Cw Laser Power Research Articles

Analysis of micro-hole formation in titanium nanofilms using a low power CW laser

This study investigates the mechanisms and dynamics governing microhole formation in titanium nanofilms under the influence of a continuous-wave low-power laser emitting at 1070 nm. Two distinct configurations were explored: one in which the laser interacted with the titanium film in an air environment (referred to as configuration AM), and the other in which the laser beam passed through glass before reaching the titanium film (referred to as configuration SM). Our experiments demonstrated that microhole formation is possible in both configurations. However, the threshold powers, hole characteristics, and time scales involved differ significantly between AM and SM configurations. Temperature distribution simulations, based on a linear absorption model, revealed notable differences in peak temperatures between these two configurations, primarily attributed to variations in focal spot size and Fresnel losses. These temperature variations resulted in significantly different mechanisms of material removal in both configurations. In the AM configuration, the boiling temperature was not achieved, even at the highest power; however, a melting pool was formed at powers exceeding 50 mW. Thus, the primary driver of microhole formation was the Marangoni effect, which caused molten material to flow tangentially towards the edges of the molten pool. Furthermore, titanium oxidation was identified as a competing process contributing to changes in optical transparency and potentially inhibiting the complete formation of holes. Conversely, within the SM configuration, boiling temperatures are easily achieved, leading to localized boiling and the formation of gas bubbles near the glass–titanium interface. As a result, the rupture of the bubble through the capping molten layer led to a vigorous expulsion of both gas and material, allowing for the creation of microholes even at remarkably low laser power levels (10 mW). Notably, in this configuration, the influence of titanium oxidation is negligible due to the relatively short time scale involved (hundreds of microseconds).

Laser-Induced Interference to Infrared Detector Using Continuous Wave and Short-Pulse Lasers.

The response of a DPbS3200 infrared detector irradiated by a nanosecond pulsed laser and CW laser has been investigated to study laser-induced interference. A laser interference experiment system was constructed to measure the time-varying response signal. A nanosecond pulsed laser and a CW laser of 10 Hz were used, with a 1064 nm wavelength and a millimeter-scale irradiation spot diameter. Firstly, the characteristics of transient interference signals induced by pulsed lasers were analyzed. Then, the characteristics of response signal interference by both CW laser and pulsed laser irradiation were further investigated. The results showed that the pulsed laser only produced transient interference. However, the CW laser led to a significant amplitude reduction of the response signal, which could continuously interfere in the operating time. For transient interferences, the amplitude of the interference signal increased linearly with the laser fluence. The relation between the pulse repetition rate of the incident laser and the operating frequency of the detector determined the numbers of transient interference signals in one response period; for the interference induced by both the CW laser and pulsed laser, CW laser interference played a leading role when CW laser power density increased to 4.1 W/cm2 or more. As the CW laser fluence reached 6.1 W/cm2, the PbS infrared detector was no longer able to detect any signal, which caused temporary blindness. In the end, a probit model was used to determine the interference threshold.

Flight Testing Of A Single Point Frequency Sweeping Filtered Rayleigh Scattering Probe

