JP2005292033A - Liquid absolute refractive index measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absolute refractive index measuring device capable of accurately measuring an absolute refractive index of a liquid for an arbitrary wavelength.
A laser beam emitted from a laser light source 1 that selectively emits a plurality of laser beams having different wavelengths from the same emission port is divided into two-beam laser beams L1 and L2 by a beam splitter 3. The reference laser beams L1A and L2A incident on the polarization interference optical circuit 4 and further divided from the laser beams L1 and L2, and the laser beams L1B and L2B after passing through both the vacuum region 63 and the sample region 64 Interference light is generated respectively. The counter 21 counts the wave number of the intensity change of each interference light detected by the optical sensor 8 when the optical path lengths of the vacuum region and the sample region are changed.
The polarization interference optical circuit 4 uses the same polarization optical element for all wavelengths of laser light emitted from the laser light source 1.
[Selection] Figure 1

Description

  The present invention relates to a liquid absolute refractive index measuring apparatus, and more particularly, to an absolute refractive index measuring apparatus using Michelson polarization interferometry.

  One apparatus for measuring minute displacements is an interferometer using Michelson interferometry. This Michelson interferometer splits one laser beam into two beams using a beam splitter, etc., introduces one laser beam as a reference laser beam into a fixed-length optical path, and the other laser beam into a variable-length optical path. Introduce. Then, both the laser beams that have passed through the respective optical paths are combined to generate interference light, and the intensity of the interference light varies according to the change in the phase of the laser light accompanying the variation in the optical path length of the variable length optical path. The fluctuation amount of the optical path length is obtained by utilizing the fluctuation of the optical path. That is, when the fluctuation amount of the optical path length is equal to the wavelength of the laser light, the intensity of the interference light changes by one period during the fluctuation of the optical path length, and therefore the wave number (hereinafter referred to as the fringe number) of the intensity fluctuation of the interference light. And the product of the wavelength of the laser beam in the optical path is equal to the fluctuation amount of the optical path length.

  An apparatus for measuring the absolute refractive index of air using the Michelson interferometry has been proposed (see Non-Patent Document 1).

  The above-mentioned absolute refractive index measurement device for air has a configuration in which the optical path lengths of the vacuum region and the air region composed of variable-length vacuum cells can be varied simultaneously and by the same amount, and each laser beam is further divided into two light beams. Four light beams are used, and two of these light beams are used for measuring the optical path length variation amount in the vacuum region, and the other two light beams are used for measuring the optical path length variation amount in the air region.

  By the way, the absolute refractive index of air is defined as (light velocity in vacuum) / (light velocity in air). As the nature of light, the frequency does not change even in vacuum or in air, so (absolute laser light wavelength in vacuum) / (wavelength of laser light in air) is the absolute refractive index of air. .

  Further, as described above, in the interferometer using the Michelson interferometry, the wavelength of the laser light in the air can be expressed by (variation in optical path length in the air region) / (number of fringes in the air region). The wavelength of the laser light in vacuum can be expressed by (variation in the optical path length in the vacuum region) / (number of fringes in the vacuum region).

  Therefore, when the variation amount of the optical path length in the air region and the vacuum region is the same, the absolute refractive index of air can be obtained from (the number of fringes in the air region) / (the number of fringes in the vacuum region).

  In the measuring apparatus described in Non-Patent Document 1, the same optical path length that has passed through the vacuum region (the optical distance is different because the optical distance is different) is used as the reference laser light that generates interference light corresponding to the fluctuation amount of the optical path length in the air region. )) Is used. For this reason, the absolute refractive index is obtained by a formula different from the above, but the measurement principle is the same.

