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Showing 3 results for Sers.

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.

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.

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