High Incident Power Research Articles

Simultaneous sealing and bisection of porcine renal blood vessels, ex vivo, using a continuous-wave, infrared diode laser at 1470 nm

Electrosurgical and ultrasonic devices are used in surgical procedures for hemostatic sealing and bisection of vascular tissues. Previous benchtop studies alternatively demonstrated successful infrared laser sealing and cutting of blood vessels, in a sequential, two-step approach. This study describes a smaller, laparoscopic device compatible design, and simultaneous approach to sealing and bisection of vessels, with potential optical feedback. A 1470-nm infrared diode laser sealed and bisected 40 porcine renal arteries, ex vivo. A reciprocating, side-firing, optical fiber, housed in a transparent square quartz optical chamber (2.7 × 2.7 × 25 mm outer dimensions), delivered laser energy over an 11 mm scan length, with a range of incident powers (41–59 W) and treatment times (5–21 s). Vessel diameters ranged from 2.5 to 4.8 mm. Vessel burst pressure measurements were performed on each cut end (n = 80) with success indicated by pressures exceeding 360 mmHg. All vessel ends were successfully sealed and bisected (80/80). The highest incident power, 59 W, yielded short treatment times of 5–6 s. Peak temperatures on the external chamber surface reached 103 oC. Time to cool down to body temperature measured 37 s. Infrared lasers simultaneously seal and bisect blood vessels, with treatment times comparable to, and temperatures and cooling times lower than reported for conventional devices. Future work will focus on integrating the fiber and chamber into a standard 5-mm-outer-diameter laparoscopic device. Customization of fiber scan length to match vessel size may also reduce laser energy deposition, enabling lower peak temperatures, treatment times, and cooling times.

Nonlinear optical effects in polycrystalline transparent Al2O3 ceramics using femtosecond laser pulses—supercontinuum generation and laser damage

Nonlinear optical properties play a key role in technologies such as broadband laser light sources and ultrafast laser machining. With the emergence of transparent nanocrystalline Al2O3 ceramics as an alternative to single crystal alumina (sapphire), it is critical to understand their nonlinear optical behavior. Here, we report the demonstration of supercontinuum generation in polycrystalline alumina ceramics. Substantial broadening was observed when a focused 515 nm pulsed (260 fs) laser propagated through the ceramic sample. The broadening increased with increasing laser power and displayed stokes/anti-stokes asymmetries. At higher incident power, permanent damage was observed. Our results show that transparent nanocrystalline Al2O3 ceramics have a higher material removal rate than single crystal alumina. These results have interesting implications for laser machining as well as integrated photonics.

Ultrafast low-jitter optical response in high-temperature superconducting microwires

We report ultrafast optical response in high-Tc superconductor (YBa2Cu3O7−δ) based microwires operating at 76 K and we find a rise time ∼850 ps and a fall time ∼1250 ps and an upper limit of timing jitter of ∼100 ps, using twice the standard deviation of the fitted data. In our experiment, incident power is proven to be an important factor for a device jitter. At low incident power, a lower rate of hot-spot generation by a smaller number of absorbed photons results in a longer latency time to obtain the required number of hot-spots for superconductor-to-normal transition. The lower hot-spot generation rate also results in larger timing jitter of the device. Whereas, at high incident power, a higher hot-spot generation rate yields shorter latency and smaller timing jitter. These observations agree well with our statistical model. Enhancing the sensitivity of the current device can enable future high-Tc superconductor nanowire single photon detectors, toward the widespread use of ultrafast quantum technologies.

High power multicolor composite fluorescent glass coated with graphene monolayer for laser lighting

Laser lighting technology has become a new star in the field of modern lighting. However, the thermal quenching of optical conversion materials occurs at high incident power density, so it is an urgent problem to improve their heat resistance. In this paper, a kind of Lu3Al5O12:Ce&CaAlSiN3:Eu2+ (LuAG&CASN) composite phosphor-in-glass (PiG) suitable for high power laser diode is prepared, which shows high brightness and high display. In addition, the graphene monolayer grown by chemical vapor deposition (CVD) is coated on the surface of LuAG&CASN-PiG to further improve the luminescence performance of PiG. The saturation power threshold of the graphene-PiG (G-PiG) sample can reach 4.5 W and the maximum output lumen flux can reach 317.95 lm when the system is excited with 450 nm blue light using the reflective structure. Compared with the samples without graphene coating, the luminescence efficiency of G-PiG was improved by 23.2%. This single-layer graphene surface coating method provides a new idea for the preparation of high-performance fluorescence conversion materials for laser lighting applications, which may play an important role in the future laser lighting.

