The group has currently 5 full-time and one retired faculty members:

• Aghamir, Farzin M. (Professor)
• Ghorbanzadeh, Atamalek (Associate Professor)
• Hassani, Khosrow (Associate Professor)
• Mahjour-Shafiei, Masoud (Associate Professor, associate member)
• Nahal, Arashmid (Associate Professor)
• Rahimi-Keshari, Saleh (Assitant Professor)
• Sarreshtedari, Farrokh (Assistant Professor, head of the group)

Light and its interaction with matter is, perhaps, the most adequate term to describe the broad research areas in our group. Depending on the academic background and personal interest, people in our group look at this subject from their own perspective and with their favorite techniques. Some of the major topics currently investigated in our group, are summarized as follows:

• Optical Diffractometry: The quantitative treatment of Fresnel diffraction, a well known topic in classical optics, has proved to be a promising technique with many novel applications to measure literally any phenomenon that can cause abrupt changes in light amplitude, phase, or even polarization. This new emerging technique which has mainly developed by Prof. Tavassoly and his co-workers, is currently used by him, Dr. Hassani, and their students to measure thin film thickness and nanometer displacements with a few nanometer resolution, refractive index of solids and liquids with high precision, optical constants of metal layers, and spectroscopy of relatively wide spectrum sources with great precision..
   
• Interaction of Light with Metallic Nanoparticles: As a results of  interaction of laser beam with silver-ion-exchanged glasses reduction of ionic clusters occurs  and, at the same time, produced neutral clusters aggregate and form nanoparticles. During this interaction fluorescence spectra of the samples changes, indicating the resizing and changes in the interaction of nanoparticles with their matrix. Interaction of the focused high power laser beam results in formation of fractal structures made from the silver nanoparticles. Simultaneous heating and exerting external uniform electric field parallel to the surface of the samples result in arrangement of the produced neutral nanoparticles along the field, which makes them dichroic photonic materials. Dr. Nahal and his team study these phenomena, extensively.
• Moiré Technique, including Moiré interferometry, and metrology:
  Moiré technique is a very powerful and relatively simple optical method with several fascinating applications. This technique has been studied and applied, mainly by Prof. Tavassoly and his co-workers, to solve various problems, including the measurement of refractive index, atmosphere turbulence, and Optical Transfer Function (OTF), just to mention a few. Please, refer to the publication list of our group for more exact information. Prof. Tavassoly believes that the capabilities of this technique has not yet fully exploited and there is still plenty of space to work on this phenomenon. Moire measurements have a fairly rich tradition in Prof. Tavassoly's research.
• Laser-induced Properties in Light-Sensitive Thin Films: Interaction of laser beam with thin AgCl films doped by Ag nanoparticles, results in excitation of waveguide modes of the thin AgCl film and consequently interference of the excited mode with the incident  beam. Silver nano-clusters move into the minima of the interference pattern, which results in formation of Spontaneous Periodic Structures in the AgCl-Ag film. The shape of the produced gratings depends on the polarization state of the incident beam. Dr. Nahal and his students are actively pursuing this field, as well.
• Dynamic Light Scattering:  If coherent light is incident on a sample containing moving or evolving elements, the light scattered from nearby particles can interfere and produce low or high intensity signals. Some of the static (e.g. particle sizes and distributions) or dynamic (Diffusion constant, flow rate, speed, etc.) of sample particles under study can be extracted from the statistical analysis of the scattered light intensity. If each photon on average scatters only once, this technique is traditionally known as Dynamic Light Scattering (DLS) or Photon Correlation Spectroscopy (PCS). If, however, photons get the chance to scatter many times before leaving the sample, the information regarding the initial direction of the incident photons is lost and photons behave, more or less, like small particles undergoing diffusion in a fluid. If an extended light detector (such as a CCD camera) is used in front of the scattered light, random areas of constructive interference (known as speckles) form. Again, the dynamical properties of the scatterers in the sample can be inferred from careful analysis of these speckle patterns. This multi-scattering regime, depending on the details of the measurement, is known as Diffusing Wave Spectroscopy (DWS) or Speckle Visibility Spectroscopy (SVS).  Dynamic light scattering techniques have got many applications in soft condensed matter physics and biology. Dr. Hassani in collaboration with Dr. Miri (from the Condensed Matter group) try to apply some of these techniques to the samples of interest.
• Plasma applications: Pulsed cold plasmas are employed to convert methane, the major constituent of natural gas, into more valuable products. The molecular dissociation is mainly realized through molecular vibrations, when the plasma excitation is very fast. In this case, a short lived stage (few hundreds nanoseconds) of highly nonequilibrium thermodynamics is developed where the vibrational temperature is considerably higher than the translational temperature. During this stage, the energy required for dissociation is predominantly supplied from the vibrational reservoir of energy. The vibrational temperature even reaches 5000 K while the translational one hardly exceeds 2000 K. This highly nonequilibrium state greatly enhances the rate constants of chemical reactions.
  The products of repetitive pulsed plasma are hydrogen, acetylene, ethylene and hydrocarbons up to C7. Conversion abilities more than 3 milli mole/Joule for methane has been obtained. The chemical energy efficiencies beyond 40% and conversion rates around 50% have been obtained in repetitive pulsed plasmas, which are well better than those figures for the other plasmas such as corona, DBD that have efficiencies below 10%.Our goal is the optimization of the nonequilibrium state and more studies of this molecular state by the help of spectroscopy, as the future plan. We have also focused on an adequate simulation model of this nonequilibrium thermodynamics, to predict the experimental results. The preliminary results of the model have predicted the overwhelming role of vibrations, when compared to the equilibrium thermal processes, in the dissociation process. These activities are conducted in the Plasma Research Laboratory under supervision of Dr. Ghorbanzadeh.
   
