Laser Technology Research Articles

Symmetry breaking in 2D materials for optimizing second-harmonic generation

Abstract Second-harmonic generation (SHG) is the generation of 2ω (or half wavelength) light from incident light with frequency ω as a nonlinear optical response of the material. Three-dimensional (3D) SHG materials are widely investigated for developing laser technology to obtain shorter wavelengths in photolithography fabrication of semiconductor devices and the medical sciences, such as for imaging techniques that do not use fluorescent materials. However, to obtain the optimized SHG intensity, the 3D material is required to have no spatial-inversion symmetry (or non-centrosymmetry) and special crystal structure (or so-called phase-matched condition). Recently, engineering symmetry breaking of thin two-dimensional (2D) materials whose 3D structure has the inversion symmetry can offer a breakthrough to enhance the SHG intensity without requiring the phase-matched condition. Over the past decade, many 2D SHG materials have been synthesized to have broken inversion symmetry by stacking heterostructures, twisted moire structures, dislocated nanoplates, spiral nanosheets, antiferromagnetic order, and strain. In this review, we focus on the recent progress in breaking inversion and rotational symmetries in out-of-plane and/or in-plane directions. The theoretical calculations and experimental setup are briefly introduced for the non-linear optical response of the 2D materials. We also present our perspectives on how these can optimize the SHG of the 2D materials.

A case study on entropy generation in MHD nanofluid flow in L- shaped triangular corrugated permeable enclosure

Enclosure with irregular boundaries by providing surface corrugations is considered an efficient strategy to elevate the heat transfer mechanism in laser technology, cooling of electronic instrument, photonic systems in material processing, magnetic resonance, and the automobile industry are few to mention. In view of such mesmerizing utilization present work is articulated by considering L-shaped corrugated enclosure saturated with water and copper (Cu) nanoparticles are included. The physical impacts of a horizontally oriented magnetic field and permeable medium are accounted along with measurement of entropy. Mathematical modelling of the problem is attained in dimensionless version through a set of similar variables. Computational experiments are conducted through the application of commercial software (COMSOL) based on the finite element approach. A grid independence and comparison tests are also accounted to ensure credibility of simulations. Impact of parameters is revealed through sketches. Quantities of interest, including local and average Nusselt numbers, Bejan number, and total entropy, are also evaluated for flat and correlated surfaces. Induction of nanoparticles in the base fluids tends to reduce the entropy generation by up to 12.45 %. Growth in NuAvg (3.08 % approx.) is attained by increasing the frequency of imposed triangular waved corrugation.

Fractional thermal load in cryogenically cooled Yb:YLF and Yb:YAG lasers

We present a method for the direct measurement of the fractional thermal load (FTL) in cryogenically cooled laser crystals. The experimental methodology involves characterizing the liquid nitrogen evaporation rate in a dewar containing the laser crystals, allowing for the accurate determination of FTL. The FTL is measured to be 1.7 × quantum defect (QD) for Yb:YLF and 1.5 × QD for Yb:YAG under continuous wave lasing conditions. The measured FTL values are then used to calculate the temperature distribution inside the crystals as a function of pump power, and the simulation results are found to be in very good agreement with the in-situ temperature measurements using contactless optical luminescence thermometry. The method and findings presented in this work hold great potential to benefit laser engineers and scientists working with cryogenic lasers to address and overcome temperature-dependent handicaps.

Application of CO2-Laser Micro-Perforation Technology to Freeze-Drying Whole Strawberry (Fragaria ananassa Duch.): Effect on Primary Drying Time and Fruit Quality

Freeze-drying (FD) processing preserves foods by combining the most effective traditional technologies. FD conserves the structure, shape, freshness, nutritional/bioactive value, color, and aroma at levels similar to or better than those of refrigerated and frozen foods while delivering the shelf-stable convenience of canned/hot-air-dehydrated foods. The mass transfer rate is the essential factor that can slow down the FD process, resulting in an excessive primary drying time and high energy consumption. The objective of this study was to reduce the FD processing time using CO2 laser technology to improve product competitiveness in the preservation of whole strawberries. The research process consisted of the selection and characterization of fresh strawberries, followed by preparation, pre-treatment, freeze-drying, a primary drying time assessment, and a quality comparison. Experiments were carried out using strawberries without micro-perforation and with five and eight micro-perforations. Quality parameters were determined for fresh, frozen/thawed, and freeze-dried/rehydrated strawberries. It was found that the primary drying time can be significantly reduced by 20% (95% CI) from 26.7 h for non-perforated fruits to 22.3 h when five micro-perforations are made on each strawberry. The quality parameters used to evaluate the strawberries did not show significant differences when comparing frozen/thawed fruits with freeze-dried/rehydrated fruits. The experiments conducted in this study showed that freeze-drying may efficiently compete with freezing technology when processing whole strawberries.