The air absolute refractive index measuring apparatus is resistant to vibration and relatively easy to adjust optically. Therefore, Michelson polarization interferometry using a polarizing optical element in the optical system is used.
Ken-ichi Fujii and three others, “A New Refractometer by Combining a Variable Length Vacuum Cell and a Double-Pass Michelson Interferometer ”, IEEE Transactions ON Instrumentation And Measurement, Vol. 46, No. 2, April 1997, p. 191-195

  For example, in a refractometer or the like, a standard solution having a known absolute refractive index is used. There is a demand to accurately measure the absolute refractive index of a liquid, such as obtaining the absolute refractive index of such a standard solution.

  On the other hand, the wavelength of the light source for measuring the absolute refractive index of the object to be measured needs to be strictly defined because the refractive index has wavelength dependency. In the case of liquid, sodium D-line (wavelength 589.3 nm) is conventionally used as the wavelength of the light source for measuring the refractive index.

  For this reason, there is no laser light source near the wavelength of the sodium D line, even if the absolute refractive index measurement device for air using the Michelson polarization interferometry described above is applied to the absolute refractive index measurement of liquid. It is practically impossible to realize a device for measuring the absolute refractive index of a liquid to be measured at the wavelength of sodium D-line by using a device using a single wavelength light source such as a conventional absolute refractive index measuring device for air. It is.

  It is also conceivable that the absolute refractive index at a plurality of wavelengths of the liquid to be measured is obtained using laser light other than the sodium D line, and the absolute refractive index at the sodium D line is obtained by interpolation from these absolute refractive indices. .

  However, since a polarizing optical element such as a wave plate used in the optical system of the absolute refractive index measuring apparatus for air has a very large wavelength dependency, a dedicated polarizing optical element that matches the wavelength of the laser beam used as the light source is used. It is common sense to use and measure. For this reason, when measuring the absolute refractive index by applying the above configuration to a plurality of wavelengths, it is necessary to replace the polarizing optical element with an element suitable for the wavelength every time the wavelength is changed.

  As described above, when measuring the absolute refractive index by exchanging the polarizing optical element at each wavelength, the measurement takes time, and the measured values of the absolute refractive index measured by different optical systems have the same accuracy. It is also difficult to prove that Therefore, it is not preferable to obtain the above-mentioned absolute refractive index of the sodium D line by performing interpolation based on these measured values.

  From the viewpoint of using Michelson interferometry, it is possible to construct an absolute refractive index measurement device by adopting non-polarization interferometry that does not use a polarizing optical element in the optical system. An optical system composed only of elements is vulnerable to vibration during measurement, and it is difficult to remove an adjustment error of the optical system, so dissatisfaction with measurement accuracy remains.

  The present invention has been proposed based on the above-described conventional circumstances, and an object thereof is to provide an absolute refractive index measuring apparatus capable of accurately measuring the absolute refractive index of a liquid with respect to an arbitrary wavelength.

  The present invention employs the following means in order to achieve the above object. That is, the liquid absolute refractive index measurement apparatus using the Michelson polarization interferometry according to the present invention selectively emits a plurality of laser beams having different wavelengths from the same emission port, and emits from the laser light source. And a beam splitter that divides the laser beam to be divided into a vacuum side laser beam that passes through the vacuum region and a sample side laser beam that passes through the sample region filled with the liquid to be measured.

  Each laser beam divided by the beam splitter is incident on a polarization interference optical circuit, and after passing through both the regions, a reference laser beam further divided from each of the divided laser beams before passing through both the regions. Interference light with each laser beam is generated.

  And the wave number of the intensity change of each said interference light which an optical sensor detects when the optical path length of the said laser beam of the said vacuum area | region and sample area | region is changed with a counter is counted.

  The polarization interference optical circuit uses the same polarization optical element for all wavelengths of laser light emitted from the laser light source.

  According to the above configuration, it is possible to accurately measure the absolute refractive index of the liquid to be measured at each wavelength, and when changing the measurement wavelength, it is not necessary to replace the light source and the optical element, and to adjust the optical circuit, There is no need to take into account measurement errors associated with changing the wavelength of the light source.

