Imaging system comprising a beam guiding element with high solarization resistance

Abstract

The invention relates to an imaging system comprising at least one laser light source having a wavelength in the visible spectral range and a beam guiding element having a high solarization resistance at high beam power densities. The invention also relates to the use of the imaging system, in particular in projectors and material processing.

Description

TECHNICAL FIELD

[0001] The present invention relates to an imaging system comprising at least one laser light source having wavelengths in the visible spectral range and beam guiding elements having a high solarization resistance at high beam power densities. The invention further relates to the use of the imaging system, in particular in projectors and material processing. BACKGROUND

[0002] Currently, light sources for projectors are undergoing a change from xenon to luminescent laser materials and pure RGB laser light sources with increasing luminous flux and power density. Today's movie projectors with laser light sources achieve luminous fluxes of up to 75,000 lumens and surface power densities of up to 50 W / cm 2 or more. With increasing luminous flux and power density, the thermal load of the optical components increases, which impairs the quality of the projection and the long-term stability. The optical system of a movie projector usually consists of a bulk arrangement of prisms and projection objectives. In particular, the arrangement of prisms is subjected to a high thermal load. Therefore, the requirements for the optical glass regarding low absorption losses, i.e. maximum transmission, and low solarization, i.e. low induced absorption losses in the application, are increasing.

[0003] Conventional xenon-based movie projectors have a maximum luminous flux of up to 45,000 lumens. In the latest laser-based projectors, however, luminous fluxes of up to 75,000 lumens and surface power densities of up to 50 W / cm 2 or more are achieved. Intense blue laser light excites the emission of yellow light in the converter. With the aid of dichroic filters, the green and yellow channels are extracted from the yellow light. A part of the blue light is used for the blue channel. Then, all three channels are used for projection.

[0004] The projection system usually consists of a complex arrangement of prisms for guiding the monochromatic channels to the DLP chip and mixing the signals to generate an image. The optical path length can be more than 100 to 200 mm. Any light absorption within the prism arrangement leads to temperature gradients and thermal lens effects. Therefore, the prism glass should have as high a transmission as possible in the visible wavelength range. Another effect that becomes more and more important with increasing luminous flux of the projector is the solarization effect in the glass. The generation of defect centers induced by the absorption of the prism glass can lead to a reduction in transmission, which in turn coexists with the thermal lens effect.

[0005] However, this solarization effect is not only relevant for the optical system of the latest projectors. Also in material processing applications, this phenomenon plays an increasingly important role. SUMMARY

[0006] It is therefore an object of the present application to provide an imaging system with a beam guiding element which is characterized by a high weathering resistance in the visible spectral range, in particular in the blue spectral range, and thus can be used not only excellently in projectors, but also in material processing applications.

[0007] An imaging system is in particular a system with at least one light source and at least one beam guiding element, in particular a lens, a prism, an aspherical mirror and / or a light guide rod. Such light guide rods make use of total reflection at the interface glass / air, and usually their length does not exceed 300 mm. Such imaging systems are used for example in projectors, in particular in film projectors. In this case, an image is generated (by targeted beam guidance of the light of the light source) on a screen for example using the imaging system, which is recognizable for an observer. Usually, the highest power densities occur in the prisms, in particular in the prisms responsible for the color channel mixing. It is therefore of particular importance to provide such prism-beam guiding elements which are made of a material which can withstand these power densities without relevant weathering effects. Imaging systems are also used in material processing. By targeted beam guidance, the light of the light source can be focused onto the material to be processed, so that the energy input of the light radiation can be used for the material processing.

[0008] This object is achieved by the subject matter of the claims. The object is in particular achieved by an imaging system, comprising:

[0009] a) at least one laser light source selected from the group consisting of a laser light source B having a wavelength λ B in the spectral range of 380 nm to 490 nm, a laser light source G having a wavelength λ G in the spectral range of > 490 nm to 585 nm and a laser light source R having a wavelength λ R in the spectral range of > 585 nm to 750 nm, and

[0010] b) a beam guiding element,

[0011] wherein the laser light source is adapted to generate an average surface power density of more than 10 W / cm 2 in at least one point of the beam guiding element, and the beam guiding element consists of a glass having a figure of merit F(436 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k, wherein F(436 nm) < 700 ppm / W.

[0012] The imaging system according to the application can comprise further components, for example an image generating chip (in particular a DLP chip) and / or projection optics.

[0013] The imaging system according to the application can comprise a laser light source having a wavelength λB of the laser light source B. Preferably, the imaging system comprises a laser light source B having a wavelength λ B in the spectral range of 400 nm to 480 nm, further preferably 420 nm to 470 nm, further preferably 425 nm to 460 nm, further preferably 430 nm to 450 nm.

[0014] The imaging system according to the application can comprise a laser light source G having a wavelength λ G in the spectral range of > 490 nm to 585 nm. Preferably, the imaging system comprises a laser light source G having a wavelength λ G in the spectral range of 510 nm to 580 nm, further preferably 520 nm to 570 nm, further preferably 530 nm to 560 nm, further preferably 540 nm to 550 nm.

[0015] The imaging system according to the application can comprise a laser light source R having a wavelength λ R in the spectral range of > 585 nm to 750 nm. Preferably, the imaging system comprises a laser light source R having a wavelength λ R in the spectral range of 600 nm to 720 nm, further preferably 610 nm to 700 nm, further preferably 620 nm to 680 nm, further preferably 630 nm to 660 nm, further preferably 640 nm to 650 nm.

[0016] The imaging system according to the application can comprise exactly one laser light source selected from the group consisting of a laser light source B having a wavelength λ B in the spectral range of 380 nm to 490 nm, a laser light source G having a wavelength λ G in the spectral range of > 490 nm to 585 nm and a laser light source R having a wavelength λ R in the spectral range of > 585 nm to 750 nm. According to the application, for example, the imaging system comprises only one laser light source B having a wavelength λ B in the spectral range of 380 nm to 490 nm, or only one laser light source G having a wavelength λ G in the spectral range of > 490 nm to 585 nm, or only one laser light source R having a wavelength λ R in the spectral range of > 585 nm to 750 nm.

[0017] In other embodiments, the imaging system according to the application can comprise exactly two laser light sources selected from a laser light source B having a wavelength λ B in the spectral range of 380 nm to 490 nm, a laser light source G having a wavelength λ GThe laser source G and the wavelength λ in the spectral range of >585nm to 750nm R A group consisting of laser light sources R. According to the invention, for example, an imaging system includes a laser light source R having a wavelength λ in the spectral range of 380 nm to 490 nm. B The laser source B has a wavelength λ in the spectral range of >490nm to 585nm. G The laser source G, however, does not have a wavelength λ in the spectral range of >585nm to 750nm. R Laser source R. According to the present invention, the imaging system includes a wavelength λ in a spectral range of exactly 380 nm to 490 nm. B The laser source B has a wavelength λ in the spectral range of >585nm to 750nm. R The laser source R, however, does not have a wavelength λ in the spectral range of >490nm to 585nm. G Laser source G. According to the present invention, the imaging system comprises a wavelength λ in a spectral range of >585 nm to 750 nm. R The laser source R and the wavelength λ are exactly in the spectral range of >490nm to 585nm. G The laser source G, however, does not have a wavelength λ in the spectral range of 380 nm to 490 nm. B Laser source B.

