JPH10104510A - Ultraviolet ray converging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet ray converging lens capable of forming a spot of diffraction limit by utilizing a light source in an ultraviolet range having a wavelength <=300nm. SOLUTION: This lens is composed, in order from the side of a light source, of a first lens group GI including a meniscus lens whose concave surface confronts the side of a light source and expanding the diameter of a light beam and a second lens group GII composed of a first lens whose convex surface confronts the side of the light source, a second biconcave lens, a third and a fourth biconvex lenses, a fifth and sixth positive meniscus lenses whose convex surfaces confront the side of the light source and all lens elements are formed with quartz. The following conditions: -0.11<f/f1<0.05, 0.30<|rm1|/dm<1.00, rm1<0 are satisfied, where, f, f1, are the focal distances of the whole system and the first lens group, rm1, dm are the radius of curvature and the thickness of the surface of the meniscus lens on the side of the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet focusing lens suitable for using ultraviolet light having a wavelength of 300 nm or less as a light source.

[0002]

2. Description of the Related Art The recording density of an optical disk tends to increase gradually, for example, as can be seen by comparing the standard of an early compact disk with the standard of a recent digital video disk. Since the recording density of an optical disk is inversely proportional to the square of the spot diameter of a laser beam, it is necessary to reduce the spot diameter in order to increase the recording density. 2. Description of the Related Art Conventionally, an optical head of an apparatus for producing a master of an optical disc has an objective lens for converging laser light to a diffraction limit. Since the spot size at the diffraction limit becomes smaller as the wavelength becomes shorter, the wavelength of the light source is gradually shortened from the visible region to the near ultraviolet region in order to form a smaller spot.

If the wavelength used changes, the design of the objective lens also needs to be changed. For example, Japanese Patent Application Laid-Open No. 4-274206
Japanese Patent Application Laid-Open Publication No. H11-163,086 discloses an objective lens suitable for a wavelength in the near ultraviolet region of about 350 nm.

[0004]

However, since the above-mentioned conventional objective lens is designed for the near ultraviolet region, a wavelength of 300 nm is required to further reduce the spot size.
It cannot be used when ultraviolet rays of nm or less are used. That is, in the ultraviolet region having a wavelength of 300 nm or less, the lens material that can secure a sufficient transmittance is limited to quartz glass and fluorite. The rate decreases, and a sufficient amount of light cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides an ultraviolet convergent lens capable of forming a diffraction-limited spot by using an ultraviolet light source having a wavelength of 300 nm or less. The purpose is to do.

[0006]

The ultraviolet converging lens according to the present invention is a lens for converging a parallel light beam in the ultraviolet region emitted from a light source, and has a function of increasing the light beam diameter in order from the light source side. A lens group and a second lens group having an action of converging a light beam are arranged and configured. All the lens elements of the first and second lens groups are formed of quartz. The first lens group includes a meniscus lens having a concave surface facing the light source. The second lens group is arranged in order from the light source side.
A first lens having a convex surface facing the light source side, a biconcave second lens, a biconvex third lens, a biconvex fourth lens, and a positive meniscus fifth lens having a convex surface facing the light source side. And a positive meniscus sixth lens having a convex surface facing the light source side. Assuming the above configuration, the following conditions
(1) and (2) are satisfied. −0.11 <f / f1 <0.05 (1) 0.30 <| rm1 | / (dm) <1.00, rm1 <0 (2) where f is the focal length of the entire system and f1 Is the focal length of the first lens group, rm1 is the radius of curvature of the light source side surface of the meniscus lens of the first lens group, and dm is the thickness of the meniscus lens of the first lens group.

The first lens group has a concave surface facing the light source side.
It is composed of one meniscus lens or, in order from the light source, a first lens having a weak power and a second meniscus lens having a concave surface facing the light source.
When the first lens group is composed of two lenses, it is desirable that the focal length fI1 of the first lens satisfies the following condition (3). f / | fI1 | <0.08 (3)

The sixth lens located closest to the image side of the second lens group desirably satisfies the following conditions, with the radius of curvature of the surface on the light source side being rII6 and the thickness being dII6. 0.70 <rII6 / dII6 <0.95 (4)

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an ultraviolet focusing lens according to the present invention will be described. The ultraviolet convergent lens of the embodiment is a lens that converges a parallel light beam in the ultraviolet region emitted from the light source. For example, as shown in FIG. 1, the light beam diameter is sequentially reduced from the light source side (not shown) on the left side in the figure. A first lens group GI having an action of expanding and a second lens group GII having an action of converging a light beam are arranged and arranged. In order to secure a wide working distance, the first lens group GI temporarily increases the light beam diameter, and the second lens group GII converges the light flux diameter to secure a long back focus.

