DE102012007609A1 - Optical spectrometer e.g. polychromator has detectors whose optoelectronic detection elements are provided with different spectral detection regions - Google Patents

Abstract

The optical spectrometer (10) has housing which is provided with entry gap (1) and dispersive element (2). A beam splitter (4) which is arranged between dispersive element and detector (3A) made of silicon for deflecting the portion of split-up light (S) with respect to detector (3B) made of indium gallium arsenide, germanium or lead sulfide. The optoelectronic detection elements (3A-1-3A-10) of detector (3A) are provided with spectral detection region which is different from spectral detection region of optoelectronic detection elements (3B-1-3B-9) of detector (3B).

Description

The invention relates to an optical spectrometer (polychromator) having a housing, which has an entrance slit, a dispersive element and a spatially resolving detector with a plurality of optoelectronic detection elements, the dispersive element light, which falls through the entrance slit into the housing, depending on the wavelength in the direction of different detection elements directs. Moreover, in such spectrometers further optical elements such as lenses or mirrors can be arranged in a known manner. The dispersive element itself and / or the further optical elements form the entrance slit on the detector. Due to the spectral splitting at the dispersive element, it is imaged wavelength-dependent on different locations of the detector.

For the purposes of the invention, light is any electromagnetic radiation that can be manipulated by optical means and, in particular, includes ultraviolet (UV) and infrared (IR) radiation.

For the purposes of the invention, an optoelectronic detection element is a component that is capable of absorbing incident photons by means of a semiconductor material and converting them into electrical charge carriers (electrons and holes). Examples of optoelectronic detection elements are photodiodes, phototransistors and photoresistors.

Depending on the design, optoelectronic semiconductor detectors have a spectrally limited detection sensitivity for light. In order to be able to measure samples spectrometrically in a wide spectral range, a plurality of spectrometers with spectrally different detection ranges are generally used, the detection ranges of the different spectrometers typically partially overlapping each other spectrally. Such a spectrometer system is, for example, in DE 10010213 A1 disclosed.

Different spectral detection ranges are present when the semiconductor detectors of the two spectrometers have a different spectral sensitivity curve, that is to say when the lower limit wavelengths of the spectrometers are not identical or the upper limit wavelengths of the spectrometers are not identical. The boundaries (cut-off wavelengths) of the detection range of a spectrometer describe the spectral detection range of its detector, which is defined for example in that the detector has at least 10% of its maximum spectral sensitivity in the relevant wavelength range. Regardless of this specification, a detector can also be used in certain applications in a broader spectral range, if the then limited sensitivity is sufficient.

For example, for a total spectral range to be detected from 400 nm to 1680 nm, a first spectrometer with a silicon detector (Si) having a detection range of 400 nm to 1100 nm, and a second spectrometer with an indium gallium arsenide detector (InGaAs), which has a detection range of 950 nm to 1680 nm used. Near their upper cut-off wavelength, the detection sensitivity of Si detectors is low and they have a strong temperature dependency on the signal amplitude they emit. The more expensive InGaAs detector in the second spectrometer for the longer wavelength part of the spectrum advantageously has a less temperature dependent detection sensitivity, at least in this spectral range, but has higher noise.

The use of two or more spectrometers in addition to the required large space nor the disadvantage that the optical paths are different from the sample to the respective detectors and that the spectrometer usually have a different optical structure, so that in the measured spectrum, a discontinuity in the form of a jump arises. For sensitive applications, this leads to measurement errors.

The invention is therefore based on the object to improve a spectrometer of the type mentioned in order to allow a higher measurement accuracy.

The object is achieved by a spectrometer which has the features specified in claim 1.

Advantageous embodiments of the invention are specified in the subclaims.

According to the invention, in the spectrometer a second detector having a plurality of optoelectronic detection elements and a beam splitter arranged between the dispersive element and the first detector which deflects a portion of the split light to the second detector are arranged, the detection elements of the first detector (by a different composition) have a different spectral detection range than the detection elements of the second detector.

At least one collimating optical system can be arranged between the entrance slit and the detectors, so that different wavelengths and diffraction orders in the spectrally split light strike the beam splitter in parallel. A collimating optics may be arranged between the entrance slit and the dispersive element and / or in each case between the beam splitter and the detectors. It is advantageous if the collimation optics is color-corrected. As an alternative to a separate collimating optics, the dispersive element itself may be designed as a collimator, for example in the case of an imaging grating. However, the spectrometer works well without collimating optics. In particular, a spectral transition region in which the beam splitter does not sharply (due to wavelength-dependent angle of incidence) is advantageous for a temperature fluctuation compensation.

The spectrometer according to the invention with a beam splitter and two (or more) line or matrix detectors, which have different spectral detection ranges due to different types of optoelectronic detection elements and are illuminated as far as the beam splitter along the same beam path, can be regarded as an advantageous wide-range spectrometer. It is no longer necessary to divide the sample light on two different spectrometers and thus on widely different beam paths. A second spectrometer is omitted. Since the beam splitter is arranged only behind the dispersive element and therefore the division takes place only directly in front of the detectors (including any respective camera optics in front of each detector), the number of degrees of freedom to be adjusted in comparison to separate spectrometers with separate dispersive elements is significantly reduced. This enables a higher measuring accuracy. In particular, the discontinuity between the parts of a spectrum composed of the readings of both (or even more) detectors is smaller.