[0018] Particularly preferably, the imaging system according to the invention comprises exactly three laser sources selected from the spectral range of 380 nm to 490 nm, each having a wavelength λ. B Laser source B has a wavelength λ in the spectral range of >490nm to 585nm. G The laser source G and the wavelength λ in the spectral range of >585nm to 750nm R The system comprises a group of laser light sources R. Particularly preferably, the imaging system according to the invention includes a wavelength λ in the spectral range of 380 nm to 490 nm. B Laser source B has a wavelength λ in the spectral range of >490nm to 585nm. G The laser source G and the wavelength λ in the spectral range of >585nm to 750nm R The laser source R.

[0019] Laser sources (especially those with wavelength λ in the spectral range of 380nm to 490nm) B Laser source B has a wavelength λ in the spectral range of >490nm to 585nm. G The laser source G and / or has a wavelength λ in the spectral range of >585nm to 750nm. Rof the beam guidance element, preferably over an area of at least 0.1 cm 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 of the beam guidance element, of more than 10 W / cm 2 . Preferably, the laser light source (in particular the laser light source B having a wavelength λ B in the spectral range of > 490 nm to 585 nm, the laser light source G having a wavelength λ G in the spectral range of > 585 nm to 750 nm and / or the laser light source R having a wavelength λ R in the spectral range of > 750 nm to 830 nm) is adapted to generate an average surface power density of more than 10 W / cm 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 of the beam guidance element, of more than 10 W / cm 2 to 75 W / cm 2 , further preferably 15 W / cm 2 to 60 W / cm 2 , further preferably 20 W / cm 2 to 50 W / cm 2 , for example 25 W / cm 2 to 45 W / cm 2 or 30 W / cm 2 to 40 W / cm 2 .

[0020] Preferably, the laser light source B is adapted to generate an average surface power density of more than 10 W / cm 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2More preferably, at least 2cm 2 More preferably, at least 3cm 2 More preferably at least 5cm 2 More preferably, at least 7cm 2 More preferably, at least 9cm 2 A region with a strength greater than 10 W / cm 2 The average surface power density. More preferably, the laser source B is adapted to be at at least one point of the beam guiding element, preferably at least 0.1 cm from the beam guiding element. 2 More preferably at least 0.5cm 2 More preferably, at least 1cm 2 More preferably, at least 2cm 2 More preferably, at least 3cm 2 More preferably at least 5cm 2 More preferably, at least 7cm 2 More preferably, at least 9cm 2 A region with a strength greater than 10 W / cm 2 Up to 75W / cm 2 More preferably 15W / cm 2 Up to 60W / cm 2 More preferably 20W / cm 2 Up to 50W / cm 2 For example, 25W / cm 2 Up to 45W / cm 2 Or 30W / cm 2 Up to 40W / cm 2 The average surface power density.

[0021] Preferably, the laser source G is positioned at at least one point of the beam guiding element, preferably at least 0.1 cm from the beam guiding element. 2 More preferably at least 0.5cm 2 More preferably, at least 1cm 2 More preferably, at least 2cm 2 More preferably, at least 3cm 2 More preferably at least 5cm 2 More preferably, at least 7cm 2 More preferably, at least 9cm 2 A region with a strength greater than 10 W / cm 2 The average surface power density. More preferably, the laser source G is adapted to be at least one point of the beam guiding element, preferably at least 0.1 cm above the beam guiding element. 2 More preferably at least 0.5cm2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 of the area. The average surface power density is preferably greater than 10 W / cm 2 , further preferably 15 W / cm 2 , further preferably 20 W / cm 2 , further preferably 25 W / cm 2 , further preferably 30 W / cm 2 , further preferably 35 W / cm 2 , further preferably 40 W / cm 2 , further preferably 45 W / cm 2 , further preferably 50 W / cm 2 , further preferably 55 W / cm 2 , further preferably 60 W / cm

[0022] Preferably, the laser light source R is adapted to generate an average surface power density of greater than 10 W / cm 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 of the area. The average surface power density is preferably greater than 10 W / cm 2 , further preferably 15 W / cm 2 , further preferably 20 W / cm 2 , further preferably 25 W / cm 2 , further preferably 30 W / cm 2 , further preferably 35 W / cm 2 , further preferably 40 W / cm 2 , further preferably 45 W / cm 2 , further preferably 50 W / cm 2 , further preferably 55 W / cm 2 , further preferably 60 W / cm 2 , further preferably 65 W / cm 2up to 75 W / cm2 2 , further preferably 15 W / cm2 2 up to 60 W / cm2 2 , further preferably 20 W / cm2 2 up to 50 W / cm2 2 , for example 25 W / cm2 2 up to 45 W / cm2 2 , or 30 W / cm2 2 up to 40 W / cm2 2 .

[0023] Preferably, the laser light source B, the laser light source G and the laser light source R are adapted to generate an average surface power density of more than 10 W / cm2 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 in at least one point of the beam guiding element, preferably over an area of at least 0.1 cm 2 , further preferably at least 0.5 cm 2 , further preferably at least 1 cm 2 , further preferably at least 2 cm 2 , further preferably at least 3 cm 2 , further preferably at least 5 cm 2 , further preferably at least 7 cm 2 , further preferably at least 9 cm 2 up to 75 W / cm2 2 , further preferably 15 W / cm2 2 up to 60 W / cm2 2 , further preferably 20 W / cm2 2 up to 50 W / cm2 2 , for example 25 W / cm2 2 up to 45 W / cm2 2 , or 30 W / cm2 2 up to 40 W / cm2 2 .

[0024] The imaging system according to the application comprises a beam guiding element which consists of a glass having a figure of merit F(436 nm) = S(436 nm) * (Ext0(436 nm) + Ext1(436 nm)) / k, wherein F(436 nm) < 700 ppm / W.

[0025] Under irradiation with high-energy photons in the UV range, defects are induced in the material, which lead to a change in the spectral transmission. This is accompanied by an undesired color change when they are in the visible spectral range. In the case of optical components made of glass, in particular, this phenomenon is not desired. Surprisingly, it has now been shown that under high laser power densities, likewise in the visible spectral range, for example at 450 nm, defect centers (=solarization) can be induced which are only found when emitting in the UV / NUV with conventional light sources. Without being bound to a specific explanation, it is assumed here that the occurrence of the solarization effect under visible radiation can be attributed, in particular, to nonlinear effects, which are a concomitant of high power densities. When excitation with sufficient power density is carried out, two-photon absorption can occur, which corresponds to the energy of a photon having half the wavelength (e.g. 450 nm / 2 = 225 nm), thus similar to UV absorption. In contrast to conventional UV solarization, this effect is not usually limited to the glass volume near the surface facing the light source, but can occur along the entire optical path length. The defect centers formed induce new absorption bands, which reduce the transmission intensity.

[0026] The induction of absorption bands is accompanied by an increase in the internal temperature of the optical material / glass; due to the change in the refractive number and the geometric path with temperature, a wavefront deceleration and undesired aberrations result.

[0027] From this, particularly high demands are placed on the material of the beam guiding element used in the imaging system, which is suitable for generating an average surface power density of more than 10 W / cm 2 in at least one point of the beam guiding element. It is therefore an object of the present application to provide an imaging system which avoids or at least strongly reduces undesired aberrations.

