JP7472637B2 - Spectrometer - Google Patents

Description

The present invention relates to a spectrometer that is incorporated into a spectrophotometer such as an ultraviolet-visible spectrophotometer or an atomic absorption spectrophotometer, a tunable monochromatic light source, etc.

Spectrophotometers, such as ultraviolet-visible spectrophotometers and atomic absorption spectrophotometers, are known as devices for qualitative and quantitative analysis of samples. Spectrophotometers irradiate a sample with monochromatic light of a specified wavelength and measure the amount of light transmitted at that time to determine the absorbance at the specified wavelength, thereby performing qualitative and quantitative analysis of the sample. In spectrophotometers, a spectroscope (monochromator) is usually used to obtain monochromatic light of the specified wavelength.

The spectrometer is equipped with a housing having an entrance slit and an exit slit, a diffraction grating (wavelength dispersion element) housed in the housing, and a rotation drive mechanism for changing the angle of the diffraction grating with respect to the light incident from the entrance slit. The light incident from the entrance slit is irradiated onto the diffraction grating, and only the light traveling in a specific direction among the light dispersed by the diffraction grating is extracted from the exit slit. By adjusting the rotation angle position of the diffraction grating to an appropriate position, monochromatic light of any desired wavelength (target wavelength) can be extracted (Patent Document 1). The rotation angle position of the diffraction grating is usually calculated based on an arithmetic formula with the wavelength as a variable. The arithmetic formula has parameters such as the spectrometer deviation angle (the angle between the incident light and the outgoing light of the diffraction grating) and the groove spacing of the diffraction grating, and is set for each spectrometer.

JP 2013-253820 A

In such spectrometers, installation errors occur when attaching the entrance slit, exit slit, diffraction grating, rotation drive mechanism, etc. to the housing. Therefore, in order to calibrate the installation errors, various adjustment procedures are performed before the product is shipped from the factory.

One of the adjustment tasks is to adjust the optical axis of the light that has been wavelength-dispersed by the diffraction grating. This is a task of adjusting the direction of the diffraction grooves of the diffraction grating and the tilt direction (perpendicular to the direction of the diffraction grooves) so that the diffracted light of the laser light (wavelength 632.8 nm in the case of a He-Ne laser) that enters the housing from the light source through the entrance slit passes through approximately the center of the exit slit. Specifically, a target member is placed just outside the entrance slit of the housing, and after visually confirming that the light from the light source enters the center of the target member, the target member is removed and the light from the light source is allowed to enter the housing from the entrance slit. Next, a target member is placed outside the exit slit of the housing, and the tilt of the tilt direction of the diffraction grating is adjusted while visually confirming that the zeroth order light enters the center of the target member. After that, the tilt of the groove direction of the diffraction grating is adjusted so that the first order diffracted light enters the center of the target member.

In some cases, optical fibers are used to input and output light to and from the housing, due to their high degree of freedom in handling. In such cases, in spectrometers incorporated into devices that do not require a large amount of light, general-purpose optical fibers are connected to the housing using common connectors such as FC connectors and SMA connectors, rather than expensive bundle fibers. However, in spectrometers that have undergone the above-mentioned optical axis adjustment work, when an optical fiber is connected to the exit slit using a connector, the amount of first-order diffracted light extracted from the exit slit decreases, and when incorporated into a spectrophotometer, a sufficient amount of light cannot be obtained to obtain the required analytical accuracy and analytical sensitivity.

The problem that this invention aims to solve is to make it possible to extract a sufficient amount of first-order diffracted light from a spectroscope at various wavelengths, not just the wavelength used for optical axis adjustment.

The spectrometer according to the present invention, which has been made to solve the above problems, comprises:
a housing having an inlet and an outlet;
a wavelength dispersion element disposed within the housing, which disperses the wavelength of light incident from the inlet and outputs light of a target wavelength from the outlet;
a rotation drive mechanism that rotates the wavelength dispersion element;
a storage unit that stores an arithmetic expression for calculating a rotation angle position of the wavelength dispersion element corresponding to the target wavelength;
a control unit that causes the rotary drive mechanism to rotate the wavelength dispersion element so that the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic expression,
The wavelength dispersion element and the rotation drive mechanism are set within the housing such that, in a state where the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a first wavelength as the target wavelength, when light containing light of the first wavelength is incident from the inlet, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet, and, in a state where the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a second wavelength which is different from the first wavelength as the target wavelength, when light containing light of the second wavelength is incident from the inlet, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through the predetermined range of the outlet.