The first lens group GI includes a meniscus lens Im having a concave surface facing the light source. The second lens group GII is
The first lens II1 with the convex surface facing the light source side in order from the light source side
A biconcave second lens II2, a biconvex third lens II3,
A biconvex fourth lens II4, a positive meniscus fifth lens II5 with a convex surface facing the light source side, and a positive meniscus sixth lens II6 with a convex surface facing the light source side are arranged.

Since the converging lens has a strong positive power as a whole, the aberration generated in each positive lens is suppressed to a small value, and the residual aberration is canceled by the negative lens or the diverging surface, thereby increasing the numerical aperture. It becomes possible to narrow the spot to the diffraction limit. For this purpose, the height of incidence of marginal rays on the second lens group is increased by enlarging the beam diameter in the first lens group, and five positive lenses are provided in the second lens group to increase the positive power. And condensed light gradually on a loose convergence surface.

In the ultraviolet region, lens materials capable of ensuring a sufficient transmittance are limited to quartz glass and fluorite, but fluorite is difficult to process because of its low hardness, so practically it is limited to quartz glass. Can be For this reason, all the lens elements of the first and second lens groups are formed of quartz glass.

The meniscus lens Im included in the first lens group GI diverges the light beam on the concave surface on the light source side and converges it on the convex surface on the exit side. .

The convex surface on the light source side of the first lens II1 of the second lens group GII has a function of converging light emitted from the first lens group. If the diverging surface is disposed at this position, the degree of divergence of the light beam becomes excessive, and the height of incidence of the marginal ray to the subsequent lens becomes too large, so that the amount of spherical aberration generated becomes excessive.

The second negative lens II2 has a function of correcting the spherical aberration of the convergent lens having a positive power as a whole. If all the second lens group GII is a positive lens, the working distance can be increased, but in this case, only the diverging surface of the first lens group is used to correct the under spherical aberration generated in the second lens group. Can not. On the other hand, since the height of the marginal ray at the time of incidence on the first lens group GI is low, the effect of correcting spherical aberration is weak even if the surface on the light source side has a strong diverging power. Therefore, in order to correct this spherical aberration, the second lens group GII has a negative second
A lens II2 is provided.

Each of the third lens II3 to the sixth lens II6 is a positive lens and has a function of converging a light beam. Since quartz has a low refractive index, four positive lenses are required to obtain sufficient convergence power without generating excessive spherical aberration. When five or more positive lenses are provided, the overall length of the converging lens becomes longer.

The converging lens according to the embodiment satisfies the following conditions (1) and (2) on the premise of the above configuration. −0.11 <f / f1 <0.05 (1) 0.30 <| rm1 | / (dm) <1.00, rm1 <0 (2) where f is the focal length of the entire system and f1 Is the focal length of the first lens group, rm1 is the radius of curvature of the light source side surface of the meniscus lens of the first lens group, and dm is the thickness of the meniscus lens of the first lens group.

Condition (1) defines power distribution to the first lens group GI. By satisfying this condition, the divergence of the light emitted from the first lens group having an enlarged diameter becomes appropriate, the occurrence of spherical aberration in the second lens group GII is suppressed, and a predetermined length is obtained without increasing the overall length. It is possible to secure a working distance. When the value goes below the lower limit of the condition (1), the negative power of the first lens group becomes too strong, and high-order spherical aberration occurs in the second lens group GII, so that the numerical aperture cannot be increased. . When the value exceeds the upper limit of the condition (1), the positive power of the first lens unit becomes excessive, and the divergence of the meniscus lens is required to keep the exit height of the marginal ray to a predetermined value in order to secure a working distance. It is necessary to increase the distance between the surface and the converging surface, so that the entire length of the meniscus lens becomes longer and the converging lens becomes larger as a whole.

