JP5055612B2 - Prism and spectroscope - Google Patents

Description

  The present invention relates to a prism and a spectroscope.

  As is well known, the declination prism is used as a wavelength dispersion element or an anamorphic prism for laser beam shaping. Since the refractive index of a transparent medium such as glass used for the declination prism is usually a function of temperature, the light beam declination by the declination prism changes according to the temperature change. For this reason, it has been avoided so far to use the declination prism in an environment where temperature changes occur.

However, since an anamorphic prism for laser beam shaping inevitably absorbs a part of the laser beam and changes in temperature, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-124531, It has been proposed to combine declination prisms made of two types of materials such as fluorite and minimize the change in the declination of the light beam due to temperature changes by utilizing the difference in refractive index temperature coefficient of each medium.
Japanese Patent Application Laid-Open No. 2000-124531

  However, in the conventional (anamorphic) prism as described above, since the material of the prism is limited to quartz glass and fluorite, the application is limited and generality is lacking.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a temperature-independent (athermal) prism applicable to general applications. Moreover, it aims at providing the spectrometer provided with such a prism.

In order to achieve such an object, the prism according to the present invention is a prism for wavelength-dispersing light, and is provided with a first transmission surface capable of transmitting light and an inclination with respect to the first transmission surface. A first deflection prism having a second transmission surface capable of transmitting light, a third transmission surface capable of transmitting light, and a fourth transmission surface provided to be inclined with respect to the third transmission surface and capable of transmitting light A second declination prism having a refractive index different from that of the first declination prism, a fifth transmission surface through which light can be transmitted, and a light provided so as to be inclined with respect to the fifth transmission surface. The first transmissive prism has a transmissive sixth transmission surface, has the same refractive index as that of the first deflection prism, and an apex angle formed between the fifth transmission surface and the sixth transmission surface is the first deflection prism first. A third declination prism having the same angle as the apex angle formed by the transmission surface and the second transmission surface; The first declination prism is joined to the second declination prism in contact with the third transmission surface, and the third declination prism is in the first declination state while the fifth transmission surface is in contact with the fourth transmission surface. The first transmissive surface, the second transmissive surface, the third transmissive surface, the fourth transmissive surface, the fifth transmissive surface, and the sixth transmissive surface are in a predetermined same plane. It is configured to be perpendicular to each other.

Then, the refractive index of the first declination prism and the third declination prism in the light having a predetermined reference wavelength is n ₁ , the refraction index of the second declination prism in the light having the reference wavelength is n ₂ , Let T be the temperature around the prism, and ε ₁ be the angle between the incident light incident on the first transmission surface of the first declination prism from the outside and the light refracted through the first transmission surface from the outside. Is defined as τ ₁ , the angle formed between the incident light and the normal lines in the second transmission surface and the third transmission surface is τ ₂ , and the angles ε _1, τ ₁ , and τ ₂ is measured with the incident light as a starting point, and the sign is positive when counterclockwise is positive. Τ ₁ = tan ⁻¹ {(n ₁ sinε ₁ ) / (n ₁ cosε ₁ −1)}
τ ₂ = tan ⁻¹ {(n ₁ sinε ₁ ) / (n ₁ cosε ₁ −n ₂ )}
However,
ε ₁ = cos ⁻¹ {n ₁ − (n ₂ −1) (∂n ₁ / ∂T) / (∂n ₂ / ∂T)}
Where the incident light beam and the reference optical axis of the prism are set in parallel, and the angle formed by the reference light axis and the light beam refracted through the first transmission surface from the outside is ε ₁ , and the reference optical axis When the angle formed by the normal line of the first transmitting surface and tau _1, the angle between the normal at the reference light axis and the second transmitting surface and the third transmission surface on the basis of the parameters and tau _2, the above formula Is required.

  Furthermore, the spectrometer according to the present invention is a spectrometer provided with a wavelength dispersion element that wavelength-disperses incident light, and a dispersion prism that corrects nonlinearity of the emission angle with respect to the wavelength of the emission light emitted from the wavelength dispersion element. The dispersion prism is composed of the prism according to the present invention.