Preferably, the first detector for detecting a shorter-wavelength spectral detection range, for example, substantially for VIS light, and the second for detecting a longer-wavelength spectral detection range, for example substantially for IR light formed, or vice versa. In the case of the detection range termed shorter-wavelength, the lower limit wavelength is less than the lower limit wavelength of the detection range designated as longer-wavelength, and the upper limit wavelength of the detection range designated as shorter-wavelength is less than the upper limit wavelength of the detection range designated as longer-wavelength.

The two spectral detection areas do not need to be disjoint (upper limit wavelength of the detection area designated as shorter wavelength approximately equal to the lower limit wavelength of the detection area designated as longer wavelength), but may also advantageously overlap one another (upper limit wavelength of the detection area designated as shorter wavelength greater than the lower limit wavelength of FIG longer wavelength designated detection area). Embodiments with more than two detectors are also possible. At least two of them must according to the invention have different spectral detection ranges from one another.

Expediently, the optoelectronic transducers of one detector (essentially) are a semiconductor layer of silicon and the optoelectronic transducers of the other detector (essentially) a semiconductor layer of at least one of the materials indium gallium arsenide, germanium and lead sulfide.

The spectrometer is particularly advantageous if the beam splitter selectively splits the split light at least in a subarea of its surface (or over its entire surface) - ie at least in sections it is a color splitter. Full-surface wave selectivity enables a high detection efficiency of the spectrometer, since as little sample light as possible is lost in this way. Partial wavelength selectivity enables quasi-simultaneous detection of the respective spectral regions (which strike the beam splitter in the wavelength-selective section). Thus, due to the filtering effect of the first optoelectronic transducer on light in the shorter-wavelength detection range, different wavelength ranges in different diffraction orders can be recorded with the same detection element.

There are various possibilities for the type of division (spectral long-pass, shortpass, bandpass) and the spectral position of the dividing edge (s). Advantageously, the arrangement of the detectors is such that their spectral detection ranges (approximately) with the respective from the beam splitter coincident emerging spectral part, wherein the - otherwise undesirable - finite width of the spectral edge zone can be advantageously used for temperature compensation. For example, in the case of a training as a short pass, the edge zone in the overlap region of the spectral detection ranges of the two detectors, with an Si and an InGaAs detector, for example, between 950 nm and 1100 nm. The shorter wavelengths then pass through the beam splitter in the direction of the Si detector while the higher wavelengths are deflected to the InGaAs detector. The wavelengths in the overlap region of the spectral detection areas exit the beam splitter in both directions. In this case, the spectrometer can be formed by the arrangement and width of the two detectors along the dispersion direction and / or by additional filters so that light from the overlap area only gets into exactly one of the two detectors. For the above-mentioned temperature compensation, however, it is just advantageous if light passes from the overlap area in both detectors.

The second detector may therefore be arranged such that at least one of its detection elements is arranged symmetrically with respect to the beam splitter to a detection element of the first detector. For the purposes of the invention, two detection elements arranged symmetrically with respect to the beam splitter are referred to as a pair of corresponding detection elements (corresponding pair). In other words, the second detector can preferably be arranged in such a way that a virtual orthogonal projection of a virtual mirror image of the second detector resulting from a plane reflection at the beam splitter into a plane extending through the first detector (in particular defined by it) in this plane with the first Detector overlaps. This overlapping may in particular be such that a detection element of the projected detector mirror image overlaps with a detection element of the first detector, in particular (congruently) coincides, and / or such that several or all detection elements of the mirror image projected into the plane are coupled to a respective detection element of the overlap first detector, in particular (congruent) coincide. In each case a detection element of the first detector and the (in the projected mirror image) overlapping detection element of the second detector then form a mutually corresponding pair in the context of the invention. In particular, the second detector can be arranged such that the spectrometer has a plurality of corresponding pairs. A detection element without a corresponding element on the other detector is said to be unpaired.

For example, in embodiments having multiple pairs of corresponding detection elements, the pairs may represent a true subset of all detection elements. There is then at least one wavelength range which is converted opto-electronically only in exactly one detector, namely in an unpaired detection element. Alternatively, all detection elements may be members of a respective pair. Then there are no unpaired detection elements.

The pair (or pairs) of the mutually corresponding detection elements enables a quasi-simultaneous detection of the split light with two different spectral detection ranges. This can be used in several ways:
A spectral overlap of the spectral detection ranges of the detectors allows the compensation of temperature-dependent fluctuations of the electrical signals of the detection elements with high accuracy, if a (spectral) sensitivity of the detection elements of a detector substantially temperature-independent or at least (significantly) less temperature-dependent than a corresponding (spectral) sensitivity the detection elements of the other detector is. For temperature compensation, in principle, a single pair of corresponding detection elements is sufficient. From the electrical signals of the two detection elements can be determined with high accuracy, a relation between the internal temperatures of the two detectors, by means of which the compensation can be performed. In conjunction with the approximately uniform beam path, this allows a particularly high measuring accuracy.

In two or more beam splitters with different wavelength selectivity, so three or more detectors with different spectral detection ranges, three or more different diffraction orders corresponding to three or more wavelength ranges can be detected simultaneously with the same detection elements, the upper and lower limits of the second, third and optionally higher wavelength ranges in each detection element corresponding to many different multiples of the upper and lower limits of the first wavelength range. A spectrometer with n beam splitters then has n + 1 detectors. It can then correspond to each other between two and n + 1 detection elements. They are then referred to as triple, quadruples, commonly called n-tuples.

The dispersive element can be for example a prism or a grating, in particular an imaging grating, for example a holographic grating. In the case of a grating, different diffraction orders occur in the split light.

