Standard Laser Research Articles

Visual Improvements After Excimer Laser Multiple Light Redirection in Eyes With Central Visual Loss From Macular Degeneration and Geographic Atrophy: First Report of Cases

Purpose To analyze outcomes after multiple light redirection (MLR) by photoablation of a small paracentral portion of Bowman's layer in each corneal quadrant using standard myopic laser in situ keratomileusis (LASIK) software with non-customized fenestrated MLR corneal light shields (Excimer-MLR) without postoperative visual training or magnification in pseudophakic eyes with central visual loss from age-related macular degeneration (AMD) with geographic atrophy (GA). Methods Retrospective analysis of two cases. Results Outcomes after Excimer-MLR in the worse-seeing eyes of an 86-year-old and a 65-year-old pseudophakic man with AMD and GA revealed corrected distance/near visual acuity gains of 6.0/6.0 and 11.8/10.0 lines within 12 days and 5.0/5.0 and 12.2/9.8 lines at 9 months, respectively, with improved Amsler grids, no distance or near glasses change, no complications, and no adverse events related to Excimer-MLR. Contrast sensitivity and stereopsis, measured in case 2, improved postoperatively. Conclusions This first report showed that Excimer-MLR safely produced large improvements in visual function up to 9 months postoperatively in two eyes with central visual loss from AMD. [ Journal of Refractive Surgery Case Reports. 2024;4(4):e29–e35.]

Revealing the influence of ring-shaped beam profiles in high-speed laser beam microwelding by synchrotron x-ray imaging

Laser beam microwelding is a precise technique for joining miniature metal components with high feed rates, which is crucial for productivity. However, high feed rates provoke humping formation—periodic beadlike protuberances along the weld seam—that compromise weld integrity. While humping has been associated with the keyhole transition from a narrow to an elongated shape using standard laser intensity distributions (e.g., Gaussian, top-hat), the impact of complex beam profiles, like ring-shaped intensity distributions, remains less understood. In this work, the influence of core-only, ring-only, and superimposed core-ring intensity distributions on humping formation during laser beam microwelding is investigated by means of synchrotron x-ray imaging. Single-track experiments on stainless steel (1.4404) at 1000 mm/s reveal that the keyhole geometry shifts from deep and narrow with core-only power input to shallow and elongated with ring-only power input. Using a superimposed core-ring intensity distribution (Pc = 300 W, Pr = 600 W) results in a U-shaped capillary and the reduction of the humping amplitude by nearly 80% (from 45.61 μm with core-only to 10.29 μm). The additional laser power comes with the tripling of the melt pool width (from 81 μm with core-only to 263 μm) likely decreasing the melt flow velocity. The reduced variability of the capillary length present for the superimposed intensity distribution further indicates a stabilized evaporation behavior. This work provides valuable insights into mitigating humping formation during laser beam microwelding of stainless steel at elevated feed rates using core-ring intensity distributions.

An optical system for cellular mechanostimulation in 3D hydrogels

We introduce a method utilizing single laser-generated cavitation bubbles to stimulate cellular mechanotransduction in dermal fibroblasts embedded within 3D hydrogels. We demonstrate that fibroblasts embedded in either amorphous or fibrillar hydrogels engage in Ca2+ signaling following exposure to an impulsive mechanical stimulus provided by a single 250 µm diameter laser-generated cavitation bubble. We find that the spatial extent of the cellular signaling is larger for cells embedded within a fibrous collagen hydrogel as compared to those embedded within an amorphous polyvinyl alcohol polymer (SLO-PVA) hydrogel. Additionally, for fibroblasts embedded in collagen, we find an increased range of cellular mechanosensitivity for cells that are polarized relative to the radial axis as compared to the circumferential axis. By contrast, fibroblasts embedded within SLO-PVA did not display orientation-dependent mechanosensitivity. Fibroblasts embedded in hydrogels and cultured in calcium-free media did not show cavitation-induced mechanotransduction; implicating calcium signaling based on transmembrane Ca2+ transport. This study demonstrates the utility of single laser-generated cavitation bubbles to provide local non-invasive impulsive mechanical stimuli within 3D hydrogel tissue models with concurrent imaging using optical microscopy. Statement of significanceCurrently, there are limited methods for the non-invasive real-time assessment of cellular sensitivity to mechanical stimuli within 3D tissue scaffolds. We describe an original approach that utilizes a pulsed laser microbeam within a standard laser scanning microscope system to generate single cavitation bubbles to provide impulsive mechanostimulation to cells within 3D fibrillar and amorphous hydrogels. Using this technique, we measure the cellular mechanosensitivity of primary human dermal fibroblasts embedded in amorphous and fibrillar hydrogels, thereby providing a useful method to examine cellular mechanotransduction in 3D biomaterials. Moreover, the implementation of our method within a standard optical microscope makes it suitable for broad adoption by cellular mechanotransduction researchers and opens the possibility of high-throughput evaluation of biomaterials with respect to cellular mechanosignaling.