CO2 Laser Frenuloplasty: Advancing Minimally Invasive Techniques for Rapid Healing and Improved Patient Outcomes

This study explores the innovative use of CO2 laser technology in frenuloplasty, a significant shift from classic methods like scalpel surgery or electrocautery towards a minimally invasive approach. The research involved 15 patients aged 25 to 50, undergoing frenuloplasty with a CO2 laser system equipped with a 7-inch defocused handpiece, set at 20 Hz and 0.3 W. This method diverges from conventional laser techniques, focusing on controlled laser passes combined with manual traction to elongate the fibrous tissue of the frenulum. The results demonstrated that the CO2 laser technique allowed for a precise and progressive modification of the frenulum, significantly reducing the risks of hemorrhage and secondary intention fibrosis. The healing process was notably expedited, with patients reporting satisfactory outcomes within a two-week period. Statistically significant improvements were observed in patient-reported outcomes, as evidenced by the increases in the Short Form Health Survey (SF-12) scores, with the mean Physical Component Summary (PCS) score rising from 32.5 to 47.5 and the mean Mental Component Summary (MCS) score from 39.3 to 52.3 (p < 0.001 for both). The study concludes that CO2 laser frenuloplasty is an effective and safe technique, offering substantial benefits in terms of reduced healing time and enhanced patient satisfaction. The significant improvements in SF-12 scores underscore the positive impact on patient quality of life, advocating for the broader application of this technique in clinical practice. Further research is warranted to explore its potential in a wider clinical context.

3D Laser Writing of Low-Loss Cross-Section-Variable Type-I Optical Waveguide Passive/Active Integrated Devices in Single Crystals.

Optical waveguides fabricated in single crystals offer crucial passive/active optical components for photonic integrated circuits. Single crystals possess inherent advantages over their amorphous counterpart, such as lower optical losses in visible-to-mid-infrared band, larger peak emission cross-section, higher doping concentration. However, the writing of Type-I positive refractive index modified waveguides in single crystals using femtosecond laser technology presents significant challenges. Herein, we introduce a novel femtosecond laser direct writing technique that combines slit-shaping with an immersion oil objective to fabricate low-loss Type-I waveguides in single crystals. This approach allows for precise control of waveguide shape, size, mode-field and refractive index distribution, with a spatial resolution as high as 700nm and a high positive refractive index variation on the order of 10-2, introducing new degrees of freedom to design and fabricate passive/active optical waveguide devices. As a proof-of-concept, we successfully produced a 7mm-long circular-shaped gain waveguide (∼10µm in diameter) in an Er3+-doped YAG single crystal, exhibiting a propagation loss as low as 0.23dB/cm, a net gain of ∼3dB and a polarization-insensitive character. The newly-developed technique is theoretically applicable to arbitrary single crystals, holding promising potential for various applications in integrated optics, optical communication, and photonic quantum circuits. This article is protected by copyright. All rights reserved.

What is the definition of stone dust and how does it compare with clinically insignificant residual fragments? A comprehensive review.

