DE2904984C3 - Measuring arrangement for determining the spectral sensitivity of photodetectors - Google Patents

Description

a) the light distributor is a known radiation-integrating, photometric measuring sphere (9) with a quasüdeal, diffusely reflective white interior covering,

b) the measuring ball (9) has an inlet opening (12) through which the quasi-monochromatic Light beam (2) from the light source (1) arranged outside the measuring sphere onto one of the Inlet opening (12) opposite inner wall region (13) is directed,

c) symmetrically to the. inlet opening (12), preferably in its central plane, the Measuring ball (9) further wall openings (11), generally of different sizes, on to which the test items (4.1 to 4.5) and the standard detector (3) can be attached.

2. Measuring arrangement according to claim 1, characterized in that diffusely reflective, white disks are provided to cover wall openings (11) of the measuring ball (9) that are not required for test objects (4.1 to 4.5J) for reducing the wall openings (11) and thus for adapting the area of these wall openings to the active area of the photodetectors ( 3, 4, 1 to 4, 3).

3. Measuring arrangement according to claim 1 and 2, characterized in that the standard detector Π) is directly connected to an associated amplifier (19), while the test items (4.1 to 4.5) can optionally be connected to another amplifier (20) via a step switch (18).

4. Measuring arrangement according to claim 1 to 3, characterized in that the pulse modulation of the quasi-monochromatic Light beam (2) a chopper (6) is provided and that the amplifiers (19, 20) are selective amplifiers that only those with the. Frequency of the chopper (6) modulated output signals of the photodetectors (3 or 4.1 to 4.5) strengthen.

5. Measuring arrangement according to claim I to 4, characterized in that the outputs of the amplifier (19 and 20) are led to a dividing unit (21) in which the quotient of the two output signals is formed and displayed or recorded in analog or digital form.

6. Measuring arrangement according to claim 'to 5, characterized in that the quasi-monochromatic Light beam (2) via a flexible light guide (8) to the inlet opening (12) of the measuring ball (9) got.

Photo detectors are photoelectronic components, according to DIN standard 44020, sheet 1, is a photoelectronic component an electronic component, in which electrical quantities are at the Change exposure to photons. The usual photodetectors are in the standard sheet mentioned listed and briefly explained

One of the most important parameters of any photodetector is its sensitivity. It is defined as the quotient of the output variable (e.g. the photocurrent) and the input variable (e.g. the radiation conduction). In this case, the sensitivity is expressed in A / W. However, the indication of a sensitivity is only unambiguous if the wavelength of the radiation at which the sensitivity was measured is also stated.

The dependence of the sensitivity of a photodetector on the wavelength is called spectral sensitivity. A distinction is made between absolute and relative spectral sensitivity. The absolute spectral sensitivity 5 (A) is defined according to DIN standard 44020, blue!, At wavelength A in the infinitesimal wavelength range άλ around λ as the quotient of the output variable (photocurrent / ρ /, (A)) and the physical radiation input variable (radiation power or radiation flux Φ (A)):

φ (λ)

The relative spectral sensitivity 5 (A) _re / is defined as the ratio of the absolute spectral sensitivity 5 (A) at wavelength A to the absolute spectral sensitivity 5 (Ao) at a reference wavelength Ao:

_ SU)

Usually 5 (Ao) = 5 (A) _ma j is chosen, ie Ao is then the wavelength at which the absolute spectral sensitivity is maximum. S (A) _re / is given as a dimensionless number or as a percentage.

In the practical application of photodetectors in light measurement practice, mostly a maximum spectral sensitivity in the radiation range of interest is required. To be clear Comparison of the spectral sensitivities of different photodetectors must therefore necessarily be the absolute spectral sensitivity curves must be known.

The invention relates to a measuring arrangement for determining the spectral sensitivity of photodetectors according to the preamble of claim 1. In a known measuring arrangement for this purpose a monochromatic light beam at the output of a monochromator 1 is first according to FIG onto the active surface of a photodetector 3 with known spectral sensitivity properties mapped, then on the surface of the photodetector to be measured 4. Since the light output of the This sequential process shows that the light source of the monochromator and also other factors are time-dependent possibly large measurement errors. Also from the fact that the monochromatic light beam must constantly fall with its entire surface on the active surface of the photodetector, measurement errors can

arise, especially when these areas differ significantly in size. Since the If the intensity distribution in beam 2 is not homogeneous, the photodetector surface is also not uniform illuminated In addition, this process is time-consuming as the photodetectors are examined one after the other Need to become.

Another known measuring arrangement (two-beam measuring method) is shown in Fig. Ib. This is where the quasi-monochromatic Beam 2 halved by a beam splitter 5 ι ο The two partial beams 2a and 26 illuminate in each case the standard detector 3 and the photodetector to be measured 4. But here, too, the beam focusing on the active photodetector surfaces, especially when changing detectors! is difficult or only a π Photodetector can be measured simultaneously with the standard detector, the aforementioned apply Disadvantages here too.

The invention is based on the last-mentioned measuring arrangement. The invention has the task based on specifying a measuring arrangement of the type mentioned in the preamble of claim 1, which the simultaneous determination of the social ^ sensitivity multiple photodetectors in relation to a standard photodetector allowed with all active Photodetector surfaces are completely and evenly illuminated.

According to the invention, this object is achieved by the characterizing features of claim 1 solved Advantageous further developments of the invention are specified in the subclaims.

