Showing 11 results for Sers
G. Tissoni, I. Protsenkob, R. Kheradmand, F. Prati, M. Brambilla, A. Lugiato,
Volume 1, Issue 1 (6-2007)
Abstract
CSs have been theoretically predicted and recently experimentally demonstrated in broad area, vertical cavity driven semiconductor lasers (VCSELs) slightly below the lasing threshold. Above threshold, the simple adiabatic elimination of the polarization variable is not correct, leading to oscillatory instabilities with a spuriously high critical wave-number. To achieve real insight on the complete dynamical problem, we study here the complete system of equations and find regimes where a Hopf instability, typical of lasers above threshold, affects the lower intensity branch of the homogeneous steady state, while the higher intensity branch is unstable due to a Turing instability. Numerical results obtained by direct integration of the dynamical equations show that writable/erasable CSs are possible in this regime, sitting on unstable background
R. P. Mildren,
Volume 1, Issue 1 (6-2007)
Abstract
Solid-state Raman lasers are known as important sources at normally difficult to access wavelengths, and our recent studies have shown that they also form the basis of a class of wavelength selectable lasers. This paper summarizes our recent studies in wavelength selectable Raman lasers in the visible (532-650 nm) and ultraviolet (266-321 nm).
Ian Leung, Gang-Ding Peng,
Volume 2, Issue 1 (2-2008)
Abstract
The composite cavity fiber laser (CCFL) is relatively simple in its fabrication, as it is essentially three wavelength matched Bragg gratings in a section of doped fiber. By using internal feedback with unequal sub-cavity lengths, unidirectional CCFLs with significantly asymmetric output power from its two outputs can be achieved. Preliminary results also show that it is possible for the lasing frequency of the two outputs to be different by a few GHz.
H. Ghomi, M. Yousefi, Sh. Rostami, Y. Hayashi, E. Hotta,
Volume 4, Issue 2 (6-2010)
Abstract
A capillary plasma z-pinch as an alternative active medium of soft X-Ray lasers was studied experimentally and theoretically. The theoretical analysis was based on the self consistent solution of the so called “snow plow” model. The dynamics of pinched plasma is determined by the capillary parameters and by the time dependence of electrical current passing through it. The current time dependence is strongly influenced by the electrical circuit connected to the capillary. In order to optimize the pinch dynamics from the point of view of laser pumping, the effects of the electrical circuit parameters on plasma evolution are studied in this paper
Akbar Jafari, Khosro Mabhouti, Maryam Heydari Heydarabad,
Volume 8, Issue 1 (1-2014)
Abstract
In this paper, considering optical feedback as an optical injection, and taking in to account round-trip time role in the external cavity, a standard small signal analysis is applied on laser rate equations. By considering the relaxation oscillation (f2) and external cavity frequencies (f) ratio for semiconductor laser, field amplitude response gain, optical phase and carrier number for long external cavities (LEC) and short external cavities (SEC) are obtained. Laser output intensity and resonance peak dynamics have been shown by bifurcation diagrams. Furthermore, the effects of some control parameters, such as enhancement factor, pumping current and feedback strength, on response gain have been discussed in short and long external cavities. As a result, in optical injection, for SEC, compared to LEC, more varied dynamics are observed. Also, higher values of the response gain peak in SEC, in comparison with LEC, make SEC to be affected more by the injected beam. SEC provides greater bandwidth, and also better performance in the range of compared to LEC.
Ms Fatemeh Kazemizadeh, Prof. Rasoul Malekfar, Dr. Fatemeh Shahshahani,
Volume 10, Issue 2 (11-2016)
Abstract
The present article is concerned with an analytical solution for some parts of rare earth doped fiber laser equations. The presented model is valid for both four and three-level fiber lasers consisting high reflectivity mirrors. A typical method to obtain initial value in the numerical solutions of fiber laser equations is shooting method, which is based on an iteration process. Whereas this standard method needs to repeat computational loops to correct an initial guess value in order to satisfy the boundary conditions, which is a time consuming task.
The model and its analytical solution, presented in this article, and the accuracy of the obtained values reveals that the method significantly reduces the time computation. The proposed method has been used for an erbium doped fiber laser and it shows that when the reflectivity of mirrors is more than 0.6 (60%), the calculated results are in agreement with the results of standard numerical methods and the error is less than 10 percent.
Dr Maryam Sanaee, Prof Abbas Zarifkar,
Volume 11, Issue 1 (1-2017)
Abstract
The modulation response, relative intensity noise (RIN) and frequency noise (FN) characteristics of quantum dot (QD) lasers are investigated theoretically in the presence of an external optical beam. Using small signal analysis of the rate equations for carriers and photons, it is demonstrated that by injecting excess carriers into the QDs excited state through optical pumping, the modulation response of QD laser enhances and its bandwidth increases. The external optical pump also helps QD laser to turn on during shorter delay time. Further, it is deduced that the RIN level of QD laser reduces and the damping factor increases due to external beam. Moreover, the frequency noise level of QD laser and correspondingly its linewidth decreases by applying the optical beam.
