JPH07294729A - Thin-film spectral filter - Google Patents

Abstract

PURPOSE:To form a thin-film filter which is inexpensive and has excellent environmental resistance and high performance by constituting this filter of multilayered films formed by alternately laminating discontinuous metallic thin films formed as island shapes and dielectric thin films. CONSTITUTION:This thin-film spectral filter is composed of the multilayered laminates formed by alternately laminating the dielectric thin films 1 which have a dielectric constant epsilon1 and the metallic thin films 2 which have a dielectric constant epsilon2 and are formed as the island shapes on a dielectric substrate 7 of a prism type or plate type which is a base. As a more specific example, the filter is obtd. by forming the Ag thin film layers 2 by vacuum vapor deposition on the incident face of a prism (base) 7 of glass and heating the films after the vapor deposition by a heating method with radiation heat and trimming the shapes of the island-shaped Ag particles to a spherical shape. The SiO2 thin-film layers 3 are formed by sputtering vapor deposition in the upper part of the Ag layers and further, the Cu thin-film layers 4 are formed by vacuum vapor deposition thereon. The films after the vapor deposition are heated to trim the shape of the island-shaped Cu particles to the spherical shape. At this time, the multilayered laminate formed in such a manner is functioned as the thin-film spectral filter for incident light of a wavelength 0.8mum.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improved thin film spectral filter having optical absorption wavelength selectivity.

[0002]

2. Description of the Related Art A conventional filter is a filter that uses colored ions such as one in which a certain solution is put in a cell or one in which a coloring agent is put in plastic, or a large number of dielectric thin films are laminated on a substrate. For example, there is a filter utilizing interference of multilayer thin films.

[0003]

Among the conventional filters, those using colored ions have a problem in environmental performance because their performance is remarkably lowered or damaged due to environmental temperature change. Further, in the case of utilizing interference, the performance of the filter is limited due to the internal stress of the thin film, and it is difficult to achieve high performance. In order to solve the above problems, the present invention provides a high-performance thin film filter that is inexpensive and has excellent environment resistance.

[0004]

SUMMARY OF THE INVENTION The present invention comprises a support and a prismatic or plate type dielectric on the substrate of the dielectric constant epsilon ₁ dielectric thin film 1 and the thin metal film 2 were islands of dielectric constant epsilon ₂ It is composed of a multilayer body in which the layers are alternately laminated. When the metal thin film 2 is deposited very thinly, the film is discontinuous in the initial stage.
The property of the metal at this time is different from that of the normal bulk, and light absorption occurs for light of a specific wavelength. Further, the wavelength of the absorbed light changes depending on the type of metal thin film material and the particle size of the island-shaped particles. That is, by controlling the thin film substance and the particle size, it is possible to function as a thin film spectral filter for an arbitrary wavelength.

[0005]

In the island-shaped metal particles, there are free electrons, and these free electrons play the role of connecting many positive ions to each other. Unless two adjacent positive ions pull apart one free electron, two positive ions are indirectly bound. Although these electrons move around in the island-shaped metal particles, another free electron is located at the position of the moved free electron (free electron), so that it is in a stationary state when viewed from the outside.
When no electric field is applied, the island-shaped metal particles are an electrically neutral mixture of stationary ion spheres and stationary free electron spheres.

When a uniform electric field having the same size and direction is applied to such island-shaped metal particles everywhere, these stationary conduction electrons receive a force from the electric field and become opposite to the direction of the electric field. Start moving. Ions are considered to remain stationary. Under a uniform electric field, the electrons moving anywhere in the island-shaped metal particles move the same amount, so the electrons move in the direction opposite to the electric field while maintaining the sphere shape. As a result, the sphere formed by the ions and the sphere formed by the free electrons are deviated from each other, and a portion where only free electrons exist and a portion where only the left-over ions exist are formed. Then, on the surface of the sphere,
Negatively charged portions and positively charged portions are generated, and induced charges are generated.

In this case, since the electric field changes its direction 10 ¹⁵ times in response to the frequency of light per second, this electron sphere also moves up and down and moves up and down 10 ¹⁵ times. Thus, when the incident light passes through the island-shaped metal particles, free electrons are shaken by the oscillating electric field. As the incident light continues to hit the island-shaped metal particles, the free electrons continue to oscillate with an amplitude that is in equilibrium, being shaken by the oscillating electric field on the one hand and stopped by electrical resistance on the other hand.

