Low Peak Power Research Articles

Ethanol-infiltrated circular photonic crystal fiber for low peak power supercontinuum generation from near-infrared to mid-infrared region

Ethanol-infiltrated circular photonic crystal fiber for low peak power supercontinuum generation from near-infrared to mid-infrared region

In vivo biological safety investigation of Yb-CALGO femtosecond laser dental surgery.

While lasers have found their successful applications in various clinical specialties, in clinical dental practice, traditional mechanical drills are still predominantly utilized. Although erbium-doped lasers have been demonstrated for dental therapy, their clinical performance is still not satisfactory due to the long pulse width, low peak power, and small repetition rate. To attain a smaller thermal diffusion thus better biological safety and surgical precision, as well as more rapid ablation, the advancement of femtosecond laser techniques has opened another route of dental surgery; however, no biological safety investigation has been reported. Here, we present a systematic study of dental ablation by a Yb:CaAlGdO4 regenerative amplifier with a central wavelength of 1040 nm and pulse width of 160 fs. The in vivo experiment of dental surgery investigating the inflammatory response has been reported, for the first time to the best of our knowledge. It is demonstrated that dental surgery by Yb:CaAlGdO4 femtosecond laser ablation has better biological safety compared to the turbine drilling, thanks to its non-contact and ultrafast heat dissipation nature.

Design and analysis of the C6H6-filled circular photonic crystal fiber with ultra-flat dispersion for broadband supercontinuum generation with peak power of 130 W and 250 W

This article introduces a new model of a circular silica-based photonic crystal fiber with a hollow core filled with C6H6. The difference in the air hole size and the distance between them in the first ring around the core has a profound effect on the dispersion, leading to ultra-flat dispersion with values as low as ±0.996 ps nm−1· km in wavelength range 0.74 µm. The high nonlinear coefficient of several 1000 W−1 · km−1 and the low confinement loss of a few tens of dB m−1 suggest proposing three fibers with dispersion and nonlinear properties suitable for broadband supercontinuum generation at low peak power. The influence of peak power on the broadening of the supercontinuum spectrum is also investigated. Fibers with a flat all-normal dispersion profile provide a smooth spectrum with bandwidths of 1.215 and 1.626 µm at 30 dB with a peak power of 250 W. A fiber with an anomalous dispersion regime generates a supercontinuous spectrum, broadening to 3.868 µm in the mid-infrared region (2.467 µm bandwidth at 30 dB) under laser pulse excitation with 130 W peak power. Our results provide further insights into the generation of broadband mid-infrared supercontinuum using liquid-core silica-fibers, which have great potential for applications in the fields of optical communications and optical sensing.

Novel effective spectrum broadening technology pumped by 2 μm picosecond laser for mid-infrared supercontinuum generation

Using thulium-doped fiber laser to pump fluoride fiber is one of the most common methods to generate mid-infrared supercontinuum (SC). But it is difficult to generate SC spectrum with wavelength more than 4 μm by directly pumping short fluoride fiber with 2 μm picosecond (ps) laser. Although some studies with SC exceeding 4 μm have also been reported, the proportion of spectral power in the long-wavelength region is not very high. To address this issue, a novel and simple approach to solve low peak power of 2 μm ps pump sources is introduced by adding a short piece of holmium-doped fiber. This method can make full use of the gain bandwidth of Ho3+ and soliton self-frequency shift effect to enhance soliton energy and promote spectral broadening. The effectiveness of the approach is verified by constructing a theoretical model to solve the generalized nonlinear Schrödinger equation. We demonstrate through simulations that addition of holmium-doped fiber can yield significantly improved output spectral range, power ratio in the long-wavelength region and optical–optical conversion efficiency compared to the previous technical. Especially, the implementation of the new technology can effectively expand the SC long-wavelength edge by ∼470 nm after applying a 3 dB gain, and can easily build a simple, compact and low-cost mid-infrared light source system.

Octave-spanning supercontinuum generation in a CMOS-compatible thin Si3N4 waveguide coated with highly nonlinear TeO2.

