JPS6169020A - Beam expander - Google Patents

Abstract

PURPOSE:To change continuously the diameter of an exit beam while keeping a beam waist position in the exit side invariable by constituting the whole of a system of two or more groups and moving two groups at least in the direction of the optical axis. CONSTITUTION:A beam expander 14 consists of two or more groups, and two groups, namely, a group (i) and a group (j) are made movable in the direction of the optical axis at least, and a diameter W0' of a beam waist 16 in the exit side is changed continuously without changing the position of this beam waist 16 with respect to a laser beam 11 in the incidence side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a beam expansion system, and more particularly to a beam expansion system that is suitably used in an optical system using a laser beam having a cross-sectional intensity distribution having a Gaussian distribution.

[Conventional wave 61] Because the TEMoo mode laser beam has a small spread and is close to a parallel beam, it is used in optical systems such as scanning optical systems and interferometers.This laser beam has a cross-sectional intensity distribution or a Gaussian distribution. and is called Usbeam. Although this beam is almost parallel, as is well known, the beam diameter changes even when propagating in free space.
The beam diameter is minimum at a certain position (beam waist), and the beam diameter gradually increases on either side of the minimum position.

When using such a laser beam, a beam exchanging device is used to adjust the laser beam emitted from the Rade resonator to a desired beam diameter. However, most of the conventionally used beam xnongs have a fixed magnification (for example, Br1xn@r + Jo
ur-Opt, Soe, Amer, 64 (19
74), 565), therefore, in order to obtain a desired beam diameter in an optical system with different specifications, there is a problem that a special beam expander must be used according to the specifications.

As a solution to this inconvenience, a variable magnification beam x-nongoo has been proposed (Japanese Patent Laid-Open No. 55-149).
915, JP-A-55-151612, and JP-A-55-155328).

However, all of these variable magnification beam ex-4ders are afocal type exo-4ders, and do not take into account the characteristics of the Gaussian beam.

That is, as shown in FIG. 6, the Gaussian beam 21 emitted from the Rade resonator 20 has a beam waist 22, which is called wo'c beam waist diameter.

Incidentally, reference numeral 23 is an incident-side reference plane selected as a plane perpendicular to the optical axis at an appropriate position on the optical axis, and the reference plane 23 is separated from the beam waist 22 by a distance of 2. When this Gaussian beam 21 is made incident on the optical system 24, the output beam 2
5, a beam waist 26 also occurs. Note that 27 is a reference surface on the exit side, and the reference surface 27 is separated from the exit side beam waist 26 by a distance of 2'. As above,
When a Gaussian beam with a beam waist) f on the input side is input to an optical system, a beam waist also occurs on the exit side.
The above-mentioned variable magnification beam extender does not take into account the existence of the beam waist.

On the other hand, a zoom lens for a yuss beam has been proposed, but although the diameter of the gauss beam can be continuously changed with the zoom lens proposed so far, the beam waist position on the exit side also changes. (Opt, Tech
nol, vol. 1 (1968) p. 24).

Since the wavefront condition is the best at the beam waist position, it is convenient for handling that the beam waist position of the beam emitted from Ex Gungu does not change at any magnification.

[Purpose of the invention]

In view of the above-mentioned prior art, it is an object of the present invention to provide a beam expander capable of continuously changing the exit beam diameter while keeping the beam waist position on the exit side completely unchanged for a constant incident beam. purpose.

[Summary of the invention]

According to the present invention, the above object is achieved by two or more groups in the entire system, at least two of which are movable in the optical axis direction, without changing the beam waist position on the exit side with respect to the laser beam on the input side. This is achieved by the beam ex-mango, which is characterized by continuously changing the beam waist diameter on the exit side.

[Embodiments of the invention]

Hereinafter, the present invention will be specifically described with reference to the drawings.

FIG. 1 is a schematic diagram of the beam expander of the present invention in use. In the figure, 11 is an incident side beam, 12 is its beam waist, 13 is an incident side reference plane, and 14 is a bi, -m, exno, two, and ni group. Reference numeral 15 denotes an N'·exit side beam, 16 its beam waist, and 17 an exit side reference plane. The entrance side beam waist 12 (diameter V) is located at a distance of 2 from the entrance side reference surface 13, and the exit side beam waist 16 (diameter W10) is located at a distance of 2' from the exit side reference surface 17. In the beam extender 14, the first group and the first group are movable groups, and the others are fixed groups (1≦l+j≦k and 1+j). l details and 1
Let the moving amounts of the groups be Xj and Xj, respectively.

