Commercial Laser Sources Research Articles

Results from Cryo-PoF: Power over fiber for fundamental and applied physics at cryogenic temperature

The Power over Fiber (PoF) technology delivers electrical power by sending laser light through an optical fiber to a photovoltaic power converter, in order to power sensors or electrical devices. This solution offers several advantages: removal of noise induced by power lines, robustness in a hostile environment, spark free operation when electric fields are present and no interference with electromagnetic fields.This technology is at the basis of the Cryo-PoF project: an R&D funded by the Italian Institute for Nuclear Research (INFN) in Milano-Bicocca (Italy). This project is inspired by the needs of the DUNE Vertical Drift detector, where the VUV light of liquid argon must be collected at the cathode, i.e. on a surface whose voltage exceeds 300 kV. We developed a cryogenic system, which is solely based on optoelectronic devices and a single laser input line, to power both the Photon Detection devices and its electronic amplifier. The Milano-Bicocca setup employ a commercial GaAs laser source with 2 W maximum power and a photovoltaic power converter with efficiency of ∼ 30% at liquid nitrogen temperature. The results obtained in Milano Bicocca will be presented with emphasis on performance and potential application in the field of applied physics.

Real-Time Temperature-Controlled Retinal Laser Irradiation in Rabbits.

Subdamaging thermal retinal laser therapy has the potential to induce regenerative stimuli in retinal diseases, but validated dosimetry is missing. Real-time optoacoustic temperature determination and control could close this gap. This study investigates a first in vivo application. Two iterations of a control module that were optically coupled in between a continuous-wave commercial laser source and a commercial slit lamp were evaluated on chinchilla rabbits. The module allows extraction of the temperature rise in real time and can control the power of the therapy laser such that a predefined temperature rise at the retina is quickly achieved and held constant. Irradiations with aim temperatures from 45°C to 69°C were performed on a diameter of 200 µm and a heating time of 100 ms. We analyzed 424 temperature-guided irradiations in nine eyes of five rabbits. The mean difference between the measured and aim temperature was -0.04°C ± 0.98°C. The following ED50 values for visibility thresholds could be determined: 58.6°C for funduscopic visibility, 57.7°C for fluorescein angiography, and 57.0°C for OCT. In all measurements, the correlation of tissue effect was higher to the temperature than to the average heating laser power used. The system was able to reliably perform temperature-guided irradiations, which allowed for better tissue effect control than simple power control. This approach could enhance the accuracy, safety, and reproducibility of thermal stimulating laser therapy. This study is a bridge between preclinical ex vivo experiments and a pilot clinical study.

Fiber-optic temperature sensor based on fabry-perot laser diode strong feedback

A novel, simple, and low-cost optical fiber temperature detection system is proposed and demonstrated in this paper, which uses the strong feedback of the Fabry-Perot Laser Diode (FP-LD) at 1550 nm to demodulate the temperature in real time in the resonator cavity. The experimental system consists of a commercial telecommunication laser source (FP-LD) and a fiber-optic Sagnac ring. In the sensing test, the change in temperature has a perfectly linear relationship with the shift of beat frequency signals (BFS). Measuring signals of different frequency will have different sensing sensitivities. System has an external photodetector (PD) in the first experiment. The temperature monitoring sensitivities is estimated to be 14.87 kHz/°C@2.49 GHz. In the second experimental system, there is no external PD, and the built-in monitor PD of FP-LD is used for photoelectric conversion. The sensitivity of the temperature sensor is 8.14 kHz/°C@1.382 GHz. In this paper, a fiber sensing system with the lowest cost and simplest structure is proposed, which consists of only a laser diode and a Sagnac ring.

Photonic integrated circuit with sampled grating lasers fabricated on a generic foundry platform for broadband terahertz generation.

We demonstrate a monolithically integrated photonic integrated circuit (PIC) for terahertz spectroscopy with wide spectral bandwidth. The PIC includes two widely tunable sampled grating DBR (SG DBR) lasers, semiconductor optical amplifiers (SOAs), and passive components to combine signals. The SG DBR lasers cover 22 nm and 24 nm tuning range, respectively, with 4 nm overlap in the C band. The side mode suppression ratio (SMSR) exceeds 37 dB with a linewidth below 4.3 MHz. We used the PIC to generate THz radiation with a state-of-the-art photodiode emitter. The measured THz power spectrum between 0.03 and 1 THz compares well with the spectrum generated with commercial tunable laser sources. This demonstrates the suitability of our PIC for future miniaturized continuous wave (cw) THz systems.