"We present a successful in-flight application of filtered Rayleigh scattering (FRS) for temperature measurement in close proximity to the air plane using a newly developed single point, frequency sweeping probe. The temperature measurement is of relevance in the quantification of the density required for the evaluation of velocity from Pitot-probe measurements to obtain the true air speed (TAS). Laser optical air data sensors have the potential for contactless measurements outside the aerodynamic boundary layer. They are capable of self-diagnosis of fault conditions (e.g. signal loss, increased measurement uncertainty or spectral distortion for FRS) thereby increasing the safety of the aircraft. Compared to classical probes, they are less susceptible potential icing and blockage issues. The FRS-results presented here, are the outcome of two separate flight campaigns, carried out in the Alpine region as well as in the North Sea area. Measurement data provided information on the functionality of the FRS-system under various flight and weather conditions. Furthermore, the implementation of the FRS measurement system in the aircraft is presented; application aspects and improvements are discussed. In particular, the measurement accuracy at the actually achievable measurement rate was analyzed. For straight ahead flights at constant height, temperature mean values were in good agreement with the flight data system of the DLR research aircraft Dassault Falcon 20 (D-CMET). Aiming at in-flight air data measurements, the optical FRS measurement system requires a real-time temperature sample rate of a few Hz. We demonstrate that 2 FRS spectra per second can be acquired by a newly developed method using frequency sweeps for temperature determination. The low signal intensity of cw-laser based FRS is countered using a combined transmitter/receiver optic that focusses the entire cw-laser power into one measuring point. The light backscattered from the probe volume is collected by the same optics, filtered and imaged in a confocal arrangement onto a photomultiplier. An improved and miniaturized version of the presented FRS system could be a part of a future optical air data system (OADS). However, the strength of FRS signal relative to bright ambient conditions (e.g. sunlight, cloud backscatter) must be further improved in order to be able to measure well above cloud cover. The potential for further development is foreseen even if the accuracy required for flight data systems (~0.5 K) has not yet been achieved at a temperature measurement rate of 2 Hz. "

Multi-kilowatt cw laser power measurement comparison between national standards

We present here the first comparison between National Metrology Institutes of high accuracy continuous wave optical power measurements in the kilowatt regime. The National Institute of Standards and Technology (NIST) performed measurements with a power meter relying on photon momentum. The Physikalisch-Technische Bundesanstalt (PTB) performed measurements with a modified off-the-shelf thermal power meter. The non-absorbing photon momentum measurement approach permits the two power meters to measure the same laser beam optical path simultaneously, resulting in a direct comparison of the meters supported by an optical system to accommodate differences in instrument settling times. The results show agreement within the expanded uncertainties for each instrument. NIST and PTB illustrate a degree of equivalence of 0.49% with an expanded uncertainty of 1.37% (k = 2) for an average result across all power levels.

Research on the core factors affecting the temperature rise of dichroic mirrors in wavelength beam combination system under high-power CW laser

The wavelength beam combination is considered an important method for improving the source power of high-energy laser weapons while maintaining high beam quality. The dichroic mirror is the key component that decisively determines the laser beam quality of the wavelength beam combining system. However, the temperature rise of the dichroic mirror due to continuous high-power laser irradiation can significantly deteriorate the beam quality and decrease the efficiency of the systems. Along these lines, in this work, the factors that influence the temperature rise of the dichroic mirror under high power CW laser were systematically examined. The temperature field equation of the dichroic mirror under transmission and reflection laser was also calculated. The variation of the dichroic mirror temperature by the laser power, laser spot size, diameter, and thickness of substrates, as well as material of substrates and thin-film absorption was simulated. The simulated results were verified by performing experiments on both sapphire and quartz substrates. The transmittance absorption was proved to be the main cause of the temperature rise and the laser power had a linear relationship with the maximum temperature. Interestingly, the temperature decreased with the thermal conductivity and the laser spot size. As a result, the optimization of the substrate size can significantly reduce the temperature of the dichroic mirror. Our work provides valuable insights into the design and increase in performance of dichroic mirrors in the wavelength combination system.

Thermal, spectroscopy and optimized ∼3 µm CW laser properties for Ho,Pr:YAP crystal.

We demonstrate the thermal, spectroscopy and laser properties of Ho,Pr doped YAP crystal grown successfully by Cz method. The thermal expansion coefficient, thermal conductivity, absorption and emission spectra of Ho,Pr:YAP crystal are investigated in detail. Additionally, the level lifetimes suggest that Pr3+ is a suitable deactivating ion for Ho:YAP crystal. Particularly, the actual laser performance is optimized by doping active ion Ho with high concentrations and introducing deactivated Pr3+, resulting in decreased laser threshold, increased laser output power and slope efficiency. A 3.01 µm laser with output power of 502 mW, slope efficiency of 6.3% and beam quality factors of 1.42/1.43 is achieved in the Ho,Pr:YAP crystal, as far as we know this is the highest ∼3 µm CW laser power realized in Ho3+ doped oxide crystals.

Glucose diagnosis system combining machine learning and NIR photoacoustic multispectral using a low power CW laser.