Ultrashort pulse focusing through a planar interface between free space and a nonlinear medium

We present a method to calculate the spatiotemporal electric field distribution of ultrashort pulses focused by an aberration-free lens through a planar interface between free space and a nonlinear medium. The method combines the Fresnel diffraction integral, which is used to model the propagation of the focused pulse in free space, and the angular spectrum propagation method, used to propagate the focused pulse within the nonlinear medium by introducing the irradiance-dependent nonlinear refractive index in the angular spectrum propagator. We have modeled the propagation of ultrashort mildly focused pulses through a Ti:sapphire crystal, characterized only by its linear and nonlinear refractive indices, for pulses with different powers and durations, finding that the proposed method is able to reproduce the self-focusing phenomenon observed in nonlinear media. Our results show that the focal spot within the nonlinear medium is closer to the interface, and it is slightly wider for pulses with higher incident power. However, despite the dependence of the effective refractive index of the nonlinear medium on irradiance, which is the power per unit area, and assuming that the group velocity dispersion and the propagation time difference are suitably corrected, the focused pulse duration is essentially unaffected by the incident power and remains virtually constant during propagation in the nonlinear medium. Finally, the proposed method also reproduces the spatiotemporal coupling arising from the intrinsic correlation between spatial and temporal properties of the focused pulse.

Nonreciprocal transmission in a nonlinear coupled heterostructure.

A nonlinear coupled heterostructure, metal-nonlinear-metal-insulator-metal, is proposed. The heterostructure is a non-Hermitian system that possesses reciprocal and nonreciprocal optical transmission characteristics. With low incident power, linear optical characteristic is observed whereas at high incident power, nonlinear optical characteristics is observed. Under the low incident power there is no nonlinear effect, the forward and backward transmission are reciprocal. With appropriate geometric parameters, for forward propagation two exceptional points where the reflection coefficients equal zero can be obtained simultaneously. With high power incident nonlinear effect becomes significant, leading to reciprocity broken and optical bistability observed. We investigated the behaviours of forward and backward transmission as well as the optical bistability under different incident powers using nonlinear coupled mode theory. There is excellent agreement between the simulation results and theoretical modelling. The theoretical study of proposed heterostructure shows it has several novel optical responses under different incident conditions. The proposed heterostructure is relatively simple to fabricate and therefore can be experimentally verified with ease. These unique optical characteristics allow more possibilities for the design of multifunctional devices.

Low-voltage extraction characteristics of ion beams and space potential measurements on ECRIS

We have been using an electron cyclotron resonance ion source (ECRIS) for ion beam production, and it is desirable to construct a universal ECRIS that can produce ions with a wide range of mass/charge ratios, e.g. from several to several thousand. We investigated the characteristics of ions with high mass/charge ratios, e.g., iron endohedral fullerenes production, which requires low voltage beam extraction. We investigated the characteristics of the ion beam extraction at low extraction voltage. It is found that the beam current almost obeyed the Child-Langmuir law for various ion species. The space potential of the plasma in the ion source can be obtained from the relation between the extraction voltage and the square of the magnetic field strength of the dipole magnet. It is found that space potential values are larger with large charge state of ions, in low gas pressure condition and in high microwave incident power. At the same time, the plasma space potential was measured by using a Langmuir probe and compared with the ion beam method. It is found that same trend is confirmed with probe method.

Experimental investigation of linear and third-order nonlinear optical properties of pure CuO thin film using femtosecond laser pulses

This paper experimentally investigated the linear and third-order optical nonlinearities of a pure CuO thin film deposited on a soda-lime glass substrate. A single-phase film with 62 nm thickness was prepared using the direct current (DC) sputtering deposition process, the film structure was measured using x-ray diffraction (XRD) and a surface profilometer, while the film’s linear optical properties were measured using a UV-Vis spectrophotometer. The Z-scan technique was used to measure the nonlinear optical properties of a film that had been irradiated with 100 fs laser pulses using different excitation wavelengths at different incident laser powers. The results showed that increasing the excitation wavelength from 740 nm to 840 nm reduces the nonlinear absorption coefficient of the film from − 3.5 × 1 0 − 6 to − 2.04 × 1 0 − 6 c m / W , and the nonlinear refractive index n 2 decreases from − 4.98 × 1 0 − 18 to − 1.2 × 1 0 − 18 c m 2 / W . The optical limiting of the CuO thin film was studied and found to be excitation wavelength dependent with limiting at high incident power.