  According to the present invention, it is possible to apply a declination prism or a dispersion prism to a region where the temperature change is severe and the application of the declination prism or the dispersion prism is difficult.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. An athermal prism 1 of the first embodiment is shown in FIG. Here, the athermal prism is a declination prism in which the declination of light having a reference wavelength does not change due to a change in environmental temperature. The athermal prism 1 includes a first deflection prism 2 and a second deflection prism 3 joined to the first deflection prism 2.

  The first declination prism 2 is formed in a triangular prism shape using a transparent material such as glass or plastic, and has a first transmission surface 21 through which light can be transmitted and a first transmission surface 21 with respect to the first transmission surface 21. A second transmission surface 22 that is inclined and transmits light is formed. Similar to the first deflection prism 2, the second deflection prism 3 is formed in a triangular prism shape using a transparent material such as glass or plastic, and has a third transmission surface 31 through which light can be transmitted. And a fourth transmission surface 32 that is inclined with respect to the third transmission surface 31 and can transmit light. However, the second deflection prism 3 has a refractive index different from that of the first deflection prism 2.

  The first deflection prism 2 and the second deflection prism 3 are joined in a state where the second transmission surface 22 and the third transmission surface 31 are in contact with each other, and the first transmission surface 21 and the second transmission surface 22 are joined. The third transmission surface 31 and the fourth transmission surface 32 are respectively perpendicular to a predetermined same plane (the surface in which each drawing is described in FIG. 1). In addition, light rays incident on the first transmission surface 21 of the first deflection prism 2 from the outside pass through the first transmission surface 21 and travel through the first deflection prism 2, and then the second transmission surface 22 and the first transmission surface 21. The light passes through the third transmission surface 31, travels through the second declination prism 3, and exits from the fourth transmission surface 32.

  Here, the angle of the light beam transmitted through the first and second declination prisms 2 and 3 will be considered. First, from Snell's law, the following formulas (1) to (3) hold.

Here, the refractive index of the external space on the first deflection prism 2 side in the light having a predetermined reference wavelength is n ₀ , the refractive index of the first deflection prism 2 in the light having the reference wavelength is n ₁ , and the reference The refractive index of the second declination prism 3 in the light having the wavelength is n _2, and the refraction index of the external space on the second declination prism 3 side in the light having the reference wavelength is n ₃ . Further, the angle formed with a predetermined reference optical axis AX1 as shown in the incident light beam L1 and Figure 1 incident from the outside to the first argument first transmitting surface 21 of the prism 2 and epsilon _0, a first transmitting surface 21 from the outside the angle at which the transmitted light L2 is refracted by and the reference optical axis AX1 forms and epsilon _1, light L3 and the reference being refracted from the first deviation prism within 2 passes through the second transmitting surface 22 and the third transmission surface 31 The angle formed by the optical axis AX1 is ε _2, and the angle formed by the light beam L4 refracted through the fourth transmission surface 32 from the second declination prism 3 and the reference optical axis AX1 is ε ₃ .

Further, the angle between the normal line V1 and the reference optical axis AX1 of the first transmitting surface 21 and tau _1, the angle between the normal line V2 and the reference optical axis AX1 in the second transmitting surface 22 and the third transmission surface 31 and tau _2, the angle between the normal line V3 and the reference optical axis AX1 of the fourth transmissive surface 32 and tau _3. The angle is measured starting from the reference optical axis AX1, and the sign is positive in the counterclockwise direction.

  Here, Expressions (1) to (3) are respectively modified to derive Expressions (4) to (6).

  Next, when the equations (1) to (3) are partially differentiated by the temperature T, the equations (7) to (9) are obtained. The temperature T is the temperature around the athermal prism 1 and the prism (environment).

  Here, in order to simplify the discussion, the incident light beam L1 is set parallel to the reference optical axis AX1, and is represented by Expression (10).

ε ₀ = 0 (10)

  Further, as a practical application range, the space around the prism is limited to the atmosphere or vacuum. In this embodiment, it is assumed that the space around the prism is filled with air, and the transparent medium (of the prism) employs a relative refractive index. In other words, it is assumed that Equation (11) and Equation (12) hold regardless of temperature.

n ₀ = 1 (11)

n ₃ = 1 (12)

Now, assuming that the partial differential coefficient with respect to the temperature T at the angle ε ₃ is 0 in the light having the reference wavelength, it can be expressed as in Expression (13).