Non-invasive, portable, economical, dynamic blood glucose monitoring device has become a functional requirement for diabetes in his regulating entire life. In a photoacoustic (PA) multispectral near-infrared diagnosis system, the glucose in aqueous solutions was excited by low power (order of milliwatts) CW laser whose wavelengths were from 1500 to 1630 nm. The glucose in aqueous solutions to be analyzed was contained within the photoacoustic cell (PAC). The PA multispectral signals were measured using a piezoelectric detector, and then the voltage signals from the piezoelectric detector were amplified with a precision Lock-in Amplifier (MFLI500K). The continuously tunable lasers were used to verify the various influencing factors of the PA signal, and the PA spectrum of the glucose solution was examined. Subsequently, six wavelengths with high power were selected at approximately equal intervals from 1500 to 1630 nm, and the gaussian process regression of the quadratic rational kernel was used to collect data through these wavelengths to predict the glucose concentration. The experimental results showed that the near-infrared PA multispectral diagnosis system could be engineered for the prediction of the glucose level (more than 92%, zone A of Clarke Error Grid). Subsequently, the model trained with glucose solution was used to predict serum glucose. With the increase of serum glucose content, the prediction results of the model also showed a high linear relationship, indicating that the photoacoustic method was sensitive to the detection of glucose concentration changes. The results of our study have the potential to not only better develop the PA blood glucose meter but also extend the viability into the detection of otherwise blood components.

Microfabricated sensor device for CW and pulsed laser power measurements.

On-line measurement is a trend of development toward laser-based applications. We present a fiber-integrated force sensor device for laser power measurement with both CW mode and pulse mode based on laser radiometric heat and radiation force sensing simultaneously. The sensor device is fabricated using a standard microfabrication process. Laser intensity is determined through the displacement of a movable mirror measured by an integrated Fabry-Perot interferometer. Compared with the performance of the device in the ambient condition, a non-linearity error of 0.02% and measurement uncertainty of 2.06% is observed in the quasi-vacuum condition for CW laser illumination. This device can measure a CW laser power with a 46.4 μW/Hz1/2 noise floor and a minimum detection limit of 0.125 mW. For a pulsed laser, a non-linearity error of 0.37% and measurement uncertainty of 2.08% is achieved with a noise floor of 1.3 μJ/Hz1/2 and a minimum detection limit of 3 μJ.

Performance Analysis of a Linear Gaussian- and tanh-Apodized FBG and Dispersion Compensating Fiber Design for Chromatic Dispersion Compensation in Long-haul Optical Communication Networks

This paper investigates a novel compensation technique of dispersion effect mitigation using a combination of three- and four-stage-apodized fiber Bragg gratings (FBG) and dispersion compensating fiber (DCF) designs. Two designs using three-stage and four-stage FBG and DCF in combination have been proposed and compared for their performance in mitigating chromatic dispersion effects at 100 km SMF. The performance of each design has been evaluated using Q-factor results using linear Gaussian- and tanh-apodized fiber Bragg gratings. Each profile manifested different Q-factor results over a range of 5 dBm, 7.5 dBm, and 10 dBm of CW laser power over FBG grating lengths from 4 mm to 8 mm. The results obtained using the three-stage and four-stage FBG and DCF designs showed that an apodization profile using a tanh function can be used successfully with FBG lengths from 4 mm to 8 mm, regardless of the CW launched power. In contrast, the results using a Gaussian apodization profile for three- and four-stage FBG and DCF designs are applicable to FBG lengths from 5 mm to 8 mm. Designs using three-stage FBG and DCF generated higher Q-factor results than designs using only four-stage FBG and DCF, regardless of the launched power. The highest Q-factor of 18.58 was obtained for three-stage tanh-apodized FBG and DCF used in combination for an FBG length of 6 mm. The highest result obtained for a three-stage Gaussian-apodized FBG and DCF design was a Q factor of 17.13 using an FBG length of 8 mm. The proposed method was also compared to current similar works and can be successfully implemented in long-haul optical communication.