[0028] Figure 1 An exemplary embodiment of the imaging system according to the application is shown schematically. According to this embodiment, the imaging system is a DLP projector. The phrase "DLP" is an abbreviation of the term "Digital Light Processing". Figure 1 The imaging system according to the application shown comprises a laser light source 1 and a beam guiding element 2. According to the application, the imaging system comprises at least one laser light source which is selected from laser light sources B having a wavelength λ B in the spectral range of 380 nm to 490 nm, laser light sources G having a wavelength λ G in the spectral range of > 490 nm to 585 nm and laser light sources R having a wavelength λR The laser light source R can for example be a blue laser light source, a green laser light source and a red laser light source. It is also possible that the laser light source R consists of a group of laser light sources of different colors. Thus, it is also possible that more than one of the mentioned laser light sources, in particular blue laser light sources, green laser light sources and red laser light sources, are present in the imaging system according to the application. In Figure 1 The laser light source 1, which is shown as a single block in a simplified manner in Fig. 1, can for example represent three diode lasers of different colors, in particular a blue diode laser, a green diode laser and a red diode laser. It is also possible that only one laser light source, for example a blue laser light source, is present. In some embodiments, it is possible that the blue light emitted by the blue laser light source by luminescence is converted into light of a longer wavelength, for example into yellow, green, red and / or yellow-green light, by means of a converter, in particular a ceramic converter.

[0029] In Fig. 1, the laser light source 1 is shown as a single block. The laser light source 1 can for example represent a blue laser light source, a green laser light source and a red laser light source. It is also possible that the laser light source 1 consists of a group of laser light sources of different colors. Thus, it is also possible that more than one of the mentioned laser light sources, in particular blue laser light sources, green laser light sources and red laser light sources, are present in the imaging system according to the application. In Figure 1 The DLP projector described in Fig. 1 works as follows: The laser light source 1 emits blue, green and red light (indicated by arrows 5). This can for example be achieved by the fact that the laser light source 1 represents the presence of blue, green and red diode lasers. It is also possible that only blue lasers are present and that the additionally emitted green and red light is generated by using conversion materials. After leaving the laser light source 1, the three colors 5 emitted by the laser light source 1 reach the beam guiding element 2. The beam guiding element 2 comprises at least one prism and can for example also represent a prism arrangement comprising several prisms. The prism arrangement can for example consist of two or three prisms. By means of arrows 6, it is shown that the beam guiding element 2 redirects the three colors of light emitted by the laser light source 1 to the image generating chip 3. Preferably, each color of light (blue, green and red) is redirected to one image generating chip 3, respectively. For the sake of simplicity, Figure 1 Only one single block representing the image generating chip 3 is shown. The preferred image generating chip 3 is a DLP chip 3. Preferably, the imaging system comprises one image generating chip 3 for each color channel, respectively. Thus, preferably, Figure 1 The block shown represents three image generating chips 3 (each for blue, green and red, respectively), in particular three DLP chips 3.

[0030] The images generated by the DLP chip 3 (in particular images in blue, green and red, respectively) then reach the beam guiding element 2, in particular the prism 2 or the arrangement of prisms 2. This is shown by arrows 7.

[0031] The beam guiding element 2 then ensures that a composite color image reaches the projection optics 4. This is shown by arrows 8.

[0032] In particular in the region of the beam guiding element 2, very high surface power densities can occur. It is therefore important that the beam guiding element 2 consists of a glass having a figure of merit according to the application.

[0033] This object is achieved, inter alia, by the fact that the beam guiding element consists of a glass having a figure of merit F(436nm) = S(436nm)*(Ext0(436nm)+Ext1(436nm)) / k, wherein F(436nm) < 700 ppm / W.

[0034] The figure of merit F takes into account different factors, the combination of which found here leads to a reduction in aberrations. Here, both wavelength-dependent and wavelength-independent factors are taken into account. The figure of merit F(436nm) at a wavelength of 436 nm represents the behavior of the glass in the spectral range from 380 nm to 490 nm. This range in turn represents the behavior of the glass in the entire visible spectral range. According to the application, the following condition is met: F(436nm) < 700 ppm / W.

[0035] In certain cases, the behavior of the glass outside the range from 380 nm to 490 nm can lead to aberrations, albeit to a lesser extent. In principle, the figure of merit F(436nm) is sufficient to describe the quality of the glass. However, in certain cases, it can be reasonable to take into account, in addition to the behavior of the glass at a wavelength of 436 nm, the behavior at a wavelength of 546 nm, which represents the wavelength range from > 490 nm to 585 nm, and / or the behavior at a wavelength of 644 nm, which represents the wavelength range from > 585 nm to 750 nm. Preferably, the beam guiding element consists of a glass having a figure of merit F(546nm) = S(546nm)*(Ext0(546nm)+Ext1(546nm)) / k, wherein F(546nm) < 215 ppm / W, and / or of a glass having a figure of merit F(644nm) = S(644nm)*(Ext0(644nm)+Ext1(644nm)) / k, wherein F(644nm) < 85 ppm / W.

[0036] From the behavior of the glass at 436 nm, 546 nm and 644 nm, a figure of merit F(RGB) can be determined. Preferably, the beam guiding element consists of a glass having a figure of merit F(RGB) = F(436nm) + F(546nm) + F(644nm) = S(436nm)*(Ext0(436nm)+Ext1(436nm)) / k + S(546nm)*(Ext0(546nm)+Ext1(546nm)) / k + S(644nm)*(Ext0(644nm)+Ext1(644nm)) / k, wherein F(RGB) < 1000 ppm / W.

[0037] The figure of merit F takes into account the heatiness S(λ), the non-induced absorbance Ext0(λ), the induced absorbance Ext1(λ) and the thermal conductivity k of the glass. The heatiness, the non-induced absorbance and the induced absorbance are parameters that are dependent on the wavelength. The thermal conductivity is independent of the wavelength. Depending on its intended purpose, the non-induced absorbance Ext0(λ) can be used as a measure of the absorbance in the delivery condition or of the absorbance before use. The induced absorbance Ext1(λ) can be used as a measure of the absorbance potentially induced by appropriate operation.

[0038] According to the present application, the following condition is fulfilled: F(436 nm) < 700 ppm / W. Preferably, F(436 nm) is at most 600 ppm / W, further preferably at most 500 ppm / W, further preferably at most 400 ppm / W, further preferably at most 350 ppm / W, further preferably at most 300 ppm / W, further preferably at most 275 ppm / W, further preferably at most 250 ppm / W, further preferably at most 225 ppm / W, further preferably at most 210 ppm / W, further preferably at most 200 ppm / W, further preferably at most 150 ppm / W, further preferably at most 100 ppm / W, further preferably at most 75 ppm / W, further preferably at most 50 ppm / W, further preferably at most 25 ppm / W, further preferably at most 20 ppm / W, further preferably at most 15 ppm / W, further preferably at most 10 ppm / W. In some embodiments, F(436 nm) is at least 0.1 ppm / W, at least 0.5 ppm / W, at least 1 ppm / W or at least 2 ppm / W.

[0039] Preferably, the following condition is met: F(546 nm) < 215 ppm / W. Further preferably, F(546 nm) is at most 200 ppm / W, further preferably at most 175 ppm / W, further preferably at most 150 ppm / W, further preferably at most 125 ppm / W, further preferably at most 100 ppm / W, further preferably at most 90 ppm / W, further preferably at most 80 ppm / W, further preferably at most 70 ppm / W, further preferably at most 60 ppm / W, further preferably at most 50 ppm / W, further preferably at most 40 ppm / W, further preferably at most 30 ppm / W, further preferably at most 20 ppm / W, further preferably at most 15 ppm / W, further preferably at most 10 ppm / W, further preferably at most 8 ppm / W, further preferably at most 6 ppm / W, further preferably at most 5 ppm / W. In some embodiments, F(546 nm) is at least 0.001 ppm / W, at least 0.005 ppm / W, at least 0.01 ppm / W, at least 0.02 ppm / W, at least 0.1 ppm / W, at least 0.5 ppm / W, or at least 1 ppm / W.