  In addition, the calculation means is configured to derive a relational expression between the absolute refractive index of the measured liquid and the wavelength from the absolute refractive index of the measured liquid measured at each wavelength, so that the absolute refractive index at an arbitrary wavelength is obtained. It is also possible to obtain with high accuracy.

  According to the present invention, it is possible to accurately determine the absolute refractive index of the liquid to be measured at each wavelength emitted from the laser light source.

  Further, by deriving the wavelength dependence of the absolute refractive index of the liquid to be measured using the absolute refractive index values at the respective wavelengths, the absolute refractive index at an arbitrary wavelength of the liquid to be measured can be accurately obtained. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing an optical system provided in the absolute refractive index measuring apparatus of the present invention. FIG. 2 is a schematic diagram for explaining an optical path in the optical system shown in FIG.

  As shown in FIGS. 1 and 2, the absolute refractive index measuring apparatus 10 of the present invention includes a multi-wavelength laser light source 1 capable of emitting a plurality of laser beams having different wavelengths, and a laser emitted from the multi-wavelength laser light source 1. Both the non-polarizing beam splitter 3 that splits the light into two light beams and the split laser light are incident, each laser light is introduced into the vacuum region and the sample region to be measured, and the laser light that has passed through both regions An interference optical circuit 4 that generates interference light with a reference laser beam described later is provided.

  The multi-wavelength laser light source 1 has an excitation tube sealed with He gas and Ne gas, output side mirrors and total reflection mirrors arranged at both ends of the excitation tube, and includes the total reflection mirror and the excitation tube. By changing the optical distance, laser light having wavelengths of 543 nm, 594 nm, 604 nm, 612 nm, and 633 nm can be selectively emitted from the same emission port.

  The laser light emitted in the horizontal direction from the multi-wavelength laser light source 1 has a polarization angle of 45 degrees by the half-wave plate 2 so that the laser light can be divided by the polarization beam splitter 41 described later. After that, the light beam is incident on the cube-type non-polarizing beam splitter 3 and is split into two beams of laser light traveling straight in the non-polarizing beam splitter 3 and laser light traveling in the direction of 90 degrees horizontally with respect to the incident direction. Divided.

  In addition, a laser beam which is reflected by the non-polarizing beam splitter 3 in the direction of 90 degrees from the non-polarizing beam splitter 3 is moved away from the non-polarizing beam splitter 3 by a predetermined distance in the traveling direction of the linear laser beam. A mirror 5 that changes in the same direction as the light is provided. That is, the laser beam emitted from the multi-wavelength laser light source 1 is split into parallel laser beams traveling in the same direction by the non-polarizing beam splitter 3 and the mirror 5, and both laser beams are incident on the interference optical circuit 4. Is done. Hereinafter, the laser light whose traveling direction is changed by 90 degrees by the mirror 5 will be referred to as vacuum-side laser light L1, and the laser light whose traveling direction has been changed by 90 degrees by the non-polarizing beam splitter 3 will be described as sample-side laser light L2. Is described.

  The interference optical circuit 4 is disposed above the polarizing beam splitter 41, a cube-shaped polarizing beam splitter 41, a mirror 42 that changes the traveling direction of the laser light that has traveled straight through the polarizing beam splitter 41 vertically downward, and A corner cube 46 that folds laser light incident from below vertically downward at a point-symmetrical position with respect to a predetermined reference point. Further, ¼ wavelength plates 43, 44, and 45 that change the polarization angle by 90 degrees when the laser light passes twice are provided above and below the polarizing beam splitter 41 and below the mirror 42.

  As shown in FIG. 2, the vacuum laser beam L1 incident on the interference optical circuit 4 is reflected by the polarization beam splitter 41, for example, in the direction of 90 degrees with respect to the s-polarized (lateral) component traveling straight and the incident direction. Into p-polarized (vertical) components.