Supercontinuum generation (SCG) is an important nonlinear optical process enabling broadband light sources for many applications, for which silicon nitride (Si3N4) has emerged as a leading on-chip platform. To achieve suitable group velocity dispersion and high confinement for broadband SCG the Si3N4 waveguide layer used is typically thick (>∼700 nm), which can lead to high stress and cracks unless specialized processing steps are used. Here, we report on efficient octave-spanning SCG in a thinner moderate-confinement 400-nm Si3N4 platform using a highly nonlinear tellurium oxide (TeO2) coating. An octave supercontinuum spanning from 0.89 to 2.11 µm is achieved at a low peak power of 258 W using a 100-fs laser centered at 1565 nm. Our numerical simulations agree well with the experimental results giving a nonlinear parameter of 2.5 ± 0.5 W-1m-1, an increase by a factor of 2.5, when coating the Si3N4 waveguide with a TeO2 film. This work demonstrates highly efficient SCG via effective dispersion engineering and an enhanced nonlinearity in CMOS-compatible hybrid TeO2-Si3N4 waveguides and a promising route to monolithically integrated nonlinear, linear, and active functionalities on a single silicon photonic chip.

Numerical Analysis of Optical Properties Using Octagonal Shaped Ge15As15Se17Te53 Chalcogenide Photonic Crystal Fiber

A novel Ge15As15Se17Te53 chalcogenide-based photonic crystal fiber with an octagonal cladding was designed which exhibits low confinement loss and high nonlinearity. The dispersion properties were investigated over a wide wavelength range of up to 11 µm. Based on preliminary simulation results, three fibers with suitable characteristic quantities are proposed for supercontinuum generation. Among these fibers, fiber #F1 (Ʌ = 3.1 µm, d/Ʌ = 0.3) exhibits all-normal dispersion with a small value of −0.374 ps/[nm.km]. At the same time, the highest nonlinear coefficient of 2876.861 W−1.km−1 at the pump wavelength of 5.45 µm is also found. The #F2 fiber (Ʌ= 4.5 µm, d/Ʌ = 0.3) has anomalous flat dispersion with one zero dispersion wavelength. This fiber has the smallest dispersion and lowest confinement loss values of 0.281 ps/[nm.km] and 1.360×10−9 at 5.7 µm pump wavelength, respectively. With the anomalous dispersion, #F3 fiber (Ʌ = 3.5 µm, d/Ʌ = 0.3) offers a small effective mode area of 20.892 µm2 and a low confinement loss of 4.974×10−8 dB/m at 5.25 µm wavelength. The proposed fibers can be a low peak power, broadband supercontinuum source, suitable for application fields such as optical communication and biomedical sensors.

Experimental and numerical approach for the evaluation of PV-system performance on energy and environmental behavior of nearly zero energy buildings: Case study in Mediterranean climate

Nowadays, the performance of photovoltaic (PV) systems has strategic role for satisfying the standard of net or nearly zero energy building with in-situ production. In this frame, the novelty of the paper is the proposal of a combined experimental and numerical approach for evaluating the mismatch between PV production and consumptions during design, operational and future performance under expected emissions scenarios. First of all, it proposes a comparison of production estimation by means of several tools for the evaluation of the energy balance in the design phase; then the expected and real behavior is compared with also the evaluation of the performance ratio (PR) evolution as function of cell temperature. Finally, a sensitivity analysis is proposed in the short and medium scenarios by varying the size of installed system and considering the degradation rate under future weather conditions. The approach is applied to a case study in a typical Mediterranean climate, starting from the monitoring data available for the building energy request and the renewable production (2016–2022). The results of the case study indicate that the PR greatly influences the performance, mainly under expected climate changes, since the operational emissions could increase of more than 15 % compared to actual performance also if the zero energy balance is satisfied. Furthermore, through a sensitivity analysis on the PV-system size, the study demonstrates that with a maximum linear degradation rate of 1.51 %/year, the building could be configured as nearly zero energy in the medium term (20 years) also with lower peak power. The analysis also suggests that the maximization of installed power is a prerequisite to follow the implementation of positive energy goal because, under all considered climatic evolutions it can balance the penalties both due to technical aspects that to modification of consumption and production profiles.

