ing resonances to realize low-distortion, broadband slow light. While the properties of this double resonance system have been studied previously in the context of stimulated Brillouin scattering in optical fibers [16] and the hyperfine structure of atomic vapors [17–21], the usable bandwidth is limited to approximately 1 GHz. To greatly enhance the bandwidth of the slow light region, we follow the approach of Broadbent et al. [3] and make use of the region of normal dispersion between the fine structure absorption doublet in a warm Rubidium vapor. Here, we focus on characterizing experimentally the wavelength and tem- perature dependence of n$_{g}$ between the D1 and D2 lines in Rubidium (comprising a splitting of 7 THz or 14 nm centered at 787 nm) as well as studying the propagation dynamics of ultrashort pulses propagating through the vapor. Using a simple, first-principles model, we obtain excellent agreement between our experimental results and theoretical predictions. We observe a maximum value of n$_{g}$ equal to 1.03, which is uniform (less than 50% variation) over a Δ ν = 3 THz (Δ λ = 6 nm) bandwidth with a nearly exponential sensitivity to tem- perature. Also, we measure the distortion of pulses transmitted through the vapor, and show that pulses as short as 250 fs can undergo fractional delays of almost 20 while suffering a fractional broadening f$_{B}$ of less than 0.65. 

The paper is organized as follows. The next section outlines the theoretical model we use to describe the transmission of light through the vapor cell. Section 3 describes the experimental setups we use to characterize the slow light medium, Sec. 4 compares the experimental and theoretical results, and Sec. 5 concludes the paper and gives possible future applications of our results. 

## 2. Theory 

Atomic vapors are a well understood material whose optical properties can be precisely pre- dicted and controlled. In this work, the optical frequency is so far detuned (by > 3 THz) from either the D1 or D2 resonances of Rubidium that we can treat each atom as consisting of multiple two-level systems ( i.e. , ignore coherences between the levels considered). Further- 