Here, the light including the light of the first wavelength and the light including the light of the second wavelength may be either monochromatic light or polychromatic light (multi-wavelength light), and may be either directional light or non-directional light. Examples of directional light include laser light, light mechanically given directionality using a slit, etc. Furthermore, the light including the light of the first wavelength and the light including the light of the second wavelength may be the same or different.

The spectrometer according to the present invention is obtained as follows.
In the optical axis adjustment before the product is shipped from the factory, the first wavelength is set as the target wavelength. As a result, the rotary drive mechanism rotates the wavelength dispersion element so that the wavelength dispersion element is located at a rotation angle position corresponding to the first wavelength calculated from the arithmetic expression. Then, when light including the light of the first wavelength is incident from the inlet in this state, the light is wavelength-dispersed by the wavelength dispersion element, and the light of the first wavelength, which is a part of the dispersed light, travels from the wavelength dispersion element to the outlet, so that the optical axis of the light passes through a predetermined range in the center of the outlet. Then, the arrangement of the wavelength dispersion element and the rotary drive mechanism is adjusted for the second wavelength as well, in the same procedure as for the first wavelength, so that the optical axis of the light of the second wavelength traveling from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet. At this time, if the optical axis of the light of the second wavelength dispersed by the wavelength dispersion element and traveling to the outlet passes through a predetermined range in the center of the outlet without changing the arrangement of the wavelength dispersion element and the rotary drive mechanism, the optical axis adjustment work is terminated. On the other hand, if the arrangement of the wavelength dispersion element and the rotary drive mechanism is changed when the second wavelength is set as the target wavelength, the first wavelength is set as the target wavelength again and the above-mentioned operation is performed to confirm whether the optical axis of the light of the first wavelength dispersed by the wavelength dispersion element and heading toward the outlet passes through the specified range of the outlet. If the optical axis of the light passes through the specified range of the outlet, the optical axis adjustment operation is terminated. In short, the optical axis adjustment operation is terminated at the point in time when it is confirmed that both the light of the first and second wavelengths dispersed by the wavelength dispersion element and heading toward the outlet have passed through the specified range in the center of the outlet.

Here, the first wavelength and the second wavelength are preferably wavelengths that satisfy a predetermined condition. The predetermined condition will be described later. Examples of the wavelength dispersion element include a diffraction grating and a prism. When the wavelength dispersion element is a diffraction grating, the optical axis adjustment operation involves adjusting the inclination of the groove direction of the diffraction grating and the inclination of the direction perpendicular to the groove direction and along the grating surface of the diffraction grating so that the optical axis of the first-order diffracted light passes through a predetermined range in the center of the outlet. The fact that the optical axis of the light heading toward the outlet from the wavelength dispersion element has passed through the predetermined range in the center of the outlet may be confirmed by visually checking the position of the spot of light formed on a target member placed near the outlet, or by detecting the amount of light emitted from the predetermined range of the outlet with a detector and confirming that the amount of light is maximized.

In the spectrometer according to the present invention, when two different wavelengths are set as target wavelengths, the wavelength dispersion element and the rotary drive mechanism are arranged so that the optical axis of light of the target wavelength traveling from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet, so that it is possible to extract a sufficient amount of light at various target wavelengths, not limited to the wavelength used for adjusting the optical axis.

FIG. 1 is a schematic diagram showing the configuration of an embodiment of a spectrometer according to the present invention. FIG. 4 is a diagram showing a spot of first-order diffracted light near an exit slit. 13 is a graph showing the size of a spot of first-order diffracted light formed near an exit slit when laser light with a diameter of 200 nm is incident on a housing through an entrance slit. 11 is a graph showing a change in the intensity ratio of 1st-order diffracted light to 0th-order light due to differences in optical axis adjustment methods. 11 is a flowchart showing a procedure for adjusting an optical axis.

Hereinafter, an embodiment of a spectrometer according to the present invention will be described with reference to the drawings.
1 is a schematic diagram of a spectrometer 100 of this embodiment. The spectrometer 100 includes a housing 1 having an entrance 11 and an exit 12, a diffraction grating 2 as a wavelength dispersion element disposed inside the housing 1, a mirror 3 having a first reflecting surface 33 and a second reflecting surface 34, a rotation drive mechanism 5 for rotating the diffraction grating 2, an origin sensor 6 for detecting that the rotational position of the diffraction grating is at the mechanical origin position, a control unit 7, and an input unit 8.