Subthalamic nucleus synchronization between beta band local field potential and single-unit activity in Parkinson's disease.

Local field potential (LFP) oscillations in the beta band (13-30 Hz) in the subthalamic nucleus (STN) of Parkinson's disease patients have been implicated in disease severity and treatment response. The relationship between single-neuron activity in the STN and regional beta power changes remains unclear. We used spike-triggered average (STA) to assess beta synchronization in STN. Beta power and STA magnitude at the beta frequency range were compared in three conditions: STN versus other subcortical structures, dorsal versus ventral STN, and high versus low beta power STN recordings. Magnitude of STA-LFP was greater within the STN compared to extra-STN structures along the trajectory path, despite no difference in percentage of the total power. Within the STN, there was a higher percent beta power in dorsal compared to ventral STN but no difference in STA-LFP magnitude. Further refining the comparison to high versus low beta peak power recordings inside the STN to evaluate if single-unit activity synchronized more strongly with beta band activity in areas of high beta power resulted in a significantly higher STA magnitude for areas of high beta power. Overall, these results suggest that STN single units strongly synchronize to beta activity, particularly units in areas ofhigh beta power.

Optimization of dispersions in benzene-core square photonic crystal fibers for mid-infrared supercontinuum generation with very low peak power

An ultra-broadband, very low peak power supercontinuum source is proposed based on a novel benzene-filled structured photonic crystal fiber. The modification of the structural parameters has been highly effective in improving dispersion properties, an ultra-flat all-normal dispersion is achieved with fluctuations of ±1.174 ps/(nm.km) in the 0.458 µm wavelength region. Three fibers with suitable optical properties best meet the requirements of supercontinuum generations with low peak power based on numerical simulation results. With anomalous dispersion regime, the first fiber offers the supercontinuum spectra in the mid-infrared region spanning from 0.784 µm to 3.973 µm (2.539 µm bandwidth at 30 dB) using laser pulses excited at 1.55 µm has a peak power of 150 W. A pulse with a peak power of 280 W propagates in a 5 cm length of the second fiber results in a supercontinuum spectrum covering from 0.744 µm to 1.859 (bandwidth 1.063 µm at 30 dB) at a pump wavelength of 1.3 µm with all-normal dispersion regime. A smooth, highly coherent supercontinuum spectrum spanning from 0.843 µm to 2.517 µm (bandwidth at 30 dB of 1.608 µm) is achieved when the third fiber has all-normal ultra-flat dispersion profile pumped at 1.75 µm wavelength with laser pulse peak power of 350 W. With very low peak power, these proposed three-fiber based broadband supercontinuum sources could be a low-cost alternative to traditional glass-core fiber, which has great potential for mid-infrared spectroscopy.

Commissioning of X-LAB: a very high-capacity X-band RF test stand facility at the University of Melbourne

The Compact Linear Collider (CLIC) beam-based acceleration baseline uses high-gradient travelling wave accelerating structures at a frequency of 12 GHz. In order to prove the performance of these structures at high peak power and short pulse width RF, two klystron-based test facilities will be put in operation this year. The first Southern Hemisphere X-band Laboratory for Accelerators and Beams (X-LAB) is currently being commissioned at the University of Melbourne, it will house half of the CERN X-band test stand XBOX3, which has been renamed Mel-BOX. Like XBOX3, Mel-BOX employs a novel means of combining high average power but relatively low peak power (6 MW) klystron units to direct power to two testing slots with a repetition rate of up to 400 Hz. As well as the repetition rate, peak power, pulse length and pulse shape can be customised to fit the testing requirements. This novel means of producing high power and high repetition RF pulses can eventually be used for many other applications where multiple test slots are required. This proceedings focuses on the integration and 1st commissioning of Mel-BOX with short pulses. There are also plans for it to form the basis for developing a compact accelerator for medical or university applications, such as radiotherapy and compact light sources [1].