Advantageously, in this case, a long-pass filter covers a real portion of the detector with the shorter-wavelength detection range up to and including its long-wave end. Instead, it is also possible for a separate long-pass filter to be arranged before the second or in front of each detector. This avoids that unwanted higher diffraction orders reach the detector in question and are detected there. The long-pass filter for the shorter wavelength range is required if the ratio of the longest wavelength to the shortest wavelength to be detected is greater than 2: 1, otherwise for the wavelength range from twice the shortest wavelength to be detected no clear wavelength allocation of the detected light longer possible would. Without a long-pass filter, light of the first and second orders of diffraction (half wavelength) would hit the same detection element.

A long-pass filter can be applied (directly) to the relevant detector. Alternatively, it may be arranged on a separate support, for example made of glass. The carrier may conveniently be arranged directly on the detector. The carrier may be tuned in its thickness so that the focal lines of the respective wavelength ranges are adapted to the different distances of the individual detectors from the diffraction grating. As a result, a greater accuracy of measurement can be achieved. Alternatively, the long-pass filter can be arranged (directly) on or in the beam splitter, integrated in the beam splitter, or arranged between the beam splitter and the relevant detector.

Detection elements that form a corresponding pair are referred to as wavelength-selective corresponding in the context of the invention, if one or more spectral filters are arranged in front of at least one of these detection element or the beam splitter at least in a section through which the pair corresponds wavelength-selectively divides. If the pair is arranged so that it corresponds to a wavelength which lies in the spectral edge zone of the filter / beam splitter, then light of this wavelength reaches both detectors, ie both detection elements of this pair.

Particularly preferred are embodiments with a wavelength sensitivity of the beam splitter at least in a portion of its surface through which a pair of detection elements corresponding wavelength selective with each other, in particular with an evaluation unit, an electrical signal of a detection element of the one detector as a raw signal for the absorbed energy in a first A wavelength range processed and an electrical signal of a corresponding detection element of the other detector as a raw signal for the absorbed energy in a second wavelength range whose lower limit wavelength is k times the lower limit wavelength of the first wavelength range and whose upper limit wavelength k times the upper limit wavelength of the first wavelength range, k being a quotient of two (integer) diffraction orders to be detected. The factor k is therefore a rational number. In this way, different diffraction orders of different wavelengths with the relevant pair of wavelength-selective corresponding detection elements can be detected quasi-simultaneously, so that the spectral resolution of the spectrometer can be increased. If the beam splitter is a spectral neutral splitter, then a long-pass filter in front of the detector with the longer-wavelength detection region is expedient for such an embodiment.

For example, k = 2: 1, then the lower limit of the second wavelength range is twice the lower limit of the first wavelength range and the upper limit of the second wavelength range is twice the upper limit of the first wavelength range. The spectral width of the optically combined detectors via the beam splitter can thus be used twice, which doubles the spectral resolution of the spectrometer, at least in the wavelength-selective sections. As an alternative to the first and second diffraction order, for example, the second and the third diffraction order of different wavelengths can be detected simultaneously with a pair of wavelength-selective corresponding detection elements (k = 3: 2).

Preferably, the beam splitter splits the split light wavelength selective in the region of all corresponding pairs (in a manner identical for all pairs). Thereby, the portion where the spectral resolution is increased is maximum. The spectrometer can then have minimal size.

Embodiments with an evaluation unit that are based on at least one electrical signal of a detection element of the first detector and at least one electrical signal are preferred a detection element of the second detector which corresponds to this wavelength-selectively determines a value of a temperature of the relevant detection elements. Assuming that both detectors have (approximately) the same temperature or that the detector with the longer-wavelength detection range has a negligible temperature dependence of its detection sensitivity and that the detector with the shorter-wavelength detection range has a uniform temperature (over all its detection elements), it can be separated Temperature sensors are omitted. The temperature value according to the invention can be determined, for example, in the unit ° C or K, but alternatively it can also depend on the temperature according to any one-to-one function.

Embodiments in which the detectors, in particular the detection elements of the detectors, are connected to one another in a heat-conducting manner are advantageous. As a result, their temperatures are at least approximately identical.

Preferably, the spectrometer comprises (at least) two pairs of respective wavelength-selective corresponding detection elements whose detection elements are arranged so that a diffraction order of a wavelength of the incident light in a detection element of the one pair passes and another diffraction order of the same wavelength in a detection element of the other pair. As a result, assuming an (approximately) identical temperature of the detectors, an internal temperature of the detectors without separate temperature sensors can also be determined in arrangements in which two different diffraction orders are diffracted to the same detection elements.

Embodiments in which an evaluation unit determines a value of a temperature of the detector on the basis of four electrical signals of two pairs of wavelength-selective corresponding detection elements are preferred. Spatial arrangement of the pairs corresponds to two different wavelength ranges or two different diffraction orders of the same wavelength range. As a result, assuming (approximately) identical temperatures of the detectors, an internal temperature of the detectors without separate temperature sensors can also be determined in arrangements in which two different diffraction orders are diffracted to the same detection elements.

für M Beugungsordnungen (m = 1, ...M), M Detektoren (i = A, B, ...) und M Detektionselemente (p = 1, ...M) ermitteln, wobei U_i,p die Werte der betreffenden elektrischen Signale und D_i,m,p die betreffenden spektralen Empfindlichkeiten sind.Conveniently, the evaluation unit, the value of the temperature of the detector by solving the equation system

for M diffraction orders (m = 1, ... M), M detectors (i = A, B, ...) and M detect detection elements (p = 1, ... M), where U _{i, p are} the values of relevant electrical signals and D _{i, m, p are} the relevant spectral sensitivities.

