JPH0875639A - Light-absorption-spectrum measuring apparatus making use of slab optical waveguide - Google Patents

Abstract

PURPOSE: To provide a light absorption spectrum measuring apparatus by which the extremely large number of reflections is obtained and by which a light absorption spectrum can be measured with high sensitivity by a method wherein condensed light is introduced into an optical waveguide layer and light which has been reflected totally inside the layer is taken out. CONSTITUTION: Radiated light from a light source 10 is condensed 11 so as to be incident on an incidence side prism 12, and light in a wavelength range is introduced at once into an optical-waveguide layer 52 in a slab optical waveguide 13. The introduced light is totally reflected extremely many times inside the layer 52, and evanescent light is generated very close to the surface of the layer 52. When the incident light inside the layer 52 is passed just under a sample 54, the generated evanescent light is absorbed by the sample 54, the incident light is weakened, and the intensity of incident light from the layer 52 is reduced. The light whose total reflection has been repeated inside the layer 52 is taken out at once by a radiant light side lens 15, and it is separated 41 into its spectral components so as to be sent to a detector. Consequently, the light is introduced into the layer 52 from both sides, i.e., the side of the sample 54 and the side of a reference part 53 in which the sample does not exist, its total reflection is repeated, and the intensity of the radiated light is measured. When a measured result is compared and analyzed 42, the light-absorption spectrum of the sample can be measured with high sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for highly sensitively measuring an optical absorption spectrum of an interface, a surface adsorbate, a thin film, an extremely small amount of a sample, etc. by using a slab optical waveguide.

[0002]

2. Description of the Related Art As a conventional technique using an optical waveguide, there is an optical waveguide sensor using a laser as a light source. An optical waveguide sensor that uses a laser as a light source uses a prism or a grating to introduce light from the laser into the optical waveguide, and the light that is totally reflected inside the optical waveguide is extracted using a prism or a grating. By measuring the light intensity by detecting with, the physical measurement of pressure, electric field, magnetic field, etc., or chemical measurement of the concentration of a substance is carried out. Further, the ATR method is known as a method for measuring the light absorption spectrum of a sample using evanescent light. The ATR method is to introduce light into a trapezoidal crystal having a thickness of several mm called an internal reflection element (IRE) with a sample placed on the surface, and take out the light totally reflected inside the element,
The light absorption spectrum of the sample is measured by measuring the light intensity. In the conventional optical absorption measuring device, L
For the concentration equivalent to a monolayer in the B film, 1/2 or 1 /
When the porphyrin dye is contained at a concentration of 10, that is, when the surface concentration is as low as about 0.5 molecular layer or 0.1 molecular layer, the absorbance measured by a usual method is, for example, Even for a sample having a very high molar absorptance of tens of thousands to hundreds of thousands, it is possible to obtain 0.5.
About 0.05, about 0.01 for 0.1 molecular layer, it becomes very difficult to measure the light absorption spectrum of the dye with a usual spectroscopic measurement device. The lower limit of detection of a normal spectroscopic measurement device is about 0.001 abs in terms of absorbance.

[0003]

Since a mode called a so-called waveguide mode is formed in the optical waveguide layer, only light having a specific angle can enter the optical waveguide layer. Further, since the incident angle of light into the optical waveguide layer differs for each wavelength, only using a prism or a grating can cause only light of a specific wavelength, for example, laser light, to enter and exit the optical waveguide layer. Therefore, it is impossible for the conventional optical waveguide sensor to measure the light absorption spectrum. On the other hand, the ATR method can measure the optical absorption spectrum, but the thickness of the element is several meters.
Since it is thick as m, the number of reflections of light is at most several to several tens of times, and sufficient sensitivity cannot be obtained. If the thickness of the element is reduced to improve the sensitivity, mechanical strength cannot be maintained. There was a problem. In addition, it was necessary to darken the optical waveguide or the element and its periphery so as not to be affected by the background light during the measurement. Further, since the optical waveguide has a light transmission mode and the incident angle is extremely limited, it has been difficult to determine the incident and outgoing angles of the light. The present invention, in view of the above problems,
A slab optical waveguide that can measure a high-sensitivity light absorption spectrum, can measure the light absorption spectrum without being affected by background light, and can easily set the incident and exit angles of light. It is an object of the present invention to provide an optical absorption spectrum measuring device using the same.