Utilizing a Diffractive Focus Beam Shaper to Enhance Pattern Uniformity and Process Throughput during Direct Laser Interference Patterning.

Uniform periodic microstructure formation over large areas is generally challenging in Direct Laser Interference Patterning (DLIP) due to the Gaussian laser beam intensity distribution inherent to most commercial laser sources. In this work, a diffractive fundamental beam-mode shaper (FBS) element is implemented in a four-beam DLIP optical setup to generate a square-shaped top-hat intensity distribution in the interference volume. The interference patterns produced by a standard configuration and the developed setup are measured and compared. In particular, the impact of both laser intensity distributions on process throughput as well as fill-factor is investigated by measuring the resulting microstructure height with height error over the structured surface. It is demonstrated that by utilizing top-hat-shaped interference patterns, it is possible to produce on average 44.8% deeper structures with up to 60% higher homogeneity at the same throughput. Moreover, the presented approach allows the production of microstructures with comparable height and homogeneity compared to the Gaussian intensity distribution with increased throughput of 53%.

Estimation of nominal ocular hazard distance and nominal ocular dazzle distance for multibeam laser radiation.

This paper presents a method of estimation of the nominal ocular hazard distance (NOHD) and the nominal ocular dazzle distance (NODD) for multibeam laser radiation. For the analysis, laser beams propagating in the same optical path (overlapping) but with different wavelength, power, and divergences in two perpendicular planes were assumed. To the authors' best knowledge, such a comprehensive analysis of multiple beams, considering the above parameters, is being presented for the first time. The dazzling possibilities described thus far assumed a single beam of radiation with a circular cross-section. This article also presents the calculation results of the NOHD and the NODD values for three laser beams with wavelengths in the red, green, and blue radiation spectrum with assumed parameters. Similar calculations were also made for a commercial laser source with potential use for laser dazzling. The presented analysis did not take into account the attenuation of radiation by the atmosphere. Moreover, the study provides recommendations on how to design effective, but safe, multiwavelength laser dazzlers.

Delivery of CW laser power up to 300 watts at 1080 nm by an uncooled low-loss anti-resonant hollow-core fiber.

In this paper, we report the use of a 3-meter low-loss anti-resonant hollow-core fiber (AR-HCF) to deliver up to 300 W continuous-wave laser power at 1080 nm wavelength from a commercial fiber laser source. A near-diffraction-limited beam is measured at the output of the AR-HCF and no damage to the uncooled AR-HCF is observed for several hours of laser delivery operation. The limit of AR-HCF coupling efficiency and laser-induced thermal effects that were observed in our experiment are also discussed.

Sub-THz Optical Frequency Comb Generation by Efficient Repetition-Rate Multiplication of a 250-MHz Mode-locked Laser

We demonstrate pulse repetition-rate multiplication (RRM) of a low-rate (sub-GHz) commercial mode-locked laser (MLL) source, and show the potential of the method for optical frequency comb (OFC) generation with ultra-broad frequency spacings. Experimentally, MLL pulses at a 250-MHz repetition rate are sent to a dispersion compensating fiber where pulse RRM is produced through temporal self-imaging, achieving record-high multiplication factors (up to 1540). The rate multiplied pulses are used as a pump signal to modulate the phase of a continuous-wave light through cross-phase modulation (XPM) in a highly nonlinear fiber, leading to the generation of OFCs with ultra-broad frequency spacings (up to 385 GHz). Furthermore, a detailed numerical analysis of the demonstrated scheme is also carried out, involving simulations of the RRM and XPM processes. Through this analysis, the effects of residual dispersions and pump power are investigated towards optimization of the performance of the OFC generation mechanism. The demonstrated approach is efficient in that it fundamentally preserves the input pulses' energy, it offers an important degree of versatility, e.g., in regards to the central optical wavelength and frequency spacing of the produced combs, and it requires no high-speed electronics.

Upconversion detection of 1.25 Gb/s mid-infrared telecommunications using a silicon avalanche photodiode.