Latex-Bridged Inverse Pickering Emulsion for Durable Superhydrophobic Coatings with Dual Antibacterial Activity.

There is agreement that every colloidal structure produces its own set of unique characteristics, properties, and applications. A colloidal phenomenon of latex-bridged water in a dimethyl carbonate (DMC) Pickering emulsion stabilized by R202 hydrophobic silica was investigated for its ability to act as a superhydrophobic coating (SHC) for cellulose substrates. First, various emulsion compositions were screened for their stability and droplet size. The final composition was then cross-examined by cryogenic scanning electron microscopy and optical and fluorescent microscopy to verify the colloidal structure. The drying pattern of the coating was investigated by using labeled samples under a fluorescent microscope and by scanning electron microscopy on a paper substrate. After the final ∼3 μm of dry coating was applied, it exhibited superhydrophobicity (advancing contact angle = 155°) and full functionality after 5 min at room temperature (RT). Coated samples maintained superhydrophobicity after 20 abrasion cycles and mechanical integrity after 50 s of water immersion. The SHC-coated paper demonstrated compatibility with a standard laser printer, and the coated paper demonstrated superhydrophobicity after printing. Finally, a propolis/DMC extract was produced and then analyzed by gas chromatography-mass spectroscopy (GC-MS) and infused into the SHC (PSHC). The newly formed PSHC demonstrated its ability to act effectively against E. coli biofilm and S. aureus planktonic cells and reduce their viability by over 90% and 99.99%, respectively.

Investigation of the laser fluence and wavelength dependence in surface-assisted laser desorption/ionization mass spectrometry using gold nanoparticles.

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) builds on the use of nanostructured surfaces (e.g., coatings of colloidal nanoparticles) to promote analyte desorption and ionization. The SALDI process is believed to occur mainly through thermal processes, resulting from heating of the nanosubstrate upon absorption of the photon energy, and by assisting ionization steps. Mostly due to the accessibility of the respective hardware, the majority of SALDI-MS studies use standard laser wavelengths for MALDI (i.e., 337 or 355 nm), even though peak absorption of the SALDI nanosubstrate might completely differ from these values. Here, we investigated the wavelength dependence in SALDI-MS to determine if wavelength adjustment would be beneficial, and to provide new experimental data for a better understanding of the SALDI mechanism. To this end, gold nanoparticles (AuNPs) sprayed onto microscope glass slides were employed as SALDI nanosubstrates and L-arginine as a model analyte. In addition, we used 2,5-dihydroxyacetophenone (2,5-DHAP) for classical MALDI-MS using the same experimental setup. Arginine ion signals were recorded as a function of laser wavelength and laser fluence. Mass spectra were acquired in the wavelength range between 310 and 630 nm, including the absorption maximum of the sprayed AuNPs around 550 nm and that of 2,5-DHAP around 380 nm. Laser fluence thresholds for the generation of arginine ions were found to be dependent on the laser wavelength and to inversely correlate with the absorbance profiles of the deposited AuNPs and 2,5-DHAP, respectively. Very differently to MALDI, in SALDI ionization efficiency was found to strictly linearly decrease with increasing laser wavelength. Our results, therefore, corroborate the general assumption that material ejection in SALDI-MS is mainly driven by thermal processes in the low laser fluence range and add new evidence that the ionization process is directly influenced by photon energy when AuNPs are employed as nanosubstrates.

Highly efficient multifunctional metasurface integrating lens, prism, and wave plate

The miniaturization of optical systems is crucial for various applications, including compact augmented reality/virtual reality devices, microelectromechanical system sensors, ranging technologies, and microfabricated atomic clocks. However, reliance on bulky discrete optical elements has been a significant obstacle to achieving this miniaturization. This work introduces a highly efficient multifunctional metasurface (MFMS) that seamlessly integrates a lens, prism, and quarter-wave plate (QWP). This innovation allows simultaneous collimation, beam deflection, and polarization conversion within a singular thin element. Specifically, for the prism-QWP bifunctional integration, we achieved a high diffraction efficiency of 72.8% and a degree of circular polarization of −0.955 under exposure to linearly polarized light at a wavelength of 795 nm, proving its potential for ultracompact atomic clock applications. Moreover, the lens-prism-QWP trifunctional integration successfully showed diffraction-limited focusing performance with a numerical aperture of 0.4, which was sufficient to collimate a beam with a divergence angle of 20∘, corresponding to the light emitted from a standard vertical-cavity surface-emitting laser.