Numerical Study on the Influence of the Plasma Properties on the Keyhole Geometry in Laser Beam Welding

Keyhole laser welding is the benchmark for deep-penetration joining processes. It needs high incident laser beam power densities at the workpiece surface to take place. The gaseous phase plays a fundamental role to keep the deep and narrow keyhole cavity open during the process. The plasma created in this process is a mixture of ionized metal vapors and the environmental gas and it develops inside the keyhole (keyhole plasma) and above the workpiece surface (plasma plume). The presence of plasma implicates absorption, scattering, and refraction of laser beam rays. These phenomena alter the power density of the laser beam irradiating the workpiece surface and thus affect the resulting welding process. In this work, a mathematical and numerical model has been developed to calculate the keyhole shape taking into account the plasma absorption effects. The model considers the keyhole walls as the liquid-vapor interface and computes the keyhole geometry applying a local energy balance at this interface. In addition, the model takes into account the multiple reflections effects inside the cavity through an iterative ray-tracing technique, and calculates the absorption mechanism due to inverse Bremsstrahlung for each ray along its segmented path inside the keyhole. Results show the effect of plasma properties on the keyhole shape and depth.

Robust Visible-Blind Wearable Infrared Sensor Based on IrP2 Nanoparticle-Embedded Few-Layer Graphene and the Effect of Photogating.

It is challenging to realize a visible-blind infrared photodetector as the materials that absorb infrared light also absorb visible light. Here, we report the synthesis of IrP2 nanoparticle-embedded few-layer graphene by one-step solid-state pyrolysis and its application in visible-blind infrared sensing. A linear photodetector device was fabricated by drop casting IrP2 nanoparticle-embedded few-layer graphene onto a flexible PET substrate with two gold electrodes separated by ∼16 μm. The photoconductive gain was found to be as high as ∼145% with response and decay times of ∼0.4 and ∼2.8 s, respectively, under 1550 nm irradiation of 800 mW cm-2. The room-temperature responsivity was ∼1.81 A W-1 at 80 mW cm-2 and ∼0.54 A W-1 at a high incident power of ∼2200 mW cm-2 under a bias of 1 V. Interestingly, the device showed response even in the long-wavelength infrared region, but no response was found under visible light. The embedded IrP2 nanoparticles act as trap centers inducing photogating in the device, and the average trap state energy was estimated to be ∼16.5 ± 1.5 meV from the temperature-dependent photocurrent studies. The device was found to be immune to air exposure and bending, suggestive of use a a wearable sensor.

High-Performance Energy Selective Surface Based on the Double-Resonance Concept

In this article, a high-performance energy selective surface (ESS) is proposed based on a double-resonance concept, which has a nonlinear transmission response for high-power electromagnetic protection. With well-designed grid and cross patterns as well as properly chosen p-i-n diodes, bandpass and band-stop resonances are excited by the ESS at the same frequency under low and high incident power levels, respectively, resulting in low insertion loss (IL) and high shielding effectiveness (SE) of the ESS. Two samples of single-layer and double-layer ESSs operating at 3 GHz are designed to demonstrate the double-resonance concept. By utilizing a double-layer structure, a second-order band-stop resonance is produced to achieve a broader bandwidth with high SE in comparison with the single-layer ESS. Equivalent circuit models are employed to explain how the double resonances are produced and a wide bandwidth of high SE is obtained. Field circuit cosimulation is conducted to estimate the nonlinear performance of the ESS designs. Moreover, the ESS designs are measured in a rectangular waveguide setup. Good agreement is observed between the simulation and measurement. Simulated and measured results demonstrate that low IL less than 1 dB and high SE larger than 24 dB can be obtained under low and high incident power levels, respectively.

A sliding-bed particle solar receiver with controlling particle flow velocity for high-temperature thermal power generation

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution, which could provide a heat source with better stability, better uniformity and higher temperature for subsequent thermal power generation and other thermal applications. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to move slowly and controllably in the form of a sliding-bed, which is why we call this receiver a sliding-bed receiver. The sliding-bed receiver's structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 °C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 °C and efficiency of 82% under higher incident power. The effects of the effects of the incident power distribution, the particle velocity distribution and the quartz glass on aperture on the receiver performance were detailly analyzed, which could also help optimize the design and operation of other particle receivers such as free-falling particle receivers.