During endoscopic stone surgery, Holmium:YAG(Ho:YAG) and Thulium Fiber Laser(TFL) technologies allow to pulverize urinary stones into fine particles, ie DUST. Yet, currently there is no consensus on the exact definition of DUST. This review aimed to define stone DUST and Clinically Insignificant Residual Fragments(CIRF). Embase, MEDLINE(PubMed) and Cochrane databases were searched for both in vitro and in vivo articles relating to DUST and CIRF definitions, in November 2023, using keyword combinations: "dust", "stones", "urinary calculi", "urolithiasis", "residual fragments", "dusting", "fragments", "lasers" and "clinical insignificant residual fragments". DUST relates to the fine pulverization of urinary stones, defined in vitro as particles spontaneously floating with a sedimentation duration ≥ 2sec and suited for aspiration through a 3.6Fr-working channel(WC) of a flexible ureteroscope(FURS). Generally, an upper size limit of 250µm seems to agree with the definition of DUST. Ho:YAG with and without "Moses Technology", TFL and the recent pulsed-Thulium:YAG (pTm:YAG) can produce DUST, but no perioperative technology can currently measure DUST size. The TFL and pTm:YAG achieve better dusting compared to Ho:YAG. CIRF relates to residual fragments(RF) that are not associated with imminent stone-related events: loin pain, acute renal colic, medical or interventional retreatment. CIRF size definition has decreased from older studies based on Shock Wave Lithotripsy(SWL)(≤ 4mm) to more recent studies based on FURS(≤ 2mm) and Percutaneous Nephrolithotomy(PCNL)(≤ 4mm). RF 2mm are associated with lower stone recurrence, regrowth and clinical events rates. While CIRF should be evaluated postoperatively using Non-Contrast Computed Tomography(NCCT), there is no consensus on the best diagnostic modality to assess the presence and quantity of DUST. DUST and CIRF refer to independent entities. DUST is defined in vitro by a stone particle size criteria of 250µm, translating clinically as particles able to be fully aspirated through a 3.6Fr-WC without blockage. CIRF relates to ≤ 2 RF on postoperative NCCT.

Photothermal tissue reconstruction and the use of phytoestrogens in the treatment of genitourinary menopausal syndrome

Introduction. Genitourinary syndrome of menopause (GSM) is a complex of symptoms resulting from changes to the vulvovaginal region, urethra and bladder due to estrogen and other sex steroid deficiency. Vulvovaginal atrophy is one of its manifestations, and vaginal dryness, dyspareunia, burning and itching are the most common symptoms.Aim. To analyse 20 clinical cases of the use of innovative laser procedures combined with phytoestrogens in patients with vulvovaginal atrophy as a symptom of GSM vs the standard systemic protocol for menopausal hormone therapy.Materials and methods. A clinical case-control study was conducted among 20 postmenopausal women. The age of the subjects ranged from 50 to 65 years with amenorrhea for at least 1 year, a follicle-stimulating hormone level of >30 IU/L and various presentations of GSM. The women were divided into two groups: group 1 (n = 10) received laser therapy combined with phytoestrogens, group 2 (n = 10) received systemic menopausal hormonal therapy. To evaluate the results, a survey with a specialized international vulvovaginal symptom questionnaire (VSQ) was carried out to determine the vaginal health index scores before and after treatment.Results. After treatment, both groups showed significant improvement in the form of the reduction or disappearance of symptoms of vulvovaginal atrophy. The prescription of phytoestrogens provided an additional positive effect after 3 sessions of carbon dioxide laser treatment.Conclusion. The carbon dioxide laser exposure resulted in the reduction or disappearance of the local symptoms of climacteric syndrome in the form of GSM, and the use of phytoestrogens as part of Mense BAA supplemented the treatment of psychoemotional and neurovegetative changes, which allowed us to make a conclusion about the feasibility, high efficiency and safety of the complex treatment for women, who do not wish to take menopausal hormone therapy and (or) have absolute contraindications. However, further research on the laser technologies and other non-hormonal techniques to treat GSM is required to carry out a more complete and accurate assessment of the effectiveness and safety of these treatments.

Crystallization-Driven Tuneable Lasing of Perylene Doped into the Nematic Liquid Crystal

Versatile devices with tunable capabilities for controlling lasing wavelength and intensity are in high demand. Liquid crystals (LCs) exhibit immense potential for such applications, offering fine-tuning possibilities through external factors. On the other hand, laser technology is currently a research hotspot in optoelectronics, and also in practical applications. The recent market introduction of laser television marks a significant stride toward making such advanced technology accessible in every household. In synergy with laser pumping, the LCs unquestionably can be rediscovered. This study presents a comprehensive investigation into the crystallization phenomenon within a host-guest device, compact in size, free from moving parts, and integrating the liquid crystalline (LC) matrix doped with 3,4,9,10-tetra-(3-alcoxy-carbonyl)-perylene (THCP) dye. The focus lies in examining the influence of varying dye concentrations on multicolor fluorescence, lasing behavior, and device morphology. The systematic analysis of Random Lasing (RL) energy thresholds and the impact of DC voltage on light intensity modulation is demonstrated. Morphological changes were monitored in real-time using optical microscopy techniques, including crossed polarizer, and fluorescence imaging under 450 nm excitation. Utilizing advanced Transmission Electron Microscopy (TEM) techniques, we explore exceptional insights into our set of devices, providing novel information about the THCP crystallization process for the first time in the literature. To gain a comprehensive understanding of the crystal forming and molecular geometry we examined additionally the THCP dye, using X-ray diffraction and Raman spectroscopy. Furthermore, we showcase that varying the pumping energy enables multicolor tuning in the fabricated systems, presenting an attractive feature in the context of laser display technologies.