With an ever-increasing interest in secure and reliable free-space optical communication, upconversion detectors enabled through nonlinear optical processes are an attractive route to transmitting data as a mid-infrared signal. This spectral region is known to have a higher transmissivity through the atmosphere. In this work, we present an upconversion scheme for detection in the silicon absorption band using magnesium-oxide doped periodically poled lithium niobate to generate 21 mW of a 3.4 µm signal from commercial laser sources using a difference frequency generation process. Following a further nonlinear frequency conversion, via sum-frequency generation, the resulting signal at 809 nm is detected. We achieve >50 µW of signal and bit error rates of 10-7 from a single-pass nonlinear conversion for both the transmitter and receiver systems without the need for additional optical amplifiers at the receiving end. The error rates due to potentially reduced laser powers at the receiver end are investigated and laser noise transfer through our system is discussed.

Experimental design for CO2 laser cutting of sub-millimeter features in very large-area carbon nanotube sheets

In this work, laser cutting methodologies have been demonstrated for defining submillimeter features in commercially available carbon nanotube (CNT) sheet materials (24 and 74-µm thick) using a commercial CO2 laser source with a maximum power output of 30 W. Full factorial and central composite designs of experiments were used to investigate the effect of various factors, including the laser power (10–90% of max), speed (10–90% of max), and pulses per inch (100–1000 PPI), on the resulting kerf width and the kerf width variation for 5 mm long single straight-line features. Maximizing the pulses per inch yielded laser cuts with reduced variability, while the power and speed were determined to be the significant factors affecting the kerf width. Fabrication of more complex grid structures, consisting of 100 square openings (0.838 mm wide), revealed that the conditions used for cutting straight lines were insufficient for cutting grids. Thus, for a fixed number of pulses-per-inch, the ratio of the values of power and speed, P/S ratio, was determined to be most significant for affecting the feature quality of these grid structures, as it determines the heat input energy and the delivered energy density. It was determined that, for a fixed PPI of 1000, a percent power value 1.6 × higher than the percent speed value was needed as the input parameter to cut the 24 µm thick CNT sheet, and a percent power value 3.5 × higher than the percent speed value was required to successfully cut the 74 µm thick CNT sheet. Ultimately, refinement in the laser cutting conditions by increasing the energy delivered per pulse and using two passes to account for sheet non-uniformities, enabled patterning of large area (up to 280 mm × 280 mm) CNT sheets with close-packed circles. A structure of this size has over 48,000 openings, and analysis via optical microscopy determined the features have a measured diameter of 0.78 mm ± 0.01 mm, exhibiting reproducibility over the entire CNT sample. Finally, multiple intricate geometries with variable feature spacing were fabricated all on a single CNT sample, demonstrating the utility of laser machining as an alternative technology solution to traditional CNT patterning techniques. These results provide a scalable methodology to determine the laser cutting parameters for use in fabricating very large-area CNT structures with intricate features.

Nonlinearity-compensation-free optical frequency domain reflectometry based on electrically-controlled optical frequency sweep

A nonlinearity-compensation-free optical frequency domain reflectometry (OFDR) scheme is proposed and experimentally demonstrated based on the electrically-controlled optical frequency sweep. In the proposed scheme, the linear frequency sweep light is generated by propagating an ultra-narrow-linewidth continuous-wave (CW) light through an electro-optic frequency shifter which consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and an electronic 90° hybrid, where the electro-optic frequency shifter is driven by a linear frequency modulated signal generated by a direct digital synthesizer (DDS). Experimental results show that the spatial resolution and signal-to-noise ratio (SNR) of the proposed OFDR scheme without the nonlinear phase compensation are comparable to those of OFDR employing a commercial tunable laser source (TLS), an auxiliary interferometer, and a software-based nonlinear phase compensation method. The proposed OFDR scheme is helpful to reduce the complexity of the optical structure and eliminate the difficulty of developing the nonlinear phase compensation algorithm.

Stimulated Raman Excited Fluorescence Spectroscopy of Visible Dyes.

Fluorescence spectroscopy and Raman spectroscopy are two major classes of spectroscopy methods in physical chemistry. Very recently, stimulated Raman excited fluorescence (SREF) has been demonstrated ( Xiong, H.; et al. Nature Photonics , 2019 , 13 , 412 - 417 ) as a new hybrid spectroscopy that combines the vibrational specificity of Raman spectroscopy with the superb sensitivity of fluorescence spectroscopy (down to the single-molecule level). However, this proof-of-concept study was limited by both the tunability of the commercial laser source and the availability of the excitable molecules in the near-infrared. As a result, the generality of SREF spectroscopy remains unaddressed, and the understanding of the critical electronic preresonance condition is lacking. In this work, we built a modified excitation source to explore SREF spectroscopy in the visible region. Harnessing a large palette of red dyes, we have systematically studied SREF spectroscopy on a dozen different cases with a fine spectral interval of several nanometers. The results not only establish the generality of SREF spectroscopy for a wide range of molecules but also reveal a tight window of proper electronic preresonance for the stimulated Raman pumping process. Our theoretical modeling and further experiments on newly synthesized dyes also support the obtained insights, which would be valuable in designing and optimizing future SREF experiments for single-molecule vibrational spectroscopy and supermultiplex vibrational imaging.

