Deutsche Forschungsanstalt Fur Luft-und Raumfahrt E.v.

Deutsches Zentrum Fur Luft-und Raumfahrt E.v.

Peter Haschberger

Volker Tank

Erwin Lindermeir

Helmut Dietl

Oliver Mayer

Burkhard Jansen

Franz Schreier

Klaus Scheider

Birger Schimpp

Rainer Thiessen

Nicholas King

Erwin Lindermeier

For quantitative analysis of gas volumes, specifically combustion exhaust gases, by means of emission or absorption spectrometry in the ultraviolet, visible and infrared spectral range, geometrically defined and reproducibly adjustable observation planes are oriented perpendicular to the longitudinal axis of an exhaust stream. In a first series of measurements a number of m spectral measurements is performed, in such a way that the optical axis of a spectrometer is always located in the respective observation level but is shifted in a parallel direction by a first distance from one measurement to the next. In a second series of measurements n measurements are performed, in such a way that the optical axis is again located in the observation plane and is shifted in a parallel direction by a second distance from each measurement to the next. The (m&plus;n) measurements produce two orthogonal sets of line of sights, which form a grid with (m&middot;n) intersecting volumes. With the aid of the (m&plus;n) measurements, each measurement yields the spectral transmission &tgr;(v), or the spectral radiation intensity I(v) which is integrated via the total gas volume in the beam of rays of the spectrometer field of view.

Process for the quantitative analysis of gas volumes, specifically exhaust and waste gases from combustion systems or incineration plants, as well as systems for performing these processes

The correction method of the invention synthesizes a distortion-free interferogram (or spectrum) from a measured interferogram, which has been distorted by detector non-linearities, and a finite series of orthogonal functions derived therefrom. The coefficients of the series of functions are selected with a priori knowledge about the limited spectral sensitivity of the radiation detector, preferably with the method of Gaussian least squares fit of observation, such that the resulting spectrum assumes the value of zero of the distortion-free spectrum outside of the sensitivity range, and in freely-definable ranges. The method of the invention can be used to correct detector non-linearities, as occur in Fourier spectroscopy.

Method of spectroscopic investigation of electromagnetic radiation by

In a Michelson interferometer, two plane mirrors of the mirror unit (50) are embodied as two plane mirrors (51, 52) of different sizes, disposed eccentrically and parallel to one another. A hollow shaft (63), rotatably supported in a bearing block (62) and driven by a drive unit (65), is also provided, which is disposed between a beam splitter and the mirror unit (50) and whose axis of rotation (61) coincides with the axis of rotation of the mirror unit (50). The mirror unit (50) is secured to the hollow shaft (63) in such a way that the axis of rotation (61) of the hollow shaft passes through the mirror face of the smaller plane mirror (51), whose axis of rotation forms an acute angle (.beta.) with the vertical to the smaller plane mirror (51), so that the two beams formed at the beam splitter (1) pass, via the tilted mirrors, through the hollow shaft (63) to strike the centrally disposed mirror face of the smaller plane mirror ( 51), are reflected by it to the opposite mirror face of the larger plane mirror (52) and from there to two stationary plane mirrors (71, 72) in such a way that they strike the stationary plane mirrors (71, 72) vertically, and--reflected by those mirrors--take the same path in the opposite direction, recombine at the beam splitter, and are focused by means of an optical element onto a detector (4).

Rotating mirror interferometer

In each arm of a Michelson interferometer (IF) a retroreflector (110; 110') having its aperture plane aligned perpendicularly to the optical axis is mounted on a respective holder (106; 106') which in turn is rigidly connected to one end of a shaft (105; 105') rotatably mounted in a connecting member (103; 103'). To the other end of the shaft (105; 105') a first gear (107.sub.1 ; 107.sub.1 ') is secured which is coupled via a toothed belt (909; 109') to an identically configured second gear (107.sub.2 ; 107.sub.2 ') which concentrically to a drive shaft (102; 102') of an electric motor (101; 101') is rigidly connected to the housing (1010; 1010') thereof. At a predetermined distance from the shaft (105; 105') the drive shaft (102; 102') is fixedly connected to the connecting member (103; 103') so that on rotation of the motor drive shafts (102; 102') the length of the optical paths is shortened in one interferometer arm and lengthened synchronously therewith in the other interferometer arm, or vice versa. Furthermore, the aperture planes of the two retroreflectors (110, 110') always remain unchanged aligned perpendicularly to the optical axis (FIG. 2 ).