40 W Continuous Wave Ce:Nd:YAG Solar Laser through a Fused Silica Light Guide

The solar laser power scaling potential of a side-pumped Ce:Nd:YAG solar laser through a rectangular fused silica light guide was investigated by using a 2 m diameter parabolic concentrator. The laser head was formed by the light guide and a V-shaped pump cavity to efficiently couple and redistribute the concentrated solar radiation from the parabolic mirror to a 4 mm diameter, 35 mm length Ce(0.1 at.%):Nd(1.1 at.%):YAG laser rod. The rectangular light guide ensured a homogeneous distribution of the solar radiation along the laser rod, allowing it to withstand highly concentrated solar energy. With the full collection area of the parabolic mirror, the maximum continuous wave (cw) solar laser power of 40 W was measured. This, to the best of our knowledge, corresponds to the highest cw laser power obtained from a Ce:Nd:YAG medium pumped by solar radiation, representing an enhancement of two times over that of the previous side-pumped Ce:Nd:YAG solar laser and 1.19 times over the highest Cr:Nd:YAG solar laser power with a rectangular light-guide. This research proved that, with an appropriate pumping configuration, the Ce:Nd:YAG medium is very promising for scaling solar laser output power to a higher level.

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Performance analysis of APD and PIN diode with and without EDFA in GPON

Abstract Gigabit-capable passive optical network (GPON) is a passive optical network that provides faster data transmission and reception using point-to-multipoint access technology with single fiber. Using passive splitter in distribution network to keep the costs down, its 2.5 Gbits/sec bandwidth can be split up to 64 times. This paper presents the study of max Q-factor, min bit error rate (BER) using Opti system 17. In this study return to zero (RZ) and nonreturn to zero (NRZ) line codes analyzed by using P-insulator-N (PIN) and avalanche photo diode (APD) receivers. This paper also studies the impact of CW laser power on Q factor and min BER of GPON with and without erbium-doped fiber amplifier (EDFA).

Comparative Analysis of DCF based Dispersion Compensation Techniques in Optical Fiber Communication Link using Different Input Transmitter Conditions at 10 Gbps

In this paper, Dispersion Compensating Fiber (DCF) based various dispersion compensating techniques (pre, post and symmetrical) with different modulation format like Non Return to Zero(NRZ), Return to Zero(RZ), Carrier Suppressed Return to Zero(CSRZ) and Duo Binary(DB) along with PN, FCC and Walsh code input sequences are implemented. Simulation and analysis of these implemented techniques were done at 10 Gbps bit rate and input laser power ranging from 1 mW to 10 mW at transmission distance of 240 km using BER Analyzer in Optisystem 17.0 software. Comparison between different techniques was done in terms of Q factor and BER versus input CW laser power for different modulations and input sequences. From the analysis, it is concluded that when Walsh code as user defined input sequence are used for all the implementation, it gives higher value of Q factor and lower value of Bit Error Rate as compared to PN and FCC codes for most of the input CW laser power.

Emergence of fifth-order optical nonlinearity in 2-(2-Quinolyl)-1,3-indandione with strong third-order nonlinear effect under low power CW laser excitation

The present work reports the presence of fifth-order optical nonlinearity in 2-(2-Quinolyl)-1,3-indandione, an organic dye, at low intensity level. Photophysical, structural and vibrational properties were studied by theoretical and experimental methods. Z-scan study of the dye revealed that the compound has a self-defocusing behaviour at continuous Nd:YAG 532 nm laser excitation and exhibited reverse saturable absorption. The positive fifth-order nonlinear refractive index (n4) is of the order of 10−10 cm4/W2. The nonlinearities present in the compound has both thermal and electronic origin. This study reveals that the material is a potential candidate as an optical limiter at low power.

Actualization of an efficient throttleable laser propulsion mode

Conventional propulsion systems are difficult to change between propelling and non-propelling modes. Throttleable propulsion that results from the control of the input energy is a significant further step toward application in various space missions. We present our work on a novel propulsion mode producing throttleable thrust under the control of our low power CW laser. This photosensitive propellant is fully capable of repeated ignition and interruption, while generating gases that are more environmentally friendly with decreased solid residues. Laser ignition and combustion performance of such modes are characterized. Laser-controlled combustion behavior examples are shown and discussed. These results show potential applications in many aspects of space missions, such as maneuvers in space, attitude control, orbit raising and microsatellite deorbiting.

