DD291424A5 - ARRANGEMENT FOR GENERATING A HOMOGENEOUS LASER BEAM PROFILE - Google Patents

Abstract

The invention relates to an arrangement for generating a homogeneous laser beam profile in which in a known per se arrangement, the Elektrodenflaechen plan formed and partially provided with a dielectric. There are proposed two ways of applying the dielectric. First, a coating-like, for example, galvanically applied layer, on the other hand, a mask-like cover. Both embodiments of the electrode surfaces can be produced relatively easily in comparison to those in known arrangements and, moreover, are distinguished by improved, very steep edge elevations with an approximately rectangular laser beam profile. Electrode surfaces plan; Dielectric; galvanic coating; thin film; solid material; Mask; rectangular intensity profile}

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to an arrangement for producing a homogeneous laser beam profile, for example for pulse gas lasers. Gas lasers are increasingly used for material processing, for example for drilling, scribing and labeling.

Characteristics of the known prior art

To achieve high laser powers in TE pulsed lasers, a homogeneous energy input into the active medium is necessary. For this purpose, electrical arrangements with electrode profiles are required which generate a sufficiently homogeneous electric field. It is desirable a largely rectangular distribution of the laser intensity over the beam cross section, i. In a given area the field strength should be approximately constant and decrease rapidly outside this area.

The known arrangements have metal full electrodes, between which the discharge takes place. Depending on the electric field strength, the surfaces of the electrodes, between which the discharge process takes place, have complicated flat curved surfaces (profiles) which are rounded towards the sides. Predicting these profiles against extensive calculations.

It should be noted that too strong curved sides, the electric field strength at the edges assumes too high values, which have undesirable flashovers result.

There are a variety of approaches to mathematically describe the electrode profiles that produce a laser beam profile that approximates the stated requirements. For example, US Pat. No. 4,523,320 describes the so-called Stapperts profiles. This is a method according to which one can calculate the profiles with arbitrarily chosen distribution of the electric field in the plane of symmetry. Other known possibilities are shown by the Rogowski profiles (W. Rogowski, Arch. Electrical Engineering 12,1 [19231], Chang ((TYChang, Rev. Scient. Instr. 44 [1973) 405] and Ernst (GJ Ernst, Optics Comm 47 11983147).

Disadvantage of all these electrode arrangements is the complicated production of the electrode profiles, which requires the use of NC machines. Furthermore, the intensity profile of the laser beam changes in width as a function of the energy fed into the laser plasma.

Object of the invention

The aim of the invention is a simple and inexpensive to produce arrangement for generating a homogeneous laser beam profile, for example for pulse gas laser.

-2- 291424 Presentation of the essence of the invention

The object of the invention is to provide a einfcch producible arrangement for generating einos homogeneous, approximately rectangular laser beam profile with steep rise Danson whose Drolto is independent of the Enorgloolnspolsung in the laser plasma.

According to the invention the object is achieved in that in a bokannten arrangement of electrodes, for example in gas lasers, the Eloktrodonilächon plan formed and partially provide with a dielectric. For the type of application of the dielectric zwoi variants have been proposed. For oinon a üborzugsartig applied dielectric is possible, on the other hand in the form oiner mask.

The liborzugartigo dielectric can in a known manner vorgonommcnos applying thinor films, galvanic coatings but also solid materials soin.

With the mask, dio electrodon areas have been covered Dio attachment is done by known means. In order to exclude unwanted Üborschlägo, the Masko is greater in their total extent than dio to be covered Elektrodonflächo. It towers over these in all directions. The Eloktrodonflächen with the übzugzugartigon dielectric are rounded for the same reasons at the edges.

The width of the dielectric is chosen so that the average electric field in the covered electrode space changes only so much that koino discharge takes place and the field distribution in the discharge space is only minimally reduced.

As materials for the dielectric are all don - geoignet - for example, prevailing in the gas laser - discharge conditions holding non-conductive Matorialion geoignet.

The erfindungsgomäßo arrangement has the same Einsatzbedingungon don over the known advantage that the electrode surfaces simple, easy to produce geometric surfaces aufweison. In addition, the area of the discharge in the electrode space is firmly defined and thus a constant, predetermined in its width laser cross-section achievable.

Furthermore, by acting also outside the discharge area middle electric field before dome breakdown dio field pre-homogenization in the discharge boroich so far that with the electrode arrangement so steep, compared to the known arrangements improved edge slopes of the Lasorstrahlquerschnittcs be achieved.