Information transmission when a laser beam enters and exits an optical system is based on Kogee'nik's theory (BellS
System Technical Journal,
Maom44.1965. p.

According to 455), it is expressed as. Here, j is an imaginary unit, λ is the wavelength of the laser beam, qFi indicates the value on the incident side, and q' indicates the value on the exit side. In addition, A, B, C, and D are expressed using Gaussian brackets as follows (Tanak-a2 0pt
lk, vol, 64. 1983. p13, p
89).

・・・・・・・・・・・・・・・(3) Here, φ. is the refractive power of the nth group, and e'. is the nth group and the (n+1)th group
Represents the principal point spacing between groups.

From the above, calculating the distance z''k from the reference plane 17 on the exit side to the beam waist 16 on the exit side, omitting the intermediate process, ...... ) and υ, exit side beam waist diameter vr'o Ha, to=w0/((Cz+
D) 2+02(πw02/λ) 2) −・−・・−
(5) becomes.

From Equations (4) and (5), when the entrance side beam waist position (z) and beam diameter (wo) remain unchanged, the exit side beam waist position (2') always remains fixed and the exit side beam waist It can be seen that in order to continuously vary the diameter (w',), at least two groups movable in the optical axis direction are required.

In addition, in the embodiment shown in FIG. 1, the principal point interval "Jte' between the n-th group and the (n+1)-th group before zooming is set to 0,
Principal point interval t between the nth group and the (n+1)th # after zooming
−e′. Then, between these, the following 1=1□! Once the I section is completed... (6) While the beam waist position on the exit side remains unchanged, the beam waist diameter given by equation (5) can be changed continuously. still,
It is desirable that the above relational expressions hold strictly true, but in reality, if these relational expressions are substantially satisfied, it is possible to continuously change the beam waist diameter while the beam waist position can be considered to be virtually unchanged. Therefore, the permissible error range of the above relational expression can be determined as appropriate depending on the purpose of use.

Table 1 shows the lens configuration data of the first example of the beam exo-yander of the present invention. In the table, R1-R8 is the radius of curvature (simplified) of each refractive surface, D, ~DB are the intervals (,,,) between each refractive surface, N1-N4 are the refractive index of the glass material, , ~v4 is the number of glass materials.

The configuration diagram of this example is shown in FIG. 2.

D□ Table 1 R, = 8.98501 = 3.20 N, = 1.51
462 M, = 64.1R2 = 62.169 0
2=Variable R,=-12,010D3=1.00 N2=1.72
309 1/2=28.5R4=5.353 1)
4=Variable R5=162.787 D5=3.80 N5=1.7
7861 173=25.7R6= 88.806
D6=3.60R,=147.748 D7=4.
90 N4=1.51462 C4=64.1R8
=-54,507 This example consists of three groups, positive, negative, and positive, from the incident side.
The positive group (1) and the second group (II) are movable, and the third
The positive group (lft) is fixed. If the ratio of the beam waist diameter on the exit side to the beam waist diameter on the entrance side is taken as a magnification, then in this example, the magnification is continuously variable from 10.1 times to 3.9 times. Magnification and beam extender when changed to D2 and D4 Focal length of 4-dar 1 f't - Table 2 shows.

Table 2 Magnification 10.1x 5.5x 3.9x D23.13
397.1879 8.4310D492.52959
0°279588.5295f' 1. IX1
05-4.5X10" -3, lX105 Figure 3 shows the wavefront aberration at the exit side beam waist position at magnifications of 10.1x, 5.5x, and 3.9x in this example (&)
, shown in (b) and (e).

Next, Table 3 shows the lens configuration data of the second example of the beam expanding device of the present invention. Further, a configuration diagram of this example is shown in FIG.