[0004]

As a result of various studies in view of the above problems, the inventors of the present invention collect light having a constant wavelength width by an incident light side lens and make it incident on an incident light side prism. By this, light in a wide wavelength range can be introduced into the optical waveguide layer at once, and light that has undergone total internal reflection in the optical waveguide is extracted from the prism on the output light side by the lens on the output light side at once, and the detector It has been found that the measurement makes it possible to measure a highly sensitive optical absorption spectrum using a slab optical waveguide. The present invention has been accomplished based on these findings.

That is, according to the present invention, (1) a light source, an incident light side lens for condensing light emitted from the light source, a predetermined distance from the incident light side lens, and the incident light lens in the optical waveguide layer. The incident light side prism for introducing the light condensed by the, the slab optical waveguide having the optical waveguide layer for introducing the light emitted from the incident light side prism, and the light for which the total reflection is repeated inside the optical waveguide layer Emission light from the sample measuring unit, which has a sample measuring unit including an emitting light side prism and an emitting light side lens having a predetermined distance from the emitting light side prism and introducing light emitted from the emitting light side prism And an optical absorption spectrum measuring apparatus using a slab optical waveguide, wherein (2) the light source is white light. Utilizing a waveguide Absorption spectrum measuring device, (3) A device for converting the light from the light source into intermittent light with a constant period between the light source and the lens on the incident light side, and a device for amplifying only the emitted intermittent light. And (4) an optical absorption spectrum measuring apparatus using the slab optical waveguide according to (1) or (2), and (4) a light source and an incident light side lens, and an emission light side lens and a spectroscope. An optical absorption spectrum measuring apparatus using the slab optical waveguide according to item (1), (2) or (3), characterized in that an optical fiber is used.

Next, the present invention will be described in detail. The optical absorption spectrum measuring apparatus using the slab optical waveguide of the present invention,
Using a combination of a lens and a prism, light in a wide wavelength range can enter and exit the optical waveguide layer at once.
It is characterized in that it is possible to measure a highly sensitive light absorption spectrum by using a slab optical waveguide. In the present invention,
The light source is selected from those that emit light having an arbitrary wavelength range from far ultraviolet to far infrared. Of these, it is preferable to select a light source that emits white light.
In this case, white light means light having a certain wavelength width, and does not mean light of white color. In the present invention, in order to clearly distinguish the light from the light source from the other light, it is preferable that the light from the light source is an intermittent light with a constant period. The light from the light source is made into intermittent light of a certain cycle, is made incident on the optical waveguide layer, and the intermittent light transmitted through the inside of the optical waveguide layer is emitted, and the emitted light is measured, so that it is affected by the background light. It becomes possible to measure the light absorption spectrum without using it. It is desirable to use an optical chopper to turn the light from the light source into intermittent light with a constant period. In this case, it is also preferable to amplify only the light emitted from the optical waveguide layer. In the present invention, it is preferable to use an optical fiber between the light source and the incident light side lens and between the output light side lens and the spectroscope in order to change the position and direction of the light. By using an optical fiber between the light source and the lens on the incident light side, and between the lens on the outgoing light side and the spectroscope, it is possible to easily and subtly adjust the distance between the lens and the prism on the incoming light side or the outgoing light side, the incident angle and the outgoing angle. You will be able to adjust. In the present invention as well, a prism is used to enter and exit light in the optical waveguide layer having a high refractive index, but in order to enter and exit light in a wide wavelength range at once into the optical waveguide layer, the incident light is incident. An incident light side lens is provided on the light side at a constant distance from the incident light side prism, and an outgoing light side lens is provided on the outgoing light side at a constant distance from the outgoing light side prism. The slab optical waveguide used in the present invention has a transparent optical waveguide layer placed on a substrate. As the substrate, a transparent plate such as a glass plate or a quartz plate whose refractive index is higher than that of air is used. Non-fluorescent glass slides may be used to improve the short wavelength transmission. The thickness of the substrate is not particularly limited as long as it can support the entire shape, but is about 0.5 mm to several tens of mm, preferably about 1 mm to several mm.
It is a degree. The optical waveguide layer is required to have a higher refractive index than the substrate, has a thickness of 0.1 μm to several tens of μm, and has a refractive index of sodium ions on the surface of soda glass and glass such as potassium ions and thallium ions. It is preferably prepared by ion exchange with a substance having a high effect or by thinly coating a substance having a high refractive index by a method such as a sol-gel method or a spin coating method. In the present invention, light in a wide wavelength range is extracted at once from the outgoing light side lens, and the light emitted from the inside of the optical waveguide layer is dispersed by the spectroscope and sent to the photomultiplier tube.