Bahareh Morovvati , Rasoul Malekfar,
Volume 13, Issue 2 (12-2019)
Abstract
The active substrates in surface enhanced Raman scattering (SERS) spectroscopy were prepared through self-assembly of nanoparticles on functionalized glasses. Colloidal silver nanoparticles (Ag NPs) were prepared chemically in two different sizes by reduction of AgNO3 using trisodium citrate and sodium borohydride. Gold–silver core–shell nanoparticles were also prepared to compare between the optical behaviors of their silver shell and Ag NPs. Absorption spectra of nanoparticles were measured by ultraviolet–visible (UV–Vis.) spectroscopy, and their approximate sizes were determined by dynamic light scattering (DLS). The core–shell nanoparticles were approximately the same size as the largest Ag NPs (35 nm) and had the same maximum absorption wavelength. The potential of these substrates for detection applications was investigated with 1 M and 0.1 mM solutions of Raman-active molecule of crystal violet (CV) dye. The Raman enhancement signal was recorded for 0.1 mM solution with 532 nm laser wavelength, and the obtained spectra enhancement factor (EF) was calculated. EF values indicated that although the silver and gold–silver core–shell nanoparticles had the same surface plasmon resonance, the substrate with smaller Ag NPs had the highest enhancement factor compared to other substrates, which was 9.5´103, and the core–shell substrate even had a slightly lower enhancement factor in compare with the large Ag NPs.
Vahideh Rezaie Kahkhaie, Mohammad Hassan Yousefi, Seyyed Mohammad Reza Darbany, Abolhassan Mobashery,
Volume 13, Issue 2 (12-2019)
Abstract
stabilized Ag Nanoparticles (NPs) were synthesized using Lee-Meisel method under three different conditions in an oil bath. UV-Vis spectroscopy of the Ag NPs showed a Localized Surface Plasmon (LSP) band around 430 nm, indicating Ag NPs had a size range around 40 nm. To fabricate a surface Enhanced Raman Spectroscopy (SERS) substrate, LSP properties of Ag NPs was employed with the goal of detecting Rhodamine 6G dye. SERS spectrum was recorded by using 180 degrees, back-scatter Raman configuration in a custom-made mount. The results showed that ideal Ag NPs agglomeration condition had been achieved by applying centrifuging process and due to this, adding NaCl salt to the SERS substrate was found to be unnecessary. The optimum rate of tri-sodium citrate versus silver nitrate and its influence on UV-Vis and SERS spectra was determined. It was understood that in order to obtain a uniform SERS intensity profile, employing a heater-stirrer instead of an oil bath alongside controlling the atmospheric condition and also drying the substrate in the Argon gas medium are the most necessary conditions for Ag NPs synthesize. The novelty point is obtained when SERS of R6G on a certain substrate, immediately after fabrication and after one month, were compared with a bare R6G dye substrate which, have revealed exceptional performance.
Vahid Eskandari, Nafiseh Sharifi,
Volume 14, Issue 1 (1-2020)
Abstract
In this study, silver nanoparticles were chemically synthesized and deposited on glass substrates using a reducing agent of sucrose, at 50°C. Different characterizations including atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and Raman spectroscopy were obtained to study silvery substrates. Then, the silvery substrates were used as the SERS substrates to detect vibrational modes of phenylalanine amino acid up to the concentration of 10-7 M. The importance of phenylalanine amino acid detection is due to the early diagnosis of phenylketonuria in neonates. Therefore, the blood plasma of a healthy neonate and a neonate with phenylketonuria disease were adsorbed on the SERS substrates. They enhance the intensity of molecular vibration peaks of phenylalanine amino acid of two kinds of blood plasmas. The intensities of molecular vibrations of unhealthy plasma are stronger than healthy plasma due to the higher concentrations of phenylalanine amino acid, which is the sign of Phenylketonuria disease.
Peymaneh Rafieipour, Abbas Ghasempour Ardakani,
Volume 14, Issue 2 (12-2020)
Abstract
The random laser (RL) emission characteristics can be improved by many different routes including either the material processing or optimizing the concentration of the relevant constituents. These routes can be very hard and even not practical in many cases, leaving us with the search of new schemes for the externally improvement of the random laser performance. In this paper, we suggest a simple approach for the externally enhancement of the random laser emission properties that can be applied in any designed transparent random lasing structures with single mode or multi-mode emission. This approach is based on using an adhesive tape in order to introduce an external scattering medium to the lasing structure and also return back the amplified leaking photons. For our investigated sample with nonresonant feedback, it is demonstrated that the emission intensity can be increased by a factor of 4.2 and the random laser threshold can be decreased by a factor of 1.8.