The condition (2) defines the action of expanding the light beam by the first lens group. By satisfying this condition, it is possible to keep the exit height of the marginal light beam at a predetermined level while keeping the thickness of the meniscus lens moderate. When the value is below the lower limit of the condition (2), the diverging power of the diverging surface becomes excessive and high-order spherical aberration is generated, or the lens thickness becomes excessive and the entire converging lens becomes large. conditions
When the value exceeds the upper limit of (2), the diverging power of the diverging surface becomes too small or the lens thickness becomes too small. In order to secure the incident height of the marginal ray,
It is necessary to provide the lens unit with a negative power to secure a wide interval between the lens unit and the second lens unit, so that the size of the converging lens becomes large as a whole.

The first lens group is composed of a single meniscus lens having a concave surface facing the light source side as shown in FIG. 1 and weaker in order from the light source side as shown in FIG. 7, for example. It comprises a first lens I1 having power and a second lens Im of a meniscus having a concave surface facing the light source side.
When the first lens group GI is composed of two lenses, it is desirable that the focal length fI1 of the first lens satisfies the following condition (3). | FI1 | / f <0.08 (3)

Condition (3) is a condition for making the first lens I1 of the first lens group GI replaceable for adjusting spherical aberration. When the first lens group is composed of two lenses, if a lens having extremely weak power is arranged on the light source side,
When spherical aberration occurs due to an error in assembling other lens elements of the converging lens, the spherical aberration can be corrected by replacing the first lens with a lens having a different power. However, when the power of the first lens I1 exceeds the upper limit of the condition (3), astigmatism and coma tend to occur due to the eccentricity and inclination generated at the time of replacement. By satisfying the condition (3), it is possible to suppress the aberration that occurs when the first lens I1 is decentered or tilted to a level that does not pose a practical problem.

The sixth lens located closest to the image side of the second lens group desirably satisfies the following conditions, with the radius of curvature of the surface on the light source side being rII6 and the thickness being dII6. 0.70 <rII6 / dII6 <0.95 (4)

The condition (4) defines the shape of the lens on the spot side where the light beam converges most. When the value goes below the lower limit of the condition (4), the convergence effect of the sixth lens becomes excessive, so that the spherical aberration increases and the working distance becomes short. Further, in order to ensure a predetermined working distance, the thickness of the sixth lens becomes excessively large, and the entire converging lens becomes large. On the other hand, when the value exceeds the upper limit of the condition (4), a high numerical aperture cannot be secured and the spot diameter increases, or the lens thickness becomes thin, so that processing of this lens becomes difficult.

[0024]

EXAMPLES Next, six specific examples that satisfy the conditions of the above-described embodiment will be presented. Each of the embodiments is a convergent lens for forming a diffraction-limited spot using ultraviolet rays, and is used as an objective lens of a digital video disc master making apparatus having a higher recording density than a compact disc.

[0025]

FIG. 1 shows a lens configuration of an ultraviolet focusing lens according to a first embodiment. The numerical configuration of the lens is shown in Table 1. Example 1 is a lens for an ultraviolet ray having a used wavelength of 266 nm. In the table, NA is the numerical aperture, f is the focal length of the entire system (unit: mm), ω is the half angle of view, fB is the back focus (unit: mm), and r is the radius of curvature of each lens surface.
(Unit: mm), d is the lens thickness or lens interval (unit:
mm), n266 is the refractive index of each lens at a wavelength of 266 nm.

[0026]

[Table 1]

In the first embodiment, the first lens group GI is
The second lens group GII is composed of a negative meniscus Im having a concave surface facing the light source side represented by the second surface and the second surface.
A positive first lens having a convex surface facing the light source side represented by the fourth surface
II1, a biconcave second lens II2 represented by the fifth and sixth surfaces,
Biconvex third lens II3 represented by seventh and eighth surfaces, ninth
Surface, the biconvex fourth lens II4 represented by the tenth surface, the eleventh lens
From the fifth lens II5 of the positive meniscus having a convex surface facing the light source side represented by the surface and the twelfth surface, and from the sixth lens II6 of the positive meniscus having a convex surface facing the incident side represented by the thirteenth and fourteenth surfaces. It is configured.