[0007]

An embodiment of the present invention will now be described in more detail with reference to the drawings. The present invention is not limited to the embodiments. FIG. 1 is a schematic diagram showing the configuration of an example of an optical absorption spectrum measuring apparatus using the slab optical waveguide of the present invention. In the figure, 10 is a light source, 30 is an optical chopper, 31 is an incident light side optical fiber, 11 is an incident light side lens, and 12 is an incident light side prism. 13 is a slab optical waveguide, 14 is an outgoing light side prism, 15 is an outgoing light side prism, 32 is an optical fiber, 41 is a spectroscope, and 42 is a computer. 43 is a photomultiplier tube and 44 is an amplifier. Reference numeral 16 is a control mechanism for the position and angle of the slab optical waveguide. 33,
Reference numeral 34 represents a lens. In FIG. 1, a light source 10 emits light having an arbitrary wavelength range from far ultraviolet to far infrared, and uses a Xe lamp as a white light source. The optical chopper 30 converts the light from the light source into intermittent light having a constant cycle, and is provided between the light source 10 and the incident light side optical fiber 31. The sample measuring section has an incident light side lens 11, an outgoing light side lens 15, an incident light side prism 12, an outgoing light side prism 14, a slab optical waveguide 13, and a position control mechanism 16. The incident light side lens 11 is provided at the exit side end of the incident light side optical fiber 31 at the exit light side lens 1.
5 is provided at the tip of the exit side optical fiber 32 on the entrance side. FIG. 2 is a plan view and FIG. 3 is a sectional view of the above-mentioned slab optical waveguide. As shown in both figures, the incident-light side prism 12 and the outgoing-light side prism 14 are arranged on the slab optical waveguide 13, and are elongated so that the sample and the reference portion can be measured without reattaching the prism. To do. The slab optical waveguide 13 includes a substrate 51 for supporting the optical waveguide layer 52 and an optical waveguide layer 52. The sample 54 rides on one side of the slab optical waveguide 13 in a band shape, and the opposite side, that is, the part without the sample 54 becomes the reference part 53. As shown in FIG. 1, the detection unit has a spectroscope 41, a photomultiplier tube 43, an amplifier 44, and a computer 42. The white light emitted from the light source 10 is emitted by the light chopper 3
After being made into intermittent light with a constant period of 0, it is introduced into the incident light side optical fiber 31. The intermittent light introduced into the incident light side optical fiber 31 passes through the incident light side optical fiber 31,
It is condensed by an incident light side lens 11 provided at the tip on the light emission side, and is introduced into the incident light side prism 12 at an appropriate angle.
The intermittent light collected by the incident light side lens 11 is introduced into the incident light side prism 12 and then enters the optical waveguide layer 52 of the slab optical waveguide 13. The intermittent light that has entered the optical waveguide layer 52 undergoes total reflection within the optical waveguide layer 52, then exits from the optical waveguide layer 52, and is introduced into the outgoing light side prism 14. The intermittent light introduced into the outgoing light side prism 14 is extracted by the outgoing light side lens 15 provided at the tip of the outgoing light side optical fiber 32 on the incoming side, and is sent to the spectroscope 41 by the outgoing light side optical fiber 32. . The intermittent light separated by the spectroscope 41 is supplied to the photomultiplier tube 4
3. The light absorption spectrum is obtained by being sent to the computer 42 for analysis via the amplifier 44.