Targeting the Next Generation of Deep-Ultraviolet Nonlinear Optical Materials: Expanding from Borates to Borate Fluorides to Fluorooxoborates.

Coherent light radiation down to the deep-ultraviolet spectral range (λ < 200 nm) produced by common laser sources is extensively used in diverse fields ranging from ultrahigh-resolution photolithography to photochemical synthesis to high-precision microprocessing. Actually, it is hard to immediately obtain certain wavelengths, deep-ultraviolet coherent light in particular, from commercial laser sources. However, the direct second harmonic generation process governed in part by nonlinear optical crystals is a feasible and effective approach to generate deep-ultraviolet coherent light, which motivates chemists and materials scientists to find potential deep-ultraviolet nonlinear optical materials that can practically meet the scientific requirements. The research progress required to go from a new single-crystal structure to final device applications involves many pivotal steps and is highly time-consuming and challenging, and therefore, it is necessary to commence systematic studies aimed at shortening the research cycle and accelerating the rational design of deep-ultraviolet nonlinear optical materials. In this Account, we choose borates as raw materials because they have ever-greater possibilities to form desired noncentrosymmetric structures, wide optical transparency windows, rich structural chemistry, and also large polarizabilities to guarantee the coexistence of large second-order nonlinear optical coefficients and suitable birefringence. Besides, the effects of fluorine atoms on the structural chemistry and optical properties of borates have been summarized and analyzed. On the basis of these favorable influences, three specific rational design strategies, including experimental and theoretical methods, have been proposed in order to shorten the investigational cycle of discovering the new expected compounds with high physicochemical performances required for practical applications. In this way, the progress of searching for candidates for the next generation of deep-ultraviolet nonlinear optical materials was accelerated from borates to borate fluorides to fluorooxoborates with three effective strategies: (1) expansion of the frontier from borates to borate fluorides with the introduction of fluorine to achieve enhanced optical performance; (2) computer-assisted design of new deep-ultraviolet nonlinear optical materials with a newly introduced systematic global structure optimization method; and (3) expansion of the frontier from borate fluorides to fluorooxoborates by proposed functionalizedoxyfluoride [BO xF4- x]( x+1)- ( x = 1, 2, 3) chromophores to balance multiple criteria. The preliminary development of fluorooxoborates exhibiting high performance as a new fertile field to search for deep-ultraviolet nonlinear optical materials is highly encouraging and inspiring and can guide chemists and materials scientists with new directions and thoughts aimed at finding the next generation of practical deep-ultraviolet nonlinear optical materials.

Tuneable dual-comb spectrometer based on commercial femtosecond lasers and reference cell for optical frequency calibration

Two commercial femtosecond laser sources have been used to implement a dual-comb spectrometer tuneable across a spectral range from 1.5 to 2.2 μm. The optical linewidth of the comb modes was characterized for different time scales in order to estimate the achievable spectral resolution for an optimal acquisition time. The transmission spectra of three different gas samples were recorded, demonstrating good agreement with reference data. Frequency axis calibration was provided via the parallel monitoring of a reference sample. This technique allows an accurate calibration of the frequency axis of the spectrometer, with no need for stabilization or optical referencing of the frequency combs. Our set-up represents a good compromise for a compact and versatile dual-comb spectrometer based on commercially available parts with possible applications in trace-gas monitoring, remote sensing and spectroscopy of short-lived processes.

Bright, “Clickable” Porphyrins for the Visualization of Oxygenation under Ambient Light

AbstractA new group of “clickable” and brightly emissive metalloporphyrins has been developed for the visualization of oxygenation under ambient light with the naked eye. These alkynyl‐terminated compounds permit the rapid and facile synthesis of oxygen‐sensing dendrimers through azide–alkyne click chemistry. With absorption maxima overlapping with the wavelengths of common commercial laser sources, they are readily applicable to biomedical imaging of tissue oxygenation. An efficient synthetic methodology, featuring the stable trimethylacetyl (pivaloyl) protecting group, is described for their preparation. A paint‐on liquid bandage containing a new, click‐synthesized porphyrin dendrimer has been used to map oxygenation across an ex vivo porcine skin burn model.