Table 3 R, = 8.545 D, = 3.20 N, = 1.51
462ν, = 64.1R2 = 43.920 D2
=Variable R,=-9,34703=1.0ON2=1.
72309shi2=28.5R4=6.161
D4=variable R5=-128,945D5=4.90N
5=1.51462ν,=64.1,R6=-69,
11506=3.60R,=-459,239D,=3
．． 80 N4=1.69415 ν4=55.5
R8= -97,997 In this example, the input side is composed of positive, negative, and positive 3#s, and the first
The positive group (1) and the second negative group (II) are movable, and the third positive group (1) is fixed. In this example, the magnification is continuously variable from 10 times to 4 times. Table 4 shows the magnification and focal length f' of the beam extender when D2 and D4 are changed.

Table 4 Magnification 10x 5.5x 4x D23.060
6 7.1146 8.3577D4 93.5
165 91.2665 89.5165f' 8
．． 4X1056.9X10' -3, lX105 Wavefront aberration ti5 diagram (at,
Shown in (b) and (c).

〔Effect of the invention〕

According to the present invention, even when a Gaussian beam is incident, the exit side beam diameter can be continuously changed while the exit side beam waist position remains unchanged, and the wavefront aberration is good, making it extremely effective.・Gunder is obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the beam expander of the present invention, FIGS. 2 and 4 are diagrams of the beam expander of the present invention, and FIG. 3 (aJ, (b), (c)
5(a), (b) + (e) are wavefront aberration diagrams. FIG. 6 is an explanatory diagram of a Gaussian beam. 1 is the incident side beam, 12: incident side beam waste), 13
: Incidence side reference plane, 14: Beam extender 74, 15
: Exit side beam, 16: Exit side beam waist, 17:
Injection side reference surface. Figure 1 Figure 6 Figure 3 (a) Figure 3 (b) Figure 3 (C) Figure 5 (()) Figure 5 (b) Figure 5 (C)

Claims (4)

[Claims] (1) The entire system consists of two or more groups, of which at least two
A beam expander characterized in that the group is movable in the optical axis direction, and the exit side beam waist diameter can be continuously changed with respect to the entrance side laser beam without changing the exit side beam waist position. (2) The entire system is composed of k groups (k≧2), of which the i and j groups (1≦i, j≦k and i≠j) are movable groups, and the other groups are fixed groups, φ_n: Refracting power of the n-th group e′_n_, _0: Principal point distance between the n-th group and the (n+1)-th group before the i-th group and the j-th group are moved e′_n: The i-th group and the j-th group The nth group and (n
+1) Principal point distance from the group w_o: Incident side beam waist diameter z: Distance from the incident side reference surface to the incident side beam waist z': Distance from the exit side reference surface to the exit side beam waist x_i: The diameter of the incident side beam waist Amount of movement x_j: Amount of movement of the j-th group λ: As the wavelength of the laser beam, z' is approximately [(A_z+B)(C_z+D)+AC(πw_o^2
/λ)^2]/[(C_z+D)^2+C^2(πw_
o^2/λ)^2] (where A=[φ_1, e'_1, φ_2, -e'_2, ..., φ
＿k, −e′_k]B=[−e′_0, φ_1, −e′
_1, φ_2, ..., φ_k, -e′k]C=[φ_1,
-e'_1, φ_2, -e'2, ..., -e'_k_-_
1, φ_k]D=[-e'_0, φ_1, -e'_1,
φ_2, ..., -e'k-1, φ_k]e'_i_-_1
=E'_i_-_1+x_ie'_i=E'_i-x_
i E'_i_-_1={e'_i_-_1_,_0 (i
-1≠j), e'_i_-_1_, _0-x_j
(When i-1=j) E'_1={e'_i_,_0
(when i+1≠j), e′_i_, _0−x_j(i
+1=j) e′_j_−_1={e′i, 0(i
+1=j), e'_j_1_, 0-x_j(i+
When 1≠j) e′j={e′_i_−_1_, _0
(when i-1=j), e'_j_, _0-x_j(i
The beam expander of the first term is equal to (when -1≠j). (3) z′=[(A_z+B)(C_z+D)+AC(πw_
o^2/λ)^2]/[(C_z+D)^2+C^2(
πw_o^2/λ)^2], the beam expander of the second term. (4) The entire system consists of three groups, the first group has positive refractive power, the second group has negative refractive power, the third group has positive refractive power, and the first and second groups have positive refractive power. The beam expander of the first or second term, wherein the group is a movable group and the third group is a fixed group.