Advantageously, the evaluation unit can use the determined value of the temperature to normalize an electrical signal of another detection element (in particular an unpaired detection element) of the detector with the greater temperature dependence of its spectral sensitivity-typically the detector with the shorter-wavelength spectral detection range, according to a (predetermined) temperature-dependent spectral sensitivity , As a result of this compensation of the temperature-dependent fluctuations in the spectral sensitivity of the detection elements, as already described above, the measurement accuracy is improved.

Appropriately, in the incident light (in front of the dispersive element, in particular in front of the entrance slit), a long-pass filter may be arranged which blocks wavelengths below the shorter-wavelength (for more than two detectors: shortest wavelength) spectral detection range. This avoids that unwanted higher orders of diffraction and undesired short-wave light enter the detector and there falsify the measurement of the desired wavelengths.

The invention will be explained in more detail by means of exemplary embodiments.

In the drawings show:

1 a wide-range spectrometer with a corresponding pair of detection elements,

2 a wide-range spectrometer with only correspondingly paired detection elements,

3 an assignment of wavelengths to detector pixels and

4 a wide-range spectrometer with a beam splitter and two detectors with exclusively unpaired detection elements.

In all drawings, like parts bear like reference numerals. For simplicity, only the center rays of the (wavelength-dependent) beam paths are shown.

1 represents a multichannel optical spectrometer 10 with a spectral detection range of λ _min = 310 nm (lower limit wavelength) to λ _max = 1680 nm (upper limit wavelength), wherein only the first diffraction order (m = 1) of the incident light L is detected. The spectrometer 10 includes for this purpose an entrance slit 1 , an imaging diffraction grating 2 , two detectors 3A and 3B , a collimation optics 11 , a beam splitter 4 , a control and evaluation unit 5 and for example two temperature sensors 6 in contact with the detector 3A stand and can be omitted in alternative embodiments. In front of the entrance slit 1 is an optical long-pass filter 7 arranged. In front of a partial area of the detector 3A is an optical long-pass filter 8th arranged. The detectors 3A and 3B are in around the beam splitter 4 arranged symmetrical planes. The spectrometer is enclosed 10 from a housing 9 , Not shown are known connections to the power supply and an external interface to the control and evaluation 5 , The interface can be used, for example, to transmit the measured values or to control or program the control and evaluation unit 5 serve.

The first detector 3A is, for example, a silicon detector for the optoelectronic conversion of diffracted light S in the wavelength range of 310 nm to 1100 nm. For the sake of clarity of the drawing, it only has ten equally wide, mutually separate detection elements 3A.1 ... 3A.10 on, which can be referred to as pixels. The second detector 3B is for example an indium gallium arsenide detector for optoelectronic conversion of diffracted light S in the wavelength range of 950 nm to 1680 nm. He has the sake of clarity of the drawing, for example, only nine equal width, separate detection elements 3B.1 ... 3B.9 on, which can be referred to as pixels. Each of the detection elements 3A.1 ... 3A.10 comprises in a known manner a p-doped Si layer and an n-doped Si layer and thus has its own pn junction. Each of the detection elements 3B.1 ... 3B.9 consists in a known manner of a p-doped InGaAs layer and an n-doped InGaAs layer and thus has its own pn junction.

The second detector 3B is arranged so that the detection element 3B.1 through the beam splitter 4 with the detection element 3A.10 corresponds, as in a plane mirror at the beam splitter 4 the virtual mirror image of the one detection element is congruent with the other detection element. Because the beam splitter 4 For example, in the form of a full-area dichroic short-pass film having a spectral splitting edge at 1025 nm in an edge region of 950 nm to 1100 nm which selectively splits split light S, diffracted light in the wavelength region of 950 nm to 1100 nm is equally divided into both detection elements 3A.10 and 3B.1 , The detection in the overlapping wavelength range (950 nm to 1100 nm) thus takes place both with the InGaAs detector 3A as well as with the Si detector 3B , Although the latter has a lower noise, it in turn has a higher temperature dependence than the InGaAs detector A.

The longpass filter 7 blocks light L of a wavelength of, for example, up to 300 nm and allows light L of a wavelength from, for example, 310 nm almost completely to the entrance slit 1 happen. The longpass filter 8th lets in the grid 2 diffracted light S below a wavelength of, for example, 550 nm maximum, for example, 1% transmission to the detector 3A to and above, for example, 590 nm at least for example, 90% transmittance.

An overview of the fate of the different wavelengths λ of the incident light L is given in the following table: λ fate ≤ 300 nm First through long pass filter 7 away. 310 to 590 nm Absorption in the Si detector 3A without prior filtering; Diffraction orders m ≥ 2 in advance by long-pass filter 7 away. 590 to 600 nm Absorption in the Si detector 3A with or without long pass filter 8th (Position of the filter edge); Diffraction orders m ≥ 2 in advance by long-pass filter 7 away. 600 to 950 nm Absorption in the Si detector 3A with longpass filter 8th ; Diffraction orders m ≥ 2 in advance by long-pass filter 8th away. 950 to 1100 nm Absorption in the Si detector 3A with longpass filter 8th (Diffraction orders m ≥ 2 in advance by long-pass filter 8th removed) and in the InGaAs detector 3B (with longpass filter 8th ; Diffraction orders m ≥ 2 in advance by beam splitters 4 away). 1100 to 1680 nm Absorption in the InGaAs detector 3B ; Diffraction orders m ≥ 2 in advance by beam splitters 4 away.

