A new interferometric method is described which allows the separate analysis of the individual transverse modes of multimode laser beams. The determination of the phase and the amplitude distribution of the modes by means of a Mach–Zehnder‐type interferometer is possible with a homodyne or heterodyne measurement method. The required tunable single‐frequency reference wave which serves as an optical local oscillator is generated from the multimode beam itself by means of acousto‐optical frequency shifting and mode selecting devices which are positioned in the reference branch of the interferometer. In homodyne operation the individual modes are characterized by specific stationary interference patterns obtained by the synchronization of the reference wave frequency with the respective mode frequency. The use of conventional phase‐shifting methods yields the phase distribution of the individual modes. The corresponding mode order can be determined from the phase jumps by π occurring in the fringe pattern. Results of the investigation of a slow‐flow cw‐CO2 laser with stable resonator configuration are presented, proving the feasibility of on‐line diagnosis provided by the system.

1.
K.
Du
,
R.
Flieger
, and
P.
Loosen
,
Proc. SPIE
1868
,
85
(
1993
).
2.
D.
Ehrlichman
,
U.
Habich
, and
H.-D.
Plum
,
Proc. SPIE
1868
,
77
(
1993
).
3.
Y.
Takenaka
,
M.
Kuzumoto
, and
K.
Yasui
,
IEEE J. Quantum Electron.
28
,
1855
(
1992
).
4.
A.
Borghese
,
R.
Canevari
,
V.
Donati
, and
L.
Garifo
,
Appl. Opt.
20
,
3547
(
1981
).
5.
R. Kramer, Ph.D. thesis, RWTH Aachen, Germany, 1991.
6.
E.
Beyer
,
G.
Herziger
,
R.
Kramer
, and
P.
Loosen
,
Proc. SPIE
650
,
170
(
1986
).
7.
D.
Hull
and
A. F.
Stewart
,
Lasers Appl.
4
, No.
11
,
71
(
1985
).
8.
K. Du, Ph.D. thesis, RWTH Aachen, Germany, 1992.
9.
W. H. Steel, Interferometry, Cambridge Studies in Modern Optics, 2nd ed. (Cambridge University, Cambridge, 1987).
10.
A. E. Siegman, Lasers (University Science, Mill Valley, 1986).
11.
U. P.
Oppenheim
and
M.
Naftaly
,
Appl. Opt.
23
,
661
(
1984
).
12.
R. N.
Smartt
and
W. H.
Steel
,
Jpn. J. Appl. Phys.
14
,
351
(
1975
).
13.
C.
Koliopoulos
,
O.
Kwon
,
R.
Shagam
,
C. R.
Wyant
, and
J. C.
Hayslett
,
Opt. Lett.
3
,
118
(
1978
).
14.
K. Creath and E. Wolf, Progress in Optics XXVI (Elsevier, New York, 1988).
15.
H. P.
Stahl
and
C.
Koliopoulos
,
Appl. Opt.
26
,
1127
(
1987
).
16.
N. A.
Massie
,
R. D.
Nelson
, and
S.
Holly
,
Appl. Opt.
18
,
1797
(
1979
).
17.
A. G.
White
,
C. P.
Smith
,
N. R.
Heckenberg
,
H.
Rubinsztein-Dunlop
,
R.
McDuff
,
C. O.
Weiss
, and
Chr.
Tamm
,
J. Mod. Opt.
38
,
2531
(
1991
).
18.
H. Weber, Optische Resonatoren, Grundlagen und Anwendungen (Optisches Institut Techn. Universität Berlin, Berlin, 1988).
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