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New Journal of Physics

Evidence of slow-light effects from rotary drag of structured beams

Emma Wisniewski‐Barker, Graham M. Gibson, Sonja Franke‐Arnold, Zhimin Shi, Robert W. Boyd, Miles J. Padgett

Published Aug 8, 2013• 16 citations
Publisher

Abstract

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 pulse-reshaping 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.

DOI
10.1088/1367-2630/15/8/083020

Related papers

Slow Darkness and Rotary Photon Drag

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We observe rotary photon drag significantly enhanced in magnitude by slow-light methods. Specifically, we observe the angular displacement of an image-carrying beam as it passes trough a spinning self-pumped ruby rod. We observe that both the dark and bright regions of the beam are dragged by similar amounts, showing that the slow-light effect extends to slow-darkness too.

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Reply to Comment on ‘Evidence of slow-light effects from rotary drag of structured beams’

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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.

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Comment on ‘Evidence of slow-light effects from rotary drag of structured beams’

G. G. Kozlov, S. V. Poltavtsev, I. I. Ryzhov +1 more

The paper Wisniewski-Barker E et al (2013 New J. Phys. 15 083020) is intended to distinguish experimentally between two mechanisms of pulse delay in ruby and to provide evidence in favor of the slow-light model. The proposed test is based on the idea of monitoring time delay of a ‘dark pulse’ or ‘intensity null’, rather than that of some Gaussian-like pulse. We show that, because of certain experimental inconsistencies, the results of the measurements do not allow one to prefer one of the models and, thus, are interpreted inadequately. In this comment, we propose and realize a simple modification of the experiment Wisniewski-Barker E et al (2013 New J. Phys. 15 083020), which allows us to unambiguously resolve this dilemma. We show that the effect of pulse delay in ruby is perfectly described by the simple model of pulse reshaping and does not require invoking the coherent population oscillation-based slow-light effects.

New Journal of Physics•Mar 28, 2014•6 citations

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Transmission through a spinning window slightly rotates the polarization of the light, typically by a microradian. It has been predicted that the same mechanism should also rotate an image. Because this rotary photon drag has a contribution that is inversely proportional to the group velocity, the image rotation is expected to increase in a slow-light medium. Using a ruby window under conditions for coherent population oscillations, we induced an effective group index of about 1 million. The resulting rotation angle was large enough to be observed by the eye. This result shows that rotary photon drag applies to images as well as polarization. The possibility of switching between different rotation states may offer new opportunities for controlled image coding.

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Slow light in ruby:a study in spatial and temporal domains

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Slow light is the study of the dramatic change in the velocity of light as it travels through certain media. This thesis focuses on slowing caused by transmitting light through a ruby crystal. When ruby experiences spatial or temporal modulation from a laser beam, the velocity of the light is greatly changed from its speed in a vacuum. The underlying mechanism for slow light in ruby is not fully understood and is, therefore, the subject of much debate. In this thesis, I examine many experimental parameters and their effects on slow light in ruby. First, I investigate the delay of images with both bright and dark regions through a spatial modulation of the ruby. I then turn to a temporal modulation of the ruby to answer the question of whether light can be delayed beyond the input pulse, the answer to which has the potential to differentiate between two proposed models for the mechanism that causes slow light in ruby. I return to the spatial domain to study the effect of spatial intensity distribution on the slow-light effect in ruby. I show that beams carrying orbital angular momentum rotate by an amount determined by the spatial feature of the beam profile. I present experimental evidence supporting a complicated mechanism of slow light in ruby, which informs the ongoing debate on the cause of slow light in ruby and provides direction for applications dependent upon the preservation of complex patterns in slow-light media.

•Jan 1, 2015•0 citations
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 pulse-reshaping 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.
A high-intensity laser pulse can lead to a change of the group index of a material, so that the pulse within that material is slowed to only hundreds of meters per second. This kind of slow-light phenomenon scales with the optical intensity of the pulse. While previous experiments have produced this effect with an elliptical beam passing through a spinning ruby window, a question remains as to whether the effect would be present in a circular beam. Here we use two different methods of producing slow light in a round beam, showing that, while less pronounced than the effect with an elliptical beam, a slow-light effect can be seen in a round beam.
The paper Wisniewski-Barker E et al (2013 New J. Phys. 15 083020) is intended to distinguish experimentally between two mechanisms of pulse delay in ruby and to provide evidence in favor of the slow-light model. The proposed test is based on the idea of monitoring time delay of a ‘dark pulse’ or ‘intensity null’, rather than that of some Gaussian-like pulse. We show that, because of certain experimental inconsistencies, the results of the measurements do not allow one to prefer one of the models and, thus, are interpreted inadequately. In this comment, we propose and realize a simple modification of the experiment Wisniewski-Barker E et al (2013 New J. Phys. 15 083020), which allows us to unambiguously resolve this dilemma. We show that the effect of pulse delay in ruby is perfectly described by the simple model of pulse reshaping and does not require invoking the coherent population oscillation-based slow-light effects.
Transmission through a spinning window slightly rotates the polarization of the light, typically by a microradian. It has been predicted that the same mechanism should also rotate an image. Because this rotary photon drag has a contribution that is inversely proportional to the group velocity, the image rotation is expected to increase in a slow-light medium. Using a ruby window under conditions for coherent population oscillations, we induced an effective group index of about 1 million. The resulting rotation angle was large enough to be observed by the eye. This result shows that rotary photon drag applies to images as well as polarization. The possibility of switching between different rotation states may offer new opportunities for controlled image coding.
Slow light is the study of the dramatic change in the velocity of light as it travels through certain media. This thesis focuses on slowing caused by transmitting light through a ruby crystal. When ruby experiences spatial or temporal modulation from a laser beam, the velocity of the light is greatly changed from its speed in a vacuum. The underlying mechanism for slow light in ruby is not fully understood and is, therefore, the subject of much debate. In this thesis, I examine many experimental parameters and their effects on slow light in ruby. First, I investigate the delay of images with both bright and dark regions through a spatial modulation of the ruby. I then turn to a temporal modulation of the ruby to answer the question of whether light can be delayed beyond the input pulse, the answer to which has the potential to differentiate between two proposed models for the mechanism that causes slow light in ruby. I return to the spatial domain to study the effect of spatial intensity distribution on the slow-light effect in ruby. I show that beams carrying orbital angular momentum rotate by an amount determined by the spatial feature of the beam profile. I present experimental evidence supporting a complicated mechanism of slow light in ruby, which informs the ongoing debate on the cause of slow light in ruby and provides direction for applications dependent upon the preservation of complex patterns in slow-light media.