  And Formula (14) is obtained from Formula (7)-Formula (13).

Further, when equation (14) is solved for τ ₃ , equation (15) is obtained.

  However, C is represented by Formula (16).

As described above, since the incident light beam L1 is parallel to the reference optical axis AX1, the light beam refracted through the first transmission surface 21 from the outside by matching the incident light beam L1 and the reference optical axis AX1. the angle between L2 and incident light L1 and epsilon _1, the angle between light ray L3 refracted from the first deviation prism within 2 passes through the second transmitting surface 22 and the third transmissive surface 31 and the incident light beam L1 is and epsilon _2, the angle formed from the second deviation prism within 3 and the fourth transmission surface 32 ray and incident light L1 is refracted after passing through the can be epsilon _3.

Further, the angle formed between the normal line V1 on the first transmission surface 21 and the incident light beam L1 is τ _1, and the angle formed between the normal line V2 on the second transmission surface 22 and the third transmission surface 31 and the incident light beam L1 is τ _2. And the angle formed by the normal line V3 and the incident light ray L1 on the fourth transmission surface 32 can be τ ₃ . At this time, the angle is measured with the incident light beam L1 as a starting point, and the sign of course is positive when it is counterclockwise.

A method for obtaining the solution of the athermal prism 1 in the athermal prism 1 having such a configuration will be described below. First, the material (transparent medium) of the first deflection angle prism 2 and the second deflection angle prism 3 is selected. At this time, if the materials of the first and second deflection prisms 2 and 3 are determined, n ₁ and n ₂ are determined.

Next, τ ₁ and τ ₂ are appropriately determined.

Subsequently, the previously determined n ₁ and n ₂ , τ ₁ and τ ₂ , and the expressions (10) and (11) are substituted into the expressions (4) and (5), and ε ₁ and ε ₂ Is calculated.

Next, the calculated ε ₁ and ε ₂ (and τ ₁ , τ ₂ ) are substituted into Equation (15) to calculate τ ₃ . Note that ∂n ₁ / ∂T and ∂n ₂ / ∂T are refractive index temperature coefficients and are determined by the materials of the first and second declination prisms 2 and 3.

Then, the calculated τ ₃ (and ε ₂ , n ₂ , n ₃ = 1) is substituted into Equation (6) to calculate ε ₃ .

In this way, the deflection angles ε _{1 to} ε ₃ and the angles τ _{1 to} τ ₃ are obtained as solutions of the athermal prism 1. For light rays having a wavelength other than the reference wavelength, declination angles ε ₁ to ε ₃ can be obtained by substituting the refractive index of the wavelength into equations (4) to (6).

  Here, as a first design example of the athermal prism 1 in the present embodiment, design parameters and evaluation results are shown in FIG.

The design reference wavelength is e-line (wavelength 546.074 nm). Further, there are five evaluation wavelengths: C line (wavelength 656.273 nm), d line (wavelength 587.562 nm), e line, F line (wavelength 486.133 nm), and g line (wavelength 435.834 nm). Moreover, the value published in the glass catalog of OHARA INC. Was used for the refractive index and the refractive index temperature coefficient. For the refractive index temperature coefficients of the C-line, d-line and F-line, the values of C′-line (wavelength 643.847 nm), D-line (wavelength 589.294 nm) and F′-line (wavelength 479.991 nm) were substituted. In FIG. 2, Δε is the amount of change in ε ₃ due to temperature change, and S-BAL14 and S-TIH4 are trade names of glass.

On the other hand, the temperature change (Δε ₂ ) of the declination angle in the conventional (non-athermal) prism is shown in FIG. As can be seen from FIG. 2 and FIG. 5, the amount of change in the declination (Δε = −7.6 × 10 ⁻¹² degrees) due to the temperature change in the first design example on the e-line as the reference wavelength is the conventional prism. Compared to the case (Δε ₂ = −7 × 10 ⁻⁵ degrees in S-TIH23), it is very small.