Technique of corneal allogenic ring segment preparation using femtosecond laser: preclinical study on human corneal grafts.

To describe a new technique for preparing corneal allogenic ring segments (CAIRSs) using femtosecond laser technology. Hospital Foundation Adolphe de Rothschild-Noémie de Rothschild institute, Paris, France. Preclinical study conducted on human corneal grafts. The corneal grafts were mounted on an artificial chamber pressurizer (ACP) with preset constant pressure, and the FSL was used to create a circular annulus with specific dimensions. The resulting CAIRSs were analyzed for their thickness and width after air drying. A total of 25 CAIRSs were prepared using the FSL. The mean width and thickness of the CAIRSs were 803 ± 77 μm and 83 ± 16 μm, respectively. Statistical analysis revealed no significant differences in width among the various quadrants of each CAIRS or between different CAIRSs. Significantly thicker CAIRSs were obtained with a higher ACP pressure. The technique of CAIRS preparation using FSL technology and controlled artificial anterior chamber pressure demonstrated reproducibility and precision. This approach holds the potential for customizing and personalizing CAIRSs based on individual corneal characteristics.

Squeezing the Threshold of Metal‐Halide Perovskite Micro‐Crystal Lasers Grown by Solution Epitaxy

AbstractMetal halide perovskite semiconductors have demonstrated remarkable progress not only in photovoltaics and X‐ray detection but also in laser technologies. Particularly appealing is the simplicity with which micro‐crystallites can be epitaxially grown, thereby forming micro‐resonators suitable for lasing. Here, the laser threshold is optimized by selecting excitation laser parameters and by improving material quality. The latter process is conducted for formamidinium lead tribromide, emitting in the green spectral range. Depending on the growth method and parameters, the sizes of the micro‐resonators can be tuned between ≈3 and 23 micrometers. Under laser excitation systematically lower thresholds are observed for micro‐resonators in the 4–7 micrometer size range, than for larger ones, irrespective of growth method. Among three optimized growth methods, epitaxial growth via antisolvent vapor‐assisted crystallization exhibits the smallest threshold powers, indicating the highest material quality. This conclusion is supported by hyperspectral microscopic luminescence imaging and by transient photoluminescence. The best laser structures exhibit record threshold powers for epitaxially grown perovskites, indicating that the selected antisolvent vapor epitaxial growth holds great promises also for other perovskite materials.

ОСОБЕННОСТИ ЭНДОДОНТИЧЕСКОГО ЛЕЧЕНИЯ C УЧЕТОМ ВЫЯВЛЕННОЙ CANDIDA ALBICANS В СИСТЕМЕ КОРНЕВЫХ КАНАЛОВ

The subject of the study was to study the properties of basic means for irrigation and physical methods of influencing the microflora of the root canal system against identified Candida Albicans. The purpose of the work was to review and analyze the features of endodontic dental treatment, taking into account the identified Candida Albicans in the root canal system. A search was conducted in domestic publications and foreign sources for studies containing information on various methods of influencing root canal biofilms during endodontic treatment. A comparison was made of the activity of various irrigants and physical methods of root canal treatment in relation to the identified microflora containing bacteria such as yeast-like fungi of the genus Candida and others. Sodium hypochlorite solution (NaOCl) is a mandatory antiseptic agent included in the recommended endodontic treatment protocol used in modern dentistry. To achieve a successful result, we consider it necessary to perform high-quality mechanical treatment of root canals, competent selection of irrigants, as well as the use of additional physiotherapeutic methods (ultrasound or laser technologies). A bacterioscopic examination of the contents of the root canals was carried out for the presence of yeast-like fungi of the genus Candida. A temporary exposure of a suspension of the drug “Fluconazole” on a paper point was introduced into the root canals at the first stage of endodontic treatment, and the drug “Fluconazole” was prescribed orally at a dose of 150 mg on the first day. Then, in the absence of exudate or odor in the root canals, as well as confirmation by bacterioscopic examination of the absence of yeast-like fungi of the genus Candida, the root canals were filled with permanent material. But despite following all clinical recommendations, in some cases it is not possible to achieve the required effect due to the resistance of biofilms containing Candida albicans, Prevotella melaninogenica, Enterococcus faecalis, Bacteroides fragelis in the root canal system to the effects. Despite the wide variety of endodontic treatment methods and drugs for influencing representatives of the root canal microflora, it is not always possible to achieve complete elimination of biofilm during irrigation and medicinal or physical influence on them. It is especially important to look for ways to modify treatment and make it easier to use and accessible in order to avoid subsequent complications.