At this time, the electrons vibrating while receiving the electric resistance emit heat due to Joule loss. As it is, the energy of vibration changes to heat and the vibration declines, but the vibration continues because the energy of vibration is continuously supplied from the incident light. Part of the energy of the incident light is converted into vibrational energy of conduction electrons, which is then emitted as Joule heat. As a result of the energy of the incident light being transferred to the free electrons, the energy of the incident light after passing through the island-shaped metal particles is reduced as compared with that before hitting the island-shaped metal particles. The incident light is weakened by passing through the island-shaped metal particles. However, since incident light of all wavelengths does not weaken at the same rate, when incident light of the same intensity at all wavelengths hits the island-shaped metal particles, the incident light of a wavelength that increases the amplitude of free electrons is Much is absorbed and energy is lost. In other words, most incident light having a wavelength that causes resonance with plasma oscillation of free electrons is absorbed and energy is lost.

When incident light of various wavelengths, in other words, incident light of various frequencies, hits the island-shaped metal particles, most of the incident light having a frequency equal to the plasma frequency is absorbed and loses energy to be attenuated. Becomes fierce. Also, even if the frequency is not exactly equal to the plasma frequency, when the frequency is close to it, a large energy reduction occurs.
The above-mentioned phenomenon occurring in the island-shaped metal particles similarly occurs in the whole discontinuous metal thin film having the island-shaped particles. In that case, the wavelength of the absorbed light is

[0010]

[Equation 1]

It is obtained by the relationship (Mie's theory). From these things, it functions as a thin film spectral filter.

[0012]

The preferred embodiments of the present invention will be described in detail below. A glass prism (refractive index 1.
47), a SiO ₂ layer (refractive index 1.47) and an Ag layer (refractive index 0.065-j4.0) are formed on the incident surface of the prism.
Constituting the SiO ₂ -Ag-Cu laminate by laminating Cu layer (refractive index 0.260-j5.26) alternately with.

First, a vacuum degree of 1.0 × 10 ⁻³ T is set on the prism.
Orr, deposition rate of 0.2 Å / sec to form a 50 Å film thickness Ag layer by vacuum evaporation, the film after evaporation is heated to around 300 ℃ by radiant heat heating method to make the island-like Ag particles spherical. Arrange. The degree of vacuum is 1.0 × 1 above the Ag layer.
Film thickness of 200 at 0 ^-3 Torr and vapor deposition rate of 2.0Å / sec
A 0Å SiO ₂ layer is formed by sputter deposition. At this time, the film is not heated. Vacuum degree 1.0 × 10
A Cu layer having a film thickness of 50 Å is formed on the SiO ₂ layer by vacuum evaporation at ^-3 Torr and an evaporation rate of 0.15 Å / sec. Further, similarly to the Cu film, the film after vapor deposition is heated to about 300 ° C. by a radiant heating method to adjust the shape of the island-shaped Cu particles into a spherical shape. At this time, it can function as a thin film spectral filter for incident light having a wavelength of 0.8 μm.

Further, the wavelength selectivity can be improved by forming a laminated body composed of alternating layers of Ag layer, SiO ₂ layer and Cu layer on both sides of the glass prism. It is also possible to split the light into a plurality of beams using a beam splitter and then use a thin-film spectral filter to make light of different wavelengths. The materials used for these are all inexpensive and highly durable.

[0015]

The durability of the thin film spectral filter can be improved by using a relatively easy manufacturing method, and various characteristics can be designed depending on the types of the dielectric and metal thin film used. As a result, it is possible to provide a high-performance thin film spectral filter that is inexpensive and has excellent environment resistance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of a thin film spectral filter according to the present invention.

FIG. 2 is a schematic diagram illustrating the operating principle of a thin film spectral filter according to the present invention.

FIG. 3 is a schematic diagram showing the configuration and operation principle of a conventional thin film spectral filter.

[Explanation of symbols]

1: Alternate layered film 6: Emitted light 2: Ag thin film layer 7: Support 3: SiO ₂ thin film layer 8: Low refractive index layer 4: Cu thin film layer 9: High refractive index layer 1 5: Incident light 10: High refractive index Stratum 2

Claims (2)

[Claims] 1. A thin film spectral filter comprising a multi-layer film in which island-shaped discontinuous metal thin films and dielectric thin films are alternately laminated. 2. A thin film comprising a multi-layer film in which island-shaped discontinuous metal thin films such as Ag, Au and Cu and dielectric thin films such as SiO ₂ and MgO ₂ are alternately laminated. Spectral filter.