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.

Steady-State 3D Trapping and Manipulation of Microbubbles Using Thermocapillary

An experimental and theoretical study on the 3D trapping and manipulation of microbubbles by means low power laser-induced temperature gradients induced in ethanol by bulk light absorption (λ = 1550 nm) is presented. Two optical fibers were used: One for bubble generation (OFG) and the other for both trapping and manipulation (OFT). Light from a Q-switched pulsed laser (λ=532 nm & pulse width τp=5 ns) propagates in fiber OFG and gets absorbed at silver nanoparticles (AgNPs), previously photodeposed, at the distal end of a fiber optic core, generating the microbubbles. In the fiber OFT, light of low power CW laser was used to trap and manipulate the bubbles by thermocapillary induced by light bulk absorption in ethanol. The microbubble generated on OFG migrates towards the fiber OFT. The equilibrium between the buoyancy force FB, drag force FD and the Marangoni force (also known as thermocapillary force) FM gives rise to a 3D stably trapping and manipulation of the microbubble for the best time to our best knowledge.

Ultralow duty cycle chopper instigated low power continuous wave laser assisted synthesis of silver nanoparticles: A novel approach

This paper is the first report of advancement in the drastic reduction of the laser power density from 105 to 7.5 W/cm2 for the synthesis of silver nanoparticles (SNPs) using a low power (60 mW) continuous-wave (cw) laser and a specially designed ultralow duty cycle (3%) optical chopper wheel for modulating the laser beam at low frequencies (2 Hz). The target is irradiated by keeping it in a liquid medium at 40–60 °C to produce quantum dots to SNPs of size less than 40 nm. The UV-visible spectroscopic and electron microscopic analyses confirm the formation of quantum dots and SNPs of size-dependent bandgap energy varying from 1.92 to 2.37 eV. The photoluminescence studies not only support the above observations but also reveal the blue emission upon UV excitation through the chromaticity diagram. The proposed greener approach using the low power cw laser is cost-effective when compared with the high-power laser-assisted synthesis of SNPs reported until now.

A Method for Evaluation of Thermal Characteristics of Complex Heat-Shield Assembles at Extremely High Energy Fluxes

A suitable laboratory test procedure is developed where a small fragment of the relatively thick multilayer heat shield is exposed to the extreme heat flux of up to several kW/cm2 in order to evaluate its performance. A nearly one-dimensional test condition has been achieved, where thermal behavior of a small fragment of a large shield became representative for the large heat-shield panel. A cylindrical test sample made of carbon-carbon composite has been surrounded by high-temperature thermal isolation made of zirconia concrete. The high heat flux has been provided by a power CW-laser. The conditions of one-dimensional axial heat flux through the cylindrical fragment of the heat shield are confirmed by the mathematical modeling of the experiment using experimentally measured temperature excursions along the sample axis.

Characterization of Continuous‐Wave Laser Heating Ignition of Ammonium Dinitramide‐Based Ionic Liquids with Carbon Fibers

AbstractAmmonium dinitramide–based energetic ionic liquid propellants (ADN‐EILPs) exhibit the advantages of high energy density, low toxicity, and handling safety, and are therefore promising monopropellants. Herein, we characterized the ignition of ADN‐EILPs induced by CW laser heating in the presence of carbon fibers, clarifying the effect of laser power and suggesting that ignition reproducibility is influenced by the difference of ADN‐EILP osmotic state in carbon fibers or carbon fiber configuration. The observed ignition behavior allowed one to conclude that (i) high‐power CW laser heating causes the formation of bubbles on the surface, which disturbs further heating; and (ii) an Arrhenius‐type relationship exists between ignition delay and heating rate, suggesting that the strategy of foreshortening ADN‐EILP ignition delay by increasing CW laser power has certain limits.