Michelson interferometer

A method for measuring and determining a rotation angle of a rotating object in which a clock track corresponding to a desired angular resolution is applied on a magnetic, optical or optomagnetic storage medium. The storage medium is then rotated synchronously with the rotating object, and during the operation a pulse sequence corresponding to the clock track is read from said storage medium. The read pulse sequence is then supplied for further processing to following electronics in which the actual rotation angle is firstly stored in a FIFO memory and secondly directly available for further uses. Furthermore, the invention provides an apparatus for measuring and determining a path difference in Michelson interferometers in which path difference are generated via a rotary movement, for example of a rotating retroreflector. A memory medium is rigidly connected to the rotation shaft of the rotating retroreflector generating a path difference and on said medium a clock track corresponding to the sampling theorem is applied and during the rotation movement is read by a read head fixedly associated with the storage medium. During operation said pulse sequence is read by the read head and supplied to following signal electronics in which from the pulse sequence the desired clock pulse and thus the path information is then obtained.

Method for measuring and determining a rotation angle of a rotating

A method and an apparatus are provided for calibrating a spectrometer, in particular a Fourier transform spectrometer (FTS), in particular for the infrared spectral range. At least four black body radiators of different temperatures are provided, which are arranged horizontally, i.e. parallel to the surface of the earth, thereby avoiding temperature gradients due to convection. The temperature of the at least four radiators is determined by means of the calibrating method without a separate measurement. In the method according to the invention, at the same time the absorption of the atmosphere is considered as a characteristic of the spectrometer, thereby eliminating separate measurement and correction thereof. In addition, for Fourier transform spectrometers the calibration is carried out by means of complex spectra.

Method and apparatus for calibrating spectral radiometers

A method and an apparatus are provided for determining a path difference in a Michelson interferometer which comprises at least one reciprocably moving mirror element and an analog to digital converter, and which is provided for the determination of an electromagnetic spectrum without a laser having to be permanently used for that purpose. On the contrary, magnetic, optical and optomagnetical storage media are arranged parallelly to the travel path of the mirror element of the interferometer. A clock track is written on the storage medium in accordance with the sample theorem. In operation a pulse sequence derived from the clock track is read by a read head mounted on the movable mirror element and the desired clock pulse and thus the path information is derived therefrom.

Method and apparatus for determining a path difference in a Michelson

In a Michelson interferometer for producing optical path differences, from a beam divider, a deflection mirror, an externally silvered corner mirror, a collective lens and a radiation detector an input/output module is formed, from two rotating retroreflectors and two stationary retroreflectors an intermediate module is formed, and from two further rotating retroreflectors and from a bilaterally silvered plane-parallel plate a termination module is formed. The three modules can be combined to an interferometer in such a manner that the plane mirrors of the corner mirror of the input/output module are each arranged opposite a respective input-side half of the two rotating retroreflectors of the intermediate module and between said reflectors which in turn are arranged directly next to and adjacent the two further rotating retroreflectors of the termination module in such a manner that the output-side aperture halves of the two stationary retroreflectors are aligned opposite the input-side aperture halves of the two further rotating retroreflectors of the termination module. In operation the respective adjacent rotating retroreflectors of the modules fixedly connected to each other in exact match rotate in-phase with respect to their rotational angle position and in opposite phase of 180.degree. with respect to the corresponding opposite retroreflectors.

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Gauting, Germany

Peter Haschberger