Laser sintering of polyamide 12 with limited thermal degradation

The paper presents, for the first time, the results of PA12 polyamide sintering using the original method of Dual Beam Laser Sintering of polymers (DBLS). The DBLS method, which is a modification of the standard polymer Laser Sintering (pLS) approach, allows to reduce the thermal degradation of the polymer by using selective (in terms of powder volume and process time) heating the material with laser radiation. The paper presents both the properties of sintered parts and the analysis of the degree of thermal degradation of post-process powders. Examination of the sintered parts included X-ray computed tomography (XCT) to visualize and analyze their porosity and a tensile test. Post-process powders were evaluated by Gel Permeation Chromatography (GPC), Melt Flow Rate (MFR), Dry Laser Diffraction Spectroscopy (DLD) and Powder Rheometer (FT4). The analysis of the result of PA12 sintering with the DBLS method was carried out in comparison with the classic pLS approach. As it has been shown, the DBLS approach allows to obtain comparable results for sintered parts compared to the pLS method. What is particularly important, it was shown that the post-process powder in the DBLS method has almost unchanged properties - the change in molecular weight and viscosity is at the level of the measurement error. Reducing thermal degradation is especially important in order to obtain continuous circulation of the powder in the manufacturing process.

Enhancing the performance of AlGaN-based DUV-LEDs with multifocal laser stealth dicing

In this study, AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) processed via standard laser dicing (SLD) and multifocal laser stealth dicing (MFLSD) were investigated. Adopting the MFLSD technology would generate a roughing surface rather than the V-shaped grooves on the sidewall of 508 × 508 µm2 DUV-LEDs, which would reduce the forward operating voltage and increase the wall-plug efficiency, light output power, and far-field radiation patterns of these devices. In addition, the wavelength shift, far-field patterns, and light-tracing simulation results of the DUV-LEDs processed with SLD and MFLSD were clearly demonstrated and analyzed. Accordingly, it was observed that the MFLSD process provided more possibilities for photon escape to increase the light extraction efficiency (LEE) of DUV-LEDs, thus decreased the wavelength-redshift and junction temperature in DUV-LEDs. These results provide a reference for advanced nano-processing practices implemented during the fabrication of semiconductor devices.

Biological Efficacy of Ionizing Radiation Sources on 3D Organotypic Tissue Slices Assessed by Fluorescence Microscopy.

Traditional cell-based radiobiological methods are inadequate for assessing the toxicity of ionizing radiation exposure in relation to the microstructure of the extracellular matrix. Organotypic tissue slices preserve the spatial organization observed in vivo, making the tissue easily accessible for visualization and staining. This study aims to explore the use of fluorescence microscopy of physiologically compatible 3D tissue cultures to assess the effects of ionizing radiation. Organotypic tissue slices were obtained by vibratome, and their mechanical properties were studied. Slices were exposed by two ionizing radiation sources; electron beams (80 Gy and 4 Gy), and soft gamma irradiation (80 Gy and 4 Gy). Two tissue culture protocols were used: the standard (37°C), and hypothermic (30°C) conditions. A qualitative analysis of cell viability in organotypic tissue slices was performed using fluorescent dyes and standard laser confocal microscopy. Biological dosimetry is represented by differentially stained 200-µm thick organotypic tissue sections related to living and dead cells and cell metabolic activity. Our results underscore the ability of fluorescence laser scanning confocal microscopy to rapidly assess the radiobiological effects of ionizing radiation in vitro on 3D organotypic tissue slices.