The rotary drive mechanism 5 includes a stepping motor and a reduction mechanism that reduces the rotation of the output shaft of the stepping motor at a predetermined reduction ratio to rotate and drive the diffraction grating 2. The origin sensor 6 is, for example, a reflective photoelectric switch, and this, together with a protrusion (not shown) provided on the diffraction grating 2, detects that the diffraction grating 2 is located at the mechanical origin. The detection signal from the origin sensor 6 is output to the control unit 7.

Attachment mounts 13 and 14 are provided at the entrance 11 and the exit 12 of the housing 1, respectively, and an entrance slit 131 and an exit slit 141 are removably attached to each mount.

A filter device 9 is disposed near the outlet 12 in the housing 1. Although detailed illustration is omitted, the filter device 9 includes a disk 91, a plurality of openings disposed along the outer periphery of the disk 91, optical filters 92 (only one optical filter is shown in FIG. 1) attached to each of the plurality of openings except one of the plurality of openings, a rotary dial 93 for rotating the disk 91, and a rotation position sensor 94 for detecting the rotation position of the rotary dial 93. As the optical filter 92, an order separation filter that transmits the first-order diffracted light from the diffraction grating 2 and cuts higher-order light having a shorter wavelength than the first-order diffracted light is used. Order separation filters having different transmission wavelength bands are selected for each of the plurality of optical filters 92. The detection signal of the rotation position sensor 94 is output to the control unit 7. The rotary dial 93 is disposed outside the housing 1, and the disk 91 is rotated by manually rotating the rotary dial 93, thereby switching between a state in which one of the optical filters 92 is disposed on the optical path of the light from the diffraction grating 2 toward the outlet 12 and a state in which the opening is disposed.

The control unit 7 controls the operation of the rotary drive mechanism 5, and includes a wavelength movement control unit 71, an initialization control unit 72, a coefficient setting unit 73, a coefficient storage unit 74, an arithmetic expression storage unit 75, and the like as functional blocks. The coefficient storage unit 74 stores the offset pulse number C1 used in the initialization process by the initialization control unit 72, and the optical mount correction coefficient C2 and the filter correction coefficient C3 used in the wavelength movement process by the wavelength movement control unit 71. The arithmetic expression storage unit 75 stores an arithmetic expression for calculating the number of drive pulses of the stepping motor required to rotate the diffraction grating 2 at the wavelength origin to a rotation angle corresponding to the target wavelength. This arithmetic expression is used in the wavelength movement process by the wavelength movement control unit 71. The coefficient storage unit 74 and the arithmetic expression storage unit 75 correspond to the storage unit of the present invention.

The control unit 7 is actually a personal computer, and the functions of each of the functional blocks are realized by running dedicated control software installed on the computer. Therefore, the input unit 8 includes a keyboard, a mouse, and other pointing devices.

The offset pulse number C1 is the number of drive pulses of the stepping motor required to move the diffraction grating 2 from the mechanical origin to the wavelength origin. The offset pulse number C1 is a different value for each individual device. The wavelength origin is the rotational position of the diffraction grating 2 when it is assumed that the target wavelength is 0 nm.

The optical mount correction coefficient C2 and the filter correction coefficient C3 are used to calculate the number of pulses required to rotate the diffraction grating 2 from the wavelength origin to a rotational position corresponding to the target wavelength. The optical mount correction coefficient C2 and the filter correction coefficient C3 are different values for each individual device. The filter correction coefficient C3 is a different value for each type of optical filter 92, and the coefficient memory unit 74 stores the same number of filter correction coefficients C3 as the types of optical filters 92 that the disk 91 has.

The number of drive pulses of the stepping motor required to move the diffraction grating 2 from the wavelength origin to a rotation position corresponding to the target wavelength is calculated using the following equation (1).
P = θ / Res ... (1)
In equation (1), P represents the number of drive pulses, θ (deg) represents the rotation angle of the diffraction grating 2 corresponding to the target wavelength, and Res (deg/pulse) represents the angular resolution of the diffraction grating 2 .

The rotation angle θ of the diffraction grating 2 is calculated from the following formula (2).
θ={arcsin(K×(1+C2)×W1)/π×180}×C3 (2)
In formula (2), K represents the optical mount constant and W1 represents the target wavelength. The optical mount constant K is a value specific to the device, which is determined by the deviation angle and the number of grooves of the diffraction grating 2. In formula (2), C2 and C3 represent the optical mount correction coefficient and the filter correction coefficient, respectively, as described above.