FIG. 2A shows the spherical aberration SA and the sine condition violation amount OSC of the lens of Example 1, and FIG. 2B also shows astigmatism (S: sagittal, M: meridional).

[0029]

FIG. 3 shows a lens configuration of a converging lens for ultraviolet light according to a second embodiment. Table 2 shows the numerical configuration. Example 2 is a lens for ultraviolet light having a used wavelength of 266 nm. In the second embodiment, the first lens group GI is
The second lens group GII includes the same six negative lenses as in the first embodiment, and includes the same negative meniscus lens Im alone as in the first embodiment. FIG. 4A shows the spherical aberration SA and the sine condition violation amount OSC of the lens of Example 2, and FIG. 4B also shows astigmatism.

[0030]

[Table 2]

[0031]

Third Embodiment FIG. 5 shows a lens configuration of an ultraviolet focusing lens according to a third embodiment. The numerical configuration is shown in Table 3. Example 3 is a lens for ultraviolet light having a used wavelength of 248 nm. The symbol n248 in the table indicates a wavelength of 248 nm.
Is the refractive index of each lens. In the third embodiment, the first
The lens group GI includes only the negative meniscus lens Im similar to the first embodiment, and the second lens group GII includes six lenses similar to the first embodiment. FIG. 6A shows the spherical aberration SA and the sine condition violation amount OS of the lens of the third embodiment.
C and (b) also show astigmatism.

[0032]

[Table 3]

[0033]

Fourth Embodiment FIG. 7 shows a lens configuration of an ultraviolet focusing lens according to a fourth embodiment. Table 4 shows the numerical configuration. Example 4 is a lens for ultraviolet light having a used wavelength of 248 nm. In the fourth embodiment, the first lens group GI is
Concave flat first lens I1 with weak negative power on the light source side
And a meniscus second lens Im having a concave surface facing the light source side. The second lens group GII includes six lenses similar to those in the first embodiment. FIG. 8A shows the fourth embodiment.
Shows the spherical aberration SA and the sine condition violation amount OSC of the lens of (a), and (b) similarly shows astigmatism.

[0034]

[Table 4]

Generally, in a lens in which spherical aberration and coma have been corrected, the spherical aberration changes depending on the degree of convergence of the light beam incident on the lens (the radius of curvature of the wavefront). Negative (under) spherical aberration occurs when divergent light is incident on a lens that converges a parallel light beam without spherical aberration, and positive (over) spherical aberration occurs when convergent light is incident. Therefore, the first lens having the weakest power on the light source side as described above
When I1 is arranged, if a positive spherical aberration occurs in the entire system due to a manufacturing error or an assembly error, the first lens I1
Is replaced with a lens having a function of more diverging the light flux than the design reference state, and when a negative spherical aberration occurs, the first lens I1 functions to converge the light flux more than the design reference state. By replacing the lens with the lens having, the generated spherical aberration can be canceled.

[0036]

Fifth Embodiment FIG. 9 shows a lens configuration of an ultraviolet focusing lens according to a fifth embodiment. Table 5 shows the numerical configuration. Example 5 is a lens for ultraviolet light having a used wavelength of 266 nm. In the fifth embodiment, the first lens group GI is
Similarly to the fourth embodiment, the second lens unit GII includes a concave first lens I1 having a weak negative power and a negative meniscus lens Im, and the second lens group GII includes six lenses similar to the first embodiment. . FIG. 10A shows the spherical aberration SA of the lens of the fifth embodiment.
And the sine condition violation amount OSC, and (b) similarly shows astigmatism.

[0037]

[Table 5]

[0038]

Sixth Embodiment FIG. 11 shows a lens configuration of a converging lens for ultraviolet rays according to a sixth embodiment. Table 6 shows the numerical structure.
Is shown in Example 6 is a lens for ultraviolet light having a used wavelength of 248 nm. In the sixth embodiment, the first lens group GI
Is composed of the same negative meniscus lens Im alone as in the first embodiment, and the second lens group GII is composed of six lenses similar to the first embodiment. FIG. 12A shows the spherical aberration SA and the sine condition violation amount OSC of the lens of Example 6,
(b) also shows astigmatism.