Deep Learning Neural Network (DNN) Coupled Laser Induced Breakdown Spectroscopy for Quantitative Analysis of Copper Alloys

Conventional Laser Induced Breakdown Spectroscopy (LIBS) quantitative analysis, employing both calibration and calibration-free techniques, is challenged by spectral overlapping, self-absorption, and spectral broadening effects, leading to decreased accuracy. Recently, integration of machine learning (ML) algorithms with LIBS has been increasingly employed to tackle these challenges. This article explores the augmentation of LIBS with deep learning neural networks (DNN) to enhance accuracy of quantitative analysis of multi-elemental copper alloys. Sufficient training data was acquired by simulating optical emission spectra for bronze (Cu-Sn) and admiralty brass (Cu-Zn-Sn) alloys under standard laser produced plasmas conditions, encompassing different alloy concentrations, electron temperatures, and densities. We designed a regularized DNN structure, fine-tuned using a validation dataset to optimize quantitative results. The model’s accuracy was assessed with test dataset. The quantitative results demonstrated reduced loss as training spectra increased from 500 to 5000 for both alloys. The decline in mean squared error, from 2.793×10−3 to 4.283×10−5 for bronze and from 3.245×10−2 to 5.598×10−4 for admiralty brass alloys, as training data increased from 500 to 5000, underscores the proposed DNN model’s potential for metallurgical alloy quantification.

The Impact of Standard vs Early Apical Release Holmium Laser Enucleation of the Prostate Technique on Postoperative Incontinence and Quality of Life

ObjectivesTo investigate the difference in postoperative incontinence and quality of life comparing standard vs early apical release (EAR) Holmium Laser Enucleation of the Prostate (HoLEP). MethodsA retrospective review was performed to identify patients who underwent HoLEP from December 2021 to December 2022 at a single teritary referral center with two participating consultant urologists. Patients were assessed with questionnaires and evaluated clinically. We performed propensity score matching with a logistic regression and a 1:1 matching method. A propensity score adjusted logistic regression (PSRM) was performed to compare the pads per day between surgical techniques controlling for age, prostate size, preoperative survey data, uroflow and post void residual. Results114 patients underwent HoLEP, of which 60 patients were treated with EAR and 54 patients with standard technique. EAR technique demonstrated shorter operative times (p= 0.046). The EAR cohort demonstrated improved AUASS (p = 0.034, p= 0.001), QOL (p= 0.001, p<0.001), and continence rates (p<0.001, p<0.001) at 6 and 12 weeks postoperatively. PSRM showed that the standard HoLEP increased the risk of requiring >2 pads per day 4.2x (p= 0.031, HR 95%, CI = 1.16, 15.35) and 8.3x (p<0.001, HR 95% CI 3.17, 21.6) at 6 and 12 weeks postoperatively. ConclusionsEarly apical release technique promoted earlier return of continence and improved quality of life within 6 weeks of surgery. Data AvailabilityThe data demonstrating the study’s results is accessible from the corresponding author in an anonymized format upon reasonable request for the purpose of review.

Control of meltpool shape in laser welding

In laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.

A new path towards ultra-high efficient laser power converters: Silicon carbide-based multijunction devices

Current high power laser transmission technology faces two major limitations to improve the efficiency of the photovoltaic receivers: the intrinsic entropic losses associated to low bandgap materials (such as GaAs) and the series resistance losses that degrade the device performance at high power densities. The use of high bandgap materials and new architectures for laser power converters (LPC) have been pointed out as alternatives to overcome these limitations. In this work, three silicon carbide polytypes (3C, 4H and 6H) are proposed as base materials for the standard horizontal laser power converter (hLPC) architecture and the Vertical Epitaxial Hetero-Structure Architecture (VEHSA). 3C SiC based hLPCs outperform the power converters based on the other two polytypes, achieving a maximum efficiency of 84.6% at ▪, but suffer from series resistance losses, that deteriorate their efficiency, at higher laser power densities. This issue is solved with 3C SiC 4 cells VEHSAs that demonstrated increasing efficiency with the input power, reaching a maximum of 87.4% at ▪. The VEHSA reduced number of cells minimize the risks of efficiency losses due to current mismatch between cells. These results support the feasibility of a new generation of LPCs capable of efficiently convert ultra-high laser power densities.

Observation of Replica Symmetry Breaking in Standard Mode-Locked Fiber Laser.

We report the first experimental demonstration of the replica symmetry breaking (RSB) phenomenon in a fiber laser system supporting standard mode-locking (SML) regime. Though theoretically predicted, this photonic glassy phase remained experimentally undisclosed so far. We employ an ytterbium-based mode-locked fiber laser with a very rich phase diagram. Two phase transitions are observed separating three different regimes: cw, quasi-mode-locking (QML), and SML. The regimes are intrinsically related to the distinct dynamics of intensity fluctuations in the laser spectra. We set the connection between the RSB glassy phase with frustrated modes and onset of L-shaped intensity distributions in the QML regime, which impact directly the replica overlap measure.