FIG. 3 shows design parameters and evaluation results as a second design example of the athermal prism 1 according to the present embodiment. In FIG. 3, S-BSL7 and S-TIH53 are trade names of glass, and the others are the same as in the first design example. Then, in the e-line, the amount of change in the declination (Δε = −2.2 × 10 ⁻¹² degrees) due to the temperature change in the second design example is the same as that of the first design example. Compared to the case (Δε ₂ = −7 × 10 ⁻⁵ degrees in S-TIH23), it is very small.

Furthermore, as a third design example of the athermal prism 1 in the present embodiment, design parameters and evaluation results are shown in FIG. In FIG. 4, S-BAM 12 and S-PHM 52 are product names of glass, and the others are the same as in the first design example. Then, in the e-line, the amount of change in the declination due to the temperature change in the third design example (Δε = −1.8 × 10 ⁻¹⁰ degrees) is the same as that in the first design example. Compared to the case (Δε ₂ = −7 × 10 ⁻⁵ degrees in S-TIH23), it is very small.

  As a result, according to the athermal prism 1 of the first embodiment, it is possible to minimize the variation of the declination due to the temperature change in the declination prism or the wavelength dispersion prism. Therefore, for example, in the optical communication field, it is possible to apply the declination prism or the dispersion prism to an area where the application of the declination prism or the dispersion prism is difficult.

  Next, a second embodiment of the athermal prism will be described with reference to FIG. The athermal prism 51 of the second embodiment is a so-called Amici-type direct-viewing spectroscopic prism in which the apex angle of each declination prism is determined so that no declination occurs with respect to a light beam having a reference wavelength. The second deflection prism 53 joined to the first deflection prism 52 and the third deflection prism 54 joined to the second deflection prism 53 symmetrically with the first deflection prism 52.

  The first declination prism 52 is formed in a triangular prism shape using a transparent material such as glass or plastic, and has a first transmission surface 71 through which light can be transmitted and a first transmission surface 71 with respect to the first transmission surface 71. A second transmission surface 72 that is inclined and capable of transmitting light is formed. Similar to the first deflection prism 52, the second deflection prism 53 is formed in a triangular prism shape using a transparent material such as glass or plastic, and has a third transmission surface 81 through which light can be transmitted. And a fourth transmission surface 82 that is inclined with respect to the third transmission surface 81 and is capable of transmitting light. However, the second deflection prism 53 has a refractive index different from that of the first deflection prism 52.

  The third declination prism 54 is formed in a triangular prism shape using the same transparent material as glass or plastic as the first declination prism 52, and on its side surface, a fifth transmission surface 91 capable of transmitting light, A sixth transmission surface 92 that is inclined with respect to the fifth transmission surface 91 and can transmit light is formed. The third deflection prism 54 has the same refractive index as that of the first deflection prism 52 and is formed in the inverted shape of the first deflection prism 52. The apex angle γ formed by the transmission surface 92 is the same as the apex angle α formed by the first transmission surface 71 and the second transmission surface 72 of the first declination prism 52.

  The first deflection prism 52 is joined to the second deflection prism 53 while the second transmission surface 72 is in contact with the third transmission surface 81, and the fifth transmission surface 91 is in contact with the fourth transmission surface 82. In this state, the third deflection prism 54 is joined to the second deflection prism 53 symmetrically with the first deflection prism 52, and the first transmission surface 71, the second transmission surface 72, the third transmission surface 81, and the fourth. The transmission surface 82, the fifth transmission surface 91, and the sixth transmission surface 92 are respectively perpendicular to a predetermined same plane (the surface in which each drawing is described in FIG. 6). Further, a light beam having a predetermined reference wavelength incident on the first transmission surface 71 of the first deflection prism 52 from the outside is transmitted through the first transmission surface 71, and the first deflection prism 52 and the second deflection prism 53. , And the third declination prism 54 in order, and then exit from the sixth transmission surface 92 in a direction parallel to the incident light beam.

  Here, the angle of the light beam transmitted through the first to third declination prisms 52, 53, and 54 will be considered. As shown in FIG. 6, the athermal prism 51 of the second embodiment has a bilaterally symmetric shape, and when the athermal prism 51 is divided along a symmetric reference plane S formed at the center of the athermal prism 51. As shown in FIG. 7, two sets of athermal prisms 61 and 66 are formed.