[0008]

The light emitted from the light source is condensed by the lens on the incident light side and is incident on the prism on the incident light side, whereby light in a wide wavelength range can be introduced into the optical waveguide layer at once. The light introduced into the optical waveguide layer undergoes a large number of total reflections inside the optical waveguide layer. Due to such internal multiple reflection, evanescent light is generated in the vicinity of the wavelength of light on the surface of the optical waveguide layer. When the light entering the optical waveguide layer passes through the optical waveguide layer directly below the part where the sample exists, the evanescent light generated on the surface of the optical waveguide layer is absorbed by the sample, so the incident light is weakened and The intensity of the emitted light decreases. The light that has undergone total internal reflection in the optical waveguide passes through the exit light side prism, is extracted at one time from the exit light side lens, and is sent to the detector via the spectroscope.
Therefore, the side with the sample, and the side without the sample, ie, both sides of the reference portion, introduces light into the optical waveguide layer, and measures the intensity of light emitted by repeating total reflection in the optical waveguide layer,
The light absorption spectrum of the sample can be obtained by comparing and analyzing the measurement results with a personal computer or the like.

Next, the present invention will be described in more detail based on test examples. Test Example 1 Using the device shown in FIG. 1, the transmittance at each wavelength was measured when the distance between the lens and the incident light side prism or the outgoing light side prism was changed to examine the light transmission characteristics of the optical waveguide layer. . A lens having a diameter of 3 mm, an effective diameter of 2 mm and a focal length of about 5 mm was used. A prism having a size of 4 × 5 × 15 mm and a refractive index of 1.87, which is larger than those of the optical waveguide layer (1.52), the substrate (1.516), and the air (1), was used. Soda glass is used for the substrate, and the surface of the soda glass is
An optical waveguide layer was prepared by immersing in a molten potassium nitrate bath at 0 ° C. for 30 minutes and treating with a potassium nitrate molten salt. The thickness of the obtained optical waveguide layer was about 1 to 2 μm as measured by the waveguide mode of light using a He—Ne laser. The optical fiber used was a multimode one having a core diameter of 250 μm. The sample contains cadmium arachiate as a main component, and a porphyrin copper complex as a pigment is added at 1.5 mo.
An LB membrane with 1% added was used. FIG. 4 shows the relationship of transmittance at each wavelength when the distance between the lens and the prism on the incident light side or the prism on the outgoing light side is changed by using the apparatus of FIG.
It was found that the transmittance is improved in a wide range on the long wavelength side and the white light in a wider range can be transmitted by bringing the lens closer to the incident light side prism or the outgoing light side prism.

Test Example 2 Two types of LB films were prepared by adding a porphyrin copper complex to cadmium arachiate on the surface of the optical waveguide layer, and using these as samples, the optical absorption spectrum was measured using the apparatus of FIG. It was The concentration of the porphyrin copper complex in the two kinds of LB films is (A) 1.5 mol%, that is, approximately 0.1 molecular layer equivalent, and (B) 13 mol%, that is, approximately 0.5 molecular layer equivalent, and the incident light side lens The distance between the incident light side prism and the incident light side prism was 23 mm. The light absorption spectra thus obtained are shown in FIG. 5 as (A) and (B). Conventionally, when the concentration of the porphyrin copper complex, which is a dye, is extremely low, which is equivalent to 0.1 molecular layer, the state of the dye changes compared to the case of high concentration, so the concentration of the dye can be increased or the sample Although it was difficult to measure the correct spectrum even if the thickness was increased, the apparatus of the present invention could measure the light absorption spectrum with high sensitivity as shown in FIG.