The electrode assembly also makes it possible to design the gas circuit constructively so that it connects directly to dioelectric electrical cover and thereby eliminate the previously occurring unwanted Verwirbolungen the laser gas before don electrodes.

In connection with the economic utilization, for example, in material processing significant advantages. With the known arrangements all holes had a conical shape in depth due to the weakening laser beam profile s. Due to the significantly improved consistent beam quality over the beam cross-section are cylindrical woitestgohond possible, in ceramics over a depth of z. B. 2 mm.

Another area of application is the scratching or marking of any documents. Due to the improved beam quality, the illumination is more homogeneous and the result is a typeface of the same intensity.

Ausfuhrungsbelspiele

The invention will be described below with reference to two embodiments! - be explained in more detail. The individual figures show

Fig. 1: an electrode with a coating applied dielectric

2 shows an electrode with a mask-like dielectric

Fig. 3: the discharge channel in cross section

4: the graphical representation of a laser profile.

FIG. 1 shows an electrode 1 whose discharge surface 2 is provided with a dielectric 3 applied in the manner of a coating. The electrode 1 is 300mm long and made of aluminum. Its cross section is 10 χ 30mm ² . The electrode surface is flat and goes to the edges in a radius of about 5mm. As a dielectric, a 50 pm thick aluminum oxide layer (Al ₂ Oa) was applied by electroplating in a known manner. The layer extends over the entire length of the electrode, but only at the edges in a width of 10mm, so that for the burning of the discharge, a central surface 5 of the electrode surface remains uncovered.

FIG. 2 shows the electrode mask-covered with dom dielectric. The electrode is identical to that described in Fig. 1, except that its edges are not rounded. The dielectric 3 is larger in size than the electrode surface 2.

It surmounted this on all sides with a projection 6 of 10mm. The size of the cut-out 4 of the mask is selected as a function of the respective desired discharge area and in the example 10 × 300 mm ² .

In Figure 3, the discharge channel is shown in cross section. To see is the discharge space 7 with the electrode surfaces 2, which are acted upon by the dielectric 3.

In laser operation, a pulse-shaped discharge between the electrodes 1 is ignited, whereby the CO ₂ amplification medium is excited and the laser process is initiated. The gas mixture used consists of CO ₂ : N ₂ : He = 0.2 atm: 0.2 atm: 0.6 atm. The electrical charge takes place in the discharge space 7 between the uncovered central area 5 of the electrode surfaces 2.

Advantageously, it is shown that due to the outer boundary 8 of the electrode space 7 through the dielectric 3, the discharge width is always constant, regardless of the size of the energy supplied.

In contrast, the discharge space in the known discharge arrangements due to the curved electrode surfaces was "open" and thus the discharge width in dependence on the power supply variable.

The arrangements of the electrodes described in the exemplary embodiments are simple with respect to the known ones

and are characterized by improved, very steep Flankonanstlego the laser profile. They also make it possible to construct the Gaskretalauf constructive so that the immediately adjoins the dielectric 3 and thereby the hitherto occurring disturbing confusion of the laser gas in front of the electrodes 1 are avoided.

With the arrangement according to the invention, laser intensities with an approximately rectangular cross-section are obtained Intensity distribution 9, as shown in Figure 4, oranges. The advantages presented in the Woson of the invention In connection with the Matorialbearbeitung have in both cases

the examples confirmed.

Claims (9)

1. Arrangement for generating a homogeneous laser beam profile, characterized in that the electrode surfaces are formed flat in a known electrode arrangement and partially provided with a dielectric. 2. Arrangement according to claim 1, characterized in that the dielectric are applied coating manner at the edges on the electrode surfaces. 3. Arrangement according to claim 2, characterized in that the electrode surfaces are rounded at the edges. 4. Arrangement according to claim 1, characterized in that the dielectric covers the electrode surface like a mask and protrudes at the edges. 5. Arrangement according to claim 1,2 and 4, characterized in that the change in the mean electric field caused thereby leads to the termination of the discharge, without substantially reducing the same before the breakdown 6. Arrangement according to claim 1 and 2, characterized in that the dielectric is a galvanic layer. 7. Arrangement according to claim 1 and 2, characterized in that the dielectric is a thin film. 8. Arrangement according to claim 1 and 2 and 4, characterized in that the dielectric is a solid support "ι. 9. Arrangement according to claim 1 and 6 to 8, characterized in that all the discharge conditions in the laser resistant non-conductive materials are suitable as a material for the dielectric.