In-situ micro-Raman study of SnSe single crystals under atmosphere: Effect of laser power and temperature

Single crystal of tin selenide (SnSe) was studied by micro-Raman spectroscopy under atmosphere conditions. The effect of varying the incident laser power on the sample up to 2 mW was analyzed. The Raman spectra showed that the number of all vibrational modes have not decreased or increased, but all peaks red-shifted and softened obviously as the laser power increased to the threshold value. The temperature-dependent micro-Raman study of the single crystal was carried out for illustrating thermal effect due to the high incident laser power. A new SnSe2 phase appeared at high temperature without vacuum and become the dominant phase at the surface of the crystal gradually because of oxidation. Detecting few amounts of SnSe2 crystals on the surface of single crystal shows the high sensitivity of Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) was also used to confirm that the newly generated SnSe2 phase is precipitated by SnSe under high temperature oxidation conditions. To study the Raman spectra of low thermal conductivity materials under high temperature and non-vacuum conditions, lower incident laser power should be used to avoid the influence of additional thermal effects.

Optimization of solar receivers for high-temperature solar conversion processes: Direct vs. Indirect illumination designs

High-temperature solar receivers are core components in concentrated solar energy utilization systems. The rational design of solar receivers relies on the fundamental understanding of coupled physics across various scales. We developed a numerical model to assess the solar thermal conversion behaviour under various porous structure designs, material choices, geometrical designs, as well as operational conditions. The 3D model solves a coupled set of equations accounting for mass, momentum, and energy conservations in the cavity and porous media domains. We have optimized the radiative transfer model to resolve the participating behaviour only in the porous domain and non-participating behaviour only for cavity and window surfaces. This cost-effective model enables fast performance evaluation for various design parameters. The windowless receiver, in general, shows higher solar-to-thermal efficiency compared to the window receiver. This superiority in optical efficiency for the windowless case can be surpassed by the window case at high incident solar power with a fixed outlet temperature. For porous media structure, both window and windowless receivers are optimized by the porosity and pore diameter. The solar-to-thermal efficiency was slightly influenced by the cavity inclination. Large porous layer thickness leads to reduced performance for the windowless receivers, while the efficiency reaches a plateau for the window receiver at large thickness. We have provided a comprehensive modeling framework for the design of solar receivers for high-temperature applications using concentrated solar energy which can be easily adapted for receiver under a wide range of designs and operation conditions.

Design validation of in-vessel mirrors and beam dump for first plasma operations in ITER

First plasma operation in ITER will start after completing the assembly of the tokamak vessel and the installation of the main sub-systems, but prior to the installation of the blanket modules and the divertor cassettes. Utilization of temporary limiters and divertor replacement structures will provide a poloidal and toroidal reference side position to the plasma edge to protect the vacuum vessel and other components already installed during operations. An additional set of mirrors is required to reflect the power injected from the upper launcher towards the plasma resonance for EC-assisted breakdown of the plasma up to a beam dump needed to trap and absorb the power of the beams after crossing the plasma in order to reduce the stray radiation escaping back into the vacuum chamber down to less than 10% of the total power. The quasi-optical system has been designed, with shape and size of the mirrors compliant with the requirements provided by ITER for their installation, realization and plasma performances, resulting in two standard focussing mirrors and one grating mirror. The beam dump consists of a box with five metal plates, the first providing a spreading of the high incident power and the others coated with absorbing material with thickness distribution studied to gradually reduce the power during the multiple reflections inside the box, avoiding damages to the coating itself. This work focuses on the validation of the quasi-optical design of the mirrors and the assessment of the dump performances, based on a multi-bounces model developed ad-hoc for this purpose. The study includes a tolerance analysis for the beam dump to include the effect of uncertainties in the thickness of the absorbing coating and misalignments of the mirrors, to verify the performances of the dump also when operating in different conditions with respect to the nominal ones.

Structural, vibrational, optical, dielectric, and shielding characteristics of (1-x)Mg(Ti0.95Sn0.05)O3-(x)SrTiO3 (0 ≤ x ≤ 0.1) ceramics

In this research, we prepared novel (1-x)Mg(Ti0.95Sn0.05)O3-(x)SrTiO3 (0 ≤ x ≤ 0.1) ceramics via traditional solid-state reaction process and explored their structural, vibrational, optical, dielectric, and shielding properties. XRD and Rietveld refinements revealed that the Mg(Ti0.95Sn0.05)O3 crystallized into the trigonal structure with space group R3¯, while the SrTiO3 phase exhibited cubic symmetry with space group Pm3¯m. A near-zero τf was obtained for the 0.95Mg(Ti0.95Sn0.05)O3-0.05SrTiO3 (εr = 16.46, tan δ = 2.06 × 10−3, and τf = 3.18 ppm/⁰C, at 1 MHz) sintered at 1250⁰C. In the Ku-band (12.4–18 GHz), this composition exhibited εr in the range of 13.49–14.01 and tan δ in the range of 1.4 × 10−2–2.8 × 10−2. Furthermore, 0.95Mg(Ti0.95Sn0.05)O3-0.05SrTiO3 with pellet thickness of 1.5 mm can restrict the penetration of 75% or higher incident power with an effective bandwidth of 3.5 GHz. Due to its suitable properties, the prepared composition can be used for 5 G applications.