[0039]

[Table 6]

Table 7 below shows the relationship between the above-mentioned conditional expressions and the examples. Conditions (1), (2) and (4) are satisfied in all the embodiments. The condition (3) is satisfied in Examples 4 and 5 in which the first lens group includes two lenses.

[0041]

[Table 7] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Condition (1) 0.0221 -0.0004 0.0153 0.0084 -0.0185 -0.0958 Condition (2) 0.940 0.881 0.980 0.769 0.483 0.742 Condition (3)- --0.0095 0.0200-Condition (4) 0.813 0.799 0.805 0.852 0.913 0.847

[0042]

As described above, according to the present invention, it is possible to provide a convergent lens suitable for forming a diffraction-limited spot using ultraviolet rays. Further, by satisfying a predetermined lens configuration, practically sufficient performance can be satisfied with a relatively small number of components.

[Brief description of the drawings]

FIG. 1 is a lens diagram of a converging lens for ultraviolet light according to a first embodiment.

FIG. 2 shows the spherical aberration of the converging lens for ultraviolet light according to the first embodiment;
It is a graph which shows a sine condition violation amount and an astigmatism.

FIG. 3 is a lens diagram of an ultraviolet focusing lens according to a second embodiment.

FIG. 4 shows the spherical aberration of the converging lens for ultraviolet light according to the second embodiment,
It is a graph which shows a sine condition violation amount and an astigmatism.

FIG. 5 is a lens diagram of a converging lens for ultraviolet light according to a third embodiment.

FIG. 6 shows the spherical aberration of the ultraviolet convergent lens of the third embodiment,
It is a graph which shows a sine condition violation amount and an astigmatism.

FIG. 7 is a lens diagram of an ultraviolet focusing lens according to a fourth embodiment.

FIG. 8 shows the spherical aberration of the ultraviolet convergent lens of Example 4,
It is a graph which shows a sine condition violation amount and an astigmatism.

FIG. 9 is a lens diagram of a converging lens for ultraviolet light according to a fifth embodiment.

FIG. 10 is a graph showing the spherical aberration, the sine condition violation amount, and the astigmatism of the converging lens for ultraviolet light of Example 5.

FIG. 11 is a lens diagram of a converging lens for ultraviolet light according to a sixth embodiment.

FIG. 12 is a graph showing the spherical aberration, the sine condition violation amount, and the astigmatism of the ultraviolet convergent lens of the sixth embodiment.

[Explanation of symbols]

 GI First lens group Im Meniscus lens GII Second lens group II1 to II6 First to sixth lenses

Claims (4)

[Claims] 1. A lens for converging a parallel light beam in an ultraviolet region emitted from a light source, the first lens group having an effect of increasing the light beam diameter in order from the light source side, and a second lens group having an operation of converging the light beam. The first lens group includes a meniscus lens having a concave surface facing the light source side, and the second lens group has a convex surface facing the light source side in order from the light source side. A first lens, a biconcave second lens, a biconvex third lens, a biconvex fourth lens, a positive meniscus fifth lens having a convex surface facing the light source side,
A sixth lens of a positive meniscus having a convex surface facing the light source side is arranged, and all lens elements of the first and second lens groups are formed of quartz, and satisfy the following conditions. UV focusing lens. −0.11 <f / f1 <0.05 0.30 <| rm1 | / (dm) <1.00, rm1 <
0 where f is the focal length of the entire system, f1 is the focal length of the first lens group, rm1 is the radius of curvature of the light source side surface of the meniscus lens of the first lens group, and dm is the thickness of the meniscus lens of the first lens group. That's it. 2. The ultraviolet converging lens according to claim 1, wherein the first lens group includes a single meniscus lens having a concave surface facing the light source. 3. The first lens group includes, in order from the light source side, a first lens having a weak power and a second meniscus lens having a concave surface facing the light source side, and satisfies the following conditions. The converging lens for ultraviolet light according to claim 1, wherein: f / | fI1 | <0.08 where fI1 is the focal length of the first lens in the first lens group. 4. The lens according to claim 1, wherein a radius of curvature of a surface of the sixth lens in the second lens group on the light source side is rII6 and a thickness is dII6, and the following conditions are satisfied. The convergent lens for ultraviolet rays according to the above. 0.70 <rII6 / dII6 <0.95