  The vacuum-side reference laser light L1A, which is a component of the vacuum-side laser light L1 that travels straight through the polarization beam splitter 41, is reflected vertically downward by the mirror 42, and is composed of a glass plate that forms the upper surface of the measuring unit 6 described in detail later. The fixed stage 61 is reached. Mirror processing is performed at a position on the fixed stage 61 where the vacuum side reference laser light L1A is incident, and the vacuum side reference laser light L1A is reflected vertically upward on the upper surface of the fixed stage 61. The vacuum-side reference laser beam L1A reflected vertically upward is incident on the polarization beam splitter 41 again via the mirror 42. At this time, the vacuum-side reference laser light L1A has a polarization angle changed by 90 degrees by passing through the quarter-wave plate 43 twice, and is reflected vertically upward by the polarization beam splitter 41.

  Then, the vacuum side reference laser light L1A that has reached the corner cube 46 and whose traveling direction has been changed vertically downward in the corner cube 46 is incident on the polarization beam splitter 41 again, but passes through the quarter wavelength plate 45. As a result, the polarization angle is changed by 90 degrees, so the light travels straight through the polarization beam splitter 41 and reaches the fixed stage 61 again. The position of the fixed stage 61 is also mirrored in the same manner as described above, and the vacuum side reference laser beam L1A is reflected vertically upward, and the polarization angle is changed by 90 degrees by passing through the quarter wavelength plate 44. The reference laser beam L1A is reflected by the polarization beam splitter 41 in the direction in which it enters the interference optical circuit 4. In addition, on the incident / exit surface 41a of the polarization beam splitter 41 where the vacuum side laser light L1 enters / exits, the incident position and the exit position of the vacuum side laser light L1 are positioned on different horizontal planes by reflection by the corner cube 46. It will be. That is, the non-polarizing beam splitter 3 and the mirror 5 are not positioned on the optical path of the vacuum side laser light L1 emitted from the polarizing beam splitter 41.

  On the other hand, in the polarization beam splitter 41, the vacuum-side length measuring laser beam L1B, which is the p-polarized component of the vacuum-side laser beam L1, reflected in a direction 90 degrees (here, vertically downward) with respect to the incident direction, Although the order of passage is different from that of the side reference laser light L2A, it passes through the same optical element and is emitted from the same position as the emission position of the vacuum side reference laser light L1A.

  In the optical path of the vacuum side length measuring laser beam L1B, a transparent light introduction window 61a is provided at a position where the vacuum side length measuring laser beam L1B reaches the fixed stage 61. The vacuum side length measuring laser beam L1B is The light is introduced into the vacuum region 63 through the light introduction window 61 a and reflected vertically upward on the upper surface of the moving stage 62 formed of a mirror provided at the lower end of the measuring unit 6.

  In other words, the optical path length of the vacuum-side reference laser beam L1A and the optical path length of the vacuum-side measurement laser beam L1B differ by four times (two reciprocations) the optical distance from the upper surface of the fixed stage 61 to the upper surface of the moving stage 62. .

  As described above, the vacuum side laser beam L1 emitted from the polarization beam splitter 41 in a state where the vacuum side reference laser beam L1A and the vacuum side length measuring laser beam L1B are overlapped can pass a laser beam having a polarization angle of 45 degrees. By passing through the polarizing plate 47 arranged in such a manner, the vacuum side reference laser light L1A and the vacuum side length measuring laser light L1B having the same polarization component are overlapped, and interference light having a light intensity corresponding to the optical path difference is obtained. Become.