Bright, "Clickable" Porphyrins for the Visualization of Oxygenation under Ambient Light.

A new group of "clickable" and brightly emissive metalloporphyrins has been developed for the visualization of oxygenation under ambient light with the naked eye. These alkynyl-terminated compounds permit the rapid and facile synthesis of oxygen-sensing dendrimers through azide-alkyne click chemistry. With absorption maxima overlapping with the wavelengths of common commercial laser sources, they are readily applicable to biomedical imaging of tissue oxygenation. An efficient synthetic methodology, featuring the stable trimethylacetyl (pivaloyl) protecting group, is described for their preparation. A paint-on liquid bandage containing a new, click-synthesized porphyrin dendrimer has been used to map oxygenation across an ex vivo porcine skin burn model.

Generating the Local Oscillator “Locally” in Continuous-Variable Quantum Key Distribution Based on Coherent Detection

Continuous-variable quantum key distribution (CV-QKD) protocols based on coherent detection have been studied extensively in both theory and experiment. In all the existing implementations of CV-QKD, both the quantum signal and the local oscillator (LO) are generated from the same laser and propagate through the insecure quantum channel. This arrangement may open security loopholes and also limit the potential applications of CV-QKD. In this paper, we propose and demonstrate a pilot-aided feedforward data recovery scheme which enables reliable coherent detection using a "locally" generated LO. Using two independent commercial laser sources and a spool of 25 km optical fiber, we construct a coherent communication system. The variance of the phase noise introduced by the proposed scheme is measured to be 0.04 (rad^2), which is small enough to enable secure key distribution. This technology also opens the door for other quantum communication protocols, such as the recently proposed measurement-device-independent (MDI) CV-QKD where independent light sources are employed by different users.

All-optical spectral linewidth reduction of lasers for coherent optical communication

We propose and experimentally demonstrate an effective spectral linewidth suppression scheme for a commercial tunable laser source. By using a long-cavity, narrow-bandwidth stimulated Brillouin scattering filter and multifrequency-selection mechanism simultaneously, a single-longitudinal-mode laser output with linewidth suppression from ~3 MHz to less than 20 kHz is successfully achieved in the whole C-band. Meanwhile, insertion loss of ~5 dB and a side-mode suppression ratio improvement of ~20 dB at a typical output wavelength of 1552.520 nm are obtained. The scheme is experimentally verified to be wavelength independent in the C-band and characterized with good performance of wavelength and power stability.

Analysis of microwave leaky modes propagating through laser plasma filaments column waveguide

A plasma column waveguide formed by a bundle of closely spaced plasma filaments induced by the propagation of ultrafast laser pulses in air and revived by a longer infrared laser pulse is shown to support microwave radiation. We consider values of both the plasma electron density and microwave frequency for which the refractive index of plasma is lower than the refractive index of air; therefore, a leaky plasma waveguide can be realized in extremely high frequency band. The guiding mechanism does not require high conductance of the plasma and can be easily excited by using commercial femtosecond laser sources. A theoretical study of leaky mode characteristics of isotropic and homogeneous plasma column waveguides is investigated with several values of plasma and waveguide structure parameters. The microwave transmission loss was found to be mainly caused by the microwave leakage through the air-plasma interface and is weakly dependent on the plasma absorption. In spite of losses of microwaves caused by leakage and plasma absorption, it is shown to be much lower than both that accompanying to surface waves attaching to single conducting plasma wire and the free space propagation over distances in the order of the filament length, which opens exciting perspectives for short distance point to point wireless transmission of pulsed-modulated microwaves.

Parameterization of local laser doping and laser-fired contacts for high efficiency c-Si solar cells

Abstract Local laser doping (LLD) and laser fired-contacts (LFC) are among the most promising techniques based on laser tools to be industrially applied in high efficiency crystalline silicon (c-Si) solar cells production. Here we present a comprehensive parameterization of LLD and LFC processes using commercial ns laser sources. The best process conditions are assessed both analysing the morphology and the electrical characteristics of the irradiated test samples. Values for the normalized LFC resistance far below 1.0 mΩcm 2 have been obtained. For LLD experiments we found irradiation conditions giving excellent diode behaviour, with ideality factors below 1.5.