[0040] Preferably, the following condition is met: F(644 nm) < 85 ppm / W. Further preferably, F(644 nm) is at most 80 ppm / W, further preferably at most 75 ppm / W, further preferably at most 70 ppm / W, further preferably at most 65 ppm / W, further preferably at most 60 ppm / W, further preferably at most 55 ppm / W, further preferably at most 50 ppm / W, further preferably at most 45 ppm / W, further preferably at most 40 ppm / W, further preferably at most 35 ppm / W, further preferably at most 30 ppm / W, further preferably at most 25 ppm / W, further preferably at most 20 ppm / W, further preferably at most 15 ppm / W, further preferably at most 10 ppm / W, further preferably at most 8 ppm / W, further preferably at most 6 ppm / W, further preferably at most 5 ppm / W. In some embodiments, F(644 nm) is at least 0.001 ppm / W, at least 0.005 ppm / W, at least 0.01 ppm / W, or at least 0.02 ppm / W, at least 0.1 ppm / W, at least 0.5 ppm / W, or at least 1 ppm / W.

[0041] Therefore, preferably the light beam directing element is composed of a glass having a figure of merit F(RGB) = F(436 nm) + F(546 nm) + F(644 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k + S(546 nm)*(Ext0(546 nm) + Ext1(546 nm)) / k + S(644 nm)*(Ext0(644 nm) + Ext1(644 nm)) / k with F(RGB) < 1000 ppm / W. Preferably, F(RGB) is at most 900 ppm / W, further preferably at most 800 ppm / W, further preferably at most 700 ppm / W, further preferably at most 600 ppm / W, further preferably at most 500 ppm / W, further preferably at most 400 ppm / W, further preferably at most 350 ppm / W, further preferably at most 300 ppm / W, further preferably at most 250 ppm / W, further preferably at most 200 ppm / W, further preferably at most 150 ppm / W, further preferably at most 100 ppm / W, further preferably at most 80 ppm / W, further preferably at most 60 ppm / W, further preferably at most 50 ppm / W, further preferably at most 40 ppm / W, further preferably at most 30 ppm / W, further preferably at most 25 ppm / W, further preferably at most 20 ppm / W. In some embodiments, F(RGB) is at least 0.5 ppm / W, at least 1 ppm / W, at least 2 ppm / W or at least 5 ppm / W.

[0042] A parameter that has a significant influence on the figure of merit F is the wavelength dependent thermal figure S( ). The thermal figure describes the relative change of the optical path s = (n - 1) * d with temperature T, where n is the refractive index and d is the sample thickness. It holds that S = 1 / s*ds / dT. Since it also holds that d = d(T) and n = n(T), it also holds that S = 1 / s*(dn / dT*d + (n - 1)dd / dT). From this it also holds that S = 1 / (n - 1)*dn / dT + 1 / d*dd / dT = 1 / (n - 1)*dn / dT + CTE. CTE is the coefficient of thermal expansion.

[0043] Preferably, the coefficient of thermal expansion is determined as described, for example, in DIN 51045-1 :2005-08 and DIN ISO 7991 1998-02. Here, a glass sample having a defined length is prepared and the relative change in length (Delta L / L) per temperature interval (Delta T) is measured in an expansion gauge. For the calculation of the thermal S( ), preferably, the average coefficient of thermal expansion is used over a temperature interval of -30 °C to +70 °C. A low coefficient of thermal expansion is advantageous, in particular in the temperature range of -30 °C to 70 °C (CTE(-30 / 70)). Preferably, the CTE(-30 / 70) is in the range of 3.0 to 14.0 ppm / K, in particular 4.0 to 10.0 ppm / K, 4.5 to 9.5 ppm / K, 5.0 to 8.0 ppm / K and / or 5.5 to 7.5 ppm / K, for example 5.6 to 7.3 ppm / K or 5.7 to 7.2 ppm / K.

[0044] The determination of dn / dT can be carried out by a prism spectrometer (with entire prism) located in a temperature chamber. Preferably, the measurement is carried out in a configuration in which the total deflection angle becomes minimal, because then the refractive number can only be calculated from the deflection angle and the known prism angle.

[0045] However, the determination of dn / dT is particularly preferably carried out by the half-prism method. For this purpose, the sample in the form of a half-prism is located in a temperature-controlled sample chamber. The prism is irradiated with light of different wavelengths and the deflection angle is determined separately. During this time, the temperature in the chamber is varied. The reflection power obtained is thus a function of the wavelength and the temperature. For the calculation of the thermal S( ), preferably, the average dn / dT is used over a temperature range of +20 °C to +40 °C. In order to keep the degree of thermal lensing as small as possible, it is advantageous if the change in the refractive index with temperature (dn / dT) is as small as possible, in particular in the temperature range of 20 °C to 40 °C. Preferably, the average dn / dT at a wavelength of 436 nm, 546 nm and / or 644 nm is in the range of 0.1 to 8.0 ppm / K, in particular 0.2 to 7.0 ppm / K, 0.3 to 6.0 ppm / K and / or 0.4 to 5.0 ppm / K in the temperature range of 20 °C to 40 °C, wherein this information relates to the absolute value (absolute amount) of the average dn / dT.

[0046] As described above, when the refractive index and the geometric path change with temperature, the induced absorption band accompanies a temperature increase in the glass, so that the wavefront slows down and unwanted aberrations occur. Therefore, preferably, the change in the optical path with temperature (thermal S) is small. In this way, even in the case of the occurrence of an induced absorption band, the aberrations can be minimized.

[0047] Preferably, S(436 nm) is at most 50 ppm / K, further preferably at most 30 ppm / K, further preferably at most 25 ppm / K, further preferably at most 20 ppm / K, further preferably at most 15 ppm / K, further preferably at most 10 ppm / K. In some embodiments, S(436 nm) is at least 0.1 ppm / K, at least 0.5 ppm / K, at least 1 ppm / K, or at least 2 ppm / K.

[0048] Preferably, S(546 nm) is at most 50 ppm / K, further preferably at most 30 ppm / K, further preferably at most 25 ppm / K, further preferably at most 20 ppm / K, further preferably at most 15 ppm / K, further preferably at most 10 ppm / K. In some embodiments, S(546 nm) is at least 0.1 ppm / K, at least 0.5 ppm / K, at least 1 ppm / K, or at least 2 ppm / K.

[0049] Preferably, S(644 nm) is at most 50 ppm / K, further preferably at most 30 ppm / K, further preferably at most 25 ppm / K, further preferably at most 20 ppm / K, further preferably at most 15 ppm / K, further preferably at most 10 ppm / K. In some embodiments, S(644 nm) is at least 0.1 ppm / K, at least 0.5 ppm / K, at least 1 ppm / K, or at least 2 ppm / K.

[0050] Preferably, S(436 nm), S(546 nm), and S(644 nm) are at most 50 ppm / K, further preferably at most 30 ppm / K, further preferably at most 25 ppm / K, further preferably at most 20 ppm / K, further preferably at most 15 ppm / K, further preferably at most 10 ppm / K. In some embodiments, S(436 nm), S(546 nm), and S(644 nm) are at least 0.1 ppm / K, at least 0.5 ppm / K, at least 1 ppm / K, or at least 2 ppm / K.