Low repetition rate passive mode-locked semiconductor disk laser

Semiconductor disk lasers (SDLs) have advantages of high output power and good beam quality. Their flexible external cavity provides convenience for inserting additional optical element to start mode locking and produce ultra-short pulse train with duration from picosecond to femtosecond. However, the very short lifetime in a range from about a few nanoseconds to tens of nanoseconds of the carrier in semiconductor gain medium limits the decrease of pulse repetition rate, thus restricting the increase of peak power of the mode-locked laser pulse to some extent. In this work, by using the relatively shallow In<sub>0.2</sub>GaAs quantum wells, which have a relatively long carrier lifetime in the active region of gain chip, as well as the particularly designed semiconductor saturable absorption mirror (SESAM) that has a relatively small saturation flux, a passively mode-locked SDL with low repetition rate and high peak power is demonstrated. The used six-mirror cavity has a spot radius of about 200 μm on the chip and a 40 μm spot on the SESAM, and the total cavity length is about 1.92 m. The SESAM passively mode-locked SDL produces a stable pulse train with a lowest repetition rate of 78 MHz. When the temperature is 12 ℃ and the transmittance of the output coupler is <i>T</i> = 3%, an average output power value of 2.1 W and a pulse duration of 2.08 ps are achieved. The corresponding pulse peak power reaches 12.8 kW, which is about twice the reported highest peak power in an SESAM mode-locked SDL. When <i>T</i> = 2% and <i>T</i> = 5%, the obtained average output power values are 1.34 W and 1.62 W respectively, and the corresponding pulse peak power values are 8.17 kW and 9.88 kW. Based on the values reported in the literature and the results of pulse repetition rate in our experiments, the estimated lifetime of the carriers of the In<sub>0.2</sub>GaAs quantum wells in the active region of the gain used chip is 16.4 ns. This high peak power mode-locked semiconductor disk laser has important potential applications in biomedical photonics, chemistry, and nonlinear microscopy.

Investigation of non-precious metal cathode catalysts for direct borohydride fuel cells.

Borohydride crossover in anion exchange membrane (AEM) based direct borohydride fuel cells (DBFCs) impairs their performance and induces cathode catalyst poisoning. This study evaluates three non-precious metal catalysts, namely LaMn0.5Co0.5O3 (LMCO) perovskite, MnCo2O4 (MCS) spinel, and Fe-N-C, for their application as cathode catalysts in DBFCs. The rotating disk electrode (RDE) testing shows significant borohydride tolerance of MCS. Moreover, MCS has exhibited exceptional stability in accelerated durability tests (ADTs), with a minimal reduction of 10 mV in half-wave potential. DFT calculations further reveal that these catalysts predominantly adsorb over , unlike commercial Pt/C which preferentially adsorbs . In DBFCs, MCS can deliver a peak power density of 1.5 W cm-2, and a 3% voltage loss after a 5 hours durability test. In contrast, LMCO and Fe-N-C have exhibited significantly lower peak power density and stability. The analysis of the TEM, XRD, and XPS results before and after the single-cell stability tests suggests that the diminished stability of LMCO and Fe-N-C catalysts is due to catalyst detachment from carbon supports, resulting from the nanoparticle aggregation during the high-temperature preparation process. Such findings suggest that MCS can effectively mitigate the fuel crossover challenge inherent in DBFCs, thus enhancing its viability for practical application.

10,600 nm High Level-Laser Therapy Dosimetry in Management of Unresponsive Persistent Peripheral Giant Cell Granuloma to Standard Surgical Approach: A Case Report with 6-Month Follow-Up.

