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Neutron interferometry and the reflection of neutrons, a comment
Physica B 173 (1991) 97 North-Holland
Neutron interferometry and the reflection of neutrons, a comment G.M. D r a b k i n Hahn-Meitner lnstitut, 1000 Berlin 39, Germany, and Leningrad Nuclear Physics Institute, Gatchina 188350, USSR
In a conventional neutron interferometer two coherent beams of neutrons, after travelling along physically different paths, are brought to interfere with each other. One of the beams is transmitted through the sample (beam 1), while the second is the reference beam. The wavefront of beam 2 is a plane wave with fixed phase, whilst the phase of beam 1 changes according to the kind of sample it traverses and its path length in it. Calling the wave function of beam 1 qq, and that of beam 2 ~2, all the information about the sample is contained in I+, + ~212. However, it is possible to compare 0~ not only with a fixed plane wave qJ2 but rather a modulated wave 02m. This result can be achieved more conveniently if the elements of the interferometer are reflecting rather than diffracting. The geometry of the instrument is sketched in fig. 1. S l and $2 are identical semireflecting mirrors, while M~ and M 2 are reflecting mirrors. The geometry is identical to that of a conventional interferometer, if a sample is inserted in the S I - M ~ flight path, and the phase shift that the neutron experiences crossing the sample is tested by inserting a calibrated bar in the flight path S~-M 2. However, the geometry of this instrument is much more open than that of a conventional interferometer; thus it is conceivable to modulate in time or in position the beam reflected by M 2. The modulation in space or time of ~2, which can be achieved by imposing a pattern on the reflectance of M 2 , c a u s e s the modulation of the intensity at the detector IqJ~+ 02(r, 012. In this way the full interference spectrum is measured at
the same time; by varying the functional form of 02 the modulation spectrum can be optimized. It is suggested that this kind of interferometer might extend the applications of neutron interferometry. Its realization, which entails the preparation of large, flat surfaces from long blocks of silicon single crystals, is entirely feasible with present day technology.
beamsolitter
sample
M2
analyzer
S 2
DETECTORS
Fig. 1. Layout of an interferometer consisting of reflecting, rather than diffracting elements.
0921-4526/91/$03.50 © 1991- Elsevier Science Publishers B.V. (North-Holland)
Neutron interferometry and the reflection of neutrons, a comment G.M. D r a b k i n Hahn-Meitner lnstitut, 1000 Berlin 39, Germany, and Leningrad Nuclear Physics Institute, Gatchina 188350, USSR
In a conventional neutron interferometer two coherent beams of neutrons, after travelling along physically different paths, are brought to interfere with each other. One of the beams is transmitted through the sample (beam 1), while the second is the reference beam. The wavefront of beam 2 is a plane wave with fixed phase, whilst the phase of beam 1 changes according to the kind of sample it traverses and its path length in it. Calling the wave function of beam 1 qq, and that of beam 2 ~2, all the information about the sample is contained in I+, + ~212. However, it is possible to compare 0~ not only with a fixed plane wave qJ2 but rather a modulated wave 02m. This result can be achieved more conveniently if the elements of the interferometer are reflecting rather than diffracting. The geometry of the instrument is sketched in fig. 1. S l and $2 are identical semireflecting mirrors, while M~ and M 2 are reflecting mirrors. The geometry is identical to that of a conventional interferometer, if a sample is inserted in the S I - M ~ flight path, and the phase shift that the neutron experiences crossing the sample is tested by inserting a calibrated bar in the flight path S~-M 2. However, the geometry of this instrument is much more open than that of a conventional interferometer; thus it is conceivable to modulate in time or in position the beam reflected by M 2. The modulation in space or time of ~2, which can be achieved by imposing a pattern on the reflectance of M 2 , c a u s e s the modulation of the intensity at the detector IqJ~+ 02(r, 012. In this way the full interference spectrum is measured at
the same time; by varying the functional form of 02 the modulation spectrum can be optimized. It is suggested that this kind of interferometer might extend the applications of neutron interferometry. Its realization, which entails the preparation of large, flat surfaces from long blocks of silicon single crystals, is entirely feasible with present day technology.
beamsolitter
sample
M2
analyzer
S 2
DETECTORS
Fig. 1. Layout of an interferometer consisting of reflecting, rather than diffracting elements.
0921-4526/91/$03.50 © 1991- Elsevier Science Publishers B.V. (North-Holland)