JPH07239448A - Laser survey instrument - Google Patents

Abstract

PURPOSE:To provide a laser survey instrument which is capable of efficiently carrying out a positioning operation to be surveyed with high accuracy and does not increase the size over the entire part of the instrument by shaping an elliptical laser spot of a semiconductor laser to a nearly circular shape while preventing a decrease of light quantity as far as possible. CONSTITUTION:This laser survey instrument uses the semiconductor laser as a light source and has an amplification filter 1 for shaping the beam spot of the laser luminous flux emitted from the semiconductor laser. This amplitude filter 1 is set at the degree of transmission which is smaller as the filter 1 parts from the center of the elliptical beam spot of the laser luminous flux toward the major axis direction of the elliptical shape. In addition, the degree of transmission is approximately constant in the minor axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser surveying instrument having a semiconductor laser as a light source and having an optical filter for shaping a beam spot of a laser beam emitted from the semiconductor laser.

[0002]

2. Description of the Related Art Conventionally, there is known a laser surveying instrument configured to emit a laser beam toward a surveyed object, detect the arrival position of the laser beam on the surveyed object, and perform leveling or the like. A gas laser such as a helium neon laser has been mainly used as a laser light source of such a laser surveying instrument, but recently, a small and lightweight semiconductor laser is often used. A typical example of a semiconductor laser having a general stripe structure is a stripe type double heterojunction type semiconductor laser. As shown in FIG. 6, the structure of the stripe type double heterojunction semiconductor laser has a positive electrode 31, a leading edge layer 32, a cap layer 33, a clad layer 34, an active layer 35 and a light emitting surface 36, a substrate crystal 37,
The negative electrodes 38 are sequentially stacked. The active layer 35 and the light emitting surface 36 have a structure in which a current flows only in the portion of the light emitting surface 36 having a striped or band-shaped cross section. The thickness of the active layer 35 is very thin, 1 μm or less, and the width of the light emitting surface 35 is usually 10 to unify the transverse mode.
It is about 20 μm. For this reason, the light emitting surface 36 of the semiconductor laser described above has a rectangular shape, and the far-field pattern of the laser beam emitted from the semiconductor laser, that is, the beam spot, is generally elliptical. The transverse mode in the direction perpendicular to the joint surface of each layer is called the vertical transverse mode, and the transverse mode in the direction parallel to the joint surface is defined as the horizontal transverse mode.

In laser survey instruments, gas lasers,
Regardless of which light source of the semiconductor laser is used, it is required to reduce the beam spot from the viewpoint of positioning accuracy. When narrowing the light beam in order to reduce the beam spot, a “stop” is generally used. However, if a filter having a uniform transmittance over the entire aperture is used as the diaphragm, interference fringes are generated at a distance, which makes positioning work difficult. Therefore, in order to perform so-called apodization, which reduces or suppresses the energy of the interference fringes of the second or higher order, the apodization filter for the light beam diaphragm has a large central transmittance and becomes smaller as the distance from the center decreases. A method using is known. When the gas laser is used as the light source, the beam spot has a circular shape. Therefore, if the luminous flux is reduced to some extent by this method, the positioning work can be performed with high accuracy. However, as described above, the beam spot of the semiconductor laser is generally elliptical. When shaping this elliptical beam spot, an apodization filter having a circular transmittance distribution as described above may be used, but in this case, when shaping it into a shape close to a circle, it is transmitted. There is an absurdity that the amount of light is greatly reduced.

FIG. 4 shows the shaping state, that is, the roundness, when an elliptical beam spot is shaped using a circular apodization filter of a certain size.
ρ ₀ is a value representing the shape of the beam spot before shaping. For example, ρ ₀ = 5 indicates that the major axis of the beam before shaping is 5 times the minor axis. The vertical axis represents the roundness ρ, which is the ratio of the beam diameter in the vertical transverse mode direction V to the beam diameter in the horizontal transverse mode direction H of the shaped beam spot, that is, the shaped beam spot. The horizontal axis represents the ratio of the diameter of the portion of 1 / e ² or more of the density distribution of the circular filter to the beam diameter of the beam spot before shaping in the horizontal transverse mode direction P
represents x. That is, Px = diameter of a portion of 1 / e ² or more of the density distribution of the filter / beam diameter of the beam spot before shaping in the horizontal transverse mode direction. For example, Px = 1 is the case where the beam diameter of the beam spot before shaping in the horizontal transverse mode direction H is equal to the diameter of the portion of 1 / e ² or more of the density distribution of the filter. As can be understood from FIG. 4, even if Px = 1, the circularity ρ
Is about 1.3, and ρ = 1 is not established. Further, when Px is set to a value close to 0, the circularity becomes a value close to 1, but the diameter of 1 / e ² or more of the density distribution of the filter is the horizontal transverse mode of the beam spot before shaping. Since the beam diameter is smaller than the beam diameter in the direction H, the light amount is greatly reduced.

