photoluminescence and FTIR) are used to study the optical properties of rGO films. After laser irradiation, the Raman spectra of rGO films showed peaks for the D, G, and 2D bands centered at 1335, 1581, and 2710 cm−1, respectively. A small increase in the (ID/IG) ratio was observed and showed that greater reduction occurred after the graphene oxide film exposure time of 3 min. The as-prepared film of graphene oxide that showed absorption peak at 235 nm was red-shifted to 270 nm after 3 min of laser diode irradiation for reduction. The PL measurements were performed, where the sample was excited by Ar-ion laser (488 nm) and the PL signal was amplified using lock in techniques. The photoluminescence emission spectrum was measured at different positions on the graphene oxide film reduced for 3 min to show the effect of the energy spatial distribution of the laser diode beam on the rGO film. The maximum PL peaks gradually blue shifted and the peak intensities decreased as the measurements go toward the center of the reduced film. The FT-IR spectrum revealed that there are no hydroxyl, carboxyl, and epoxy groups and new peaks were found assigned to functional groups such as CH2, C–H by reducing the graphene oxide with laser diode for 3 min.

Compact and Highly Sensitive NO2 Photoacoustic Sensor for Environmental Monitoring.

A nitrogen dioxide (NO2) photoacoustic sensor for environmental monitoring was developed using a low-cost high-power laser diode emitting at 450 nm. A compact low-noise photoacoustic detection module was designed to reduce the sensor size and to suppress noise. A LabVIEW-based control system was employed for the sensor. The parameters of the sensor were studied in detail in terms of laser power and operating pressure. The linearity of the sensor response with laser power and NO2 concentration confirms that saturation does not occur. At atmospheric pressure, a 3σ detection limit of 250 ppt (part per trillion by volume) was achieved with a 1-s averaging time, which corresponds to the specific detectivity of 3.173 × 10−9 W cm−1 Hz−1/2. A 72 h outdoor continuous on-line monitoring of environmental NO2 was implemented to demonstrate the reliability and validity of the developed NO2 sensor.

Optical Coherence Tomography/Angiography-Guided Tumor Ablation With a Continuous-Wave Laser Diode

Laser ablation can be an effective modality for treatment, but it is complicated to apply continuous-wave (CW) light sources for laser ablation because of the unpredictable photothermal damage. In this study, an integrated theranostic system combining a low-cost CW laser diode with optical coherence tomography (OCT)/angiography (OCTA) was utilized for the in vivo ablation of tumor tissues. To examine the effect of laser exposure on tissue scattering characteristics, the OCT backscattering intensities of non-ablated and ablated tissues were analyzed, and the effect on the skin microvasculature produced by laser ablation was quantitatively evaluated. Moreover, the integrated system and the proposed method were implemented for the treatment of skin tumor on the mouse model. The obtained results indicate that the developed laser ablation system can effectively remove tumor tissues with controllable photodamage under OCT/OCTA guidance and that the system cost may be significantly reduced by using the CW laser diode.