Application of femtosecond mode-locked SnTe thin films and generation of bound-state solitons

In the realm of ultrafast laser technology, the exploration of two-dimensional materials as saturable absorbers (SA) has garnered significant research interest. Our research investigates the characteristics of SnTe thin films, a topological crystalline insulator material, as a potential saturable absorber for ultrafast lasers. Using the molecular beam epitaxy (MBE) technique, we analyze the films’ morphology and composition through atomic force microscopy (AFM) and successfully deposit SnTe epilayers on Au(111)/mica substrates. Through the utilization of SnTe-SA, an erbium-doped fiber laser is fabricated, demonstrating a pulse output with a width of 276 fs and a center wavelength of 1560 nm, highlighting the potential of SnTe films in manufacturing ultrafast optical devices. Additionally, tightly bound solitons with a soliton interval of 1.01 ps are observed, contributing to the exploration of soliton nonlinear dynamics.

Research on Laser Dual-Mode Fusion Detection Method of Ship Wake Bubbles

Addressing the issues of weak echo signals and strong background interference in the laser detection of ships’ wakes, an analysis of the laser backscatter detection characteristics of ships’ wakes has been conducted. Based on the Monte Carlo method, a simulation model for the dual-mode fusion detection of ship wake bubbles using laser technology was constructed under different target characteristics. A dual-mode fusion detection system for ships’ wakes was designed, and an indoor experimental platform for the dual-mode fusion detection of ship wake bubbles using laser technology was established. To address problems such as a wide range of echo signal intensity changes, severe signal fluctuations, low resolution, poor image contrast, and blurred target edge information, an algorithm based on multi-timescale hierarchical fusion signal processing and temporal difference accumulation image processing was proposed. Verification experiments for ship wake detection were conducted, which revealed that the dual-mode fusion detection method for ship wake bubbles using laser technology can effectively enhance the detection signal-to-background ratio and counter the maneuvering evasion of underwater weapons by ships. It achieved high sensitivity, large dynamic range, high resolution, and a wide field of view detection and real-time signal processing of ship wake bubble targets of different magnitudes against a strong reverberation background. The effectiveness of the dual-mode fusion detection mode was validated, providing theoretical support for the overall system design and parameter settings.

Quality improvement of Nd: YAG laser marked DMC and QR codes on the surface of PBT/glass fiber composites by DOE methodology

Laser technology plays an important role in today’s industrial environment. Laser marking is typically used at the end of the production chain to personalize products and make them traceable to the point of sale. One of the challenges of laser marking is the difficulty of creating contrasts whose reflectivity can cause readability problems for electronic decoding devices on production lines, known as scanners. This problem is related to the wrong choice of marking parameters, which results in waste for companies in terms of production stoppages due to rejection, scrap, and customer complaints. Although these problems are common, this process is increasingly used in the industry. Therefore, there is a gap in studies in this field to optimize the marking parameters in many materials, such as PBT (polybutylene terephthalate). The present work was developed in a final assembly line of instrument clusters for motorcycles, where tests were carried out with different types of laser marking parameters, through the implementation of a factorial DoE, with a specific type of laser and material. The laser-marked codes were analyzed in a laboratory using a verifier to assess quality according to ISO/IEC 29158:2020. It was found that the lower the parameter values, the poorer the quality of the codes. The data were statistically processed, and it was possible to identify the marking parameters that ensured the best quality and process performance for DMC and QR codes.

THE EFFECTIVENESS OF THERAPY OF COMPLICATED FORMS OF DENTAL CARIES USING AN ER,CR:YSGG LASER WITH A WAVELENGTH OF 2780 NM

The use of laser technologies in the treatment of complicated forms of dental caries is a promising area of dentistry.
 To determine the effectiveness of therapy for complicated forms of dental caries by using an erbium-chromium laser with a wavelength of 2780 nm for biomechanical treatment of root canals
 106 patients were examined, divided into 3 clinical groups. The first (control) group included 15 patients, whose treatment was carried out by a generally accepted method. The second group consisted of 50 patients who, at the second visit, immediately before root canal obturation, were treated with erbium-chromium laser radiation.
 The third group of patients was treated in one visit and divided into two subgroups. In group 3-A , the root canal was irradiated with a laser with factory settings, and in group 3-B , the frequency and power of the laser were increased from 20 to 40 Hz and from 1.25 to 1.5 Watts.
 Results and discussion. In the first group, 59 microorganisms from all 17 strains were seeded before the treatment of the root canal system of teeth with chlorine-containing disinfectants. After treatment, the seeding rate of Streptococcus mitis decreased from 40 to 13%, Streptococcus intermedius from 20 to 6.6%, Enterococcus spp from 33.3 to 13.3%, Candida spp. from 33.3 to 20%. In group 2, after the application of a hydrokinetic laser, none of the 17 strains sown before treatment were sown. The use of a hydrokinetic laser with a wavelength of 2780 nm in the factory settings in group 3A (power 1.25 W, pulse frequency 20 Hz, air 10%, water off) left microorganisms from the genus Candida spp (5.5%) not neutralized. The combined use of the traditional protocol and the hydrokinetic Er,Cr:YSGG laser in group 3B made it possible to achieve complete elimination of microorganisms from those sown before treatment (p 0.001).
 Conclusion. Treatment of purulent pulpitis and pulp necrosis in one visit is recommended to be carried out with a hydrokinetic Er,Cr:YSGG laser with a wavelength of 2780 nm with increased parameters: power – 1.5 W, frequency – 40 Hz, air – 35%, water – 25%.

Broadband nonlinear conversion and random quasi-phase-matching in transparent glass composite

With the development of laser technology, nonlinear optics plays a crucial role in frequency conversion. However, the generation of second harmonics in nonlinear optical crystals is generally subject to rigorous phase-matching conditions that hinder the performance of broadband tunability. It is believed that introducing disorders in nonlinear optical materials is helpful to overcome this obstacle. In this work, we have prepared a nonlinear microcrystal-doped glass (NMG) composite material, allowing for tunable and polarization-independent nonlinear conversion from visible to near-infrared. The linear dependence of SHG intensity versus sample thickness indicated the facilitation of random quasi-phase matching by using the NMG. Our results provide a more stable and promising platform for disordered nonlinear photonic materials and suggest the possibility of more efficient nonlinear conversions using the NMG composite glass fibers in future.

Laser ultrasonic frequency-domain imaging and phase weighted optimization based on full matrix capture

Far-field laser technology has greatly promoted the progress of nondestructive ultrasonic imaging of bulk structures. However, under thermoelastic excitation, the body waves exhibit a relatively low signal-to-noise ratio, resulting in images with low resolution and contrast. Based on the motivation, this paper developed a frequency-domain phase weighted imaging method to improve the quality of laser ultrasonic defect imaging. Firstly, laser ultrasonic scanning was performed on the sample with artificial transverse hole defects. The cylindrical lens focused line source was used to improve the intensity of the body wave signals, and ensure that there was no damage on the material surface under high laser energies. Then, the frequency-domain phase shift migration (PSM) algorithm was used to perform multimode imaging of defects, achieving frequency-domain synthetic aperture focusing technique (F-SAFT) and total focused method (F-TFM) imaging based on full matrix capture. Furthermore, the phase circular statistical vector (PCSV) was proposed for weighted optimization, which improved the image quality, suppressed the background noise and multimode artifacts. Finally, the imaging quality of several algorithms were discussed. The results indicate that frequency-domain images were superior to time-domain results. After phase weighting, the imaging quality can be further improved, and the detection blind zone was significantly reduced. This work will contribute to the rapid and high-quality defect imaging of laser ultrasonic.

Effect of non-uniform carrier injection on two-state lasing in quantum dot microdisks with split electrical contact

In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 μm diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.

Research and Application Progress of Laser-Processing Technology in Diamond Micro-Fabrication.

Laser-processing technology has been widely used in the ultra-precision machining of diamond materials. It has the advantages of high precision and high efficiency, especially in the field of super-hard materials and high-precision parts manufacturing. This paper explains the fundamental principles of diamond laser processing, introduces the interaction mechanisms between various types of lasers and diamond materials, focuses on analyzing the current development status of various modes of laser processing of diamond, briefly discusses the relevant applications in diamond cutting, micro-hole forming, and micro-groove machining, etc., and finally discusses the issues, challenges, and potential future advancements of laser technology in the field of diamond processing at this point.