The electrical signals of the detection elements 3i.p (p = 1 ... 10), that of the control and evaluation unit 5 be supplied to the energy W upon detection of light, are U _{i, p} = D _{i, p} (T) x W (λ _p ), where in the present example: p = 1 ... 10 for i = A and p = 1 ... 9 for i = B.

In this case, D _{i, p} (T) is the spectral sensitivity of the optoelectronic transducers 3i.p in the respective diffracted wavelength ranges λ _p as a function of the temperature of the relevant optoelectronic transducer 3i.p , It must be before using the spectrometer 10 be determined at a plurality of (at least two) temperatures T _k in the intended operating temperature range with monochromatic light of known power in a so-called calibration passage. The sensitivity at any intervening temperatures can be calculated, for example, by linear interpolation in a known manner. Alternatively, a parameterized model function can be adapted to the measured temperature values T _k by means of a mathematical compensation calculation in a known manner, for example by determining the smallest deviation squares.

For the two wavelength-selective corresponding detection elements 3A.10 and 3B.1 the irradiated light energy W is identical, so that for the ratio of the signals U _{i, p} at a current temperature T _{D of} the two optoelectronic converters:

From this ratio of the current signal values U _{A, 10} / U _{B, 1} , an actual temperature value T _D for the detector element can be determined on the basis of the spectral sensitivity functions D _{A, 10} (T), D _{B, 1} (T) 3A.10 be determined. For this purpose, for example _, the quotient function q ₁₀ (T) can be formed from the spectral sensitivity functions D _{i, 10} (T):

The lower temperature dependence of the spectral sensitivity of the detector element D _{B, 1} (T) is neglected in the overlapping wavelength range (950 to 1050 nm).

By means of the inverse function q ₁₀ ^-1 to be determined from the quotient function q ₁₀ (T), the current temperature value T _D can then be calculated:

On the basis of the current temperature value T _D and the previously determined spectral sensitivity functions D _{i, p} (T), temperature-dependent fluctuations of the electrical signals U _{i, p of} all the detection elements 3i.p be compensated. To determine the actual momentary light power in the wavelength range λ ≤ 1100 nm are from the control and evaluation 5 because of the lower noise, for example, only the signals U _{A, p of} the Si converter 3A.1 ... 3A.10 used and standardized according to the respective spectral sensitivity functions D _{A, p} (T) temperature-dependent and output via an interface:

The temperature determination on the ratio of the electrical signals U _{i, p} in the overlapping wavelength range has compared to a temperature measurement with a conventional, on the outside of the detector 3A applied separate temperature sensor 6.1 the advantage that not the surface temperature of the detector substrate, but rather the temperature T of the actual detection element 3A.10 is determined and thus influences by temperature gradients (non-uniform heating, for example, due to heat conduction) are minimized. The temperature influence on the spectral sensitivity of the InGaAs detector at the long-wave end λ _max can additionally be determined either with an external temperature sensor 6.2 as close as possible to the detecting semiconductor layer or by the above-determined current detector temperature T _D (which, however, exactly only in the middle of the detection element 3A.10 prevails) are compensated. Which single compensation option or a combination of both works best depends on the thermal conditions in the spectrometer 10 especially where the lowest temperature gradients exist. The person skilled in the art is able to decide, with regard to the thermal conditions, which type of compensation causes the most accurate measurement in each case.

In real embodiments (not shown), the detector has 3 for example, a total of 256 (p = 1 ... 256) detection elements. Other numbers are possible. The above considerations apply accordingly. In the overlapping wavelength range of the detectors 3A and 3B There are then several detection elements (pixels), of which at least one of a common wavelength range is illuminated per detector and lies in the region of the overlapping detection ranges of the different detector types.

Generally applies to the ratio of the electrical signals U _{A, P} and U _{B, p} of a common wavelength range associated (in other words: corresponding) detection element pairs 3A.p and 3B.p ' :

Indicates the overlapping spectral range of the detectors 3A and 3B Several pairs of corresponding detection elements, for several of them, in particular for each of them, a separate temperature value T _D can be determined. In order to reduce the influence of noise of the InGaAs converter on the temperature value T _D determined from the different optoelectronic converters, a combined temperature value T _D can be determined from the signals of a plurality of corresponding pairs in the overlapping spectral range. Thus, a smoothing of the determined temperature can be carried out, for example by moving averaging with a predetermined time constant. This can be done, for example, in the control and evaluation unit 5 happen.

2 shows a multi-channel optical spectrometer 10 with a spectral detection range of λ _min = 400 nm to λ _max = 1680 nm, which detects only the first diffraction order (m = 1) and the second diffraction order (m = 2) of the incident light L. The construction of the spectrometer 10 corresponds to essentially the in 1 shown device, however, is the diffraction grating 2 here a plangitter. In addition, the detectors have 3A and 3B both each eighteen detection elements 3A /B.1 ... 3A /B.18 and are relative to the beam splitter 4 arranged symmetrically, so that all detection elements are paired wavelength selective corresponding. In addition, between the between the entrance slit 1 and the grid 2 , which is designed here as Plangitter, a Kollimationsoptik 11 , For example, a lens or a mirror, arranged to a maximum selectivity of the beam splitter 4 to enable. In front of each detector 3A / B is a camera optics adapted to its spectral detection range 12A / B, for example a lens or a mirror. In another embodiment (not shown), the collimation optics 11 and / or the camera optics 12A . 12B omitted.

