Slow Light Imaging Spectroscopy: Sensitivity of the Instrument Function to Optical Thickness and Gate Delay

In this study, we investigate the effect of the optical thickness of an atomic vapor cell and the delay of the gated camera on the instrument function in Slow Light Imaging Spectroscopy. In an atomic vapor medium, the slow light effect happens at certain frequency windows where there is a large slope of the index of refraction versus frequency. The extent of these windows depends on the important parameters of the vapor cell (i.e., the optical thickness). Furthermore, the gate delay determines the minimum amount of delay that a signal needs to experience before it is detected. These two parameters determine the shape of the instrument function of the spectrometer in slow light imaging spectroscopy. Simulation and experimental results show that when absorption lines of cesium vapor at 852.1 nm are used as a delay medium, the instrument function at low temperature consists of four peaks corresponding to the steep refractive index gradients at either side of the two hyperfine absorption lines. By increasing the temperature, these peaks move away from the absorption lines. When the two peaks between the two absorption lines move away from their corresponding absorption lines, they move closer to each other until they blend, forming a strong peak. By increasing the gate delay, the four peaks of the instrument function reappear.