  Similarly to the vacuum side laser beam L1, the sample side laser beam L2 passes through the interference optical circuit 4 while being divided into the sample side reference laser beam L2A and the sample side length measuring laser beam L2B. The reference laser beam L2A and the sample side length measuring laser beam L2B are emitted from the same position different from the emission position of the vacuum side laser beam L1 of the polarization beam splitter 41. At this time, the sample side reference laser beam L2A is reflected by the mirror processing portion on the upper surface of the fixed stage 61, and the sample side length measuring laser L2B is introduced into the sample region 64 through the light introducing window 61b of the fixed stage 61. Then, the light is reflected on the upper surface of the moving stage 62. Therefore, the sample-side laser light L2 emitted from the interference optical circuit 4 has a light intensity corresponding to an optical path difference that is four times the optical distance from the upper surface of the fixed stage 61 to the upper surface of the moving stage 62 (two reciprocations). Interference light having.

  As described above, the vacuum side laser light L1 and the sample side laser light L2 emitted from the interference optical circuit 4 are input to the optical sensors 8a and 8b via the mirror 7 and the light intensity is detected.

  In the example of FIG. 2, a non-polarizing beam splitter 9 is further provided on the multi-wavelength laser light source 1 side of the non-polarizing beam splitter 3 and the light intensity of the laser beam divided by the non-polarizing beam splitter 9 is detected. An optical sensor 8c is provided so that the intensity of the laser light output from the multi-wavelength laser light source 1 can be confirmed.

  In the absolute refractive index measuring apparatus 10 of the present invention, the wavelength plate 2, 43, 44, 45 and the polarizing beam splitter 41 are wavelength-dependent in the wavelength range of the laser light emitted from the multi-wavelength laser light source 1. A small polarization optical element is employed.

  FIG. 3 shows an output signal output from the optical sensor 8b when the moving stage 62 is moved downward in the absolute refractive index measuring apparatus 10 having the above configuration. In FIG. 3, the horizontal axis represents the elapsed time corresponding to the amount of movement of the moving stage 62, and the vertical axis represents the output signal of the optical sensor 8b. In the figure, the alternate long and short dash line A, broken line B, and solid line C are output signals for wavelengths of 633 nm, 594 nm, and 543 nm, respectively.

  Since the intensity of the laser light emitted from the multi-wavelength laser light source 1 varies depending on the wavelength, there is a difference in the magnitude of the output signal at each wavelength, but the intensity change of the interference light is measured at any wavelength. Therefore, the absolute refractive index can be measured in the wavelength range output by the multi-wavelength laser light source 1 by counting the wave number of the intensity change of the interference light shown in FIG.

  Here, the configuration of the measurement unit 6 will be described. The measuring unit 6 includes, for example, the disk-shaped fixed stage 61 whose upper surface is horizontally provided at the upper end, and has an upper surface parallel to the upper surface of the fixed stage 61 at the lower end, and is provided so as to be movable in the vertical direction. The disc-shaped moving stage 62 is provided.

  The vacuum region 63 is a substantially cylindrical space whose upper and lower surfaces are closed by a fixed stage 61 and a moving stage 62 and whose side surfaces are closed by, for example, bellows-like side walls that can be expanded and contracted as the moving stage 62 moves. The interior is maintained in a vacuum state of about 1 atm by a vacuum pump (not shown).

  The moving stage 62 is connected to the moving stage drive mechanism 11 that moves up and down while maintaining the parallel state of the upper surface of the fixed stage 61 and the upper surface of the moving stage 62.

  For example, as shown in FIG. 4, the moving stage driving mechanism 11 has a driving unit 112 such as a motor supported on the upper end of a frame 111 fixed on the table 12, and the driving unit 112 below the driving unit 112. Drive transmission means 113 such as a gear for converting the rotational driving force 112 into a vertical driving force is provided.

  A columnar vertical movement arm 115 extending in the vertical direction is connected to the drive transmission means 113, and an outer edge portion of the moving stage 62 is fixed to a lower end of the vertical movement arm 115 via a support member 116.

  The vertical movement arm 115 is inserted into a pipe-shaped guide means 114 provided on the table 12, and the moving stage 62 moves up and down without causing horizontal movement.