The spectral edge of the shortpass beam splitter 4 for example, is at 820 nm, the edge zone is between 800 nm and 840 nm. It is, for example, a first detector 3A made of silicon and a second detector 3B Indium gallium arsenide whose electrical signals in a known manner the control and evaluation 5 be supplied.

Over a partial area of the first detector 3A from a wavelength of for example m · λ = (1165 ± 5) nm, there is a long-pass filter 8th which allows at least for example 1% of diffracted light S up to a wavelength of, for example, λ = 560 nm and at least for example 90% at a wavelength of, for example, λ = 580 nm. The longpass filter 8th is directly on the said subarea of the detector 3A applied. In alternative embodiments (not shown), it may be arranged on a separate support, for example made of glass.

In front of the entrance slit 1 is a longpass filter 7 arranged, the wavelengths to, for example, λ = 390 nm substantially blocks and wavelengths, for example, λ = 400 nm almost completely pass. Wavelengths with λ ≤ 390 nm therefore need not be considered below.

Short-wave light S of the second order of diffraction (m = 2) with wavelengths between λ = 400 nm and λ = 800 nm, ie m · λ = 800 nm to m · λ = 1600 nm, is emitted from the beam splitter 4 mainly to the first line detector 3A passed, which generates in a known manner electrical signals U _{A, P} , and thus from the second line detector 3B kept away. Long-wave light of the first diffraction order (m = 1) with wavelengths between λ = 840 nm and λ = 1680 nm is emitted from the beam splitter 4 almost completely to the second line detector 3B deflected, which generates in a known manner electrical signals U _{B, p} . In the overlap range from 800 nm to 840 nm, light from the first diffraction order reaches both detectors 3A and 3B and is converted there optoelectronically.

• 1. Herkömmliche polychromatische Messung von 400 nm bis 840 nm mit Si-Detektor und Langpassfilter.
• 2. Herkömmliche polychromatische Messung von 800 nm bis 1680 nm mit InGaAs-Detektor.
• 3. Erfindungsgemäße polychromatische Weitbereichsmessung von 400 nm bis 1680 nm.

With the basic optical structure according to the in 2 sketched embodiment, three different modes of operation can be realized:

• 1. Conventional polychromatic measurement from 400 nm to 840 nm with Si detector and long pass filter.
• 2. Conventional polychromatic measurement from 800 nm to 1680 nm with InGaAs detector.
• 3. Polychromatic long-range measurement according to the invention from 400 nm to 1680 nm.

The higher diffraction orders (m ≥ 3) are in the spectrometer 10 through the longpass filter 7 and 8th suppressed: diffraction order m = 1 m = 2 m = 3 Detection (absorption) Mainly in InGaAs detector 3B mainly in Si detector 3A none without filter 800 ... 1680 nm 400 ... 580 nm up to 390 nm because of longpass filters 7 Filter edge, filter 8th present or not 580 ... 585 nm Long-pass filter 8th Blocking up to 560 nm, passage from 580 nm 585 ... 840 nm 390 ... 560 nm due to long-pass filter 8th

The first diffraction order of the spectral band of 800 nm to 840 nm is thereby proportional to the second diffraction order of the spectral band from 400 nm to 420 nm on both detectors 3A and 3B directed.

The evaluation unit 5 processes, for example, the electrical signal U _{A, 1 of} the detection element 3A.1 as a raw signal for the absorbed energy in the wavelength range of 400 nm to 424.4 nm and the electrical signal U _{B, 1 of} the corresponding detection element 3.1 as a raw signal for the absorbed energy in the wavelength range 800 nm to 848.8 nm. For the other corresponding detection element pairs corresponding, so far shorter wavelengths not by the long-pass filter applies 8th be suppressed. Due to the double use of the detection plane of the spectrometer 10 the spectral resolution is approximately twice as large as that in 1 illustrated embodiment.

The in the diffraction orders m ₁ = 1 and m ₂ = 2 at one over the detectors 3A and 3B uniform temperature T _D absorbed light energy W (λ _p / m _j ) can be determined on the basis of the recorded detector signals U _{i, p} (i = A, B) from the following system of equations:

D _{i, j, p} (T) is the spectral sensitivity of the optoelectronic transducers 3i.p at their associated wavelength λ _p / m _j . depending on the temperature of the relevant optoelectronic transducer 3i.p , It must be before using the spectrometer 10 be determined at a plurality of (at least two) temperatures T _k in the intended operating temperature range with monochromatic light of known power in a so-called calibration cycle:

The spectral sensitivity at any intervening temperatures can be calculated, for example, by linear interpolation in a known manner. Alternatively, a parameterized model function can be adapted to the measured temperature values T _k by means of a mathematical compensation calculation in a known manner, for example by determining the smallest deviation squares.

The temperature dependence of the detection elements 3i.p measured signals U _{i, p} , as in the embodiment according to 1 by normalization with the spectral sensitivity D _{i, j, p} (T _{D, p} ) of the detection elements 3i.p based on their current temperature T _{D, p are} compensated. Specifically, this succeeds in two ways:
If, as in 2 the case, at least a first separate temperature sensor 6.1 , preferably a second separate temperature sensor 6.2 , at the detector 3A the one or more temperatures T ₁ (and optionally T ₂ ) measured therewith may be used as the current detector temperature T _{D, p} to determine the temperature dependence of the spectral sensitivity D _{i, j, p} (T) of the optoelectronic transducers 3i.p to compensate. If two separate temperature sensors 6.1 and 6.2 at the ends of the detector 3A are arranged, the temperature T _{D, p of} the respective detection element 3.P for example, by its distance to the temperature sensors 6 be calculated by interpolation between the measured temperatures T ₁ and T ₂ .