Determination of Particle Size Distribution: Comparison of Standard Hydrometer Method and Laser Diffraction Analysis for Use in Forestry

Laser diffraction analysis is an alternative to standard sedimentation methods designed to determine particle size distribution. In this article, five samples from the forested part of the floodplain of the Svitava River in the Czech Republic were analyzed. Laser diffraction analysis and sedimentation hydrometer method were performed for each sample. The samples were divided according to soil classification into two groups depending on their classification–group A and group B. The results of laser diffraction analysis and hydrometer method were compared. Correlation relationships between both methods were established, and values were recalculated from laser diffraction analysis to the hydrometer method according to correlation equations. The article is a part of the methodology under preparation, which will include the most common soil types in the Czech Republic. This methodology focuses on the use of laser diffraction for the establishment of structures in forest environments using the regional specific standards for particle size distribution determination.

Pharmaceutical Formulations Containing Graphene and 5-Fluorouracil for Light-Emitting Diode-Based Photochemotherapy of Skin Cancer.

Nonmelanoma skin cancer (NMSC) is the most common cancer worldwide, among which 80% is basal cell carcinoma (BCC). Current therapies' low efficacy, side effects, and high recurrence highlight the need for alternative treatments. In this work, a partially reduced nanographene oxide (p-rGOn) developed in our laboratory was used. It has been achieved through a controlled reduction of nanographene oxide via UV-C irradiation that yields small nanometric particles (below 200 nm) that preserve the original water stability while acquiring high light-to-heat conversion efficiency. The latter is explained by a loss of carbon-oxygen single bonds (C-O) and the re-establishment of sp2 carbon bonds. p-rGOn was incorporated into a Carbopol hydrogel together with the anticancer drug 5-fluorouracil (5-FU) to evaluate a possible combined PTT and chemotherapeutic effect. Carbopol/p-rGOn/5-FU hydrogels were considered noncytotoxic toward normal skin cells (HFF-1). However, when A-431 skin cancer cells were exposed to NIR irradiation for 30 min in the presence of Carbopol/p-rGOn/5-FU hydrogels, almost complete eradication was achieved after 72 h, with a 90% reduction in cell number and 80% cell death of the remaining cells after a single treatment. NIR irradiation was performed with a light-emitting diode (LED) system, developed in our laboratory, which allows adjustment of applied light doses to achieve a safe and selective treatment, instead of the standard laser systems that are associated with damages in the healthy tissues in the tumor surroundings. Those are the first graphene-based materials containing pharmaceutical formulations developed for BCC phototherapy.

An investigation into the mechanisms that influence laser sintered polyamide-12 top surfaces

Purpose The purpose of this paper is to elucidate the extent to which the mechanisms of polymer melt viscous flow and finish layer powder particle adhesion influence the top surface topographies of laser sintered polyamide (PA12) components. Design/methodology/approach Laser sintered specimens were manufactured at varying laser parameters in accordance with a full factorial design of experiments. Focus variation microscopy was used to ascertain insight into their top surface heights and peak/valley distributions. Subsequently, regression expressions were generated to model the former with respect to applied laser parameters. Auxiliary experimental analysis was also performed to validate the proposed mechanisms and statistical models. Findings Within the parameter range tested, this work found the root mean square (Sq) and skewness (Ssk) roughness responses of laser sintered PA12 top surfaces to be inversely related to one another, and both also principally influenced by beam spacing. Furthermore, it was demonstrated that using optimised laser parameters (to promote polymer melt dispersion) and building without finish layers (to avert subsequent powder particle adhesion) reduced the mean Sq roughness of resultant topographies by 30.8% and 47.9% relative to standard laser sintered PA12 top surfaces, respectively. Practical implications The scope to which laser sintered PA12 top surfaces can be modified was highlighted. Originality/value This research demonstrated the impact the mechanisms of polymer melt viscous flow and finish layer powder particle adhesion have on laser sintered PA12 top surfaces.

Comparison of ureteoroscopy and laser stone fragmentation between Holmium: YAG laser with MOSES versus non-MOSES technology: a prospective single-center propensity score-matched analysis using similar laser settings.