If a known anamorphic optical system, that is, an optical system having different projection magnifications in the horizontal and vertical directions on the image plane is used, an elliptical beam spot can be shaped into a circular beam spot. it can. However, the anamorphic optical system has a drawback that the whole surveying instrument is enlarged.

[0006]

SUMMARY OF THE INVENTION The present invention shapes the elliptical laser spot of a semiconductor laser into a shape close to a circle while preventing a decrease in the amount of light as much as possible, thereby positioning the surveying object with high accuracy. An object of the present invention is to provide a laser surveying instrument that can be efficiently performed and does not increase the size of the entire instrument.

[0007]

The present invention has been made in view of the above technical problems. The present invention provides a laser surveying instrument having a semiconductor laser as a light source and an amplitude filter for shaping a beam spot of a laser beam emitted from the semiconductor laser, wherein the amplitude filter is a center of an elliptical beam spot of the laser beam. The laser surveying instrument is characterized in that the transmittance decreases with increasing distance from the ellipse in the major axis direction, and the transmittance is substantially constant in the minor axis direction. According to one embodiment of the present invention, the transmittance distribution of the amplitude filter is approximately Gaussian.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. The right side of FIG. 1 is a plan view for explaining the amplitude filter 1. In the amplitude filter 1, as shown in the transparency graph on the left side of FIG. 1, the transparency decreases as the distance from the center in the vertical transverse mode direction V increases. The transmittance in the horizontal transverse mode direction H is constant. In the following, such an amplitude filter is called a one-dimensional filter, while a conventional filter having the same transmittance on the same circumference and a circular transmittance distribution is called a circular filter. The transmittance distribution of the amplitude filter 1 has a vertical transverse mode direction V of incident laser light.
Is determined by the state of the intensity distribution of. From a geometrical optics perspective, the value obtained by multiplying the intensity distribution of the laser light flux incident on the amplitude filter 1 in the vertical transverse mode direction V by the transmittance distribution of the one-dimensional filter is the light intensity in the vertical transverse mode direction V. Distribution. Therefore, the transmittance distribution of the amplitude filter 1 is preferably such that the light intensity distribution of the transmitted light in the vertical transverse mode direction V is a Gaussian distribution or a approximation thereof. Practically, when the diameter of the amplitude filter 1 is sufficiently smaller than the elliptical major axis of the beam spot of the incident laser light, the intensity distribution of the incident laser light flux can be regarded as constant and the amplitude can be regarded as being constant. The transmittance distribution in the vertical transverse mode direction V of the filter is often a Gaussian distribution.

On the other hand, the lateral width of the amplitude filter 1 is made larger than the diameter of the laser beam in the horizontal transverse mode direction H. The reason is that if the width of the amplitude filter 1 is smaller than the diameter of the laser beam in the horizontal transverse mode direction H, interference fringes are generated in that direction. Next, a case where a beam spot is shaped using a circular filter and a case where a beam spot is shaped using a one-dimensional filter will be described in comparison. When the amplitude filter 1 is a circular filter, as shown in FIG. 2, the long radius of a portion of 1 / e ² or more of the light intensity at the center of the elliptical beam spot is ω _OY , and the short radius is ω _OX. If the radius of the portion where the filter transmittance is 1 / e ² or more is ω _f , the intensity distribution in the vertical transverse mode direction V (y direction) of the major axis in the elliptical beam spot,
The intensity distribution in the horizontal transverse mode direction H (x direction) of the minor axis is represented by the following equations. Major axis direction ω _OY = I _O exp {-2 (y / ω _OY ) ² } Minor axis direction ω _OX = I _O exp {-2 (x / ω _OX ) ² }. In addition, the transmittance distribution of the circular filter for comparison is a Gaussian distribution and is expressed as I _F = exp {−2 (r / ω _F ) ² }. However, r is the distance from the center of the filter.

