Saeed Ghavami Sabouri

Bio: Saeed Ghavami Sabouri is an academic researcher from University of Isfahan. The author has contributed to research in topics: Beam (structure) & Second-harmonic generation. The author has an hindex of 5, co-authored 44 publications receiving 120 citations.

Thermal Effects in High-Power Continuous-Wave Single-Pass Second Harmonic Generation

Abstract: We present a theoretical model which describes the effects of thermal load distribution on single-pass second harmonic generation (SP-SHG) of high-power continuous-wave (cw) radiation in MgO:sPPLT nonlinear crystal to provide green output at 532 nm. Numerical simulations are performed based on real practical values and actual operating conditions associated with a recent SP-SHG experiment, generating 10 W of cw green radiation using a Yb-fiber laser. The model is used for four oven configurations to simulate the implications of thermal effects on SH power. The observed asymmetric feature of the phase-matching curves, particularly at higher fundamental powers up to 50 W, are characterized and explained by considering the generation of heat due to crystal absorption. The concept of optical path difference (OPD) is introduced to study the formation of thermal lens and its effects on the displacement of focal point inside the thermally loaded crystal. We further study the dependence of the SH power on the different oven schemes by increasing the input fundamental power up to 50 W. It is found that a top-sinked oven design is the optimum configuration for achieving maximum SHG efficiency without saturation. Comparison of the simulation results with experimental data confirms the validity of the theoretical model.

Focusing Optimization for High-Power Continuous-Wave Second-Harmonic Generation in the Presence of Thermal Effects

Abstract: We study thermal effects in high-power single-pass second-harmonic generation (SP-SHG) of continuous-wave (cw) green radiation in MgO:sPPLT and describe optimization of critical factors including the fundamental beam waist, position, and focusing parameter, for attainment of maximum SP-SHG efficiency. By developing a numerical model combining split-step Fourier and finite-element methods, we compute the relevant parameters for optimization of SP-SHG of a cw Yb-fiber laser at 1064 nm in a 30-mm-long crystal. Real experimental parameters and boundary conditions are used to simulate nonuniform heat distribution in the crystal under high-power operation and study its effects on SP-SHG optimization. The results indicate that for input powers exceeding a certain limit, the Boyd and Kleinman (BK) criteria for optimum focusing are no longer valid. By increasing the fundamental power to 50 W, we find that the optimum focusing parameter decreases by a factor of 4, from $\xi =2.84$ to 0.7. We also find that the maximum SP-SHG output power is always obtained for fundamental waist at the center of the crystal, and we present a general strategy for the choice of ξ at different fundamental powers. Using a top-sinked oven design, the BK focusing condition can be established even at high fundamental powers.

Active Control of Thermal Dephasing Effect in High Power Continuous Wave Single-Pass Second Harmonic Generation

Abstract: In this paper, we present a theoretical model that describes the performance of a specific oven configuration used to actively control the effect of thermal dephasing on the output characteristics of a high-power single-pass second-harmonic generation (SHG) in a MgO:sPPLT nonlinear crystal. The provided model is based on using step and slope oven configurations and making a quantitative comparison with the recent results obtained by using open-top oven scheme. It is found that in the slope oven scheme the SHG power is enhanced by 190% at a fundamental power of 50 W, indicating the significance of the represented model. Eventually, the merit of the proposed slope oven indicated through saturation control in the generation of high-power SH radiation.

Structural similarity assessment of an optical coherence tomographic image enhanced using the wavelet transform technique

Abstract: We report on the quality assessment of an optical coherence tomography (OCT) image. A set of recent digital filters are used for denoising the interferometric signals. It is found that when a combination of continuous wavelet transform (WT) decomposition and the WT denoising techniques is imposed on raw signals, the highest signal-to-noise ratio of 17.8 can be reached. The structural similarity (SSIM) index is eventually employed to evaluate the modality of the reconstructed OCT image. Further, we found out that a SSIM value of about 0.95 can be reached, independent of the method used for envelope extraction.

Thermal dephasing compensation in high-power and high-repetition-rate second-harmonic generation using spillover loss

Abstract: In this paper, the effect of thermal dephasing on the efficiency of a high-power and high-repetition-rate single-pass second-harmonic generation (SHG) in the nanosecond regime is studied. We found that inside a thermal loaded crystal, in addition to the optimization of the focusing parameter and oven temperature, spillover loss can also play a controlling role in retaining the SHG efficiency. It is shown that with a proper choice of the focusing parameter and oven temperature, at about 20 W of averaged fundamental power, at least 60% SHG efficiency is achievable. Moreover, exceeding a certain limit of input power up to 80 W, inducing a spillover loss of about 10%, will help to maintain the SHG efficiency at a maximum value of about 50%.

Fiber-Optic Chemical Sensors and Biosensors (2013-2015).

Abstract: Xu-dong Wang*,† and Otto S. Wolfbeis*,‡ †Department of Chemistry, Fudan University, 200433 Shanghai, P. R. China ‡Institute of Analytical Chemistry, Chemoand Biosensors, University of Regensburg, D-93040 Regensburg, Germany ■ CONTENTS Books, Reviews, and Articles of General Interest 204 Sensors for (Dissolved) Gases and Vapors 204 Hydrogen 204 Hydrocarbons 206 Oxygen 206 Carbon Dioxide 208 Nitrogen Oxides 208 Other Gases 208 Ammonia 209 Ethanol 209 Other Volatile Organic Compounds (VOC)s 210 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 211 Humidity 211 Water Fractions in Organic Solvents 212 Hydrogen Peroxide 213 Sensors for pH Values, Ions, and Salinity 213 pH Values 213 Ions 214 Salinity and Ionic Strength 215 Sensors for Organic Species 216 Glucose Sensing 216 Sucrose 217 Oils 217 Other Organics 217 Biosensors 218 Nucleic Acid-Based Biosensors (DNAand Aptamer-Based) 218 Immunosensors 218 Enzymatic Biosensors 219 Other Biosensors 220 New Schemes and Materials 220 New Sensing Schemes 220 Molecularly Imprinted Polymer (MIP)-Based Sensors 221 Photonic Crystals 223 Author Information 223 Corresponding Authors 223 Notes 223 Biographies 223 Acknowledgments 223 References 223

Saturation properties of large-aperture photoconducting antennas

Abstract: We describe the saturation properties and power scaling of large-aperture planar photoconducting antennas. These antennas have been used to emit and detect electromagnetic pulses with terahertz bandwidth. At high optical fluences, the amplitude of the radiated electric field saturates, at a value comparable to the bias field in agreement with a simple model of the radiation. We also discuss the saturation properties of the large-aperture photoconducting antennas with different semiconductor materials.

Diode laser based light sources for biomedical applications

Abstract: Diode lasers are by far the most efficient lasers currently available. With the ever-continuing improvement in diode laser technology, this type of laser has become increasingly attractive for a wide range of biomedical applications. Compared to the characteristics of competing laser systems, diode lasers simultaneously offer tunability, high-power emission and compact size at fairly low cost. Therefore, diode lasers are increasingly preferred in important applications, such as photocoagulation, optical coherence tomography, diffuse optical imaging, fluorescence lifetime imaging, and terahertz imaging. This review provides an overview of the latest development of diode laser technology and systems and their use within selected biomedical applications. 670 nm external cavity diode laser for Raman spectroscopy built on a 13 × 4 mm2 microbench (Copyright FBH/Schurian.com).