Showing 52 results for Laser
Iman Rahmani, Majid Ghanaatshoar,
Volume 16, Issue 2 (7-2022)
Abstract
ta charset="UTF-8" >We investigate the Cu2FeSnS4 (CFTS) thin film. The raw materials of this thin film are copper, iron and tin, which are mixed in the form of tablets and then are deposited on a glass substrate through the process of pulsed laser deposition (PLD). The produced metallic thin films are then sulfurized to carry out the process of merging the element sulfur in the thin films and forming CFTS structure. We investigate the influence of sulfurization temperature and the laser pulse energy in the PLD process on the deposited CFTS thin films. The X-ray diffraction (XRD), Raman and UV-Vis analyses’ results show that by decrease in sulfurization temperature from 600 °C to 550 °C the crystal quality of the thin films is improved, which is realized by increase in volume and quality of the CFTS phase. On the other hand, the results confirm that the laser fluence is a decisive factor which should be taken into account to achieve an optimized structure.
Bita Azemoodeh Afshar, Akbar Jafari, Rahim Naderali, Mir Maqsood Golzan,
Volume 16, Issue 2 (7-2022)
Abstract
In this study, we investigated the production of silver nanoparticles by pulsed Nd: YAG laser ablation with λ=532nm in distilled water. The sodium citrate used to control the size of nanoparticles (Nps). The sample containing Ag NPs was characterized by linear absorption spectroscopy (UV-Visible spectroscopy) and transmission electron microscopy (TEM observation). The behavior of nonlinear optical properties of silver nanoparticles was studied using the Z-Scan method at two optimum numbers of the laser pulses and four optimum laser energy densities. In the Z-Scan method, the nonlinear thermal properties of Ag NPs were investigated under exposure to nanosecond laser pulse at λ=532nm. They were gained by fitting theoretical and experimental data. The values of the nonlinear refractive index (n2) and the nonlinear absorption coefficient (β ) were compared concerning to two optimum numbers and four optimum energy densities. The results of the nonlinear refractive index showed a negative value for each sample, this means that samples act as a divergent lens, and the thermal self-defocusing effect can be the main factor of nonlinear behavior. Following the comparison of two quantities, n2 and β , we found that the nonlinear refractive index increased when the number of laser pulses light increased. In addition, the nonlinear absorption coefficient decreased when the number of laser pulses light increased. As a result, the application of these Ag NPs for optical switching devices was investigated, which demonstrated that the large Ag NPs are applicable tools for optical switching devices.
Masume Moshkelgosha, Fatemeh Asem_abadi, Hajar Tavakoli,
Volume 17, Issue 1 (1-2023)
Abstract
The creation of single zeptosecond pulses is important in various scientific fields, particularly for studying time-resolved nuclear processes. In this study, a clean single sub-attosecond (270 zeptosecond) pulse is obtained in the simulation of a femtosecond laser with over dense plasma. First, the desired laser and plasma parameters are utilized to achieve the nano-bunches in the plasma surface and the desired spectrum up to 2000th harmonics is obtained. Then, different filters such as filtering the harmonics and different intensity filters are applied where, the special exponential function is due to a very clean single zeptosecond pulse.
Zahra Heydarinasab, Mohammad Karami, Farrokh Sarreshtedari,
Volume 17, Issue 1 (1-2023)
Abstract
Sub-Doppler dichroic atomic vapor laser lock (DAVLL) is a modulation-free laser stabilization method that combines DAVLL and saturated absorption spectroscopy (SAS). The performance of this highly sensitive stabilization technique strongly depends on the characteristics of the generated error signal. The slope of the error signal determines the lock sensitivity or how fast the frequency compensation could be made in the feedback loop, and the amplitude of the error signal determines the lock stability or how much noise the feedback loop can tolerate before laser unlocking. We have analytically modeled the error signal of the sub-Doppler DAVLL considering all possible transitions between Zeeman sublevels and compared it with the experimental results. Using the analytical and experimental results, it is shown that the values of the required magnetic fields for maximizing the slope and amplitude of the error signal are close to each other. Selecting the mentioned values of the magnetic field for optimization of the sub-Doppler DAVLL error signal is highly useful for sensitive and stable laser locking.
