DE8502446U1 - Gas laser with a frequency-selective dielectric layer system - Google Patents

Description

Balzers Aktiengesellschaft Our mark

For st enttarn Liechtenstein VPA 85 P 8 O O 5 DE

Siemens Aktiengesellschaft
Berlin and Munich

Gas laser with a frequency-selective dielectric layer system.

The invention relates to a gas laser according to the preamble of claim 1. Such a laser is for example from DE-OS 23 42 911 known.

Gas lasers usually emit at a variety of wavelengths. One must therefore, if only one Wavelength is required, take precautions to suppress the rest of the emission spectrum. In the For this purpose, it is proposed to use one of the two resonator mirrors as follows to be coated: In front of and behind a λ / 2-layer there are several, Pairs each formed from an optically dense and an optically thin λ / 4 layer (A = wavelength of the interfering light). Such a layer system provides a pronounced minimum reflection. One can thus from a number of relatively closely spaced laser lines easily filter out a certain line; but it causes difficulties, the other way round from the same Spectrum to suppress all lines but one.

Such a frequency characteristic could be achieved with a modified coating. For this, however, are Layer structure required, the reflection maxima of which are temperature and pressure dependent, namely in to an extent that can be felt, for example, with an Ar + laser with its relatively small line spacing Loss of performance "leads. Less critical are the conditions, if one makes the line selection through dielectric edge filters on both mirrors. The ste-les 1 Lk / 9.1.1985

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Here, however, higher costs compared to: The mirror production is complex - you have to have a relatively soft one Polishing and coating material with an often curved surface - and this leads to yields of well below 100%.

Of course one could work with broadband mirrors and let the line selection take care of etalons, frequency-selective polarizers or dispersing elements lu {uei — kjo c \ j ou ? £.? uuer tro-uo <nj fy / η-ό). Other parts in the resonator should, however, be avoided if possible, if only because they make the structure more complicated and weaken the beam.

The invention is therefore based on the object of designing a laser of the type mentioned in such a way that disruptive frequency components of the laser light can be suppressed easily and reliably. This object is achieved according to the invention solved by a laser type with the features of claim 1.

The proposed gas laser can be manufactured relatively inexpensively: additional parts are not required. The Brewster window usually consists of a hard, easily polished material (quartz) with flat surfaces; it can therefore be easily tempered and coated. The multilayer is made up of only two types of layers; the layers may vary from their Elealwert (A). differ, provided that layers of the same type are of the same thickness with a tolerance of a few%. There are also remarkable optical qualities: Compared to a frequency-selective mirror, the attenuation values for useful and interfering light are roughly the same and the effects of temperature and pressure changes are less.

Advantageous refinements and developments of the invention are the subject of additional claims.

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The proposed solution will now be explained in more detail using an exemplary embodiment shown in the drawing. In the figures of the drawing, parts that correspond to one another are provided with the same reference numerals. Show it
Fig. 1 shows the embodiment in a schematic

Longitudinal section and

FIG. 2 shows an enlarged section of the exemplary embodiment in FIG. 1, with a more detailed representation the multilayer.

The laser shown is an Ar ⁺ laser, which should only emit at a frequency of 0.488um. In detail, it contains an argon-filled discharge tube 1 which is provided with a discharge electrode 2, 3 at each of its two ends and is closed off by a Brewster window 4, 5 each. The tube is located in a resonator formed by two mirrors 6, 7.

The window 5 is covered with a dielectric multilayer 8 on its side facing the mirror 7. This layer system consists of twelve individual layers 9, 10, which alternately have a refractive index of 2.2 and 1.46, respectively, and 71.2nm and 120.5nm thick, respectively. They consist of vapor-deposited Ta2U3 or S1O2. the Brewster windows are also made of quartz.

For the individual laser lines \ with their excitation probabilities A result - for p-polarized light at an angle of incidence of 55.5 ° - the following reflection factors Rr,

Ai (nm) D f οδ ^ A. 454 11th 0.12 456 12th 0.35 466 13th 0.2 473 9.7 0.3

λ i (nm) Rp {%) A. 476 7.4 0.75 488 0,000 1.5 496 6.8 0.7 501 17.7 0.4 514 51 2.0

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With layer thickness turning of -lift and scattered light and absorption losses from a total of <0.05% the Losses on the 0.488 µm line to about 0.2%. The remaining Laser lines are attenuated; this also applies in particular to the 0.5i4um line, which is strongly excited in itself, because it is straight The R value is particularly high in this frequency range.

The invention is not limited to the illustrated embodiment. The multilayer can be used - with appropriate adaptation - for the selection of other Ar ⁺ lines or lines of other (noble) gases and, in suitable cases, even for the selection of more than one line. Apart from that, the person skilled in the art is at liberty to modify the layer system in several respects within the proposed η framework: The low and / or high refractive index layers could, for example, be chosen to be thicker (q> 1) to increase the selectivity; the multilayer could at least partially be applied to the inside of the Brewster window - a division between both sides of the window can be recommended for reasons of thermal stability; the layers can also be applied in other ways, for example by a sputtering technique. In addition, it is irrelevant whether the Brewster window forms a gas-tight pipe closure or is supported purely mechanically.

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Claims (7)

- · 5 - '■ VPA 85P 8 00 5DE - patent claims 1. Gas laser containing
1a) a discharge tube that
b). is provided with a Brewster window at at least one of its two ends; 2a) a frequency-selective dielectric layer system to suppress unwanted laser lines, with b) a multilayer consisting of several successive layers which alternately have a high refractive index n _n ("layers of the first type") and a low refractive index n ^ ("layers of the second type") (A _n = H ^ -Ii ₁ = O, 5) and in particular have the same optical thickness; characterized in that 2c) the layer system on the Brewster window (5) is arranged d) consists exclusively of the multiple layer (8), e) between five and nine layers (9, 10) of each type are provided, and that the following applies:
f) 0 ² ^ ^ l (d _im «thickness of the i-th layer of the m-th type, measured in the direction of the light passing through; q * integer - 0; A. = wavelength of the desired laser line in the respective layer). 2. Laser according to claim 1, characterized in that the following applies: 0.99d _Qm = d _im = 1.01d _Qm and 3. Laser according to claim 1 or 2, characterized in that the multiple layer (8) consists of a maximum of seven layers (9, 10) of each type and that the following applies: 1.9 = n _h = 2.5, 1.38 = ^ ^ 1,7 and ^ n = O, 6. Il) 1) - '• 6 - VPA 85P 8 O 05 QE 4. argon-ion laser according to claim 3, characterized characterized that λ = 0.488um that the Multi-layer (8) consists of at least six layers (9, 10) of each type and that the following applies: 2.1 = 1 ^ = 2.3 and 1.4 = ^ = 1.5. 5. Laser according to claim 4, characterized in that the multilayer (8) consists of six layers (9, 10) of each type, that n ^ and U ₁ values of about 2.2 and 1.46 and that the layers (9, 10) of the first and second types are about 71.2 nm and 120.5 nm thick are. 6. Laser according to claim 5, characterized in that the layers (9, 10) of the first and second type of Ta £ ° 3 ^or * ^Si0 2 7. Laser according to one of claims 1 to 6, d a d u r ch characterized in that the multilayer (8) is located on the outside of the Brewster window (5).