Spectrometer for the far infrared

Claim 2

An assembly for use in combination with an interferometer for measurement of far infrared radiation, said assembly comprising a receiver arranged to convert the infrared interferogram produced in the interferometer to an electrical signal proportional to the intensity of the interferogram, recording means arranged to record on a surface rotating at a first regular speed a modified area having a parameter which varies as a linear function of the amplitude of the said electrical signal, the period of the rotation of said surface being equal to the duration of the transmission of the complete interferogram in the form of said electrical signal, reading mans arranged to analyze periodically said parameter of said area, said reading means rotating at a second regular speed much greater than said first regular speed, thereby supplying a periodic series of electrical signals each representative of said parameter of a portion of the interferogram, said reading means comprising means for multiplying the periodic series of signals by a periodic apodisation signal having an amplitude which steadily varies from a predetermined value for a central peak of the interferogram to zero at connecting ends of successive interferograms, thereby reducing the effect of drift during recording.

Claim 3

A spectrometer for the study of a source emitting radiation in the far infrared, comprising an assembly according to claim 1, in combination with an interferometer adapted to deliver the interferogram of said radiation source and a wave analyzer adapted to analyze said series of signals and to extract components therefrom each corresponding in amplitude and infrequency to radiation of a given frequency from the source.

Claim 4

A spectrometer according to claim 2, wherein said surface is in the form of a band, and said recording means comprise a recorder in which said band passes during the delivery of the interferogram, and with which recorder means are associated for adding a periodic signal to the interferogram thus forming a resultant signal which is sent to the recorder and which serves to produce on the band said modified area, the amplitude of the periodic signal being greater than the maximum amplitude of the interferogram, and wherein said reading means comprise a rotary drum forming at least part of said moving means and receiving on its peripheral surface a part of said band which has been subjected to recording in the recorder, which part of said band is bounded by a line passing through said modified area parallel to the direction of movement of the band in the recorder, and a reading member adapted to determine the dimension, in a dIrection parallel to the axis of the drum, of said modified area formed on said part of said band rotated by the drum.

Claim 5

A spectrometer according to claim 3, wherein said reading member comprises a closed casing containing a photoelectric cell and provided on one of its faces with a slot, said casing being disposed so that its slot is very near to the peripheral surface of said rotary drum and so that its slot is parallel to the axis of rotation of said drum, and lighting means for lighting said part of said band when it passes in front of said slot, so that said photoelectric cell measures the quantity of light which is reflected by said band and whose variations reproduce the variations of the dimension of said modified area in a direction parallel to the axis of rotation of said drum.

Claim 6

A spectrometer according to claim 3, wherein said means for adding the periodic signal to the interferogram comprise a saw tooth voltage generator connected in series between the output of said interferometer and the input of said recorder.

Claim 7

A spectrometer according to claim 3, wherein said reading member operates by transmission of the light through said surface which has come from said recorder, a source of light and a detector of light being respectively placed facing each other but on opposite sides of said surface. 7. A spectrometer according to claim 2, wherein said surface is covered with a photographic emulsion and said modified area is obtained by forming on said surface the image of a luminous slot whose height varies in the same manner as the amplitude of the interferogram.

Claim 8

Spectrometer according to claim 2, comprising means to eliminate a certain proportion of successive interferograms sent in the form of a periodic succession of signals to the wave analyzer, so as to increase the number of separate spectral lines defining the infrared spectrum, to facilitate the continuous tracing of the spectrum in automatic manner.

Claim 9

Spectrometer according to claim 8, wherein said means to eliminate a certain portion of the interferograms are constituted by a crenel borne by said opaque disc in its maximal apodisation zone (of maximal vector radius), means to separate in the output signal of the said detector means the signal due to the crenel from the apodisation signal due to the eccentricity of the opaque disc, a multivibrator, of which the 0 and 1 states are synchronized by the separate signal corresponding to the crenel and have durations respectively equal to the duration of one reading and to the duration of (n - 1) readings and a mixer or gate receiving at its signal input the signal corresponding to the apodisation and at its control input the output of the multivibrator, this mixer only transmitting to the wave analyzer the signal applied at its signal input and when its control input if fed by the crenels corresponding to the state 0 of the flip-flop.

Claim 10

Spectrometer according to claim 2 including a second reading device capable of analyzing a reference interferogram previously recorded by the recorder of a second disc, the two discs of the two reading devices rotating in synchronism, and a wave analyzer with two paths controlled by a single heterodyne oscillator to preserve perfect equality of the analysis frequencies, the outputs of the two paths being applied on a ratio recorded or on a divider follower by a conventional recorder.

Claim 11

Spectrometer according to claim 2, in which the recording takes place on a photographic emulsion borne by an opaque support, especially on a photosensitive positive, on paper, of the flat-film type, by means of a slit of length variable as a function of the electrical signal delivered by the receiver from the interferometer and from a first light source, and the reading by reflection from a second light source on the recorded flat film, characterized by the fact that it comprises means associated with the reading device to analyze, on a recording, equal areas successively black or not black and to dEduct therefrom a possible correctional signal.

Claim 12

An assembly for use in combination with an interferometer for measurement of far infrared radiation as in claim 1 wherein said surface rotating at a first regular speed is a disc.

Claim 15

A spectrometer, comprising, interferometer means for measurement of far infrared radiation, an assembly comprising a receiver arranged to convert the infrared interferogram produced in the interferometer to an electrical signal proportional to the intensity of the interferogram, recording means arranged to record on a surface rotating at a first regular speed a modified area having a parameter which varies as a linear function of the amplitude of the said electrical signal, the period of the rotation of said surface being equal to the duration of the transmission of the complete interferogram in the form of said electrical signal, reading means arranged to analyze periodically said parameter of said area, said reading means rotating at a second regular speed much greater than said first regular speed, thereby supplying a periodic series of electrical signals each representative of said parameter of a portion of the interferogram, and a wave analyzer adapted to analyze said series of signals and to extract components therefrom each corresponding in amplitude and in frequency to radiation of a given frequency from the source, and further comprising means to eliminate a certain proportion of successive interferograms sent in the form of a periodic succession of signals to the wave analyzer, so as to increase the number of separate spectral lines defining the infrared spectrum and facilitate the continuous tracing of the spectrum in an automatic manner.

Claim 16

A spectrometer, comprising, interferometer means for measurement of far infrared radiation, an assembly comprising a receiver arranged to convert the infrared interferogram produced in the interferometer to an electrical signal proportional to the intensity of the interferogram, recording means arranged to record on a surface rotating at a first regular speed a modified area having a parameter which varies as a linear function of the amplitude of the said electrical signal, the period of the rotation of said surface being equal to the duration of the transmission of the complete interferogram in the form of said electrical signal, reading means arranged to analyze periodically said parameter of said area, said reading means rotating at a second regular speed much greater than said first regular speed, thereby supplying a periodic series of electrical signals each representative of said parameter of a portion of the interferogram, and a wave analyzer adapted to analyze said series of signals and to extract components therefrom each corresponding in amplitude and in frequency to radiation of a given frequency from the source, and further comprising means to eliminate a certain proportion of successive interferograms sent in the form of a periodic succession of signals to the wave analyzer, so as to increase the number of separate spectral lines defining the infrared spectrum and facilitate the continuous tracing of the spectrum in an automatic manner.