[0051] Other important parameters are the non-induced absorbance Ext0 and the induced absorbance Ext1. Ext1 (λ) describes (compared to Ext0 (λ)) the additional absorbance per centimeter at wavelength λ after irradiation of the sample. The induced absorbance Ext1 depends on the kind of the irradiation source. For the evaluation of the weather resistance of the material, it is advantageous to use a test with a mercury high-pressure lamp (HOK 4). According to the present application, the induced absorbance Ext1 (λ) describes (compared to Ext0 (λ)) the additional absorbance per centimeter at wavelength λ after irradiation of a sample with a HOK 4 for 15 hours for a sample thickness d of 10 mm. On the other hand, the non-induced absorbance Ext0 (λ) describes the absorbance per centimeter at wavelength λ before irradiation of a sample with a sample thickness d of 10 mm.

[0052] Preferably, a HOK 4 / 120 lamp of Philips is used. The spectrum of this HOK 4 / 120 lamp is shown in Figure 2 Preferably, the distance between the lamp and the sample is 7 cm. Preferably, the power density is 25 mW / cm 2 Preferably, the sample size is 20 mm x 30 mm x 10 mm. Here, the size of 10 mm is referred to as the sample thickness d, for example already described above.

[0053] It is advantageous when Ext0 and Ext1 are low. Thus, the sum of both values contributes to the quality factor F.

[0054] A low non-induced absorbance Ext0 is advantageous, since there is a similar low initial absorbance without the need for a prior irradiation with a HOK 4 lamp.

[0055] A low induced absorbance Ext1 is also advantageous. This indicates that no excessive absorption occurs after irradiation either, and thus this is a measure for the weather resistance.

[0056] The absorbance Ext (λ) is described as the natural logarithm of the quotient of the incident radiation I0 and the emitted radiation I at wavelength λ divided by the sample thickness d: Ext (λ) = ln(I0 / I) / d. In this way, both Ext0 and Ext1 can be determined. As described above, according to the present application, the sample thickness d is 10 mm.

[0057] Preferably, Ext0 (436 nm) is less than 0.01 / cm, further preferably at most 0.008 / m, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm, further preferably at most 0.002 / cm. In some embodiments, Ext0 (436 nm) is at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0058] Preferably, Ext0(546 nm) is less than 0.01 / cm, further preferably at most 0.008 / cm, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm, further preferably at most 0.002 / cm, further preferably less than 0.0015 / cm, further preferably less than 0.001 / cm. In some embodiments, Ext0(546 nm) is at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0059] Preferably, Ext0(644 nm) is less than 0.01 / cm, further preferably at most 0.008 / cm, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm, further preferably at most 0.002 / cm, further preferably less than 0.0015 / cm, further preferably less than 0.001 / cm. In some embodiments, Ext0(644 nm) is at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0060] Preferably, Ext0(436 nm), Ext0(546 nm), and Ext0(644 nm) are less than 0.01 / cm, further preferably at most 0.008 / cm, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm, further preferably at most 0.002 / cm. In some embodiments, Ext0(436 nm), Ext0(546 nm), and Ext0(644 nm) are at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0061] Preferably, Ext1(436 nm) is less than 0.3 / cm, further preferably at most 0.2 / cm, further preferably at most 0.1 / cm, further preferably at most 0.08 / cm, further preferably at most 0.06 / cm, further at most 0.04 / cm, further preferably at most 0.02 / cm, further preferably at most 0.01 / cm, further preferably at most 0.009 / cm, further preferably at most 0.008 / cm, further preferably at most 0.007 / cm, further preferably at most 0.006 / cm. In some embodiments, Ext1(436 nm) is at least 0.0005 / cm, at least 0.001 / cm, at least 0.0015 / cm, or at least 0.02 / cm.

[0062] Preferably, Ext1(546 nm) is less than 0.3 / cm, further preferably at most 0.2 / cm, further preferably at most 0.1 / cm, further preferably at most 0.08 / cm, further preferably at most 0.06 / cm, further at most 0.04 / cm, further preferably at most 0.02 / cm, further preferably at most 0.01 / cm, further preferably at most 0.009 / cm, further preferably at most 0.008 / cm, further preferably at most 0.007 / cm, further preferably at most 0.006 / cm, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm. In some embodiments, Ext1(546 nm) is at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0063] Preferably, Ext1(644 nm) is less than 0.3 / cm, further preferably at most 0.2 / cm, further preferably at most 0.1 / cm, further preferably at most 0.08 / cm, further preferably at most 0.06 / cm, further at most 0.04 / cm, further preferably at most 0.02 / cm, further preferably at most 0.01 / cm, further preferably at most 0.009 / cm, further preferably at most 0.008 / cm, further preferably at most 0.007 / cm, further preferably at most 0.006 / cm, further preferably at most 0.005 / cm, further preferably at most 0.004 / cm, further preferably at most 0.003 / cm. In some embodiments, Ext1(644 nm) is at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm, or at least 0.0005 / cm.

[0064] Preferably, Ext1(436 nm), Ext1(546 nm) and Ext1(644 nm) are less than 0.3 / cm, further preferably at most 0.2 / cm, further preferably at most 0.1 / cm, further preferably at most 0.08 / cm, further preferably at most 0.06 / cm, further at most 0.04 / cm, further preferably at most 0.02 / cm, further preferably at most 0.01 / cm, further preferably at most 0.009 / cm, further preferably at most 0.008 / cm, further preferably at most 0.007 / cm, further preferably at most 0.006 / cm. In some embodiments, Ext1(436 nm), Ext1(546 nm) and Ext1(644 nm) are at least 0.0001 / cm, at least 0.0002 / cm, at least 0.0003 / cm or at least 0.0005 / cm.

[0065] Another important parameter is the thermal conductivity k. The thermal conductivity is the product of the density, the specific heat capacity and the temperature conductivity. Preferably, the density is determined according to Archimedes’ theorem, in particular ASTM C693:1993. In order to determine the temperature dependence of the density, the expansion behavior is preferably determined by means of an expander, as described in DIN 51045-1 :2005-08 and DIN ISO 7991 :1998-02. The specific heat capacity is preferably determined by means of DSC (differential calorimetry, differential scanning calorimetry) according to DIN 51007:2019-04. The temperature conductivity is preferably determined by means of flash analysis according to ASTM E1461 :2013.

[0066] A high thermal conductivity k limits the stationary temperature increase of the optical glass in the beam path. Preferably, the thermal conductivity k is higher than 0.005 W / (cm*K), further preferably at least 0.006 W / (cm*K), further preferably at least 0.007 W / (cm*K), further preferably at least 0.008 W / (cm*K), for example at least 0.009 W / (cm*K) or at least 0.010 W / (cm*K). In some embodiments, the thermal conductivity k is at most 0.050 W / (cm*K), at most 0.040 W / (cm*K), at most 0.030 W / (cm*K), at most 0.020 W / (cm*K) or at most 0.015 W / (cm*K).

[0067] As mentioned above, the beam guiding element is made of glass, which is weather resistant to a certain extent, in particular in the blue spectral range. This is advantageous for the optical use in projectors and material processing, since the occurrence of thermal lensing effects is thereby significantly reduced. On the other hand, additional contributions can be made to reducing thermal lensing effects. For example, in the case of a given local, heat power (by absorption of laser light) with increasing thermal conductivity, the temperature difference, which is adjusted in a fixed manner, becomes smaller, and the temperature-induced aberration thereby becomes smaller. Thus, a high thermal conductivity k is advantageous.

[0068] Depending on the field of application, the refractive index can also play a role. Preferably, the refractive index at a wavelength of 436 nm, 546 nm and / or 644 nm is in the range of 1.45 to 1.65.

[0069] It has been shown that a number of different glass series can be used to obtain a glass having the quality factors according to the application. The glass is preferably selected from the group consisting of fluorophosphate glasses, silicate glasses, borosilicate glasses, niobium phosphate and aluminoborosilicate glasses. The refining agents used have a particular relevance, for example as described below.