By using a photometric measuring ball as a light distributor, as an optical integrator and as The instrument for generating diffuse illumination is difficult with the known measuring arrangements ge problem of the exact mapping of the measuring beam on the active surfaces of all photodetectors with simple Funds resolved.

Evenly illuminating a larger area by means of a photometric measuring ball, which has a quasi-ideally diffusely reflective white in-arm coating, is already known from "Grimsehl's Textbook of Physics", Volume II, Part I ₁ 8th Edition (1938), pages 602 to 604 . The measuring arrangement described there uses an integrating sphere and serves to determine the total light yield of a light source. In the following an embodiment of the invention is described with reference to the drawings. Show it

Fig. La and Ib known, in the introduction to the description mentioned measuring arrangements, F i g. Ic a measuring arrangement according to the invention,

F i g. 2 the photometric measuring ball according to FIG. Ic on a larger scale with the amplifiers and the dividing device,

3 shows a diagram with curves of the spectral Sensitivity of different photodiodes.

In the measuring arrangement according to FIG The light beam 2 emerging from the monochromator 1 is pulse-modulated by a chopper 6. This will make the Measurement insensitive to interfering light The modulated light beam is converted into one by means of focusing optics 7 flexible light guide introduced, which is attached at its other end to a photometer ball 9. The light falls through an inlet opening 12 into the sphere and illuminates the sphere wall in the wall area 13. The f.5 The ball is coated on its inner wall with a white, aselectively diffuse reflective coating 10. at ideally diffuse reflexicr, then prevails at any Place of the spherical wall (with the exception of the irradiated spherical wall area 13), i.e. also at other Wall openings 11 have the same irradiance if the openings are the same size. The number of Wall openings 11 can be adapted to the respective application and z. B. be between 2 and 100. At One of the wall openings 11 is attached to the standard detector on the other wall openings 11 the respective photodetectors to be examined (test items), which are related to their type (Ge, Si diodes, Photomultiplier etc.) and size of their active area can be different. The size of the wall openings 11 can also be adapted to the respective areas of the photodetector. Because of its flexibility of the light guide 8, the photometric measuring ball 9 is movable, what the attachment of the photodetectors relieved

The in the F i g. The photometric measuring ball shown in FIG. 2 has 6 wall openings with attached photodetectors 3 and 4.1 to 4 S. The output of the standard detector 3 is directly connected to an amplifier 19.

The outputs of the test items 4.1 to 4.5 can be via a switch 18 can be optionally or successively connected to a further amplifier 20. at the amplifiers 19 and 20 are selective amplifiers that only modulate those with chopper 6 Amplify photodetector signals. The reference signal 22 required for this is sent to the amplifiers from the chopper 6 Any extraneous light falling through any opening in the measuring ball 9 can as a result of this Measure not to falsify the measurement results.

In a simpler and cheaper arrangement, the light modulation can be dispensed with. then the chopper 6 is omitted. The amplifiers 19 and 20 are designed as DC voltage amplifiers. It must however, care must be taken that no foreign or Störiicht can get into the measuring ball 9. Even the flexible light guide can be dispensed with for the sake of simplicity. The light beam 2 then becomes solid predefined paths passed into the measuring ball 9. But then this is rigid with the monochromator connected, which can make it difficult to attach or quickly change photodetectors.

The ratio V _x (X) of the two signals at the output of the amplifiers 19 and 20 is formed in a D-video unit 21 and displayed in analog or digital form:

y _M) = -Jl

S (X) _x

χ = \ ... η; η ... number of measured
Photodetectors.

Since S (X) standard is assumed to be known, the spectral sensitivity of the photodetectors to be measured is determined by the following conversion:

S (X) _x =

■ SU) _S

Equation (4) only applies if all wall openings 11 have a smaller diameter than the active areas of the photodetectors, or if all active areas are the same size (a _s = a,).

If these boundary conditions are not met, the following applies instead of Eq. (4) Eq. (5):

(5)

a, ... active area of the standard _{detector, «v} ... active areas of the measured photodetectors.

These results can either be read off directly or displayed on a Λ- V · recorder as a function of λ, or they can be transferred to an arithmetic unit.

The wavelength Ä. at which S (A) _{1 is} measured, can be adjusted by the monochromator so that the entire sensitivity range of the detector can be examined in J /. intervals (e.g. <J /. = 10 nm). In the case of Si photodiodes, this range extends from 290 nm to 100 nm, in the case of Ge photodiodes from 300 μm to 1800 nm, in the case of Se photodetectors between 300 μm and 700 nm. 3 shows curves of the spectral sensitivity for different types of photodiodes, for example.

It must be pointed out that the total area of all measuring ball openings should not exceed about 4% of the inner area of the measuring ball, so that the optical integration is guaranteed. In the case of a measuring ball with an inside diameter of D = 80 mm , this means that a maximum of 10 openings, each with a diameter of 10 mm, may be made. With a ball diameter of 250 mm, about 100 openings of the same size can be made. B. about 100 photodetectors with an active area of 0.78 cm ² each can be measured simultaneously.

HI; ill

Claims (1)

10 20th 30th Claims; J, measuring arrangement for determining the spectral sensitivity of photodetectors, consisting from a light source to generate a quasi-monochromatic light beam of adjustable wavelength and from a light distributor that distributes the quasi-monochromatic light evenly and diffuse on at least one of the Pbotodetectors to be examined (test items) and on a photodetector with known spectral sensitivity (standard detector) allowed to conduct, characterized by the combination of the following features: