BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 schematically illustrates a view of a DFB structure, whose diffraction grating is expandable;
FIG. 2 shows a schematic view of a DFB structure with partial areas, whose diffraction gratings have different grating constants;
FIG. 3 shows a schematic view of a DFB structure with partial areas, whose diffraction gratings have a different grating constant and different dyes as laser material;
FIG. 4 shows a schematic view of a tunable lighting source;
FIG. 5 shows a schematic view of a tunable lighting source for a microscope illumination with an AOTF;
FIG. 6 shows a schematic view of a tunable lighting source for a microscope illumination with am AOM;
FIG. 7 shows a schematic view of a tunable lighting source for a microscope illumination with two laser wavelengths;
FIG. 8 shows a schematic view of a tunable lighting source for a microscope illumination with two wavelengths that can be modulated separately;
FIG. 9 shows a schematic view of a tunable lighting source for a microscope illumination, whose laser medium can be electrically excited; and
FIG. 10 shows a schematic view of a matrix of DFB structures.
DETAILED DESCRIPTION OF THE INVENTION
In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.
FIG. 1 shows a schematic illustration of a DFB laser structure 10 with an amorphous organic dye 12 on a Bragg reflection grating 14, which is introduced to an elastically extendable substrate 15. A cover layer 18 is applied in the form of an oxidation layer to the dye. The substrate is connected to a piezoelectric element 16 that can be controlled electrically. Expansion of the piezoelectric element occurs in the direction of the grating period. Depending on the applied voltage, the grating distance is expanded or compressed in discrete steps or continuously.
FIG. 2 shows a schematic illustration of a DFB laser structure 20, having two partial areas 24,25 with an inorganic dye 22 and a cover layer 23 as an oxidation layer. There are two Bragg reflection gratings 26,27. Each of the partial areas 24,25 has a different grating constant, so that coherent radiation of different wavelengths is generated, depending on energy excitation.
FIG. 3 shows a schematic illustration of a DFB laser structure 30 that has two partial areas 31,32 with a different dye and a cover layer 33 as an oxidation protection. Each of the partial areas also has a different grating constant, as well as a different profile depth of the Bragg reflection grating 34,35, so that coherent radiation of different wavelengths is generated, depending on energy excitation.
FIG. 4 schematically depicts a practical example of a lighting source 40 that is prescribed especially for a microscope. The radiation of a primary pump laser, preferably a frequency-tripled NdYAG laser at 355 nm (mode-coupled or cw), produces an energy excitation 42 of a structured laser medium 43. The laser medium in the example is an amorphous organic dye constructed on the Bragg reflection grating structure. As in each optically-pumped laser, the gain medium (the organic compound) generates optical amplification in a wavelength range corresponding to the spectral width of the gain medium. This wavelength range normally is shifted to longer wavelengths relative to the pump wavelength. Via the DFB structure, according to the conditions for Bragg reflection, laser light is emitted with a wavelength established by the period of the Bragg grating. The intensity of the emitted laser light then also depends on the laser media themselves.
By means of the DFB structure (resonator) in conjunction with the organic laser medium, coherent radiation is therefore generated at a new wavelength (generally greater than the pump wavelength). Via the grating constant of the DFB structure in conjunction with the laser medium, the generated wavelength is deliberately chosen and altered. A tunable light source can be obtained if several laser media with adapted DFB structures are introduced to the beam of the pump laser by means of a device to adjust the structure dimension in time succession 44, during displacement of the DFB structures relative to the pump beam. Since an organic dye as laser medium can emit different wavelengths lying close to each other by combination of different DFB structures, it is possible to obtain an almost continuous spectrum. The laser radiation is then supplied to an application, especially a microscope arrangement.
Coupling to the microscope arrangement can then also occur with fiber optics. Advantageously, the pump laser is switched off or blocked when the useful light obtained by the DFB structure is not required, in order to increase the useful life of the dyes serving as laser medium. In addition, the beam generated by the pump laser is positioned on different locations of the corresponding DFB structure, in order to prevent bleaching-out of one location, and therefore increase the useful life of the DFB structure.
FIG. 5 schematically illustrates a practical example according to FIG. 4, in which modulation of the laser light necessary for the application is achieved in the μs range, by guiding the newly generated laser light 51 additionally through an AOTF 52 (acousto-optical tunable filter). A guide and adjustment device 53 positions the corresponding combination of the DFB structure and laser medium 54 in the optical path between the primary pump laser 55 and the microscope arrangement 56.
FIG. 6 shows another practical example according to FIG. 5, where like reference numerals denote like elements. In the embodiment of FIG. 6, the pump light 61 of the DFB structure is modulated by a cost-effective AOM 62 (acousto-optical modulator) and the modulation of the laser light necessary for the application is achieved in the μs range.
FIG. 7 schematically illustrates another practical example for application of the lighting source in a microscope. Since in many experiments in confocal laser scan microscopy, multiple colors of the sample are common, a light source that simultaneously emits at least two wavelengths is desirable in many cases. For this purpose, the radiation of a primary pump laser 71, preferably a UV laser in the wavelength range 337 nm to 355 nm is divided by a spectrally neutral beam divider 72.
A first part of the radiation is introduced to a first partial structure of a first substrate 75, having several partial areas. This partial structure is coated with a first organic compound as a laser medium. A second part of the radiation is introduced to a second partial structure of a second substrate 76, which also has several partial areas. This partial structure is coated with a second organic compound as a laser material. By means of the two DFB structures, coherent radiation at two new wavelengths is therefore generated. By selecting the corresponding DFB structure with the corresponding guide and adjustment devises 73,74, the generated wavelength composition is deliberately chosen and varied, i.e., each of the two branches is independently tunable. A division into more than two channels is provided, just as the variation of units from the DFB structure and laser medium within the branches.
The newly generated laser light is then combined again to a beam via a dichroic filter 77 (beam combination) and passed through an AOTF 52 (acousto-optical tunable filter), with which it can be varied very quickly relative to optical power. The two beams are then overlapped and fed into the already described type of microscope arrangement 56.
FIG. 8 shows another practical example according to FIG. 7, in which the generated laser beam of each branch is guided via an AOTF 81,82. The advantage here is that the light fractions are adjusted independently of each other and each AOTF is chosen in optimized fashion for the spectral ranges being controlled. AOTF 1 thus modulates a spectral range from 400 nm to 450 nm and AOTF 2 a spectral range from 450 nm to 650 nm.
FIG. 9 shows a lighting source according to FIG. 5, in which energy excitation 91 here occurs directly electrically for the active DFB structure.
FIG. 10 schematically depicts a matrix of DFB structures on a support, which is mounted movable in the x- and y-direction, and whose partial areas can be positioned by means of a motor adjustment device in the optical path of the application. In the example, three different laser materials and nine different structures with different grating constants are schematically shown rotated out from the plane of the drawing by 90°. Such a matrix is used in the arrangements according to FIGS. 6, 7, 8 and 9. For one or each of the partial structures or for the partial structures referred to as DFB structures, one matrix is used, in which one partial area of each matrix is positioned in the optical path of the application.
Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.
Patent Application
20080043786
