We have designed a new pinhole-scan system to measure the Gaussian intensity distribution of a He-Ne laser beam that passes through a series of lenses. Our detection device uses a single-mode optical fiber as the so-called pinhole. One side of the optical fiber is fixed on the top of a motorized translation stage to capture the laser light, and the other side is connected to an optical power meter. A digital oscilloscope is used to observe the detected light intensity. When the translation stage as well as the fiber tip is moved across the laser beam, the oscilloscope displays the scanned trace of the laser beam intensity. The evolution of the intensity distribution of a focused laser beam is measured and then fitted to distributions predicted from Gaussian optics. The measured beam waist size is compared with the result of Gaussian-beam q-parameter analysis. Using this simple system we can easily observe the transverse intensity profile of a Gaussian laser beam in the (1+1)-dimensional plane in the vicinity of the focus.

1.
Robert M.
O’Connell
and
Roger A.
Vogel
, “
Abel inversion of knife-edge data from radially symmetric pulsed laser beams
,”
Appl. Opt.
26
(
13
),
2528
2532
(
1987
).
2.
Luciano
Bachmann
,
Denise Maria
Zezell
, and
Edison Puig
Maldonado
, “
Determination of beam width and quality for pulsed lasers using the knife-edge method
,”
Instrum. Sci. Technol.
31
(
1
),
47
52
(
2003
).
3.
Robert W.
Faaland
,
Zhongqi
Sun
, and
Jun
Li
, “
Transmission of a Gaussian scanning beam through circular, square, and slit apertures: Part II. experimental results for transmission through a circular aperture
,”
Health Phys.
59
(
6
),
901
909
(
1990
).
4.
Philip B.
Chapple
, “
Beam waist and M2 measurement using a finite slit
,”
Opt. Eng.
33
(
7
),
2461
2466
(
1994
).
5.
Amnon
Yariv
,
Optical Electronics in Modern Communications
(
Oxford
,
New York
,
1996
), 5th ed., pp.
48
57
.
6.
B. E. A.
Saleh
and
M. C.
Teich
,
Fundamentals of Photonics
(
Wiley
,
New York
,
1991
), pp.
80
100
.
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