A Novel Impeded Flow Particle Receiver for Better Stability and Controllability

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to slide slowly and controllably in the form of a moving bed. The receiver’s structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 o C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 o C and efficiency of 82% under higher incident power. The effects of the temperature drop section, quartz glass on aperture and slow particle flow at the edge on the receiver performance were detailly analyzed, which could help optimize the design and operation of other particle receivers such as free-falling particle receivers.

Studies on backscattering noise in reflective coherent optical communication system

For the safety information transmission technology, here an improved high-security reflective coherent optical communication system is studied in this paper. The backscattering, mainly Rayleigh backscattering and stimulated Brillouin scattering, is analyzed to adversely affect the system performance. The results show that the sensitivity of the system can be as high as -36.3 dB m and the transmission distance is 83.2 km with a low incident power and a data rate of 10Gbps. In addition, under high incident power, the sensitivity of the system is -36.4 dB m and the transmission distance is 95.4 km. Therefore, we can reach the following conclusion that the reflective system can realize high-speed and long-distance communication. It can be applied to secure communication or some special fields.

A high quantum efficiency CaAlSiN3:Eu2+ phosphor-in-glass with excellent optical performance for white light-emitting diodes and blue laser diodes

CaAlSiN3:0.2%Eu2+ (CASN:Eu2+), an excellent red phosphor, playsaleadingpart in wide color gamut and high color rendition white light-emitting diodes (wLEDs). However, this phosphor or silicone resin mixture possesses a fatal defect of an intrinsic low thermal performance, which makes it hardly useful in high-power laser lighting and displays. Here, to improve the thermal performance of the CASN:Eu2+ phosphor, a series of red-emitting phosphor-in-glass materials (R-PiGs) with different CASN:Eu2+ concentrations (5–50 wt%) and sintering temperatures (750–850 °C) were successfully synthesized by dispersing the CASN:Eu2+ phosphor into a B2O3-Na2O-SiO2-CaO glass matrix. Surprisingly, the prepared R-PiGs showed a high external quantum efficiency (EQE) of 53%, and still maintained 82% efficiency compared with the CASN:Eu2+ phosphor (65%). The R-PiGs are superior to red ceramics for low cost and rapid batch preparation. Considering the densification of the R-PiGs, a systematic study was conducted on 10 wt% R-PiG sample. A facile chromaticity tuning for the configured wLEDs was obtained within the color range change from cool white to warm white when using the R-PiGs with different CASN:Eu2+ concentrations. Besides, we have successfully assembled a warm wLED with high luminous efficacy (90.3 lm/W) and color rendering (Ra = 94.2 and CCT = 5053 K). When irradiated by a blue laser, an optimized R-PiG can show enhanced luminous flux (49.27 lm) at a high laser incident power of 1.90 W/mm2. Therefore, with their excellent performances, R-PiGs are highly promising for use as red color converters for potential applications in tunable wLEDs and high-power laser lighting.

Plasma-Based Power Limitation for Highly Linear MEMS Switch Protection and Isolation Enhancement

A novel hybrid approach integrating a MEMS switch with a gas discharge tube plasma cell to enhance switch survivability and isolation, especially at high incident power levels, is demonstrated. The theory of operation is discussed including consideration of the underlying plasma phenomena as well as the practical integration details. Measurement of a fabricated prototype is presented. Discussion of measurement challenges and potential solutions is accompanied by detailed explanations of measurement practice. Measurements provide insights into applied RF plasmas not present in the body of literature. Wideband enhancement of isolation by more than 10 dB at 50 W incident power is observed in a quasi-absorptive mode with increasing isolation over power. No penalty to the excellent linearity of MEMS switches is detected with a measured IIP3 of 75.3 dBm. Advantages in linearity as compared to semiconductor-based power limiting solutions are shown and demonstrate state-of-the-art performance. An incremental insertion loss of less than 0.2 dB with a return loss better than 12.5 dB is reported. Measurement of the effects on MEMS switch timing parameters as well as time domain characterization of the plasma breakdown is included.