This study demonstrates that tripod atom-field electronic structure can yield rich electromagnetically induced transparency phenomena, even at room temperature. In particular, we introduce double double electromagnetically induced transparency (DDEIT), wherein signal and probe fields each have two transparency windows. Their group velocities can be matched in either the first or second pair of transparency windows. Moreover, signal and probe fields can each experience coherent Raman gain in the second transparency window. Our investigation has demonstrated that the self-phase modulation (SPM) and cross-phase modulation (XPM) vanish at the center of two transparency windows for resonant coupling field. However, the values of the XPM and SPM in the region of the second EIT window are improved by a factor of
1000 compared to their values in the region of the first EIT window under the same conditions, and have non-zero values at the center of the second EIT window for nonresonant coupling field. Additionally, we derive an analytical solution for the wave equation describing the propagation of the probe field whose amplitude-envelope function is described by the fundamental mode Laguerre-Gaussian function. Our solution exhibits that the group velocity of the probe field reduces as the field propagates through the medium. The group velocity reduction is a consequence of spatially-varying susceptibility. The variation of the susceptibility is established by employing signal field whose amplitude-envelope functions is also described by the fundamental mode Laguerre-Gaussian function. For Doppler-broadened media, we devise a scheme to control and reduce the probe-field group velocity at the center of the second transparency window. We derive numerical and approximate analytical solutions for the width of electromagnetically induced transparency (EIT) windows and for the group velocities of the probe field at the two distinct transparency windows, and we show that the group velocities of the probe field can be lowered by judiciously choosing the physical parameters of the system. Our modeling enables us to identify three signal-field strength regimes quantified by the Rabi frequency, for slowing the probe field. Our scheme exploits the fact that the second transparency window is sensitive to a temperature-controlled signal-field nonlinearity, whereas the first transparency window is insensitive to this nonlinearity.
Summary form only given. The techniques of electromagnetically induced transparency (EIT) may be employed in order to create an effective nonlinear response at a given wavelength which is equal in magnitude to the linear response at that wavelength. Physically, this allows frequency converters wherein 100% photon-to-photon conversion occurs in a single coherence length, i.e., in that distance which causes a /spl pi/ phase slip between the driving polarization and the generated electromagnetic wave. This paper reports the demonstration of a vapor-phase VUV frequency converter from 233 nm to 186 nm with an energy conversion efficiency exceeding 35%; the maximum generated signal energy and power were 250 /spl mu/J and 25 kW. (The net conversion efficiency to 186 nm, including all beams, is roughly 2%.) These wavelengths were chosen to demonstrate the utility of this type of frequency converter to generate wavelengths outside the transparency window of most crystalline media.
It has been shown that control over the design of single- or multimode-transparency windows can be achieved by control-probe quantum interferometry using two delayed phase-locked ultrashort pulses. We have investigated how single- or multimode-transparency windows can be designed by eliminating the absorption to a set of odd or even vibrational levels of a molecule covered by the spectral bandwidth of the pulses. Suppression of absorption can be achieved by controlling the quantum interference of two vibrational wave packets excited by these two pulses, leading to destructive interference of transition amplitudes for one set of vibrational levels even or odd. Simuntaneously the interference becomes constructive for the other set of odd or even vibrational levels, leading to absorption to these levels. Thus, a set of transparency windows is designed in between two absorption peaks at two consecutive odd (even) vibrational levels by eliminating absorption at even (odd) vibrational levels between two absorption peaks. If the spectral bandwidth of the pulse [full width at half maximum (FWHM)] is less than the energy difference between two consecutive absorption peaks, the pulse will be transmitted without absorption through the transparency window. However, for pulses with a larger spectral bandwidth (FWHM), a set of broad transparency windows will be generated and different bands of pulse frequencies will be transmitted through these windows. We have shown that coherent control of the design of transparency windows can be achieved by controlling pulse duration, carrier frequency, delay, and the phase difference of two ultrashort pulses.