The spectrometer 100 having the above configuration is subjected to an optical axis adjustment before being shipped from the factory. The optical axis adjustment method will be described below with reference to FIG. 5. The optical axis adjustment includes a first step for determining two different wavelengths (first wavelength λ1 and second wavelength λ2) to be used for the optical axis adjustment, and a second step for adjusting the arrangement of the diffraction grating 2 and the rotary drive mechanism 5 using the two wavelengths (λ1, λ2) determined in the first step. Note that in the optical axis adjustment described below, the inclination of the groove direction of the diffraction grating 2 is mainly adjusted. The adjustment of the inclination of the tilt direction of the diffraction grating 2, which is performed prior to the adjustment of the inclination of the groove direction of the diffraction grating 2, is the same as in the conventional method, and therefore will not be described here.

(1) First step: First, the entrance slit 131 is removed from the mounting mount 13 at the entrance 11 of the housing 1, and a white light source such as a halogen lamp is connected to the mounting mount 13 via a single-core optical fiber. Then, the light emitted from the white light source is made to enter the housing 1 through the single-core optical fiber. Also, the exit slit 141 is removed from the mounting mount 14 at the exit 12 of the housing 1, and a photodiode array sensor (hereinafter referred to as "photo sensor") is installed instead. Then, a plurality of wavelengths within the wavelength range of light that can be emitted from the light source are set as target wavelengths, and while controlling the rotary drive mechanism 5 to rotate the diffraction grating 2, an image of a spot of the first-order diffracted light on the light receiving surface of the photosensor is obtained for each of the plurality of target wavelengths (step 101). Next, the size of the spot is obtained from the image of the spot (step 102). The size of the spot may be automatically calculated from the determined shape by performing a binarization process or the like on the image of the spot on the light receiving surface of the photosensor to determine the shape of the spot, or the image of the spot may be displayed on a display screen and the size of the image may be measured manually.

FIG. 3 shows the size of the spot of the first-order diffracted light obtained for a plurality of target wavelengths when the light from the light source is incident on the housing 1 using a single-core optical fiber with a core diameter of 200 nm. FIG. 2 shows the image of the spot of the first-order diffracted light when the target wavelength is set to 400 nm, 550 nm, 650 nm, 750 nm, and 800 nm. Here, the size of the spot means the vertical length (spot height (mm)) of the spot image shown in FIG. 2. The vertical direction of the spot image corresponds to the width direction of the grooves of the diffraction grating 2 (the direction in which the grooves are arranged). From FIG. 2 and FIG. 3, it can be seen that the size of the spot differs depending on the target wavelength, and that there are two minimum values in the wavelength range from 200 nm to 900 nm. The reason why the height of the spot differs depending on the target wavelength is that various aberrations exist in the optical system from the entrance 11 to the exit 12, and a wavelength with a small spot height of the first-order diffracted light represents a wavelength with small astigmatism.

Based on the results obtained in step 102, the worker performing the optical axis adjustment selects two arbitrary different wavelengths (one of these two wavelengths corresponds to the first wavelength of the present invention, and the other corresponds to the second wavelength) included in the wavelength range of the light source as the wavelengths for optical axis adjustment. For the reasons described below, it is preferable to select two wavelengths that show minimum values in the graph of FIG. 3 as the wavelengths for optical axis adjustment. In other words, showing minimum values in the graph of FIG. 3 means "satisfying a specified condition."

Comparing the position of the optical axis when the spot of the first-order diffracted light having a small spot height near the outlet 12 does not overlap the outlet 12 at all with the position of the optical axis when the spot of the first-order diffracted light having a large spot height near the outlet 12 does not overlap the outlet 12 at all, the first-order diffracted light having a small spot height is shorter from the center of the outlet 12. This means that the first-order diffracted light having a small spot height cannot be emitted from the outlet 12 (i.e. cannot be taken out from the spectrometer 100) if the position of the optical axis of the first-order diffracted light having a small spot height is only slightly shifted from the center of the outlet 12, and therefore the position of the optical axis must be strictly adjusted. The first-order diffracted light having a wavelength at which the spot height is the minimum must be adjusted most strictly, so if the optical axis is adjusted using the first-order diffracted light having such a wavelength, it is possible to take out the first-order diffracted light of a wide wavelength range from the outlet 12, not limited to the wavelength used for the optical axis adjustment.

