JPH01312521A - Optical system for vacuum device - Google Patents

Abstract

PURPOSE:To reduce the size and weight of the optical system by composing a collimator lens of one axially distributed index lens. CONSTITUTION:The single axially distributed index lens (ZGI lens) is used as the collimator lens 16. The ZGI lens is a lens given a uniform refractive index distribution which decreases gradually and linearly or nearly linearly in the direction of an optical axis 16B in a spherical lens base body while maximum at the center point 0 of a spherical lens surface 16A and is uniform in a plane 16C crossing the optical axis at right angles. Namely, the refracting index is maximum at the center point 0 on the plane 16C crossing the optical axis at right angles and decreases radially toward the periphery. Namely, the refractive index index whose refractive index contours 16D are concentric is obtained. A relay lens system 15 guides parallel light from the collimator lens 16 to an objective 17. Consequently, a small-sized unit is obtained in combination with a spot light source body 13 and high-accuracy and stable light beam irradiation is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical system for irradiating a light beam onto a sample placed in a vacuum apparatus such as an electron microscope.

[Conventional technology]

BACKGROUND ART A light beam irradiation device plays an important role in an apparatus that irradiates a high-energy light beam onto a sample placed in a vacuum apparatus such as an electron microscope and observes changes in the characteristics of the sample using an electron beam or the like. Since the sample is irradiated with an electron beam, an optical system is required that does not interfere with the electron beam. At the same time, higher energy irradiation requires the use of highly efficient optical systems.

Conventionally, as shown in FIG. 4, such a light beam irradiation optical system includes a large light source 2, typically a gas laser, placed outside a vacuum device 1, a beam expansion optical system 3, and a vacuum chamber 4. A device consisting of a laser beam transmitting window 5 provided on the side surface and a condensing reflective parabolic mirror 7 having a hole in the center through which the electron beam 6 passes was used.

[Problem that the invention seeks to solve]

In the conventional equipment mentioned above, not only each part is large, but also
The optical axis always needs to be adjusted, making it extremely difficult to handle.

[Means for solving problems]

A point light source such as a semiconductor laser or an optical fiber, a collimating lens that shapes the emitted light from the light source in parallel, and an objective lens that collects the parallel light and irradiates the sample with a spot are configured in an integrated stop unit, and An axial gradient index lens was used as the collimating lens.

[For production]

According to the above configuration, even if the metal lens barrel expands or contracts due to temperature changes within the vacuum device, the focal point does not move. Therefore, even if it is combined with a point light source to form a compact unit and placed in a vacuum device, highly accurate and stable light beam irradiation can be performed, and the adjustment of the optical axis only needs to be done once when assembling the unit. In addition, since a single axial gradient index lens is used as the collimating lens instead of a laminated lens, there is no gas generation from the adhesive even when installed in a high vacuum, and high power and high efficiency light can be produced. Irradiation can be performed.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 shows a cross section of a vacuum apparatus of an electron microscope equipped with an optical system according to the present invention. An optical system 11 for condensing and irradiating a light beam onto a sample 8 is provided in a vacuum chamber/bar 10.

FIG. 2 shows an enlarged cross section of the optical system 11 in FIG. A lens barrel 14 that holds a relay lens system is fixed to the other end opening.

A relay lens system 15 held within the lens barrel 14 includes a collimating lens 16 that forms the emitted light from the semiconductor laser 13 into parallel light, and a collimating lens 16 that focuses the parallel light that is spaced apart from the collimating lens 16. and an objective lens 17 for irradiating a spot onto the sample 8.

In order for the collimator lens 16 to collect the emitted light from the semiconductor laser more efficiently, it is preferable that the collimator lens 16 has a large numerical aperture. When the numerical aperture becomes large, a combination lens consisting of at least two lenses bonded together with an adhesive is used to correct spherical aberration in a normal spherical lens using a homogeneous medium. However, if a lens using an adhesive is placed in a high vacuum, the degree of vacuum will not increase due to gas generation, making it impractical.

Therefore, in the present invention, a single axial gradient index lens (hereinafter referred to as ZGI lens) is used as the collimating lens 16.
Use.

As shown in Fig. 3, the ZGI lens has an optical axis 16 in the spherical lens matrix with the maximum point at the center 0 of the spherical lens surface 16A.
It is a lens that gradually decreases linearly or almost linearly in the direction B, and has a −-like refractive index distribution within the surface 16C perpendicular to the optical axis, and has a center point 0 on the lens surface 16A.
The refractive index distribution has a maximum value and gradually decreases in the radial direction toward the periphery, that is, the equirefractive index lines 16D form concentric circles.

In the ZGI lens having the refractive index distribution as described above, the light rays incident on the lens surface 16A have a relatively small refraction angle at the periphery compared to a normal spherical lens with a similar refractive index. Although it is a lens, it has the same ability to correct spherical aberration as an aspheric lens.

The ZGI lens described above diffuses ions with a high refractive index, such as thallium ions, from the surface of a glass substrate into the substrate by exchanging them with ions in the glass, and creates a refractive index gradient based on the concentration distribution of the ions on the glass substrate. It is obtained by forming the lens in the thickness direction and then subjecting it to the same spherical processing as a normal lens.

For details on ZC and I lenses, see, for example, Japanese Patent Application Laid-open No. 5
9-33415 (Japanese Patent Application 1982-142991), Japanese Patent Application Publication No. 60-250319 (Patent Application 1987-105920)
It is described in.

In the relay lens system 15, the collimating lens 16
The parallel light is guided to the objective lens 17.

The objective I-nons 17 may be a conventional spherical lens made of a medium with a similar refractive index.

When the distance between the collimating lens 16 and the objective lens 17 is long, the condensing point 18 does not move even if the metal lens barrel 12 expands or contracts due to temperature changes.

The entire optical system is connected to the lens barrel section 1 where the objective lens is located.
If it is held at 4A, it will not be affected by expansion and contraction due to temperature changes, and there will be no need to use special metal parts.

By the way, in an electron microscope that uses the electron beam 19 as a probe, a charge-up phenomenon occurs in which electrons scattered from a sample are trapped in a dielectric.

In order to prevent this charge-up phenomenon, the entire glass surface 17A of the objective lens 17 closest to the sample is coated with a conductive film 20. And coating surface 17
The space between A and the metal lens barrel 14 is filled with a conductive paste 21.

Of course, instead of applying a conductive coating to the lens surface, a glass flat plate coated with this film may be inserted into the sample side of the objective lens 17 to obtain the same effect.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a light irradiation optical system that is not only extremely smaller and lighter than conventional systems, but also has stable and high-performance optical performance and can be used in a vacuum chamber.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a vacuum apparatus in which the optical system of the present invention is installed, Fig. 2 is a cross-sectional view showing an embodiment of the present invention, and Fig. 3 is an axial gradient index lens used in the present invention. FIG. 4 is a cross-sectional view showing a conventional device. 8... Sample, 10... Vacuum chamber, 11...
Light irradiation optical system, 12... Light source housing, 13...
Semiconductor laser, 14... Lens barrel, 15... Relay lens system, 16... Collimator lens, 16C... Equal refractive index surface, 16D... Equal refractive index line, 17... Objective lens, 18... Focus point, 19... Electron beam, 20.
... Conductive film, 21... Conductive paste. Figure 1 Figure 2 Figure 3 Figure 4 (Conventional device)

Claims (1)

[Claims] It consists of a point light source, a collimating lens that forms the emitted light from this light source in parallel, and an objective lens that collects the parallel light and irradiates the object with a spot. An optical system for vacuum equipment characterized by being composed of a rate distribution type lens.