[0070] Preferably, the beam guiding element consists of a glass, which comprises the following components (in wt. %)

[0071]

[0072]

[0073] For example, the glass according to the application can be a fluorophosphate glass. A particularly preferred fluorophosphate glass according to the application comprises the following components (in wt. %)

[0074] From To SiO2 0 5 B2O3 0 5 Al2O3 5 25 Li2O 0 5 Na2O 0 5 K2O 0 5 MgO 1 10 CaO 5 20 BaO 10 30 ZnO 0 5 SrO 10 25 TiO2 0 5 ZrO2 0 5 La2O3 0 5 P2O5 5 15 F 15 45 Sb2O3 0 0.5 As2O3 0 <0.3 SnO2 0 0.5

[0075] The fluorophosphate glass according to the application preferably comprises less than 0.3 wt. %, further preferably at most 0.2 wt. %, further preferably at most 0.1 wt. % of each of the components Si02, B203, Li20, Na20, K20, ZnO, Ti02, Zr02, La203, Sb203, As203and Sn02, or particularly preferably, even none of these components.

[0076] Preferably, the fluorophosphate glass comprises 7.5 to 22.5 wt. %, further preferably 10 to 20 wt. %, further preferably 14 to 19 wt. % of Al203.

[0077] Preferably, the fluorophosphate glass comprises 1.5 to 7.5 wt. %, further preferably 2 to 5 wt. %, further preferably 2.5 to 3.5 wt. % of MgO.

[0078] Preferably, the fluorophosphate glass comprises 7.5 to 15 wt.%, further preferably 9 to 14 wt.%, further preferably 10 to 13 wt.% CaO.

[0079] Preferably, the fluorophosphate glass comprises 11 to 25 wt.%, further preferably 12 to 20 wt.%, further preferably 13 to 17 wt.% BaO.

[0080] Preferably, the fluorophosphate glass comprises 15 to 24 wt.%, further preferably 16 to 23 wt.%, further preferably 16.5 to 22 wt.% SrO.

[0081] Preferably, the fluorophosphate glass comprises 6 to 12 wt.%, further preferably 7 to 11 wt.%, further preferably 8 to 10 wt.% P2O5.

[0082] Preferably, the fluorophosphate glass comprises 20 to 40 wt.%, further preferably 25 to 35 wt.%, further preferably 27.5 to 32.5 wt.% F.

[0083] For example, the glass of the present application can be a silicate glass. A particularly preferred silicate glass of the present application comprises the following composition (wt.%).

[0084]

[0085]

[0086] The silicate glass according to the present application preferably comprises less than 0.3 wt.%, further preferably at most 0.2 wt.%, further preferably at most 0.1 wt.% of each of the components B2O3, Al2O3, MgO, CaO, SrO, TiO2, P2O5, F, Sb2O3 and As2O3, or particularly preferably, even none of these components.

[0087] Preferably, the silicate glass comprises 35 to 50 wt.%, further preferably 37.5 to 47.5 wt.%, further preferably 40 to 45 wt.% SiO2.

[0088] Preferably, the silicate glass comprises 0.2 to 4 wt.%, further preferably 0.4 to 2 wt.%, further preferably 0.5 to 1.5 wt.% Li2O.

[0089] Preferably, the silicate glass comprises 2 to 15 wt.%, further preferably 3 to 10 wt.%, further preferably 4 to 7.5 wt.% Na2O.

[0090] Preferably, the silicate glass comprises 1 to 10 wt.%, further preferably 1.5 to 7.5 wt.%, further preferably 2 to 5 wt.% K2O.

[0091] Preferably, the sum of alkali metal oxides (R2O) in the silicate glass is in the range of 1 to 20 wt.%, further preferably 2 to 15 wt.%, further preferably 5 to 12.5 wt.%. Preferably, the glass does not comprise other alkali metal oxides than Li2O, Na2O and / or K2O.

[0092] Preferably, the silicate glass comprises 2 to 25 wt.%, further preferably 5 to 20 wt.%, further preferably 7.5 to 15 wt.% BaO.

[0093] Preferably, the silicate glass comprises 5 to 30 wt.%, further preferably 10 to 27.5 wt.%, further preferably 15 to 25 wt.% ZnO.

[0094] Preferably, the silicate glass comprises 1.5 to 10 wt.%, further preferably 2 to 8.5 wt.%, further preferably 3 to 7 wt.% ZrO2.

[0095] Preferably, the silicate glass comprises 2 to 20 wt.%, further preferably 5 to 15 wt.%, further preferably 7.5 to 12.5 wt.% La2O3.

[0096] Preferably, the silicate glass comprises 0.05 to 0.4 wt.%, further preferably 0.1 to 0.35 wt.%, further preferably 0.15 to 0.25 wt.% SnO2.

[0097] For example, the glass of the present application can be a borosilicate glass. A particularly preferred borosilicate glass of the present application comprises the following composition (in wt.%).

[0098]

[0099]

[0100] The borosilicate glass according to the present application preferably comprises less than 0.3 wt.%, further preferably at most 0.2 wt.%, further preferably at most 0.1 wt.% of each of the components Al2O3, Li2O, MgO, ZnO, SrO, ZrO2, La2O3, P2O5, As2O3 and SnO2, or particularly preferably, even none of these components.

[0101] Preferably, the borosilicate glass comprises 52.5 to 77.5 wt.%, further preferably 55 to 75 wt.%, further preferably 57.5 to 72.5 wt.% SiO2.

[0102] Preferably, the borosilicate glass comprises 5 to 25 wt.%, further preferably 7.5 to 20 wt.%, further preferably 9 to 19 wt.% B203.

[0103] Preferably, the borosilicate glass comprises 0 to 17.5 wt.%, further preferably 0 to 15 wt.%, further preferably 0 to 12.5 wt.% Na20. In certain embodiments, the glass comprises at least 2 wt.%, at least 5 wt.% or even at least 8 wt.% Na20.

[0104] Preferably, the borosilicate glass comprises 2 to 24 wt.%, further preferably 4 to 23 wt.%, further preferably 6 to 22 wt.% K20.

[0105] Preferably, the sum of alkali oxides (R20) in the borosilicate glass is in the range of 5 to 30 wt.%, further preferably 10 to 25 wt.%, further preferably 15 to 22 wt.%. Preferably, the glass does not comprise other alkali oxides in addition to Na20 and / or K20.

[0106] Preferably, the borosilicate glass comprises 0 to 5 wt.%, further preferably 0 to 2 wt.%, further preferably 0 to 1 wt.% CaO. In certain embodiments, the glass comprises at least 0.1 wt.% or at least 0.2 wt.% CaO.

[0107] Preferably, the borosilicate glass comprises 0 to 5 wt.%, further preferably 0 to 3.5 wt.%, further preferably 0 to 2 wt.% BaO. In certain embodiments, the glass comprises at least 0.1 wt.% BaO.

[0108] Preferably, the borosilicate glass comprises 0 to 2 wt.%, further preferably 0 to 1 wt.%, further preferably 0 to 0.5 wt.% Ti02. In certain embodiments, the glass comprises at least 0.1 wt.% Ti02.

[0109] Preferably, the borosilicate glass comprises 0 to 15 wt.%, further preferably 0 to 12.5 wt.%, further preferably 0 to 10 wt.% F. In certain embodiments, the glass comprises at least 1 wt.%, at least 2 wt.% or even at least 5 wt.% F.

[0110] Preferably, the borosilicate glass comprises 0.01 to 0.45 wt.%, further preferably 0.01 to 0.4 wt.%, further preferably 0.01 to 0.35 wt.% Sb203.