However, one of the two wavelengths for adjusting the optical axis may be a wavelength that exhibits a minimum value (minimum wavelength), and a wavelength different from the minimum wavelength may be selected as the other wavelength. For example, if there are two minimum wavelengths and the values of these two minimum wavelengths are close to each other, it is advisable to select one of the two wavelengths for adjusting the optical axis as the minimum wavelength, and the other as a wavelength near the end of the wavelength range of the light source.

(2) Second step The two wavelengths selected as the wavelengths for optical axis adjustment in the first step are set as target wavelengths (step 103). Then, while rotating the diffraction grating 2 by controlling the rotary drive mechanism 5, the amount of first-order diffracted light incident on a predetermined range of the light receiving surface of the photosensor is detected for each of the two target wavelengths (step 104). The process of step 104 is repeated while changing the arrangement of the diffraction grating 2 and the rotary drive mechanism 5 in a state where the diffraction grating 2 is positioned at a rotation angle position corresponding to the target wavelength. As a result, the inclination of the groove direction of the diffraction grating 2 is adjusted so that the amount of detected light of the photosensor is maximized. In this case, it is preferable that the amount of detected light of the photosensor is maximized at both of the two wavelengths for optical axis adjustment, but the amount of detected light at one or both wavelengths does not have to be the maximum value as long as the total value of the amount of detected light of the photosensor obtained for the two wavelengths is maximized.

FIG. 4 shows the results obtained when the light emitted from the white light source is incident on the housing 1 and the diffraction grating 2 is rotated by controlling the rotary drive mechanism 5 using the spectrometer 100 after the optical axis adjustment is performed by the above method, and the amount of light of the first-order diffracted light is detected for each of a plurality of target wavelengths. Here, the two minimum wavelengths in the graph shown in FIG. 3 are used as the wavelengths for optical axis adjustment. FIG. 4 also shows the results of detecting the amount of light of the first-order diffracted light using a conventional spectrometer in which the optical axis adjustment is performed with the first-order diffracted light of one wavelength. The horizontal axis of FIG. 4 represents the target wavelength (nm), and the vertical axis represents the ratio of the amount of light of the first-order diffracted light to the amount of light of the zeroth order light. As can be seen from this figure, the amount of light of the first-order diffracted light is increased in the spectrometer of this embodiment compared to the conventional spectrometer.

In the above description, the light source used in the first step (step of determining the wavelength for optical axis adjustment) is the same as the light source used in the second step (optical axis adjustment step). However, in the second step, a laser that emits laser light (monochromatic light) close to the wavelength for optical axis adjustment may be used as the light source.
In addition, in the optical axis adjustment work, not only the arrangement of the diffraction grating 2 and the rotary drive mechanism 5 but also the attitude of the mirror 3 (the inclination of the first and second reflecting surfaces 33, 34) may be adjusted.

In the above-mentioned optical axis adjustment method, the amount of light emitted from the outlet 12 of the housing 1 is measured by a photosensor, but it is also possible to connect a single-core optical fiber with a specified core diameter to the attachment mount 14 of the outlet 12, and adjust the arrangement of the diffraction grating 2 and the rotation drive mechanism 5 so that the amount of light passing through it detected by the detector is maximized. In this example, the core of the optical fiber corresponds to a specified range in the center of the outlet 12. Also, a target member may be installed near the outlet 12, and the arrangement of the diffraction grating 2 and the rotation drive mechanism 5 may be adjusted so that the spot of the first-order diffracted light formed on the target member is located within a specified range in the center of the target member.

The above embodiment is merely one example of the present invention, and it is clear that any modifications, additions, deletions, etc. made within the scope of the claims are also encompassed by the present invention.

[Various aspects]
It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

(Item 1) The spectrometer according to the present invention comprises:
a housing having an inlet and an outlet;
a wavelength dispersion element disposed within the housing, which disperses the wavelength of light incident from the inlet and outputs light of a target wavelength from the outlet;
a rotation drive mechanism that rotates the wavelength dispersion element;
a storage unit that stores an arithmetic expression for calculating a rotation angle position of the wavelength dispersion element corresponding to the target wavelength;
a control unit that causes the rotary drive mechanism to rotate the wavelength dispersion element so that the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic expression,
The wavelength dispersion element and the rotation drive mechanism are set within the housing so that, in a state where the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a first wavelength as the target wavelength, when light containing light of the first wavelength is incident from the inlet, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet, and, in a state where the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a second wavelength which is different from the first wavelength as the target wavelength, when light containing light of the second wavelength is incident from the inlet, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through the predetermined range of the outlet.