Erfan Abbaszadeh Jabal Kandi, Khosro Mabhouti, Rahim Naderali, Neda Samadzadeh,
Volume 17, Issue 1 (1-2023)
Abstract
In this article, the conditions of pulse production in two mutually coupled lasers are studied. Based on the obtained characteristic equation and its roots, the dynamical behavior of the system and the threshold of the instability are analyzed. For the stable operation of the system and with the use of the time series curves, it is possible to study the dynamical behavior and the stability ranges of the laser in the presence of the saturable absorber and the gain environment. This paper aims to achieve from quasi-periodic behavior in a solitary laser to the generation of a pulse train from two mutually coupled lasers in the presence of saturable absorbers. Also, the stability range for a solitary laser and then for two coupled lasers in the presence of saturable absorbers have been studied.
Hasan Ebadian, Mohammad Mahdi Moslem, Nabiollah Azarpoor,
Volume 17, Issue 1 (1-2023)
Abstract
The simulation results of a 10-kW heat capacity slab laser are presented. Two different schemes for optical pumping with high-power laser diodes are investigated. The simulation of optical pumping using ZEMAX software demonstrates a uniform pump distribution within the laser slabs. Additionally, the temperature distribution in the laser slab is examined using COMSOL. The findings for two distinct laser designs reveal that increasing the slab dimensions reduces the temperature distribution and thermal issues. Furthermore, cooling schemes indicate that the cooling phase of a 10-kW HCL falls within the range of 20-40 seconds. A comparison of water and air cooling of the optically pumped slabs during the cooling phase demonstrates that water cooling is more efficient than air cooling. The simulation results confirm that the proposed laser will be an efficient device for laser material processing. A focused 10-kW HCL laser will melt the steel sheet after less than 1 s at 1490 K.
Reza Pourahmad, Sheila Shahidi, Amirhossein Sari, Mohammadreza Hantezadeh,
Volume 17, Issue 1 (1-2023)
Abstract
In this research, an attempt is made to approach a specific type of carbon, such as graphene or carbon nanotubes by using pulsed laser ablation technique in deionized water environment with changing the laser factors such as wavelength and fluence. Nd:YAG laser with two wavelengths of 1064 and 532 nm and three fluence of 0.8, 1 and 1.2 J/cm2 were selected that number of pulses was 5000 with a frequency of 10 Hz to be irradiated on the graphite target at about 10 minutes. The medium was distilled water. Graphite was located in the 40 ml of distilled water.
The effects of wavelength and fluence of the laser have been experimentally investigated on types of carbon characteristics with different analysis such as Raman scattering spectrum, FE-SEM images, UV–Vis-NIR spectrum and X-ray diffraction (XRD). By using the mentioned analysis, the type of synthesized nano carbon is studied.
This study evaluates the effects of the pulse energy and laser wavelength on properties of synthesized carbon nanoparticle in laser ablation method in medium of distilled water.
Neda Yaghoubi, Hassan Masumi, Mohammad Hossein Fatehi, Fereshteh Ashtari, Rahele Kafieh,
Volume 17, Issue 1 (1-2023)
Abstract
Background: Multiple Sclerosis (MS) is a chronic immune-mediated disease affecting the central nervous system, leading to various disturbances, including visual impairment. Early and accurate diagnosis of MS is critical for effective treatment and management. Scanning Laser Ophthalmoscopy (SLO) is a non-invasive technique that provides high-quality retinal images, serving as a promising resource for the early detection of MS. This research investigates a vessel-based approach for MS detection in SLO images using Long Short-Term Memory (LSTM) networks.