[0111] For example, the glass of the present application can be an aluminoborosilicate glass. A particularly preferred aluminoborosilicate glass of the present application comprises the following composition (in wt.%).

[0112]

[0113]

[0114] The aluminoborosilicate glass according to the present application preferably comprises less than 0.3 wt.-%, further preferably at most 0.2 wt.-%, further preferably at most 0.1 wt.-% of each of the constituents Li20, MgO, CaO, SrO, Ti02, Zr02, La203, P205, As203and Sn02, or particularly preferably, even none of these constituents.

[0115] Preferably, the aluminoborosilicate glass comprises 62.5 to 77.5 wt.-%, further preferably 65 to 75 wt.-%, further preferably 67.5 to 72.5 wt.-% of Si02.

[0116] Preferably, the aluminoborosilicate glass comprises 7.5 to 25 wt.-%, further preferably 10 to 20 wt.-%, further preferably 12.5 to 17.5 wt.-% of B203.

[0117] Preferably, the aluminoborosilicate glass comprises 0.2 to 10 wt.-%, further preferably 0.5 to 5 wt.-%, further preferably 1 to 3 wt.-% of Na20.

[0118] Preferably, the aluminoborosilicate glass comprises 2 to 17.5 wt.-%, further preferably 5 to 15 wt.-%, further preferably 10 to 14 wt.-% of K20.

[0119] Preferably, the sum of alkali metal oxides (R20) in the aluminoborosilicate glass is in the range of 2 to 25 wt.-%, further preferably 5 to 20 wt.-%, further preferably 10 to 15 wt.-%. Preferably, the glass comprises no further alkali metal oxides than Na20 and / or K20.

[0120] Preferably, the aluminoborosilicate glass comprises 0.02 to 5 wt.-%, further preferably 0.05 to 2 wt.-%, further preferably 0.1 to 1 wt.-% of BaO.

[0121] Preferably, the aluminoborosilicate glass comprises 0.05 to 5 wt.-%, further preferably 0.1 to 2 wt.-%, further preferably 0.15 to 1 wt.-% of ZnO.

[0122] Preferably, the aluminoborosilicate glass comprises 0.1 to 5 wt.-%, further preferably 0.2 to 2 wt.-%, further preferably 0.5 to 1.5 wt.-% of F.

[0123] Preferably, the aluminoborosilicate glass comprises 0.02 to 0.45 wt.-%, further preferably 0.05 to 0.4 wt.-%, further preferably 0.1 to 0.35 wt.-% of Sb2O3.

[0124] Of particular relevance is the refining agent used as well as CeO2and Fe2O3, i.e. independent of the glass system used. Thus, the following information is valid for all glass series.

[0125] Preferably, the glass is free of CeO2and Fe2O3. Thus, particularly low Ext0 values can be achieved.

[0126] Preferably, As2O3 in the glass according to the application is less than 0.3 wt.-%, preferably at most 0.2 wt.-%, further preferably at most 0.1 wt.-%. Still further preferably, the glass is free of As2O3. Thus, particularly low Ext1 values can be achieved.

[0127] Preferably, Sb2O3 in the glass according to the application is at most 0.5 wt.-%, preferably at most 0.4 wt.-%, further preferably at most 0.3 wt.-%, for example at most 0.2 wt.-% or at most 0.1 wt.-%.

[0128] The glass can even be free of Sb2O3. Thus, particularly low Ext1 values can be achieved.

[0129] Preferably, SnO2 in the glass according to the application is at most 0.5 wt.-%, preferably at most 0.4 wt.-%, further preferably at most 0.3 wt.-%, for example at most 0.2 wt.-% or at most 0.1 wt.-%.

[0130] The glass can even be free of SnO2. Thus, particularly low Ext1 values can be achieved.

[0131] Preferably, the sum of As2O3 + Sb2O3 + SnO2 is at most 0.5 wt.-%, preferably at most 0.4 wt.-%, further preferably at most 0.3 wt.-%, for example at most 0.2 wt.-% or at most 0.1 wt.-%.

[0132] The glass can even be free of As2O3, Sb2O3 and SnO2. Thus, particularly low Ext1 values can be achieved.

[0133] The glass can comprise F, for example, in an amount of 0 to 45 wt.-%, in particular 0.5 to 42.5 wt.-% or 5 to 40 wt.-%. Thus, particularly low Ext1 values can be achieved.

[0134] The glass can also comprise CI, in particular due to CI refining. Preferably, it is less than 2 wt.-%, preferably less than 1.5 wt.-%, particularly preferably less than 1 wt.-%. When the content of CI is too high, this can lead to unwanted salt precipitating on the glass.

[0135] When in the specification it is mentioned that the glass does not contain a component or that they do not comprise a certain component, then it is meant that only the component is allowed to be present in the glass as an impurity. This means that it is not added in large amounts. According to the present application, less than 500 ppm, preferably less than 300 ppm, preferably less than 100 ppm, particularly preferably less than 50 ppm, most preferably less than 10 ppm, respectively by weight, is not a large amount.

[0136] Preferably, the beam guiding element is a lens, a light guide rod, a prism or an aspheric mirror, particularly preferably a prism.

[0137] The present application also relates to a glass having a figure of merit according to the present application.

[0138] The present application also relates to the use of an imaging system according to the present application, in particular in a projector or in material processing.

[0139] The present application also relates to a projector, in particular a DLP projector, comprising an imaging system according to the present application. BRIEF DESCRIPTION OF DRAWINGS

[0140] Figure 1 An embodiment of the present application is schematically shown. An exemplary design of an imaging system as a DLP projector is shown. After leaving the laser light source 1, the three colors blue, green and red (arrow 5) generated by the laser light source 1 reach the beam guiding element 2. The beam guiding element 2 redirects the light to the image generation chip 3 (arrow 6). Then, the image generated by the image generation chip 3, in particular one image in blue, green and red, respectively, reaches the beam guiding element 2. This is shown by arrow 7. Then, the beam guiding element 2 ensures that the composite color image reaches the projection optics 4. As shown by arrow 8.

[0141] Figure 2 The emission spectrum of a Phillips HOK 4 / 120 lamp is shown. On the x-axis the wavelength in nm is shown. On the y-axis the relative intensity relative to the maximum intensity is shown.

[0142] Figure 3 is a bar chart showing the figure of merit F(436 nm) and the figure of merit F(RGB) for 5 embodiments 1-5 according to the present application and a comparative example A not according to the present application. DETAILED DESCRIPTION

[0143] Five samples of 10 mm thickness of example glasses 1-5 according to the application and one comparative sample A not according to the application were irradiated with a HOK 4 lamp for 15 hours. A HOK 4 / 120 lamp of Philips was used. The spectrum of the HOK 4 / 120 lamp is shown in Fig. 1. The distance between the lamp and the sample was 7 cm. The power density was 25 mW / cm2. The sample size was 20 mm x 30 mm x 10 mm. The composition of the glasses is shown in Table 1 (in weight %). Figure 2 2 2

[0144] Table 1

[0145]

[0146]

[0147] The figure of merit F(436 nm), the figure of merit F(546 nm), the figure of merit F(644 nm) and the figure of merit F(RGB) were calculated according to the above formula. For this, the corresponding values of the heat S, the non-induced absorbance Ext0 and the induced absorbance Ext1 for the wavelengths 436 nm, 546 nm and 644 nm and the thermal conductivity k of the glass were determined. The results are shown in Table 2. Table 2 summarizes the measured values and the calculated results. Figure 3

