A Velocity of Light Measurement Using a Laser Beam

Edmonds, Dean S.; Smith, R. V.

doi:10.1119/1.1976592

Cited by 4 publications

(6 citation statements)

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Section: Tof Measurementsmentioning

confidence: 97%

“…Notice that the present TOF measurement loosely resembles the technique described in [3] that uses a rotating mirror. A main pulse is produced by the sweep of the rotating beam over the photodetector slit (see figure 2, [3]). The difference in the present approach is that, inside the main sweeping pulse, there is a Doppler beat frequency modulation, thus making a more precise determination of the delay between the far and near signals.…”

Section: Tof Measurementsmentioning

confidence: 97%

“…The Doppler beat helps in making simpler the measurement. In the previously quoted rotating mirror technique [3] great care was necessary in aligning that part of the sweep falling on the far detector that corresponds to the position of the beam being reflected by the beamsplitter into the near detector. In our apparatus neither the alignment nor the width of the sweep pulse (i.e.…”

Section: Tof Measurementsmentioning

confidence: 99%

“…By knowing the distance between detectors, the value of the speed of light is readily calculated. Light pulses have been generated by means of rotating mirror [3], Pockels-cell modulator [4], acousto-optic modulator [5], or modulated lasers [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…The two different configurations described above are easily set up. It is possible to emulate the techniques described in [3,11], that is, an improved version of the rotating mirror technique and a variation of the interferometer of [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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Speed of light demonstration using Doppler beat

Bernal

Bilbao

2018

Eur. J. Phys.

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From an apparatus previously designed for measuring the Doppler shift using a rotating mirror, an improved, versatile version was developed for speed-of-light demonstrations in a classroom or a teaching laboratory. By adding a second detector and adequate beam-splitter and mirrors three different configurations are easily assembled. One configuration is used for time-of-flight measurements between a near and a far detector, allowing to measure the speed of light provided that the path length between detectors is known. Another variation is the interferometric method obtained by superposing the far and near signals, in such a way that a minimum of the combined signal is obtained when the time delay makes the signals arrive out of phase by π radians. Finally, the standard Doppler configuration allows the measurement of the frequency beat as a function of the rotation frequency. The main advantages of the apparatus are: a) the experimental setup is simple and completely accessible to undergraduate students, b) the light is visible, students can see the rays, which, with the use of appropriate screens, can be blocked at any point along their paths, c) the experiment can take place entirely within the teaching laboratory or demonstration room (using the interferometric method, the shortest distance to the far mirror was as small as 0.5 m), d) different configurations can be built, including some economical setups within the budget of teaching laboratories.

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Section: Tof Measurementsmentioning

confidence: 97%

Section: Tof Measurementsmentioning

confidence: 97%

Section: Tof Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Speed of light demonstration using Doppler beat

Bernal

Bilbao

2018

Eur. J. Phys.

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An inexpensive apparatus for the measurement of the velocity of light in transparent media

Barr¹

1972

J. Phys. E: Sci. Instrum.

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Measuring the dispersion curve of a PMMA-fibre optic cable using a dye laser

Zorba¹,

Farah²,

Pant³

2010

Eur. J. Phys.

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An advanced undergraduate laboratory experiment is outlined which uses a dye laser to map out the chromatic dispersion curve of a polymethyl methacrylate (PMMA) optical fibre. Seven different wavelengths across the visible spectrum are employed using five different dyes. The light pulse is split into two pulses, one to a nearby photodetector and the other coupled to the optical fibre cable at the end of which there is another photodetector. The difference in time of arrival at the detectors is used to compute the speed of light in the fibre for a given colour. In addition to a pedagogically simple and intuitive demonstration of the measurement of index of refraction, the use of a long fibre eliminates the need to direct the dangerous UV/visible laser pulse beam across a classroom, as is usually done in similar experiments. Ways to avoid systematic errors and other technical pitfalls—such as ringing oscillations—are presented.

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A Velocity of Light Measurement Using a Laser Beam

Cited by 4 publications

References 0 publications

Speed of light demonstration using Doppler beat

Speed of light demonstration using Doppler beat

An inexpensive apparatus for the measurement of the velocity of light in transparent media

Measuring the dispersion curve of a PMMA-fibre optic cable using a dye laser

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