GB1574178A - Apparatus including a laser - Google Patents

Description

(54) IMPROVEMENTS IN APPARATUS INCLUDING A LASER (71) We, DR JOHANNES HEIDENHAIN GmbH, a joint stock company organised under the laws of the Federal Republic of Germany, of Postfach 1260, D-8225, Traunreut, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention concerns apparatus including a laser for providing a parallel beam and optical means for expanding the laser beam in a single plane.

In the case of known apparatus including a laser and interposed cylindrical lens for expanding the parallel laser beam, the intensity of the laser light beyond the lens diminishes as the angle of divergence increases. This is caused by the varying distribution of luminosity over the cross-section of the parallel laser beam (Gaussian intensity distribution). This reduction of intensity is a troublesome factor in certain practical applications, e.g. with laser light barriers for ballistic measurements.

The object of the invention is to eliminate the above-mentioned disadvantages and to produce with simDle means anparatus of the kind described at the outset in which the luminosity of the diverging laser light is as evenly distributed as possible.

The invention achieves this by the insertion between the laser and the optical means for expanding the laser beam of at least one optical element for splitting up the parallel laser beam into several beams.

preferablv of equal intensity, so as to give a substantially constant distribution of luminosity over the whole angle of divergence of the laser light A further feature of the invention is that the optical element for splitting up the parallel laser beam can be a diffraction grating amplitude and/or phase grating) or a double-refraction prism (e.g. Wollaston prism), etc.

Examples of embodiments of the invention will now be described with reference to the accompanying drawings in which : Fig. 1 is a schematic plan view of an optical arrangement in accordance with the invention.

Fig. 2 is a graphical representation of the distribution of luminosity on the line of the intersection 11-11 of the laser pencil in Fig. 1, Fig. 3 is a schematic plan view of another embodiment of the invention providing a laser light barrier for ballistic measurements Fig. 4 is a section along the, line IV-IV in Fig. 3.

In Fig. 1, the invention provides for the insertion of an optical element T' between a laser L and a cylindrical lens Z,. The optical element T1 splits the parallel laser beam up into several component beams of equal intensity. This optical element T1 is a conventional rectangular phase grating.

The several laser beams are expanded in a single plane by means of the cylindrical lens Z1. The insertion of the optical element Tl (phase grating) brings about a substantially constant distribution of luminosity over the whole angle of divergence 2w beyond the lens Zl. Fig. 2 shows the distribution of luminosity thus achieved on the line of intersection IL--II of the laser light LS. The optical axis 0 of the apparatus is indicated in Figs. 1 and 2. Such an advantageous distribution of luminosity is required in many practical applications. The inven tlon can be used to particular advantage with laser light barriers for ballistic -measure- ments.

Figs. 3 and 4 show a photoelectronic arrangement for measuring the velocity of flying bodies, preferably projectiles. Here, the laser beam is expanded to a thin laser light-band LS, by means of two cylindrical lenses Z1 and Z2 and deflected by two mirrors U1 and U in such a way that two light-bands L & 1/LS2 arise which are paral to each other and at a precisely fixed distance s from each other. The laser lightband LS2 is brought by means of a cylin drical lens Z3 to a photoelectronic transducer (e.g. a photodiode) P whose analog output signal is amplified in an amplifier V and transformed into square-wave impulses J1/J2 in a trigger R. The output of the trigger R is connected to an electronic meter Z which is started when an impulse J1 occurs and stopped when an impulse J2 occurs.

The velocity of projectiles G is ascertained by measuring the flight time t for a predetermined section s of the flight path and obtaining the quotient V0 = s/t. The time t is determined by means of the time meter Z in Fig. 3 which is started and stopped by the electrical impulses J1 and J2 respectively. A starting impulse Jl is produced when the projectile G flies through the laser light-band LS1, a stopping impulse J2 when the projectile G flies through the laser lightband Ls2.

The invention provides for a further optical element T, between the laser L and the cylindrical lens Z1 which splits the parallel laser beam into several beams, preferably of equal intensity. This results in an even distribution of luminosity, as shown in Fig. 2. As shown in Fig. 5, the arrangement of the laser L1 element T, and lens Zl and Z2 has an optical axis 0, and the lens 2 renders the laser light parallel to the axis 0. Systems of interference fringes arising when the component beams overlap do not have a disturbing effect with this system.

The optical element T can as in Fig. 1 be a rectangular phase grating or a doublerefraction prism (e.g. a Wollaston prism).

Furthermore, the optical element T can consist of geometrically splitting divisionprisms or beam splitting plates, or of a conventional diffraction grating combined with a double-refraction prism. etc.

The arrangement shown in Fig. 3 has the following advantages: High accuracy of measurement, because the distribution of intensity over the whole angle of divergence 2w of the laser light LS is substantially constant.

The use of only one photodetector P, one amplifier V and one trigger R cuts out measuring errors which can arise with known systems having separate parts for producing two laser light-bands through phase delay times in the electronics.

A further advantage is the small amount of construction involved, as only one laser L and one set of the above-mentioned electronic units P/V/R are required.

WHAT WE CLAIM IS: 1. Apparatus including a laser for providing a parallel beam and optical means for expanding the laser beam in a single plane, wherein at least one optical element is inserted between the laser and the optical means for expanding the laser beam in order to split up the parallel laser beam into several beams in the said plane so as to produce a- substantially constant distributiolt of luminosity over the whole angle of di vergence of the laser light during expansion.

2. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam into component beams is a diffraction grating.

3. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam is a double-refraction prism.

4. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam consists of geometrically splitting division-prisms or beam splitting plates.

5. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam into component beams consists of a diffraction grating and a double-refraction prism.

6. Apparatus according to claim 1.

wherein the optical means for expanding the laser beam include at least one cylin drical lens.

7. Apparatus according to claim 1, wherein the said at least one optical element is such as to split the parallel laser beam into several beams of equal intensity.

8. Apparatus according to claim 3, wherein the double-refraction prism is a Wollaston prism.

9. Photoelectric arrangement for ballistic measurements, the arrangement including a laser for providing a parallel beam, optical means for expanding the beam in a single plane into a thin laser lightband, and, between the laser and the said optical means, an optical element arranged to split up the parallel laser beam into several beams in the said plane, the said laser light-beam being deflected by means of optical elements so as to produce a further parallel laser light-band at a precisely fixed distance from the first said lightband, and the said further light-band is brought by means of a lens to a photoelectronic transducer which controls an electronic evaluating system.

10. Apparatus including a laser and optical means for expanding the laser beam in a plane, substantially as described hereinbefore with reference to Fig. 1 of the accompanying drawings.

11. Apparatus including a laser and optical means for expanding the laser beam

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. drical lens Z3 to a photoelectronic transducer (e.g. a photodiode) P whose analog output signal is amplified in an amplifier V and transformed into square-wave impulses J1/J2 in a trigger R. The output of the trigger R is connected to an electronic meter Z which is started when an impulse J1 occurs and stopped when an impulse J2 occurs. The velocity of projectiles G is ascertained by measuring the flight time t for a predetermined section s of the flight path and obtaining the quotient V0 = s/t. The time t is determined by means of the time meter Z in Fig. 3 which is started and stopped by the electrical impulses J1 and J2 respectively. A starting impulse Jl is produced when the projectile G flies through the laser light-band LS1, a stopping impulse J2 when the projectile G flies through the laser lightband Ls2. The invention provides for a further optical element T, between the laser L and the cylindrical lens Z1 which splits the parallel laser beam into several beams, preferably of equal intensity. This results in an even distribution of luminosity, as shown in Fig. 2. As shown in Fig. 5, the arrangement of the laser L1 element T, and lens Zl and Z2 has an optical axis 0, and the lens 2 renders the laser light parallel to the axis 0. Systems of interference fringes arising when the component beams overlap do not have a disturbing effect with this system. The optical element T can as in Fig. 1 be a rectangular phase grating or a doublerefraction prism (e.g. a Wollaston prism). Furthermore, the optical element T can consist of geometrically splitting divisionprisms or beam splitting plates, or of a conventional diffraction grating combined with a double-refraction prism. etc. The arrangement shown in Fig. 3 has the following advantages: High accuracy of measurement, because the distribution of intensity over the whole angle of divergence 2w of the laser light LS is substantially constant. The use of only one photodetector P, one amplifier V and one trigger R cuts out measuring errors which can arise with known systems having separate parts for producing two laser light-bands through phase delay times in the electronics. A further advantage is the small amount of construction involved, as only one laser L and one set of the above-mentioned electronic units P/V/R are required. WHAT WE CLAIM IS:

1. Apparatus including a laser for providing a parallel beam and optical means for expanding the laser beam in a single plane, wherein at least one optical element is inserted between the laser and the optical means for expanding the laser beam in order to split up the parallel laser beam into several beams in the said plane so as to produce a- substantially constant distributiolt of luminosity over the whole angle of di vergence of the laser light during expansion.

2. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam into component beams is a diffraction grating.

3. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam is a double-refraction prism.

4. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam consists of geometrically splitting division-prisms or beam splitting plates.

5. Apparatus according to claim 1, wherein the optical element for splitting up the parallel laser beam into component beams consists of a diffraction grating and a double-refraction prism.

6. Apparatus according to claim 1.

wherein the optical means for expanding the laser beam include at least one cylin drical lens.

7. Apparatus according to claim 1, wherein the said at least one optical element is such as to split the parallel laser beam into several beams of equal intensity.

8. Apparatus according to claim 3, wherein the double-refraction prism is a Wollaston prism.

9. Photoelectric arrangement for ballistic measurements, the arrangement including a laser for providing a parallel beam, optical means for expanding the beam in a single plane into a thin laser lightband, and, between the laser and the said optical means, an optical element arranged to split up the parallel laser beam into several beams in the said plane, the said laser light-beam being deflected by means of optical elements so as to produce a further parallel laser light-band at a precisely fixed distance from the first said lightband, and the said further light-band is brought by means of a lens to a photoelectronic transducer which controls an electronic evaluating system.

10. Apparatus including a laser and optical means for expanding the laser beam in a plane, substantially as described hereinbefore with reference to Fig. 1 of the accompanying drawings.

11. Apparatus including a laser and optical means for expanding the laser beam

in a plane, the apparatus being adapted for use in ballistic measurements substantially as described hereinbefore with reference to Figs. 3 and 4 of the accompanying drawings.