  On the other hand, a side wall 65 is provided at the outer edge of the fixed stage 61 to prevent the liquid S to be measured from entering the upper surface of the fixed stage 61. When measuring the absolute refractive index, the measuring unit 6 is placed in a container 66 containing the liquid S to be measured whose liquid temperature is kept constant by a temperature adjusting means (not shown). It is immersed until the surface is located above the upper surface of the fixed stage 61.

  As a result, the sample region 64 in which the measurement target liquid S is filled in the region excluding the vacuum region between the fixed stage 61 and the moving stage 62 is configured.

  In the optical system, at least the interference optical circuit 4 excluding the polarizing plate 47 may be supported by the frame 111 above the measuring unit 6 through a support member or the like as appropriate. May be arranged at an arbitrary position such as on the table 12. In addition, the fixed stage 61 is supported by fixing the side wall 65 to the table 12 or the frame 111.

  As the moving stage drive mechanism 11, any configuration can be adopted as long as the moving stage 62 can be moved up and down. However, as described above, the moving stage 62 can prevent horizontal blur and vibration. A configuration is preferred.

  As described above, the absolute refractive index measurement apparatus 10 uses the optical circuit using the polarizing optical element, and uses the optical path that is incident on the measurement unit 6, that is, the vacuum side reference laser light L1A, the vacuum side length measurement laser. The light L1B, the sample-side reference laser light L2A, and the sample-side length measurement laser light L2B are reciprocated twice in a point-symmetrical positional relationship. For this reason, even if the upper surface of the moving stage 62 is inclined with respect to the upper surface of the fixed stage 61 for some reason, this inclination can be absorbed.

  Further, the corner cube 46 always folds the laser beam incident from below to a point target position with respect to the center of the corner cube 46. That is, the absolute refractive index measuring apparatus 10 can maintain the point-symmetric positional relationship of the entire optical path even when the optical system vibrates for some reason during the measurement, and thus is less susceptible to vibration. Yes.

  Now, with the measuring unit 6 immersed in the liquid S to be measured as described above, for example, laser light having a wavelength of 633 nm is emitted from the multi-wavelength laser light source 1, and the moving stage 62 is moved by the moving stage driving mechanism 11. For example, when moved downward, the vacuum side laser light L1 and the sample side laser light L2 incident on the optical sensors 8a and 8b while the moving stage 62 is moving change the intensity of light and dark according to the amount of movement of the moving stage. Will repeat.

  This intensity change is input to the counter 21 shown in FIG. 2 as an output signal of the optical sensors 8a and 8b. The counter 21 counts the number of fringes of the input signal. The counting of the number of fringes is continued over an arbitrary period from when the moving stage 62 starts moving to when it stops. As described in the background art, since the number of fringes depends on the moving amount of the moving stage 62, the movement start position and the stop position of the moving stage 62 are arbitrary.

  As shown in FIG. 5, the counter 21 includes, for each optical sensor 8, an amplifier 211 that amplifies the output signal to a predetermined signal level, and the peak and zero cross points of the output signal (the sine wave of the output signal of the optical sensor). And a counter 212 for counting the number of fringes based on the detection result of the comparator 212.

  The number of fringes may be counted by an arbitrary method, but in the present embodiment, the following method is adopted so that the moving amount of the moving stage 62 becomes small. That is, as shown in FIG. 6, an arbitrary zero cross point of the optical sensor 8a for detecting the light intensity of the vacuum side laser light L1 is set as a start point ts, and a zero cross point at which the counter value corresponding to the optical sensor 8a is a predetermined value n is set. Let it be the end point te.

  In the counting period T between the start point ts and the end point te, the number of fringes of the optical sensor 8b that detects the light intensity of the sample side laser light L2 is counted. With only the count value thus counted, the accuracy of the absolute refractive index is 1 / digit of the predetermined value n.