Peripheral giant cell granuloma (PGCG) is a non-neoplastic, tumour-like reactive lesion that exclusively involves the gingiva and/or the alveolar crest. The surgical approach with a scalpel has been the golden standard of treatment for PGCG, but the scientific literature reports a high rate of lesion recurrence. Hence, this unique case report aimed to evaluate the efficacy of λ 10,600 nm high-level laser therapy (HLLT) in eradicating persistent, aggressive, and recurrent PGCG that failed to respond to standard surgical treatment. A fit and healthy thirty-four-year-old Caucasian male presented with a two-month history of recurrent episodes of an oral mucosal lesion involving the buccal and lingual interdental papillae between the lower right second premolar (LR5) and lower right first molar (LR6), which was surgically excised with a scalpel three times previously. A λ 10,600 nm-induced HLLT was chosen as a treatment modality at a lower peak power of 1.62 W, measured with a power metre, emitted in gated emission mode (50% duty cycle), whereby the average output power reaching the target tissue was 0.81 W. The spot size was 0.8 mm. Ninety seconds was the total treatment duration, and the total energy density was 7934.78 J/cm2. Patient self-reporting outcomes revealed minimal to no post-operative complications. Initial healing was observed on the 4th day of the post-laser treatment, and a complete healing occurred at two-weeks post-operatively. The histological analysis revealed PGCG. This unique case report study demonstrated the efficacy of λ 10,600 nm-induced HLLT and its superiority to eradicate persistent aggressive PGCG over the standard surgical approach with minimal to no post-operative complications, accelerating wound healing beyond the physiological healing time associated with no evidence of PGCG recurrence at the six-month follow-up timepoint. Based on the significant findings of this unique study and the results of our previous clinical studies, we can confirm the validity and effectiveness of our standardised λ 10,600 nm laser dosimetry-induced HLLT and treatment protocol in achieving optimal outcomes. Randomised controlled clinical trials with large data comparing λ 10,600 nm with our dosimetry protocol to the standard surgical treatment modality at long follow-up timepoints are warranted.

Design of a perovskite oxide cathode for a protonic ceramic fuel cell

High catalytic activity, low-cost and stable cathode in a temperature range 550–700 °C is essential for the development of protonic ceramic fuel cells (PCFCs). Doping nickel into perovskite La0.5Sr0.5MnO3-δ(LSM) is designed as a cobalt-free cathode based on theoretical calculations and experiments. La0.5Sr0.5Mn0.9Ni0.1O3-δ (LSMNi) as cathode shows higher proton conductivity and ORR activity than the undoped LSM. The PCFCs with LSMNi exhibit low polarization resistance and high peak power density 1.1 W cm−2 at 700 °C. The density functional theory simulations indicate that doping with nickel decreases the oxygen vacancy formation energy and promotes the formation of hydroxide defects. The decrease in proton transfer energy barriers and hydration energy improves the proton conductivity. The improved performance is attributed to fast proton transfer and rapid kinetics of oxygen reduction on the surface of LSMNi. This work provides a novel approach to design cobalt-free cathode for a protonic ceramic fuel cell.

Enhanced range-doppler algorithm for SAR image formation

A Synthetic Aperture Radar (SAR) system is a powerful source of information due to its capability to operate day and night and in all weather conditions. It is essential for military and civilian purposes. Pulse-focusing is employed by the SAR system for achieving both long-range detection and fine-range resolution. The Range-Doppler Algorithm (RDA) is the most popular pulse-focusing technique for creating images from coherent SAR data. Pulse compression techniques for SAR signal processing targets seek to improve map resolution, lower peak power, and increase the Signal-to-Noise Ratio (SNR) of the detected object. This paper demonstrates an enhanced RDA algorithm that uses a modified pulse compression technique based on mismatched filter optimization where Quadratic Constrained Quadratic Program (QCQP) is used. The performance evaluation of the proposed method is performed using visual assessment and the standard image quality metrics peak-side-lobe-ratio (PSLR), impulse-response-width (IRW), and integrated-side-lobe-ratio (ISLR). Simulated and real SAR raw data are used for performance evaluation. The experimental results demonstrate the proposed method’s robustness, efficiency, and reliability in providing a higher-quality SAR image than the traditional RDA algorithm.

