We demonstrate time delayed imaging with slow light using high positive dispersion of a passive atomic gas. This filter allows for imaging of Raman, Rayleigh, and Thomson scattering without the need of a spectrometer.
We report a new spectroscopy method achieved by combined refraction and propagation delay of light pulses passing through a prism cell filled with an atomic vapor. The atomic vapor medium has strong refractive index gradients near the atomic resonant absorption features, and these features enable the separation in time and space of different spectral features of a light pulse propagating through the vapor cell. The gradient of the refractive index leads to a slowing of the light pulse, while simultaneously, the magnitude of the refractive index and the prismatic windows or internal prism elements of the atomic vapor cell spatially separate the frequencies due to dispersion. The combination of these two effects leads to high-resolution spectral selectivity and strong suppression of out-of-band light. Applications are achieved for Rayleigh, Raman, and Thomson spectroscopy for which the wavelength of the scattering spectra tracks the wavelength of the excitation laser source. The laser is tuned such that the spectral line of interest falls near the resonance of the atomic vapor. Applications for rotational Raman spectroscopy are of particular interest since specific Raman lines can be selected while other Raman lines as well as background Rayleigh and other scattering are strongly rejected.
We report an experimental realization of the delayed images in a hot rubidium atomic vapor. With a rubidium atomic vapor cell as slow light medium, the image quality of the experiment could be improved greatly, compared with the results without a slow light medium. By analyzing the results about the image visibility of the slow light imaging system under three different conditions, the image visibility becomes better with the increment of the temperature, during the time that the wavelength of the laser is within dispersion range.
Slow-light media are of interest in the context of quantum computing and enhanced measurement of quantum effects, with particular emphasis on using slow light with single photons. We use light-in-flight imaging with a single-photon avalanche diode camera array to image in situ pulse propagation through a slow-light medium consisting of heated rubidium vapor. Light-in-flight imaging of slow-light propagation enables direct visualization of a series of physical effects, including simultaneous observation of spatial pulse compression and temporal pulse dispersion. Additionally, the single-photon nature of the camera allows for observation of the group velocity of single photons with measured single-photon fractional delays greater than 1 over 1 cm of propagation.