An experiment for measuring the speed of light by measuring the distance between regularly generated optical pulses is described. The experiment utilizes optical feedback from a visible picosecond diode laser to accurately determine the distance between two successive laser pulses. The required setup is compact, and it does not implement either a fast detector or an oscilloscope. This experiment is suitable for an undergraduate physics instructional laboratory course or as an independent student project.

1.
J. H.
Shea
, “
Ole Rømer, the speed of light, the apparent period of Io, the Doppler effect, and the dynamics of Earth and Jupiter
,”
Am. J. Phys.
66
,
561
568
(
1998
).
2.
P.
Giacomo
, “
The new definition of the meter
,”
Am. J. Phys.
52
,
607
617
(
1984
).
3.
O.
Morizot
,
A.
Sellé
,
S.
Ferri
,
D.
Guyomarc'h
,
J. M.
Laugier
, and
M.
Knoop
, “
A modern Fizeau experiment for education and outreach purposes
,”
Eur. J. Phys.
32
,
161
168
(
2011
).
4.
LeyBold
, “
Determining the velocity of light by means of the rotating-mirror method according to Foucault and Michelson-measuring the image shift as a function of the rotational speed of the mirror
” <https://www.ld-didactic.de/literatur/hb/e/p5/p5611_e.pdf>.
6.
K.
Aoki
and
T.
Mitsui
, “
A tabletop experiment for the direct measurement of the speed of light
,”
Am. J. Phys.
76
,
812
815
(
2008
).
7.
A.
Ronzani
,
F.
Maccarrone
, and
A.
Di Lieto
, “
Measuring light speed with a modulated laser
,”
Eur. J. Phys.
29
,
957
965
(
2008
).
8.
M. E.
Ciholas
and
P. M.
Wilt
, “
A pulser circuit for measuring the speed of light
,”
Am. J. Phys.
55
,
853
854
(
1987
).
9.
LeyBold
, “
Determining the velocity of light in air from the path and transit time of a short light pulse
” <https://www.ld-didactic.de/literatur/hb/e/p5/p5621_e.pdf>.
10.
J. A.
Deblaquiere
,
K. C.
Harvey
, and
A. K.
Hemann
, “
Time‐of‐flight measurement of the speed of light using an acousto–optic modulator
,”
Am. J. Phys.
59
,
443
447
(
1991
).
11.
F. D.
Becchetti
,
K. C.
Harvey
,
B. J.
Schwartz
, and
M. L.
Shapiro
, “
Time‐of‐flight measurement of the speed of light using a laser and a low‐voltage Pöckels‐cell modulator
,”
Am. J. Phys.
55
,
632
634
(
1987
).
12.
G.
Pegna
, “
An extraordinary tabletop speed of light apparatus
,”
Am. J. Phys.
85
,
712
720
(
2017
).
13.
Lambda Scientific Systems, Inc
, “
Measurement of speed of light
” <https://lambdasys.com/uploads/LEOI-24.pdf>.
15.
R. E.
Crandall
, “
Minimal apparatus for the speed of light measurement
,”
Am. J. Phys.
50
,
1157
1159
(
1982
).
16.
E.
Gülmez
, “
Measuring the speed of light with a fiber optic kit: An undergraduate experiment
,”
Am. J. Phys.
65
,
614
618
(
1997
).
17.
M. B.
James
,
R. B.
Ormond
, and
A. J.
Stasch
, “
Speed of light measurement for the myriad
,”
Am. J. Phys.
67
,
681
684
(
1999
).
18.
LeyBold
, “
Determining the velocity of light with a periodic light signal at small distances
” <https://www.ld-didactic.de/literatur/hb/e/p5/p5631_e.pdf>.
19.
L.
Bernal
and
L.
Bilbao
, “
Speed of light demonstration using Doppler beat
,”
Eur. J. Phys.
39
,
035704
(
2018
).
20.
J. A.
Tatum
,
J. W.
Jennings
, and
D. L.
MacFarlane
, “
Compact, inexpensive, visible diode laser source of high repetition rate picosecond pulses
,”
Rev. Sci. Instrum.
63
,
2950
2953
(
1992
).
21.
W.
Uhring
,
C.-V.
Zinta
, and
J.
Bartringera
, “
A low cost high repetition rate picosecond laser diode pulse generator
,”
Proc. SPIE
5452
,
583
590
(
2004
).
22.
J.
Ohtsubo
,
Semiconductor Lasers Stability, Instability and Chaos
(
Springer
,
New York
,
2008
).
23.
RefractiveIndex.info
Refractive index database <https://refractiveindex.info/?shelf=other&book=air&page=Borzsonyi>.
24.
J. A.
Armstrong
, “
Measurement of picosecond laser pulse widths
,”
Appl. Phys. Lett.
10
,
16
18
(
1967
).
25.
T. D.
Donnelly
and
C.
Grossman
, “
Ultrafast phenomena: A laboratory experiment for undergraduates
,”
Am. J. Phys.
66
,
677
685
(
1998
).
26.
G. P.
Agrwal
and
N. K.
Dutta
,
Semiconductor Lasers
(
Kluwer Academic
,
New York
,
1993
), pp. 238–
293
.
27.
T.
Numai
,
Fundamentals of Semiconductor Laser
(
Springer
,
New York
,
2015
), pp.
101
280
.
28.
O.
Svelto
,
Principles of Lasers
(
Springer
,
New York
,
2010
), pp.
337
338
.
29.
See supplementary material at https://www.scitation.org/doi/suppl/10.1119/10.0007144 for a Mathematica code that uses Eqs. (5) and (6) to calculate the photon density function for the first eleven current pulses.

Supplementary Material

AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.