[0148] Table 2

[0149] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example A S(436 nm) [ppm / K] 13.7 13.3 19.6 0.88 7.99 19.6 S(546 nm) [ppm / K] 12.9 12.6 18.0 0.20 7.16 18.0 S(644 nm) [ppm / K] 12.3 12.3 17.3 -0.13 6.94 17.3 Ext0 (436 nm) [1 / cm] 0.0000 0.0016 0.0010 0.0013 0.0036 0.0016 0.0013 Ext0 (546 nm) [1 / cm] 0.0000 0.0008 0.0009 0.0004 0.0020 0.0020 0.0004 Ext0 (644 nm) [1 / cm] 0.0000 0.0012 0.0010 0.0006 0.0024 0.0022 0.0006 Ext1 (436 nm) [1 / cm] 0.0000 0.0056 0.0022 0.0817 0.0020 0.0015 0.4038 Ext1 (546 nm) [1 / cm] 0.0000 0.0029 0.0014 0.0219 0.0010 0.0001 0.1349 Ext1 (644 nm) [1 / cm] 0.0030 0.0002 0.0114 0.0013 0.0012 0.0552 k [W / (cm*K)] 0.011 0.013 0.0083 0.0076 0.0093 0.0083 F(436 nm) [ppm / W] 8.86 3.20 196.34 0.658 2.697 958.65 F(546 nm) [ppm / W] 4.33 2.20 48.44 0.078 1.631 294.33 F(644 nm) [ppm / W] 4.71 1.11 24.92 -0.063 2.543 116.38 F(RGB) [ppm / W] 17.9 6.5 270 0.674 6.9 1369

[0150] It can be seen that the figure of merit F(436 nm) < 700 ppm / W, the figure of merit F(546 nm) < 215 ppm / W, the figure of merit F(644 nm) < 85 ppm / W and the figure of merit F(RGB) < 1000 ppm / W for the glasses 1-5 according to the application compared to the comparative sample A.

[0151] Example glass 3 and comparative sample A have very similar compositions and the essential difference between them is that comparative sample A comprises a relevant content of As2O3. As a result, the performance of example 3 is shown, which is improved by a multiple. Notably, this effect can be achieved with glasses of many different glass series. Thus, examples 1 and 5 are borosilicate glasses, example 2 is an aluminoborosilicate glass, example 3 is a silicate glass, example 4 is a fluorophosphate glass.

[0152] List of reference signs

[0153] 1 laser light source

[0154] 2 beam guiding element

[0155] 3 image generating chip​​

[0156] 4 projection optics

[0157] 5 light from the laser light source to the beam steering element

[0158] 6 light from the beam steering element light redirection to the image generation chip

[0159] 7 image generated by the image generation chip to the beam steering element

[0160] 8 composite color image to the projection optics

Claims

1. An imaging system comprising a) at least one laser light source selected from the group consisting of a laser light source B having a wavelength λ B in the spectral range of 380 nm to 490 nm, a laser light source G having a wavelength λ G in the spectral range of > 490 nm to 585 nm and a laser light source R having a wavelength λ R in the spectral range of > 585 nm to 750 nm, and b) a beam guiding element, wherein The laser light source is adapted to generate an average surface power density greater than 10 W / cm 2 in at least one point of the beam guiding element and the beam guiding element consists of a glass having a figure of merit F(436 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k, wherein S(436 nm) is the heat at a wavelength of 436 nm, Ext1(436 nm) is the additional absorbance at a wavelength of 436 nm after irradiation of a sample of thickness 10 mm with a HOK 4 lamp for 15 hours compared to Ext0(436 nm), Ext0(436 nm) is the absorbance at a wavelength of 436 nm of a sample of thickness 10 mm without irradiation with a HOK 4 lamp, k is the thermal conductivity, and wherein F(436 nm) < 700 ppm / W.

2. The imaging system of claim 1, comprising a laser light source B having a wavelength λB in the spectral range of 380 nm to 490 nm, a laser light source G having a wavelength λG in the spectral range of > 490 nm to 585 nm and a laser light source R having a wavelength λR in the spectral range of > 585 nm to 750 nm, wherein B λB < 490 nm and λG > 490 nm and λR > 585 nm. G R λB < 490 nm and λG > 490 nm and λR > 585 nm. The laser light source B, the laser light source G and the laser light source R are adapted to generate an average surface power density greater than 10 W / cm 2 in at least one point of the beam guiding element, and the beam guiding element is composed of a glass composition having a figure of merit F(RGB) = F(436 nm) + F(546 nm) + F(644 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k + S(546 nm)*(Ext0(546 nm) + Ext1(546 nm)) / k + S(644 nm)*(Ext0(644 nm) + Ext1(644 nm)) / k, wherein F(RGB) < 1000 ppm / W. ​ 3. The imaging system of claim 2, wherein, F(RGB) is at most 800 ppm / W.

4. The imaging system of any of claims 1 to 3, wherein, The laser light source is a diode laser.

5. The imaging system of any one of claims 1 to 3, wherein, The beam guiding element is a prism.

6. The imaging system of any one of claims 1 to 3, wherein, The laser light source is adapted to generate an average surface power density of 15 to 60 W / cm2in at least one point of the beam guiding element. 2 The laser light source is adapted to generate an average surface power density of 15 to 60 W / cm2in at least one point of the beam guiding element.

7. The imaging system of any of the preceding claims 2 to 3, wherein, S(436 nm), S(546 nm) and S(644 nm) are at most 50 ppm / K.

8. The imaging system of any of the preceding claims 2 to 3, wherein, Ext0(436 nm), Ext0(546 nm) and Ext0(644 nm) are less than 0.01 / cm.

9. The imaging system of any of the preceding claims 2 to 3, wherein, Ext0(436 nm), Ext0(546 nm) and Ext0(644 nm) are less than 0.3 / cm.

10. The imaging system of any of the preceding claims 1 to 3, wherein, The thermal conductivity k is higher than 0.005 W / (cm*K).

11. The imaging system of any of the preceding claims 1 to 3, wherein, The average dn / dT at the wavelengths 436 nm, 546 nm and / or 644 nm in the temperature range from 20 to 40 °C is in the range from 0.1 to 8.0 ppm / K, wherein dn / dT represents the change of the refractive index with temperature.

12. A beam guiding element consisting of a glass with a figure of merit F(436 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k, wherein, S(436 nm) is the heat at the wavelength 436 nm, Ext1(436 nm) is the additional absorbance at the wavelength 436 nm after irradiation of a sample with a thickness of 10 mm with a HOK 4 lamp for 15 hours compared to Ext0(436 nm), Ext0(436 nm) is the absorbance at the wavelength 436 nm of a sample with a thickness of 10 mm without irradiation with a HOK 4 lamp, k is the thermal conductivity, wherein F(436 nm) < 700 ppm / W.

13. A glass having a figure of merit F(436 nm) = S(436 nm)*(Ext0(436 nm) + Ext1(436 nm)) / k, wherein, S(436 nm) is the heat at the wavelength 436 nm, Ext1(436 nm) is the additional absorbance at the wavelength 436 nm after irradiation of a sample with a thickness of 10 mm with a HOK 4 lamp for 15 hours compared to Ext0(436 nm), Ext0(436 nm) is the absorbance at the wavelength 436 nm of a sample with a thickness of 10 mm without irradiation with a HOK 4 lamp, k is the thermal conductivity, wherein F(436 nm) < 700 ppm / W.

14. Use of the imaging system according to any one of claims 1 to 11 in a projector or material processing.

15. A projector comprising the imaging system according to any one of claims 1 to 11.

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