  Therefore, in the present embodiment, from the analog value of the output signal of the optical sensor 8b at the start point ts and the end point te, the counter 213 is less than 1 that cannot be counted as the number of fringes of the sample side laser light L2, that is, The wave number after the decimal point (hereinafter referred to as a fraction) is obtained. Such a fraction can be obtained from the phase calculated from the ratio between the analog value and the amplitude value of the output signal of the optical sensor 8b. In the present embodiment, this calculation is performed by the A / D converter 214 and the calculation means 22 described later. Two phases are obtained by the above calculation, but the judgment of which one is the correct phase is made again by taking the analog value of the optical sensor 8b again at a time equal to or less than ¼ of the zero cross interval of the output signal of the optical sensor 8b. Acquired and judged based on the magnitude relationship between the analog value and the previously acquired analog value.

  Thus, by counting the number of fringes including the fraction from the output signal of the optical sensor 8, a more accurate absolute refractive index can be obtained with the same movement amount.

  The fringe numbers (including the fractions) of the vacuum-side laser light L1 and the sample-side laser light L2 counted as described above are input to the calculation means 22 including a microcomputer shown in FIGS. As described in the background art, the absolute refractive index of the liquid S to be measured filled in the sample region 64 is obtained as (the fringe number of the sample side laser beam L2) / (the fringe number of the vacuum side laser beam L1). Therefore, the calculation means 22 calculates (the number of fringes of the sample side laser light L2 + the number of start point X1 + the number of end points X2) / (the number of fringes of the vacuum side laser light L1) to measure the laser light having a wavelength of 633 nm. The absolute refractive index of the liquid S is acquired.

  The exact wavelength of this laser beam is obtained, for example, by using a coupling device or the like between the multi-wavelength laser light source 1 and the half-wave plate 2 before or after the measurement. The measured laser beam is measured with an optical wavelength meter.

  Such processing is performed for all wavelengths that can be selected by the multi-wavelength laser light source 1, and the absolute refractive index of the liquid S to be measured for each wavelength is acquired. Then, the calculating means 22 derives a relational expression between the absolute refractive index and the wavelength as, for example, a cubic regression expression from the absolute refractive index of the liquid S to be measured for each wavelength, and based on this relational expression, sodium The absolute refractive index for the D line (wavelength 589.3 nm) is calculated.

  As a specific example, Table 1 shows the measurement results at each wavelength when pure water and tridecane (liquid temperature 20 ° C.) are used as the liquid S to be measured.

Moreover, based on the result of the said Table 1, the absolute refractive index with respect to the sodium D line | wire (wavelength 589.3nm) calculated | required as a cubic regression equation was calculated | required as a relationship equation of an absolute refractive index and a wavelength, Pure water is 1.333356 and tridecane is 1.425957. The measured values of the respective absolute refractive indexes have good reproducibility on the order of 10 ⁻⁶ . For reference, according to literature values, the absolute refractive index of pure water is 1.33335 ("Handbook of Chemistry and Physics" 56th Edition, CRC Press).

  In addition, the graph which shows the frequency dependence of the absolute refractive index of a pure water is shown in FIG. In the above description, a cubic regression equation is used. However, the order of the regression equation is not particularly limited.

  As described above, according to the absolute refractive index measuring apparatus 10 of the present invention, the absolute refractive index of the liquid to be measured at each wavelength can be measured with high accuracy, and when changing the measurement wavelength, the light source and the optical It is not necessary to replace the elements and adjust the optical circuit, and it is not necessary to take into account measurement errors caused by changing the wavelength of the light source.

  Further, by deriving the wavelength dependence of the absolute refractive index of the liquid to be measured using the absolute refractive index values at the respective wavelengths, the absolute refractive index at an arbitrary wavelength of the liquid to be measured can be accurately obtained. it can.

  The configuration of the polarization interference optical circuit 4 described in the above embodiment shows a specific example, and does not limit the technical scope of the present application. It is possible to design arbitrarily within the range where the effects of the present application are achieved.