In vitro studies have shown that the holmium Modulated Optics Enhancement Systems (MOSES) technology can lead to an increase in the efficacy of lithotripsy and a reduction of retropulsion, but clinical evidence comparing it to non-MOSES technology is still scarce. We did a comparison of ureteoroscopy and laser stone fragmentation (URSL) between Holmium:YAG laser with MOSES versus non-MOSES technologies. Patient data and outcomes were prospectively collected and analyzed regarding patient demographics, stone parameters, and clinical outcomes. Patients undergoing URSL with standard holmium laser without MOSES technology (Group 1) were compared to holmium laser with MOSES (Group 2) using the same clinical laser settings (0.4-1 J, 20-40 Hz) with dusting and pop-dusting technique. The independent t-test, Mann-Whitney U test, and Chi-squared test were used, with a p-value of < 0.05 as significant. Given the different sizes of the cohorts, we performed a propensity score 1:1 matched analysis. A total of 206 patients (1:1 matched) with a male:female ratio of 94:112 and a median age of 56 (range: 39-68) years were analyzed. Groups 1 and 2 were matched for ureteric stones (27.7% and 22.3%, p = 0.42), pre-stenting (37% and 35%, p = 0.66), the mean number of stones (1.76 ± 1.3) and (1.82 ± 1.4, p = 0.73), and ureteral access sheath use (37% and 35%, p = 0.77) respectively.While there was no significant statistical difference in clinical outcomes, the stone size was slightly larger in Group 2, 14.8 ± 10.8 mm vs 11.7 ± 8.0 mm, for a lower operative time 42.7 ± 30.6 min versus 48.5 ± 25 min, lower perioperative complication rates 3.9% versus 4.9% and a higher stone-free rate 90.3% versus 87.4%. While the use of MOSES technology was slightly beneficial for the treatment of stones in terms of clinical outcomes, this was not statistically significant. As this debate continues, there is a need for high-quality randomized studies to show if there is a true difference in these outcomes.

Final report of APMP.AUV.V-S2: supplementary comparison on calibration of laser tachometers using mechanical generators or optical simulators

Main textThis is the final report for APMP supplementary comparison APMP.AUV.V-S2 in the area of 'vibration' (quantity of rotational speed). The aim of this comparison was to compare primary measurements of rotational speed in the range from 30 r/min to 99 996 r/min. Six Metrology Institutes from two RMOs, APMP and AFRIMETS, have participated in the comparison with the National Institute of Metrology, P.R. China as the pilot lab. NIM, NMC and NIS used a mechanical generator for calibration, with expanded uncertainties in the order from 10-3 to 10-5. NML, NIMT and KEBS used an optical simulator for calibration, with expanded uncertainties in the order from 10-4 to 10-5. All the participating laboratories provided their calibration results, which were all consistent within their declared expanded uncertainties for the measurement results. Each participant contributed to the SCRVs calculated for five rotational speed comparison values of two laser tachometers, NLYZ-02 and 03, except that NIS's measurement results of NLYZ-03 are invalid. Smaller measurement uncertainties than the order of 10-5 for the calibration of laser tachometers are difficult to achieve for either mechanical generators or optical simulators with the current technology of rotational speed standard devices and laser tachometers.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Highly sensitive interferometry with strong anti laser jamming capability based on frequency shift optical feedback

With the proliferation of diverse laser equipment, the optical environment in which highly sensitive optical systems operate has become harsh and intricate. Mitigating laser jamming originating from the operational waveband is a challenging problem encountered by laser interferometric measurement systems. In this paper, we set forth a robust anti-jamming optical interferometry with high sensitivity. This method is based on frequency shift optical feedback, namely anti-jamming laser feedback interferometry (AJLFI). A rear-end pumping Nd:YVO4 microchip laser with bidirectional output channels is employed as the interferometric system source, and the photodetector is posterior to the laser cavity. This particular laser structure and the unique detector placement method from optical feedback interferometry make the laser cavity operate as a high-stop-band filter to filter out laser jamming in the operational waveband. In the AJLFI-based system we established, the jamming laser with a wavelength equaling that of the interferometric system suffers a notable attenuation of 44.8 dB. Concurrently, jamming laser falling within a range of ±10 nm from the wavelength of interferometric system gets an attenuation exceeding 44.43 dB. In addition, we set up the standard laser feedback interferometry(LFI)-based system and the Michelson heterodyne interferometry(MHI)-based system with the same experimental parameters as the AJLFI-based system to perform anti-jamming capability comparative experiments. In the experiments, a pulsed laser beam with a peak power of 1780.9 W is employed as laser jamming in the operating wavebands, which is precisely directed toward the target in conjunction with the probe light of the interferometric systems and scattered into the interferometric systems. The experimental findings demonstrate that the AJLFI-based system exhibits superior anti-jamming capability in both phase and amplitude measurements compared to conventional LFI-based and MHI-based systems.