  The athermal prism 61 in the first half (left side in FIG. 7) is particularly configured so that the fourth transmission surface 32 ′ of the second declination prism 3 ′ is perpendicular to the reference optical axis AX1 ′. It can be seen as a form of athermal prism. The athermal prism 66 in the latter half (right side in FIG. 7) can be regarded as an athermal prism formed symmetrically with respect to the asymmetric prism 61 in the first half with respect to the symmetrical reference plane S.

First, paying attention to the athermal prism 61 in the first half, and assuming that the angle formed between the normal line V3 ′ and the reference optical axis AX1 ′ at the fourth transmission surface 32 ′ is τ ₃ ′, the fourth transmission surface 32 ′, that is, the symmetry reference. Equation (17) is established from the condition that the surface S is perpendicular to the reference optical axis AX1 ′ (parallel to the incident light beam).

τ ₃ ′ = 0 (17)

Further, since the light beam having the reference wavelength passes perpendicularly through the symmetrical reference surface S (that is, the fourth transmission surface 32 '), it is refracted through the fourth transmission surface 32' from the second declination prism 3 '. When the angle formed between the light beam L4 ′ and the reference optical axis AX1 ′ is ε ₃ ′, it is required that the equation (18) is satisfied.

ε ₃ ′ = 0 (18)

At the same time, it is self-evident that the angle formed by the light beam L3 ′ refracted through the second transmission surface 22 ′ and the third transmission surface 31 ′ from the first deflection prism 2 ′ and the reference optical axis AX1 ′ is ε _2. If it is set as ′, it is required that it is a formula (19).

ε ₂ ′ = 0 (19)

By substituting Equation (10) and Equation (11), which are the initial premise in the first embodiment, into Equation (1) and solving for τ ₁ , Equation (20) is obtained.

Next, τ ₃ ′ = τ ₃ , ε ₃ ′ = ε ₃ , ε ₂ ′ = ε _2, and Expression (17), Expression (18), and Expression (19) are substituted into Expression (2) and τ ₂ Is solved to obtain equation (21).

  Next, when Expression (19) is substituted into Expression (15), Expression (22) is obtained.

  Subsequently, when Expression (16) is substituted into Expression (22), Expression (23) is obtained.

Here, when equation (23) is solved for τ ₂ , equation (24) is obtained.

Then, substituting Equation (20) and Equation (21) into Equation (24) and solving for ε ₁ yields Equation (25).

Here, as shown in FIG. 6 and FIG. 7, from the correspondence relationship between the athermal prism 51 of the second embodiment and the two sets of divided athermal prisms 61 and 66, in the equations (20) to (25), a predetermined The refractive index of the first declination prism 52 and the third declination prism 54 in the light having the reference wavelength is n _1, and the refraction index of the second declination prism 53 in the light having the reference wavelength is n _2. it can. Further, the angle formed with a predetermined reference optical axis AX2 shown in incident light L5 and 6 incident from the outside to the first transmitting surface 71 of the first deviation prism 52 and epsilon _0, a first transmitting surface 71 from the outside the angle at which transmitted light L6 is refracted by and the reference optical axis AX2 forms and epsilon _1, light L7 and reference being refracted from the first deviation prism within 52 transmitted through the second transmitting surface 72 and the third transmission surface 81 The angle formed by the optical axis AX2 can be ε ₂ .

Further, the angle between the normal line V4 and the reference optical axis AX2 in the first transmitting surface 71 and tau _1, the angle between the normal line V5 and the reference optical axis AX2 of the second transmitting surface 72 and the third transmission surface 81 τ ₂ can be used. At this time, the angle is measured starting from the reference optical axis AX2, and the sign is positive in the counterclockwise direction. Also, in order to simplify the discussion as in the case of the first embodiment, the incident light beam L5 is set parallel to the reference optical axis AX2, and ε ₀ = 0. As described above, ε ₂ = 0. Thus, the angle between light ray L6 is refracted after passing through the first transmitting surface 71 from the outside and incident light L5 is set to epsilon _1, the angle between the normal line V4 and the incident ray L5 in the first transmitting surface 71 is τ ₁ and the angle formed by the normal line V5 and the incident light beam L5 on the second transmission surface 72 and the third transmission surface 81 can be τ ₂ .