Even without separate temperature sensors 6 can - assuming or the actual requirement that along the detectors 3A and 3B no temperature gradient, but one for all optoelectronic converters 3i.p same temperature T _D is present - this temperature T _D, for example, four detector signals U _{i, p are determined} at two different wavelengths λ _a and λ _b . If, for example, λ _b = k · λ _{a is} selected, where k = m ₂ : m _{1 is} the quotient of the two diffraction orders to be detected, here, for example, m ₁ = 1, m ₂ = 2 and thus k = 2: 1 = 2, For this purpose, the following equation system with the four unknown W (λ _a / k), W (λ _a ), W (k * λ _a ) and T _D can be solved:

For this purpose, the system of equations can be simplified at first. The determination of T _D can then take place, for example, by means of the inverse functions D _{i, j, p} ^-1 (T). Alternatively, for example, look-up tables (LUT) may be used to determine T _D.

To achieve a uniform temperature distribution across all optoelectronic converters 3i.p To a large extent, the detectors can 3A and 3B advantageously be thermally isolated from the environment. It is alternatively possible, only the (temperature-sensitive) detector 3A to temper, for example, to cool, and only the signals of the (temperature insensitive) detector 3B to correct.

From the thus determined average temperature of the detector and the measured values of the external temperature sensors, in the presence of a temperature gradient along the detector, the temperature of each individual detector element can be determined and used to correct its spectral sensitivity.

From the inventively determined average temperature T _{D of} the detectors 3A and 3B and the measured values T ₁ , T _{2 of} the external temperature sensors 6.1 . 6.2 may be in the presence of a temperature gradient along the detector 3A the temperature T _{D, p of} each individual detector element are determined and used to correct its spectral sensitivities D _{i, j, p} (T).

In real embodiments (not shown), the detectors 3A and 3B for example, in each case a total of 256 detection elements. Other numbers are possible as well as other spectral detection ranges. The above considerations apply accordingly.

Unless the spectrometer 10 detection elements 3i.p having three or more different spectral detection ranges and output a corresponding number of signals U _{i, p} (i = A, B, C, ...), the above equation system can be extended to a corresponding number M ≥ 3 of simultaneously measurable diffraction orders , In general, the equation system can be formulated as follows:

For temperature determination, in the case of M = 3, three different wavelengths must be used on three different detection elements.

In 3 is the result of the diffraction of wavelengths λ of the incident light L at the grating 2 resulting beam direction on the line detectors 3A and 3B with 256 detection elements each 3i.p shown graphically. The effects of the beam splitter 4 and the long-pass filter 8th is not taken into account.

4 shows a spectrometer 10 , which is largely the in 1 shown embodiment, but only has unpaired detection elements. Temperature compensation of the spectral sensitivity (s) is therefore only by means of the external sensors 6 possible. Nevertheless, the spectrometer is 10 much more compact than a design with two separate spectrometers according to the prior art.

It is possible in all embodiments, the control and evaluation 5 outside the spectrometer 10 to arrange, for example, in another architectural space.

In all embodiments of the invention, the calculations for determining the temperature value T _{D can be made} immediately after the measurement of the electrical signals U _{i, p} or with a time interval thereof. In both cases, they can be used in the internal control and evaluation unit 5 or at a distance from the spectrometer 10 in an external evaluation unit (not shown). For this purpose, the raw (uncompensated) signal values U _{i, p} can be stored and / or output via an interface.

In all embodiments of the invention, the compensation of temperature fluctuations can take place immediately after the measurement of the electrical signals U _{i, p} or in temporal distance thereof. In both cases, they can be used in the internal control and evaluation unit 5 or at a distance from the spectrometer 10 in an external evaluation unit (not shown). For this purpose, the raw (uncompensated) signal values U _{i, p} and / or already determined temperature values T _D can be stored and / or output via an interface. As a result, the amount of data to be stored and / or transmitted can be minimized.

In all embodiments, the detectors 3A . 3B a two-dimensional distribution of detection elements 3A / Bp _xy , preferably in the form of perpendicular to each other arranged rows and columns. In such embodiments, a single pair of detection elements 3A.pxy . 3B.pxy ' be arranged correspondingly, while all other detection elements are unpaired. Alternatively, a plurality of corresponding pairs may be provided, while all other detection elements are unpaired. Alternatively, all detection elements may be arranged in corresponding pairs. For example, the detectors 3A respectively 3B 256 × 256 detection elements each 3A / Bp _xy with respect to the beam splitter 4 are virtual mirror images of each other.

In 4 is schematically a simple wide-range spectrometer 10 shown, the only unpaired detection elements 3A.1 ... 9 and 3B.1 ... 9 and the rest of the embodiment according to 1 equivalent. For temperature compensation here are the probes 6.1 and 6.2 necessary. The beam splitter 4 may be, for example, a spectral neutral divider in an alternative embodiment.