A new type of supercontinuum generation in hexagonal lattice C6H6-core PCF with broadband and low-power pump

Most of the spectral bandwidths of previous publications are still limited by high input powers making them economically less than ideal. By using a benzene core (C6H6) photonic crystal fiber (PCF) as a new supercontinuum (SC) light source, it is possible to achieve a very large spectral broadening with hundreds of times lower peak power. Due to the change in the diameter of air holes in the first ring near the core, near-zero flattened dispersion, high nonlinearity and small attenuation can be achieved for spectral broadening. The structural geometries of two C6H6-PCFs are optimized to generate wide SC at low input energy. The SC spectrum produced in 1[Formula: see text]cm long of all dispersion fiber extends from a part of visible light to the near-infrared range at 1.3[Formula: see text][Formula: see text]m wavelength and a small pulse energy of 18[Formula: see text]pJ (or 450[Formula: see text]W of electrical input). The second PCF shows wide soliton-induced SC from 0.8 to 4.2[Formula: see text][Formula: see text]m with 71[Formula: see text]pJ pulse energy (or input power approximately 790[Formula: see text]W) at 1.5[Formula: see text][Formula: see text]m wavelength within a fiber of 12[Formula: see text]cm. The proposed structures have the potential to become a new class of microstructured optical fibers for low-cost, broad-spectrum SC generation.

Automatic defect detection in a steel sample using frequency-modulated thermal wave imaging

Non-stationary thermal wave imaging (NSTWI) techniques are primarily used to assess material properties and structural integrity without damaging a structure. Frequency-modulated thermal wave imaging (FMTWI) is a well-known NSTWI approach that uses a low-peak power heat source to examine structures in a reasonable experimentation time. Recently, various methods, such as pulse compression, Fourier transform, principal component analysis (PCA) and independent component analysis (ICA), have been introduced to handle the non-linearity of transient thermal signatures. However, handling non-linearity and developing a fully automatic defect detection system remains very challenging due to certain limitations of the aforementioned methods. To overcome these problems, this paper proposes an artificial neural network (ANN) for the identification of subsurface flaws in a mild steel sample investigated using the FMTWI approach. The accuracy and the performance of the proposed neural network (NN) are evaluated through a confusion matrix and region of convergence (ROC) analysis for the classification of defective and healthy pixels in an infrared image sequence. The developed NN model has achieved 99.7% accuracy in classifying the pixels correctly.

Broadband supercontinuum generation with low peak power in controllable C7H8-core photonic crystal fibers of characteristic quantities

Broadband supercontinuum generation with low peak power in controllable C7H8-core photonic crystal fibers of characteristic quantities

Supercontinuum spectra above 2700 nm in circular lattice photonic crystal fiber infiltrated chloroform with the low peak power

Supercontinuum spectra above 2700 nm in circular lattice photonic crystal fiber infiltrated chloroform with the low peak power

Low peak power broadband supercontinuum spectra generated in a square lattice toluene-core photonic crystal fiber with different air hole diameters

This study shows that it is possible to achieve a very large supercontinuum spectral broadening with a peak power hundreds of times lower than in previous publications. We can achieve by using a square lattice toluene-core photonic crystal fiber. With the heterogeneity in the diameter of air holes, our new design allows simultaneous optimization of characteristic quantities to ensure flat near-zero dispersion, small effective mode area, and low attenuation for efficient spectral broadening. Supercontinuum generation (SC) of proposed PCFs has been numerically simulated and studied under different pump source parameters. The first fiber with a lattice constant of 1.0 μm and filling factor of 0.65 operates in all-normal dispersion. It generates broadband of 1.045 μm by a pump pulse with a central wavelength of 1.3 μm, 40 fs duration, and energy of 18 pJ (corresponding peak power of 0.45 kW). Besides, two octave-spanning of the SC spectrum in the wavelength range of 0.775–4.3 μm are formed in the second fiber with an input pulse whose optical properties are 1.55 μm wavelength, 100 fs duration, and energy of 55 pJ (0.45 kW of the peak power). The lattice constant of second fiber is 2.0 μm and the filling factor is 0.3. They would be good candidates for all-fiber SC sources operating with low-power pump lasers. This would be a as cost-effective alternatives to glass core fibers.