Therefore, the beam distribution after passing through the film is approximately represented by the following equation. Longitudinal direction I _Y = I _O exp {-2 (y / ω _OY ) ² } · exp {-2 (y / ω _F ) ² } = I _O exp {-2 (y / ω _Y ) ² } …… Short Radial direction I _X = I _O exp {-2 (x / ω _OX ) ² } · exp {-2 (x / ω _F ) ² } = I _O exp {-2 (y / ω _X ) ² } ... , Ω _Y , and ω _X are the major and minor radii of the beam spot after passing through the circular filter, and are expressed by the following equation from the equation. ^{_{ω Y = √ω OY 2 ω F}} 2/2 × ( the ^{_{(ω OY 2 + ω F 2}} ) ...... ω X = √ω OY 2 ω F 2/2 × (ω OX 2 + ω F 2) ...... round filter If the roundness of the beam spot before passing is ρ _O = ω _OY / ω _OX , and the roundness of the beam spot after passing the filter is ρ = ω _Y / ω _X , then ρ = ω _Y / ω _X = Ρ _O √ (1 + Px ² ) / (ρ _O ² + Px ² ), where Px = ω _F / ω _OX , and the radius in the horizontal transverse mode direction of the laser beam before shaping and the density of the filter are central. Represents the ratio of the radii of a portion of 1 / e ² or more of the density of P. For example, the case of Px = 1 is the incident state as shown on the left side of FIG. The incident state is as shown on the right side of FIG.

If the amplitude filter 1 is a one-dimensional filter,
Permeability distribution of one-dimensional filters of Examples of coupling the invention, permeability of the major axis of the vertical transverse mode direction V (y-direction) is the same as the circular filter, horizontal transverse mode direction H (x direction of the short diameter ) Has a constant transparency. Therefore, the intensity distribution of the beam after passing through the one-dimensional filter is as follows. For the sake of convenience, if I _OX = I _O = 1 then the major axis direction I _Y = exp {-2 (y / ω _OY ) ² } exp {-
2 (y / ω _f ) ² } = e × p {−2 (y / ω _Y ) ² } minor axis direction _IX = I _O exp {−2 (x / ω _OX ) ² } · I _OX
= Exp {-2 (x / ω X) 2} ^{_{Therefore, ω Y = √ω OY 2 ω}} F 2/2 × (ω OY 2 + ω F 2) ω X = ω OX ∴ ρ = ω Y / ω X = ρ _O × √P _X / (ρ _O ² + P _X ² ) ... FIG. 3 shows P _{X on} the horizontal axis and ρ on the vertical axis, and shows the equations and expressions when ρ _O = 4. The solid line shows the case where a circular filter is used, and the dotted line shows the case where a one-dimensional filter is used.

In FIG. 3, when Px = 1, in the case of a one-dimensional filter, the circularity ρ = 0.97 is obtained from the equation, and a laser spot shaped into a nearly circular shape can be obtained. Become. On the other hand, in the case of a circular filter, P
The roundness ρ is about 1.4 when x = 1. When Px is set to a value close to 0, the circularity becomes a value close to 1, but in this case, there is a problem that the light amount is greatly reduced. Therefore, when the one-dimensional filter is used, it is possible to obtain a beam with a sufficiently high light quantity and a sufficiently shaped beam as compared with the case where the circular filter is used.

[0013]

According to the present invention described above, it is possible to shape the elliptical laser spot of the semiconductor laser into a shape close to a circle while preventing a decrease in the amount of light as much as possible, and it is possible to position the surveying object with high accuracy. And can be done efficiently,
A laser surveying instrument can be constructed without increasing the size of the entire instrument.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a one-dimensional filter according to an embodiment of this invention.

FIG. 2 is an explanatory diagram showing a relationship between a conventional circular filter and a beam spot.

FIG. 3 is a graph of circularity in an example of the present invention.

FIG. 4 is an explanatory diagram showing a shaping state, that is, a roundness when shaping is performed using a conventional circular apodization filter.

FIG. 5 is an explanatory diagram showing a dimensional relationship between a laser spot and a circular filter.

FIG. 6 is an explanatory diagram of a semiconductor laser.

[Explanation of symbols]

 V Vertical transverse mode direction H Horizontal transverse mode direction 1 Amplitude filter

Claims (2)

[Claims] 1. A laser surveying instrument having a semiconductor laser as a light source and having an amplitude filter for shaping a beam spot of a laser beam emitted from the semiconductor laser, wherein the amplitude filter is an elliptical beam spot of the laser beam. A laser surveying instrument, characterized in that the transmittance decreases with increasing distance from the center in the major axis direction of the ellipse, and the transmittance is substantially constant in the minor axis direction. 2. The laser surveying instrument according to claim 1, wherein the transmittance distribution of the amplitude filter is approximately Gaussian.