Material and Methods: A total of 106 Healthy Controls (HCs) and 39 MS patients (78 eyes) were enrolled. After implementing quality control measures and removing poor-quality or damaged images, the research utilized a total of 265 photos (73 MS and 192 HC). An approach for the early detection of MS in SLO images using LSTM network is introduced. This approach involves two steps: 1.It involves pre-processing and extracting vessels and then pre-training a deep neural network using the source dataset, and 2. tuning the network on the target dataset of SLO images.
The significance of vessel segmentation in MS detection is examined, and the application of the proposed method in improving diagnostic models is explored. The proposed approach achieves an accuracy rate of 97.44% when evaluated on a test dataset consisting of SLO pictures.
Through experiments on SLO datasets and employing the proposed vessel-based approach with LSTM, empirical results demonstrate that this approach contributes to the early detection of MS with high accuracy. These models exhibit the capability to accurately detect the disease with high precision and appropriate sensitivity.
Zahra Ahmadimanesh, Babak Jaleh, Mahtab Eslamipanah, Milad Daneshnazar, Hassan Hassan Sepehrmansourie, Mohammad Ali Zolfigol,
Volume 17, Issue 2 (6-2023)
Abstract
In this research, palladium nanoparticles (Pd NPs) were first synthesized using laser ablation in the deionized (DI) water environment. Also, metal-organic framework (MOF) was produced using the solvothermal method at a temperature of 150°C. To accumulate Pd NPs on the synthesized MOF, ultrasonic and magnetic stirring methods were used. Different analytical methods were used to investigate the structure and morphology of the synthesized nanocomposite. Also, the sensitivity of the synthesized nanocomposite to ethanol and methanol organic vapors was investigated. The results showed an increase in the response of the MOF in the presence of nanoparticles.
Sahar Sohrabi, Hedieh Pazokian, Mohsen Montazerolghaem,
Volume 17, Issue 2 (6-2023)
Abstract
Laser pulse overlapping (LPO) is an important factor affect the behavior of the laser treated surfaces. For laser surface treatment especially at high fluences, the laser beam must be focused to reach the desired fluence. Then laser beam or sample scanning in 2 directions is done to treat a surface area. In this paper, effect of the distance between laser treated lines (scanned in x direction) on the surface properties including morphological changes and wettability modifications of 304 stainless steel is investigated. The results show that the morphology and chemistry of the surface are influenced effectively by changing the overlap between laser treated line on the surface. Then, it should be considered as an important parameter in laser modification of a large surface with focused laser beam.
Arezou Joudaki, Babak Jaleh, Ensiye Shabanlou, Saeid Azizian,
Volume 17, Issue 2 (6-2023)
Abstract
In recent years, global climate change and population growth have exacerbated freshwater shortages. To address this issue, harvesting water from atmospheric fog has emerged as a promising technique. Inspired by natural processes, the fabrication of hybrid hydrophilic (HI) and superhydrophobic (SHB) surfaces has gained significant attention for enhancing water harvesting efficiency. This study presents a simple, cost-effective laser ablation method for creating wettability contrast surfaces with triangular and parallel patterns on brass metal. Through X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), we investigated the structural and morphological effects on the wettability behavior of irradiated and non-irradiated brass. Additionally, we examined the influence of pattern shapes on water harvesting efficiency. Our findings indicate that triangular patterns significantly enhance water harvesting performance compared to parallel patterns.
Nastaran Kahrarian, Atoosa Sadat Arabanian, Zinab Moradi Alvand, Hasan Rafati, Reza Massudi,
Volume 18, Issue 1 (10-2024)
Abstract
The modification of cell surface structures has become a focal point in cell biology, with methods like drugs, chemicals, and non-destructive techniques such as laser light exposure being utilized. In particular, exposure to femtosecond laser pulses has been found to increase cell permeability to formulations without causing thermal damage. This study aimed to observe and document the changes in the structure of Staphylococcus aureus bacteria when they were optically trapped and subjected to femtosecond laser pulses, along with the application of a medicinal substance, over 20 minutes. The research successfully determined the optimal power and exposure time of the laser light on the bacterial surface and demonstrated the ability of femtosecond laser pulses to enhance the efficacy of the medicinal substance.