Further, because of the symmetry of the athermal prism 51, the angle formed between the normal line V6 and the reference optical axis AX2 (that is, the incident light beam L5) on the fourth transmission surface 82 and the fifth transmission surface 91 is τ _3, and the sixth transmission surface Assuming that the angle between the normal V7 at 92 and the reference optical axis AX2 (that is, the incident light beam L5) is τ ₄ , τ ₃ = −τ ₂ and τ ₄ = −τ ₁ . Similarly, the angle formed between the light L8 refracted through the fourth transmission surface 82 and the fifth transmission surface 91 from the second deflection angle prism 53 and the reference optical axis AX2 (that is, the incident light L5) is ε _3. Suppose that ε ₄ is an angle formed by the light beam L9 transmitted through the sixth transmission surface 92 and refracted from the third deflection prism 54 and the reference optical axis AX2 (that is, the incident light beam L5), ε ₃ = −ε ₁ and ε ₄ = 0.

A method for obtaining the solution of the athermal prism 51 in the athermal prism 51 having such a configuration will be described below. First, two appropriate materials (transparent medium) for the first deflection prism 52 (third deflection prism 54) and the second deflection prism 53 are selected. At this time, if the materials of the first to third declination prisms 52, 53, and 54 are determined, n ₁ and n ₂ , and 1n ₁ / ∂T and ∂n ₂ / ∂T are determined.

Next, n ₁ and n ₂ , ∂n ₁ / ∂T and ∂n ₂ / ∂T determined previously are substituted into equation (25), and ε ₁ is calculated.

Next, the calculated ε ₁ (and n ₁ ) is substituted into the equation (20) to obtain τ ₁ .

Also, the calculated ε ₁ (and n ₁ and n ₂ ) is substituted into equation (21) to obtain τ ₂ .

Note that τ ₃ is calculated as τ ₃ = −τ ₂ , and τ ₄ is calculated as τ ₄ = −τ ₁ . In this way, the angles τ _{1 to} τ ₄ are obtained as solutions of the athermal prism 51.

Here, as a first design example of the amic type athermal prism 51 in the present embodiment, design parameters and evaluation results are shown in FIG. The design reference wavelength and the like are the same as in the first embodiment. In FIG. 8, Δε is the amount of change in ε ₄ due to temperature change, and S-BSL7 and S-BSM14 are trade names of glass. In the e-line, the amount of change in the declination (Δε = −9.81 × 10 ⁻¹¹ degrees) due to the temperature change in the first design example is the case of the conventional prism (Δε ₂ = −7 in S-TIH23). × 10 ⁻⁵ degrees), which is very small.

FIG. 9 shows design parameters and evaluation results as a second design example of the amic type athermal prism 51 in the present embodiment. In FIG. 9, S-BSL7 and S-BSM12 are trade names of glass, and the others are the same as in the first design example. Then, in the e-line, the amount of change in the deflection angle due to the temperature change in the second design example (Δε = −9.81 × 10 ⁻¹¹ degrees) is the same as that in the first design example. Compared to the case (Δε ₂ = −7 × 10 ⁻⁵ degrees in S-TIH23), it is very small.

Furthermore, as a third design example of the amic type athermal prism 51 in the present embodiment, its design parameters and evaluation results are shown in FIG. In FIG. 10, S-TIL6 and S-TIM22 are trade names of glass, and the others are the same as in the first design example. Then, in the e-line, the amount of change in the declination due to the temperature change in the third design example (Δε = −8.56 × 10 ⁻¹¹ degrees) is the same as that in the first design example. Compared to the case (Δε ₂ = −7 × 10 ⁻⁵ degrees in S-TIH23), it is very small.

  As a result, according to the athermal prism 51 of the second embodiment, similarly to the athermal prism 1 of the first embodiment, the fluctuation of the declination due to the temperature change in the declination prism or the wavelength dispersion prism can be minimized. . Therefore, for example, in the optical communication field, it is possible to apply the declination prism or the dispersion prism to an area where the application of the declination prism or the dispersion prism is difficult.