According to the spectrometer described in paragraph 1, when two different wavelengths are set as target wavelengths, the wavelength dispersion element and the rotary drive mechanism are arranged so that the optical axis of light of each target wavelength heading from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet. Therefore, in a configuration in which an optical fiber is connected to the outlet and light is emitted through the optical fiber, it is possible to extract a sufficient amount of light at various target wavelengths, not limited to the wavelength used for adjusting the optical axis.

(2) In the spectrometer described in 1, the wavelength dispersion element is a diffraction grating, and the first wavelength can be the wavelength at which the cross-sectional size at the outlet of the first-order diffracted light traveling from the diffraction grating to the outlet is smallest when the multi-wavelength light is incident from the inlet in a state where the diffraction grating is positioned at a rotation angle position calculated from the arithmetic formula with each of the multiple wavelengths within the wavelength range of the multi-wavelength light including the light of the first wavelength as the target wavelength.

(Clause 3) In the spectrometer described in paragraph 1, the wavelength dispersion element is a diffraction grating, and the first wavelength and the second wavelength can be the wavelengths at which the cross-sectional size at the outlet of the first-order diffracted light traveling from the diffraction grating to the outlet is the first and second smallest when the multi-wavelength light is incident from the inlet while the diffraction grating is positioned at a rotation angle position calculated from the arithmetic formula with each of three or more wavelengths within the wavelength range of the multi-wavelength light including the light of the first wavelength and the light of the second wavelength being the target wavelength.

The size of the cross section at the exit of the first-order diffracted light traveling from the diffraction grating to the exit refers to the area of the cross section, the length of a specific portion of the cross section (diameter, perimeter length), etc. The closer the imaging position of the first-order diffracted light is to the exit, the smaller the size of the cross section becomes. Compared to first-order diffracted light with a large cross section, first-order diffracted light with a small cross section may not be able to pass through the exit even if the deviation between the optical axis and the center of the exit is small, so the position of the optical axis must be precisely adjusted. In the spectrometer described in paragraphs 2 and 3, the optical axis is adjusted using first-order diffracted light of a wavelength that reduces the cross section at the exit, so that even if an optical fiber is connected to the exit, a sufficient amount of first-order diffracted light at various wavelengths can be reliably extracted from the optical fiber.

1... Housing 11... Inlet 12... Outlet 13a... Inlet slit 14a... Exit slit 2... Diffraction grating 5... Rotation drive mechanism 7... Control unit 74... Coefficient storage unit 75... Arithmetic expression storage unit 8... Input unit 100... Spectrometer

Claims (3)

a housing having an inlet and an outlet;
a wavelength dispersion element disposed within the housing, which disperses the wavelength of light incident from the inlet and outputs light of a target wavelength from the outlet;
a rotation drive mechanism that rotates the wavelength dispersion element;
a storage unit that stores an arithmetic expression for calculating a rotation angle position of the wavelength dispersion element corresponding to the target wavelength;
a control unit that causes the rotary drive mechanism to rotate the wavelength dispersion element so that the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic expression,
a first wavelength being the target wavelength, the wavelength dispersion element and the rotation drive mechanism are set within the housing such that, when the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a first wavelength as the target wavelength, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through a predetermined range in the center of the outlet, and, when the wavelength dispersion element is located at a rotation angle position calculated from the arithmetic formula using a second wavelength different from the first wavelength as the target wavelength, the optical axis of the light proceeding from the wavelength dispersion element to the outlet passes through the predetermined range of the outlet, when light including light of the second wavelength is incident from the entrance. 2. The spectrometer of claim 1,
the wavelength dispersion element is a diffraction grating,
a spectrometer in which the first wavelength is a wavelength at which a cross-sectional area at an outlet of first-order diffracted light proceeding from the diffraction grating to the outlet is minimum when the multi-wavelength light is incident from the inlet with the diffraction grating positioned at a rotation angle position calculated from the equation using each of a plurality of wavelengths within a wavelength range of multi-wavelength light including light of the first wavelength as a target wavelength. 2. The spectrometer of claim 1,
the wavelength dispersion element is a diffraction grating,
a spectrometer in which the first wavelength and the second wavelength are wavelengths at which the cross-sectional areas at the outlet of first-order diffracted light proceeding from the diffraction grating to the outlet are first and second smallest when the multi-wavelength light is incident from the inlet, with the diffraction grating positioned at a rotation angle position calculated from the arithmetic formula using each of three or more wavelengths within a wavelength range of multi-wavelength light including the first wavelength and the second wavelength as target wavelengths.

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