LIST OF REFERENCE NUMBERS

1

entrance slit

2

diffraction grating

3A / B

detector

3i.p

Detection element (i = A, B) p = 1 ... 18)

4

beamsplitter

5

Control and evaluation unit

6

temperature sensor

7

Long-pass filter

8th

Long-pass filter

9

casing

10

spectrometer

11

collimating optics

12A / B

camera optics

L

Incident light

S

Split light

T _1,2

temperature signals

U _{i, p}

Photoelectric signals

λ _min

Lower limit wavelength

λ _max

Upper limit wavelength

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10010213 A1 [0004]

Claims (13)

Optical spectrometer ( 10 ) with a housing ( 9 ), which has an entrance slit ( 1 ), a dispersive element ( 2 ) and a detector ( 3A ) with a plurality of optoelectronic detection elements ( 3A.p ), wherein the dispersive element ( 2 ) Light (L) passing through the entrance slit ( 1 ) in the housing ( 9 ), depending on the wavelength in the direction of different detection elements ( 3A.p ) of the detector ( 3A ), characterized by a second detector ( 3B ) with a plurality of optoelectronic detection elements ( 3B.p ) and one between the dispersive element ( 2 ) and the first detector ( 3A ) arranged beam splitter ( 4 ), a part of the split light (S) to the second detector ( 3B ), the detection elements ( 3A.p ) of the first detector ( 3A ) have a different spectral detection range than the detection elements ( 3B.p ) of the second detector ( 3B ). Spectrometer ( 10 ) according to claim 1, wherein the beam splitter ( 4 ) divides the split light (S) at least in a partial region of its surface wavelength-selectively. Spectrometer ( 10 ) according to claim 1 or 2, wherein at least one corresponding pair of one of the detection elements ( 3A.p ) of the first detector ( 3A ) and a detection element ( 3B.p ' ) of the second detector ( 3B ) with respect to the surface of the beam splitter ( 4 ) is arranged symmetrically, in particular such that these detection elements ( 3A.p . 3B.p ' ) by a wavelength-selective dividing portion of the beam splitter ( 4 ) correspond to one another wavelength-selectively. Spectrometer ( 10 ) according to one of the preceding claims, wherein a spectral long-pass filter ( 8th ) in front of a real subregion of at least one of the two detectors ( 3A . 3B ) is continuously arranged up to and including its long-wave end, in particular in front of the detector ( 3A ) with the shorter wavelength detection range. Spectrometer ( 10 ) according to the preceding claim, wherein the long-pass filter - on or in the beam splitter ( 4 ) or - between the beam splitter ( 4 ) and the relevant detector ( 3A / B) or - at the relevant detector ( 3A / B) is arranged. Spectrometer ( 10 ) according to one of claims 2 to 5, wherein an evaluation unit ( 5 ) an electrical signal of a detection element ( 3A.p ) of the one detector ( 3A ) is processed as a raw signal for the absorbed energy in a first wavelength range and an electrical signal of a with this detection element ( 3A.p ) through the beam splitter ( 4 ) wavelength-selective corresponding detection element ( 3B.p ' ) of the second detector ( 3B ) as a raw signal for the absorbed energy in a second wavelength range whose lower limit wavelength is k times the lower limit wavelength of the first wavelength range and whose upper cut-off wavelength is k times the upper cut-off wavelength of the first wavelength range, where k is a quotient of two is to be detected diffraction orders. Spectrometer ( 10 ) according to one of the preceding claims, wherein a sensitivity of one of the detectors ( 3B ) is substantially temperature-independent or at least less temperature-dependent than a corresponding sensitivity of the other detector ( 3A ) and / or wherein the one detector ( 3A ) one silicon detector and the other detector ( 3B ) is an indium gallium arsenide, germanium or lead sulfide detector. Spectrometer ( 10 ) according to one of the preceding claims, wherein the spectral detection ranges of the two detectors ( 3A . 3B ) overlap each other spectrally. Spectrometer ( 10 ) according to one of claims 3 to 8, wherein an evaluation unit ( 5 ) based on at least one electrical signal (U _{A, P} ) of a detection element ( 3A.p ) of the first detector ( 3A ) and based on at least one electrical signal (U _{B, P} ) of a wavelength-selective corresponding detection element ( 3B.p ' ) of the second detector ( 3B ) a value (T _D ) of a temperature of the respective detection elements ( 3A.p . 3B.p ' ). Spectrometer ( 10 ) according to one of the preceding claims, wherein an evaluation unit ( 5 ) based on four electrical signals (U _{i, p} ) of two pairs of wavelength-selectively corresponding detection elements ( 3A.p . 3B.p ' ) a value (T _D ) of a temperature of the two detectors ( 3A . 3B ), where locations of the pairs correspond to two different wavelength ranges or two different diffraction orders of the same wavelength range. Spectrometer ( 10 ) according to one of the preceding claims, in particular according to the preceding claim, wherein the evaluation unit ( 5 ) the value (T _D ) of the temperature by solving the equation system for the electrical signals (U _{i, p} ) and spectral sensitivities (D _{i, m, p} )

for M diffraction orders (m = 1, ... M), M optoelectronic transducer (i = A, B, ...) and M detection elements (p = 1, ... M) determined. Spectrometer ( 10 ) according to one of claims 9 to 11, wherein the evaluation based on the determined value (T _D ) of the temperature normalized an electrical signal of another detection element, in particular an unpaired detection element for detecting the shorter-wavelength spectral detection range, according to a temperature-dependent spectral sensitivity. Spectrometer ( 10 ) according to one of the preceding claims, wherein in the incident light (L) a long-pass filter ( 7 ), which blocks wavelengths below the shorter wavelength spectral detection range.

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