  Next, a spectroscope equipped with the athermal prism as described above will be described with reference to FIG. As shown in FIG. 11, the spectroscope 100 includes a grating 105 for wavelength-dispersing incident light incident from the entrance slit 101, and an athermal prism 1 disposed between the entrance slit 101 and the grating 105. It is configured. The athermal prism 1 is the athermal prism 1 of the first embodiment described above.

  Incident light that has entered the spectroscope 100 from the entrance slit 101 enters the athermal prism 1 as parallel light by the first collimating optical system 102. The incident light incident on the athermal prism 1 is wavelength-dispersed when passing through the athermal prism 1, and an intermediate image y2 of the entrance slit 101 is obtained from the outgoing light emitted from the athermal prism 1 using the first relay optical system 103. It is done. Next, the incident light becomes parallel light again by the second collimating optical system 104 and enters the grating 105. The incident light incident on the grating 105 is wavelength-dispersed when reflected by the grating 105, and a spectrum image y1 conjugate with the intermediate image y2 is obtained from the emitted light emitted from the grating 105 using the second relay optical system 106. The spectrum image y1 is detected by a light receiving means (not shown) such as an optical fiber.

  By the way, in the chromatic dispersion by the grating 105, there is nonlinearity of the emission angle with respect to the wavelength in the outgoing light emitted from the grating 105. That is, when the relationship between the wavelength and the position of the spectrum image is plotted, it becomes a curve instead of a straight line. Note that, also in the wavelength dispersion by the dispersion prism, there is nonlinearity of the emission angle with respect to the wavelength of the emitted light emitted from the dispersion prism.

  Depending on the use of the spectroscope, there are cases where it is desired to form spectrum images y1 of wavelength lights that are separated at equal intervals. For example, a duplexer in optical communication. Therefore, the spectroscope 100 of the present embodiment has a configuration in which the nonlinearity in the chromatic dispersion at the dispersion prism is added to the nonlinearity in the chromatic dispersion at the grating 105 to cancel each other's nonlinearity. The athermal prism 1 of the first embodiment is used as a dispersion prism for correcting the nonlinearity of the emission angle with respect to the wavelength of the emitted light.

As a design example of the athermal prism 1 used in such a spectroscope 100, its design parameters and evaluation results are shown in FIG. Note that the temperature change of the image position obtained by the wavelength dispersion of the grating 105 is extremely small as compared with the dispersion prism, and is therefore ignored in this embodiment. In FIG. 12, the description of ε ₁ and ε ₂ is omitted.

  In FIG. 12, the deviation from the linear represents a deviation from the ideal linear position, that is, non-linearity. Specifically, the relationship between the wavelength and the image position y4 is plotted on the xy coordinates to obtain a best-fit straight line, and then obtained from the value of y4 shown in FIG. 12 from the best-fit straight line corresponding to the wavelength. The value of the completely linear image position y is subtracted.

As can be seen from FIG. 12, the deviation from the linearity is greater in the case without the prism than in the case with the prism. Further, as can be seen from FIG. 12, when a single prism (material S-TIH4) is used, the deviation from linearity is smaller than in the case without a prism. As can be seen from FIG. 12, the amount of image movement due to temperature change when the athermal prism 1 is used (0 mm for e line) is the amount of image movement due to temperature change when a single prism is used (−3 for e line). × 10 ⁻⁵ mm).

  As a result, according to the spectroscope 100 having the above-described configuration, it is possible to reduce the amount of image movement due to a temperature change using the athermal prism 1. It becomes possible to use a dispersion prism for correcting the characteristics.

  In the spectroscope 100 described above, not only the athermal prism 1 of the first embodiment, but also the amic type athermal prism 51 of the second embodiment may be used as a dispersion prism.

It is a schematic diagram of the athermal prism which is 1st Embodiment of the prism which concerns on this invention. It is a table | surface which shows the 1st design example of the athermal prism in 1st Embodiment. It is a table | surface which shows the 2nd design example of the athermal prism in 1st Embodiment. It is a table | surface which shows the 3rd design example of the athermal prism in 1st Embodiment. It is a table | surface which shows the temperature change of the deflection angle in the conventional prism. It is a schematic diagram of the athermal prism of 2nd Embodiment. It is a schematic diagram which shows the state which divided | segmented the athermal prism of 2nd Embodiment into two sets of athermal prisms. It is a table | surface which shows the 1st design example of the athermal prism in 2nd Embodiment. It is a table | surface which shows the 2nd design example of the athermal prism in 2nd Embodiment. It is a table | surface which shows the 3rd design example of the athermal prism in 2nd Embodiment. It is a schematic diagram of the spectrometer which concerns on this invention. It is a table | surface which shows the example of a design of the athermal prism comprised in the spectrometer which concerns on this invention.