[0011]

The optical absorption spectrum measuring device of the present invention is
Light having a certain wavelength width, for example, white light is condensed by a lens, the light is incident on the optical waveguide layer of the slab optical waveguide from a prism set at a predetermined distance from the lens, and is totally reflected inside the optical waveguide layer. Light is extracted through a prism with a lens set at a predetermined distance from the prism, and the emitted light is separated by a spectroscope and sent to a detector, which enables a very large number of reflections and a highly sensitive optical absorption spectrum to be measured. This eliminates the need for expensive light sources, magnetic fields, electric fields, light,
Spectral measurement is possible while performing various actions such as heat, chemical treatment, pressure, sound, and biological treatment. The optical absorption spectrum measuring apparatus of the present invention makes it possible to clearly distinguish the light emitted from the light source from other light by making the light emitted from the light source an intermittent wave and passing through the inside of the optical waveguide layer. It is not necessary to shield the waveguide part and its periphery from the light, and not only the device becomes simple, but also optical spectrum measurement is possible while irradiating another light. The optical absorption spectrum measuring device of the present invention can change the distance between the lens and the prism and the direction of the light freely by using the optical fiber, and can easily determine the incident and outgoing angles of the light. The structure of can be simplified.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration of an example of an embodiment of an optical absorption spectrum measuring apparatus of the present invention.

FIG. 2 is a plan view showing an example of a slab optical waveguide in the optical absorption spectrum measuring apparatus of the present invention.

FIG. 3 is a sectional view showing an example of a slab optical waveguide in the optical absorption spectrum measuring apparatus of the present invention.

FIG. 4 is a graph showing the light transmission characteristics of the optical waveguide layer when the distance between the incident light side lens and the incident light side prism in the optical absorption spectrum measuring apparatus of the present invention is changed.

FIG. 5 is a graph showing a measurement result of an optical absorption spectrum when an LB film is used as a sample by using an example of an example of the optical absorption spectrum measuring apparatus of the present invention.

[Explanation of symbols]

 10 light source 11 incident light side lens 12 incident light side prism 13 slab optical waveguide 14 emission light side prism 15 emission light side lens 16 position control mechanism 30 optical chopper 31 incident light side optical fiber 32 emission light side optical fiber 41 spectroscope 42 computer 43 optoelectronic Multiplier tube 44 Amplifier 51 Substrate 52 Optical waveguide layer 53 Reference portion 54 Sample

Claims (4)

[Claims] 1. A light source, an incident light side lens that collects light emitted from the light source, and a predetermined distance from the incident light side lens,
An slab optical waveguide having an incident light side prism for introducing the light condensed by the incident light lens into the optical waveguide layer, an optical waveguide layer for introducing the light emitted from the incident light side prism, and inside the optical waveguide layer An outgoing light side prism that introduces light that is repeatedly totally reflected, and a predetermined interval with the outgoing light side prism,
Further, the slab optical waveguide is characterized in that it has a sample measuring section composed of an outgoing light side lens for introducing light emitted from the outgoing light side prism, and takes out outgoing light from the sample measuring section to measure a spectrum. Optical absorption spectrum measurement device using waveguide. 2. The optical absorption spectrum measuring apparatus using a slab optical waveguide according to claim 1, wherein the light source is white light. 3. A device for converting light from the light source into intermittent light having a constant period between the light source and the incident light side lens, and a device for amplifying only the emitted intermittent light. Item 1. An optical absorption spectrum measurement device using the slab optical waveguide according to item 1 or 2. 4. The slab optical waveguide according to claim 1, wherein an optical fiber is used between the light source and the incident light side lens and between the output light side lens and the spectroscope. Optical absorption spectrum measuring device.