When a pulsed light beam propagates through ruby, it is delayed by a slow-light mechanism. This mechanism has been the subject of debate (Wisniewski-Barker et al 2013 New J. Phys. 15 083020; Kozlov et al 2014 New J. Phys. 16 038001; Wisniewski-Barker et al 2014 New J. Phys. 16 038002). To distinguish between the two main proposed mechanisms, we investigate the trailing edge of a squarewave pulsed laser beam propagating through ruby. Our observation of a pronounced tail on the trailing edge of the transmitted pulse cannot be explained solely by the effects of a time-varying absorber acting upon the incident pulse. Therefore, our observation of the creation of a tail at the trailing edge of the pulse provides evidence for a complicated model of slow light in ruby that requires more than pulse reshaping. The different delays of individual Fourier components of the pulse signal explain the pulse distortion that occurs upon transmission through the ruby and must be accounted for by any model that attempts to describe the effects of slow light in ruby.

Self-pumped slow light, typically observed within laser gain media, is created by an intense pump field. By observing the rotation of a structured laser beam upon transmission through a spinning ruby window, we show that the slowing effect applies equally to both the dark and bright regions of the incident beam. This result is incompatible with slow-light models based on simple pulsereshaping arising from optical bleaching. Instead, the slow-light effect arises from the long upper-state lifetime of the ruby and a saturation of the absorption, from which the Kramers-Kronig relation gives a highly dispersive phase index and a correspondingly high group index.

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The phenomenon of self-pumped slow light, where a single beam appears to be slowed by a solid-state media, is both subtle and controversial. Here, we reply to a comment on our recent work, which uses an observation of enhanced photon drag to distinguish between group delay and pulse reshaping.It is with interest that we read the comment [1] by Kozlov et al on our recent publication in NJP entitled 'Evidence of slow-light effects from rotary drag of structured beams' [2]. The authors appear to agree with our rationale for conducting and reporting the work but not with our interpretation of the results nor our conclusions.Slow light is a generic term applied to the optical transmission through a variety of physical systems where the speed of light propagation is reduced to far below that normally encountered. One system that has received a far bit of attention is propagation of intense green light through ruby. The first reports of this system featured an intensity-modulated beam, noting