Explanation of symbols

1 Athermal prism (first embodiment of prism)
2 First Deviation Prism 3 Second Deviation Prism 21 First Transmission Surface 22 Second Transmission Surface 31 Third Transmission Surface 32 Fourth Transmission Surface 51 Athermal Prism (Second Embodiment of Prism)
52 First Deviation Prism 53 Second Deviation Prism 54 Third Deviation Prism 71 First Transmission Surface 72 Second Transmission Surface 81 Third Transmission Surface 82 Fourth Transmission Surface 91 Fifth Transmission Surface 92 Sixth Transmission Surface 100 Spectroscopy 105 grating (wavelength dispersion element)

Claims (2)

A first transmissive prism capable of transmitting light, and a first declination prism having a second transmissive surface that is inclined with respect to the first transmissive surface and capable of transmitting light;
A refractive index different from the refractive index of the first declination prism, having a third transmission surface capable of transmitting light and a fourth transmission surface provided to be inclined with respect to the third transmission surface and capable of transmitting light. A second declination prism having
A fifth transmission surface capable of transmitting light, and a sixth transmission surface which is inclined with respect to the fifth transmission surface and capable of transmitting light, and has the same refractive index as that of the first deflection prism. And the apex angle formed by the fifth transmission surface and the sixth transmission surface is the same as the apex angle formed by the first transmission surface and the second transmission surface of the first declination prism. 3 declination prisms,
The first deflection prism is joined to the second deflection prism in a state where the second transmission surface is in contact with the third transmission surface, and the fifth transmission surface is in contact with the fourth transmission surface. The third deflection prism is joined to the second deflection prism symmetrically with the first deflection prism, and the first transmission surface, the second transmission surface, the third transmission surface, and the fourth transmission surface. A prism for wavelength-dispersing light, wherein the surface, the fifth transmission surface, and the sixth transmission surface are each perpendicular to a predetermined same plane,
The refractive index of the first declination prism and the third declination prism in the light having a predetermined reference wavelength is n _1, and the refraction index of the second declination prism in the light having the reference wavelength is n ₂ , Let T be the temperature of the prism and the surroundings of the prism, and the angle formed between the incident light beam incident on the first transmission surface of the first deflection prism and the light beam refracted through the first transmission surface from the outside. ε ₁ , the angle between the incident light beam and the normal line on the first transmission surface is τ _1, and the angle between the incident light beam and the normal line on the second transmission surface and the third transmission surface is τ _2. and then, further angle epsilon ₁ and tau ₁ and tau ₂ scales the incident light beam as a starting point, the code is a counterclockwise direction is positive, the following equation ^{_{τ 1 = tan -1 {(n}} 1 sinε 1) / (n 1 cosε ₁ −1)}
τ ₂ = tan ⁻¹ {(n ₁ sinε ₁ ) / (n ₁ cosε ₁ −n ₂ )}
However,
ε ₁ = cos ⁻¹ {n ₁ − (n ₂ −1) (∂n ₁ / ∂T) / (∂n ₂ / ∂T)}
Satisfy each of the
The incident light beam and the reference optical axis of the prism are set in parallel,
The angle formed by the reference optical axis and the light beam refracted through the first transmission surface from the outside is defined as ε _1, and the angle formed by the reference optical axis and the normal line on the first transmission surface is defined as τ. _The prism is characterized in that each of the above equations is obtained based on a parameter where τ ₂ is an angle between the reference optical axis and the normal line of the second transmission surface and the third transmission surface . A wavelength dispersion element for wavelength-dispersing incident light;
In a spectroscope including a dispersion prism that corrects nonlinearity of an emission angle with respect to a wavelength in outgoing light emitted from the wavelength dispersion element,
A spectrometer comprising the prism according to claim 1.

Images