  In the above description, the configuration of the measurement unit 6 is described as a configuration in which the moving stage 62 supported on the lower end of the measurement unit 6 is moved with respect to the fixed stage 61. However, the configuration is not limited to this configuration. In other words, any configuration that can count the number of fringes of interference light corresponding to the amount of fluctuation in the optical path length in the vacuum region and the number of fringes of interference light corresponding to the amount of fluctuation in the optical path length of the sample region may be used. You may employ | adopt the structure which moves the movement stage provided above the said fixed stage with respect to the fixed stage fixed to the lower end.

  Further, the sample-side reference laser light and the sample-side length measurement laser light are not limited to the optical path, and as in the configuration described in the conventional technique, the sample-side reference laser light has a vacuum region and Arbitrary configurations can be adopted within a range where the effects of the present invention can be achieved, such as a configuration using laser light that has passed through the sample region.

  For example, the structure of the measurement unit is a vacuum region between the fixed stage and the moving stage, and a transparent light passage window is provided at a position where the sample-side length measuring laser beam reaches, and the moving stage and the moving stage are below. A fixed mirror having a fixed distance from the fixed stage that reflects laser light that has passed through the light passing window vertically upward may be provided, and a sample region may be provided between the moving stage and the fixed mirror.

  That is, laser light that has passed through the vacuum region and the sample region is used as the sample-side length measurement laser light, and laser light that has been passed through only the vacuum region is used as the vacuum-side length measurement laser light. Also with this configuration, it is possible to count the number of fringes corresponding to the amount of fluctuation in the optical path length of the sample region when the moving stage moves, and it is possible to measure the absolute refractive index.

  INDUSTRIAL APPLICATION This invention can obtain | require the absolute refractive index in arbitrary wavelengths of a to-be-measured liquid accurately, and is useful as an absolute refractive index measuring apparatus of a liquid.

1 is a schematic perspective view of the present invention. Schematic of the present invention. Explanatory drawing which shows the frequency dependence of the polarization interference optical circuit of this invention. Schematic of the moving stage drive mechanism of this invention. The schematic functional block diagram of the counter of this invention. Explanatory drawing which shows the count of the number of fringes of this invention. Explanatory drawing which shows the calculation of the absolute refractive index of the arbitrary wavelengths of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multiwavelength laser 2 1/2 wavelength plate 3, 9 Non-polarization beam splitter 4 Polarization optical circuit 5, 7 Mirror 6 Measuring part 8 Optical sensor 10 Absolute refractive index measuring device 11 Moving stage drive mechanism 21 Counter 22 Calculation means 41 Polarization Beam splitter 42 Mirror 43, 44, 45 1/4 wavelength plate 61 Fixed stage 62 Moving stage 63 Vacuum region 64 Sample region S Liquid to be measured

Claims (2)

A laser light source that selectively emits a plurality of laser beams having different wavelengths from the same emission port;
A beam splitter that divides laser light emitted from the laser light source into vacuum side laser light that passes through a vacuum region and sample side laser light that passes through a sample region filled with a liquid to be measured;
A polarization interference optical circuit that generates a reference laser beam further divided from each of the divided laser beams before passing through both the regions, and an interference light between each laser beam after passing through both the regions;
An optical sensor for detecting the light intensity of each interference light;
A counter that respectively counts the wave number of the intensity change of each interference light detected by the optical sensor when the optical path length of the laser light in the vacuum region and the sample region is changed,
The polarization interference optical circuit is a liquid absolute refractive index measurement device that uses the same polarization optical element for all wavelengths of laser light emitted from the laser light source.   Furthermore, a calculation means is provided for calculating an absolute refractive index of an arbitrary wavelength based on an absolute refractive index of the liquid under measurement at each wavelength derived from a ratio of wave numbers of interference light counted by the counter. Item 2. An apparatus for measuring an absolute refractive index of a liquid according to Item 1.

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