Quantum Beat Spectroscopy:

Quantum beat spectroscopy is a Doppler-free time domain method based on the creation of molecular coherences with a laser pulse and the measurement of their subsequent time evolution.

If two or more closely spaces molecular levels are simultaneously excited by a short laser pulse, the time-resolved total fluorescence intensity emitted from these coherently prepared levels shows a modulated exponential decay. The effect is known as quantum beats is due to interference between the fluorescence amplitudes emitted from these coherently excited states.

Fourier transformation of the time evolution allows a spectrum in the frequency domain with lifetime- limited resolution to be recovered. We use nitrogen pulse laser (337 nm) with 300 picosecond pulse, Nd:YAG (532 nm, 355 nm) with 5 ns, and various pulsed dye lasers. We are currently developing the QBS technique to apply on iodine molecules and alkali atoms.

Polarization Spectroscopy:

Experimental studies of photon interactions with atoms are dynamical field of research in Atomic and Molecular physics. We are interested in studying the various aspects of atom-photon interactions such as collisional cross section studies between polarized alkali and rare gas atoms, and thus measure a linear or circular polarization spectroscopy of the j=1/2-j'=3/2-j"=1/2,3/2 transitions in alklai atoms such as cesium and sodium colliding with ground state rare-gas atoms using a two-photon two-color double-resonance pump-probe technique.

The technique uses nanosecond pulse dye lasers which are pumped by the state-of-the art Nd:YAG solid-state laser. Nd:YAG laser is operating at 20 Hz with 6.5 ns pulse duration, and it is frequency either doubled at 532 nm or tripled at 355 nm, or generate both simultaneously. The two-photon double-resonance polarization spectrum is recorded by remotely scanning the probe laser via LabVIEW.

Electron Imaging Spectroscopy:

This new project, supported by Research Corporation, extends our spectroscopic studies toward the investigation of state-multipoles in the Rydberg state cesium atoms. A very powerful method of gaining information about the alignment and orientation (anisotropies) in the highly excited state of alkali is the electron/ion imaging which is a rapidly advancing experimental technique with full of possibilities to make important contributions to the field of atomic, molecular and collisional dynamics. Electrons/ion will be accelerated toward the microchannel plate-phosphor assembly using an accelerator (focusing lens). We will take advantage of the elegance of the imaging method that lies in its direct determination of both the speed and angular distribution from the intensity profile without distorting the electron/ion cloud.

Laser Instrumentation: Frequency narrowing high power external cavity broad area laser diodes

High power braod area diode lasers have many applications to atomic physics. One of the applications is the optically pumped spin-exchange mechanism which has exceptionally promising applications to the improvements in NMR experiments for the medical imaging of the lungs. Several techniques can be used to improve the images such as using external cavity optics to narrow the linewidth of the broadband diode lasers. We use double pass Littman-Metcalf laser cavity (grazing incidence) technique that consists of a grating for frequency selective output coupler and a mirror for feed-back mechanisms. This technique forces the diode laser to oscillate in a single longitudinal mode. This research was highlighted in Optics and Photonics News in 2002.               

Currently, we are working on the improvements for higher power (>2 W), single-mode, narrow-bandwidth operation of the external-cavity broad-area laser. Our passively stabilized external cavity is modular with a fixed pivot point so that the optical elements can be changed to access a broad frequency spectrum and enable multiple applications. Also, our cavity has tunability of 12 nm centered near 790 nm in an external cavity.

Pedagogical Studies in Atomic and Molecular Physics:

Raman Scattering Spectroscopy of liquid nitrogen

In this study, we described a straightforward and highly visual experiment designed to demonstrate Raman scattering spectroscopy by measuring the vibrational energy spacing of nitrogen molecules in the liquid phase. Interpretation of the spectrum teaches the principles of elastic and inelastic light scattering and the intrinsic properties of molecules. The use of a pulsed Nd:YAG laser with high peak power leads to a plethora of nonlinear optical phenomena. The presence of highly visible stimulated Raman scattering greatly enhances the normal Raman-shifted signal, allowing for a more engaging laboratory experience in comparison to traditional Raman scattering experiments. This research was selected to be the cover page of the American Journal of Physics - Cover page.

Laser Induced Fluorescence

Laser-induced fluorescence (LIF) is a spectroscopic method used for studying structure of molecules, detection of selective species and flow visualization and measurements. We use iodine molecules to show LIF.