Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-04-03
2004-05-18
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S578100, C359S349000
Reexamination Certificate
active
06737635
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This invention claims priority of a German patent application DE 100 16 377.7 which is incorporated by reference herein.
FIELD OF THE INVENTION
The present invention concerns an apparatus for combining light from at least two laser light sources. Moreover the invention relates to a confocal scanning microscope which has an apparatus for combining light.
BACKGROUND OF THE INVENTION
Apparatuses of the generic type have been known for some time from practical use, and are utilized principally in cases where light of different wavelengths from several laser light sources is combined into one light beam. In confocal scanning microscopy in particular, it is necessary to combine light from several laser light sources of different wavelengths into one common coaxially proceeding light beam, so as thereby to illuminate the same specimen point with light of the different wavelengths. If the light beams are not combined in exactly coaxial fashion, the undesirable result is several illumination foci at different specimen points.
DE 196 33 185 discloses, per se, a polychromatic point light source for a scanning microscope which has a beam combiner that coaxially combines the light from several laser light sources of different emission wavelengths, the beam combiner being configured as a monolithic unit.
Laser light of different wavelengths from several lasers is usually combined using so-called dichroic beam splitters. These are transparent beam splitter plates which have a coating that possesses a different transmission or emission characteristic as a function of the respective wavelength of the light.
In confocal scanning microscopy, gas lasers or mixed gas lasers whose emission light has wavelengths that are suitable for exciting fluorescent dyes are principally used to illuminate a specimen. Semiconductor lasers or solid-state lasers have hitherto seldom been used in confocal scanning microscopy, although they are considerably more economical than gas lasers in terms of acquisition price. The reason for this is the low output power of semiconductor or solid-state lasers, typically in the range of a few mW. Low-cost helium-neon lasers could also be used at some of the wavelengths of interest for confocal scanning microscopy if their output power were sufficient for the purpose.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention provide a laser light source with an increased power output at a reasonable price.
The above object is achieved by an apparatus for combining light, which comprises at least two laser light sources, each of which defining a light beam wherein the light from the laser light sources has at least approximately the same wavelength; and that at least one beam combining unit which combines the light beams at least largely lossless, wherein the combination of the light beams is accomplished with reference to at least one characteristic property of the light beams.
It is a further object of the present invention to make laser light sources of low output power usable as light sources, in particular for a confocal scanning microscope.
The above object is achieved by a confocal scanning microscope which comprises: at least two laser light sources, each of which defining a light beam wherein the light from the laser light sources has at least approximately the same wavelength; and that at least one beam combining unit which combines the light beams at least largely lossless, wherein the combination of the light beams is accomplished with reference to at least one characteristic property of the light beams.
What has been recognized firstly according to the present invention is that it is not necessary to dispense with the use of economical laser light sources having only low output power if it is possible to combine their light beams in at least largely lossless fashion. The multiple combining of laser light sources of low output power can result in an output power which corresponds to that of one conventional laser, so that the use of a conventional laser having an output sufficient for confocal scanning microscopy can be omitted. The complex and vibration-sensitive air- or water-cooling system of such a laser is thus also, advantageously, not necessary, resulting in a simplified laboratory infrastructure and, in particular, eliminating the irritating noise level of an air cooling system.
In very general terms, beam combination is accomplished with reference to at least one characteristic property of the light beams. A “characteristic property” of the light beams is to be understood in this context as, for example, the polarization.
In the context of confocal scanning microscopy in particular, it is necessary for the combined light from several laser light sources to proceed exactly coaxially, since the several light sources then have a single common illumination focus.
In terms of the dimensioning of the beam combining unit, it is very advantageous if the light beams proceed in collimated fashion. As a result, the beam cross section of the beam path is the same at all points in the beam combining unit, so that as compared to a divergent beam path, a compact design is possible.
In a concrete embodiment, linearly polarized light from two laser light sources is combined together. The light of most lasers is in any case linearly polarized, so that no further actions are necessary in order to utilize the advantages resulting therefrom, for example a small number of optical components.
Four different characteristic properties of the light, on the basis of which the beam combination according to the present invention is performed, are discussed below. These are:
the polarization of the light;
the phase of the light;
the pulse profile over time of the light; and
the identical numerical aperture of a glass fiber.
In a concrete embodiment, light combination on the basis of polarization as the characteristic property of the light could be performed with the aid of a polarization beam splitter. A Glan-Thompson prism is preferably suitable for this. The polarization beam splitter preferably combines light beams whose polarization directions are substantially perpendicular to one another.
The polarization direction of the light from the one laser light source is set in such a way that it is deflected by the polarization beam splitter. The polarization direction of the light from the other laser light source is set in such a way that it passes through the polarization beam splitter. Assuming a suitable relative arrangement of the light beams that are to be combined, the result is a combined, coaxially proceeding light beam from the two laser light sources.
In an alternative embodiment, a polarization beam splitter and a Faraday rotator are arranged between two light beams from two laser light sources proceeding coaxially with one another in opposite directions. The polarization direction of the light from the first laser light source is set in such a way that it passes through the polarization beam splitter. The polarization direction of the second laser light source is set in such a way that after passing through the Faraday rotator arranged after the polarization beam splitter, it is at least largely parallel to the polarization direction of the light from the first laser light source. The light from the two laser light sources accordingly has the same polarization direction, specifically between the Faraday rotator and the second laser. The light from the first light source can penetrate into the second laser if the wavelength of the first laser light source conforms to the resonant wavelength of the resonator of the second laser. If the resonance condition is not met, the light from the first laser light source is for the most part reflected at the coupling-out mirror of the second laser light source. In both cases, the light from the two laser light sources now proceeds coaxially in the same direction, assuming suitable alignment of the optical components.
The Faraday rotator is configured in such a way that it rotate
Bewersdorf Joerg
Birk Holger
Engelhardt Johann
Hoffmann Juergen
Storz Rafael
Houston Eliseeva LLP
Leica Microsystems Heidelberg GmbH
Porta David
Yam Stephen
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