• Laser applications: Remote sensing: The team under supervision of Dr. Ghorbanzadeh is engaging in the detection of trace gases by spectroscopic methods, especially the ways for detection of trace gases from distance. One of important gases where its leak detection is of great importance, especially for the natural gas industry, is methane. This molecule has a principal light absorption band at 3.3 microns and also at 1.65 microns as overtone. Fortunately, the overtone band coincides with the wavelength of commercial diode lasers that emits tens of milliwatt power at 1.65 microns. By support of National Iranian Gas Company (NIGC), a portable remote leak detector working at this wavelength has been recently developed in Laser Research Laboratory. This detector works based on second harmonic detection and is capable of measuring methane leak cloud having integrated concentration below 100 ppm-meter from more than 70 m distance. The range is to be further increased over 150 m for the field applications.
   
•  Magnetic Resonance and its application: Magnetic Resonance Research Laboratory (MRRL) is founded in 2016 by Dr. Farrokh Sarreshtedari in Department of Physics, University of Tehran. The research works of this laboratory include Magnetic Resonance devices and systems and Laser-atom interaction.

   

• Magnetic Resonance devices and systems: MRRL aims to explore Magnetic Resonance (MR) towards investigating, designing and developing novel MR methods, devices and systems. Magnetic Resonance is a physical phenomenon which has the ability to give precise and highly detailed magnetic information of processes at the atomic level. It combines deep principles of quantum mechanics with numerous real-world applications, including MRI and NMR spectroscopy, MR based magnetometers, etc. Magnetic resonance physics can be categorized into two areas of Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) which deals with the atomic nuclei spin and electron spin respectively. In MRRL, we are experimentally exploring both of these two fields of magnetic resonance. Some of the current MR projects include: Atomic magnetometer (Cesium), Proton precession magnetometers, Gradient spin echo enhanced PPM and Overhauser magnetometers.

  Laser-atom interaction experiments: Laser-atom interaction is an interesting area of quantum physics which deals with manipulation of atomic states using resonant laser lights. Developing an Extended cavity diode laser (ECDL) with the ability of laser locking on atomic transitions, different laser-atom interaction experiments are in progress in MRRL. Some of these experiments include developing a Laser cooling system for cooling of Cesium atoms, developing an Electromagnetic induced transparency (EIT) system, Atomic absorption and saturated spectroscopy, Implementing Laser locking by different methods, Atomic line filtering, etc.