This invention relates to an arrangement for generating electromagnetic radiation, such as in particular a laser arrangement having a high-voltage connection, a method for initiating and operating an electromagnetic radiation and for operating a laser arrangement, and uses and applications of the arrangements of the method.
The excitation of an electromagnetic radiation, such as for example of a laser, or the generation of a laser beam in a laser tube can be effected for example with high voltage, in particular in the operation of a so-called gas laser. Here a voltage adequate to generate the laser effect or laser beam is imposed, the strength of the voltage being dependent on, among many other things, the length of the tube, the pressure, under some circumstances the gases used, etc.
As a rule, gases or gas mixtures that are suitable for generating certain electromagnetic waves or colors or color mixtures are employed in gas lasers, such as for example helium-neon mixture, argon, argon-CO2 mixture, CO2, krypton mixture, etc.
Through the use of various gas mixtures it is possible to generate so-called chromatic lasers or even white-light lasers. Here it is disadvantageous, however, that undesired color contributions must be filtered out with additional optical arrangements such as for example prisms, color filters, etc. This, however, leads to a loss of the effective power relative to the power expended.
It is therefore an object of the invention to propose a practice that makes possible color filtering, or the generation of a laser beam having a precisely defined wavelength, without the necessity of an additional filter arrangement.
According to the invention there is proposed an arrangement for initiating and operating an electromagnetic radiation, such as in particular a laser arrangement, having a high-voltage connection for generating the electromagnetic radiation, wherein in addition to the high-voltage connection there is at least one further electromagnetic source for initiating the radiation.
The laser arrangement proposed according to the invention exhibits the customarily used laser rod or a laser tube, as well as a high-voltage connection for the operation of the laser beam, at least one electromagnetic radiation source, such as for example a light source, being provided in the region along the laser rod or laser tube in order to initiate the laser, in addition to the possibility of operation with high voltage.
According to one embodiment, the electromagnetic radiation source is a diode arrangement, a plurality of diodes, for example, being arranged preferably in a line along the laser rod or laser tube. Here the diode arrangement used is one having a radiant power that is sufficient, when supplementing the imposed voltage, to initiate the laser.
The diode arrangement exhibits a certain emission of electromagnetic waves, or the light emitted by the diodes exhibits a certain wavelength, that corresponds to the wavelength or color that is to be selected from the wavelength or colors excitable in the laser tube or laser rod. The electromagnetic radiation generated can only be such a radiation as can also be generated in the medium (laser tube/laser rod, etc.) by virtue of its physical properties.
The diodes of the diode arrangement are preferably operated in pulsed fashion.
Again, according to a further embodiment, it is possible to arrange a plurality of diode arrangements along the laser rod or laser tube, the individual diode arrangements emitting different wavelengths of light. Infrared rays, x-rays, microwaves, etc., or a combination of the various radiation sources can be used, among others, as electromagnetic radiation sources.
Further preferred embodiments of the laser arrangement are disclosed hereinafter.
There is further proposed a method for initiating and operating an electromagnetic radiation or for electromagnetically initiating a light source, wherein a high voltage is initially imposed with a power that is insufficient or barely sufficient to initiate the radiation of the light source, and wherein the initiation proper of the electromagnetic radiation of the light source is effected by means of an additional electromagnetic radiation source.
What is proposed according to the invention is first to utilize a high-voltage connection to impose a voltage that lies just below the initiating voltage or makes possible only an unstable initiation of the radiation source or light source and subsequently makes it possible to initiate and operate the radiation source or light source by means of an additional radiation source. The advantage of this procedure for initiating and operating an electromagnetic radiation or light source, as in particular a laser, is that there is no necessity of imposing initially a needlessly high high voltage, which causes great stress to the radiation arrangement, needlessly generates heat and is very energy-intensive. Besides, initiation by means of the additional radiation source makes it possible, after initiation, to optimize the necessary voltage by which the radiation arrangement or laser is to be operated.
What is proposed specifically is a method for generating a laser beam having a desired wavelength by imposing on a laser operated with high voltage only a portion of the voltage necessary to initiate the laser and initiating the laser with an additional electromagnetic radiation source such as a light source.
Both the laser arrangement according to the invention and the method are possible per se for any kind of laser, maser, etc., but gas lasers with mixed gases are the preferred topic of discussion.
Possible areas of application are for example image projection, light shows, the generation of certain laser effects, the use for illumination purposes or the use of special lasers in research. Further, it is possible to conceive of medical lasers having high power, low energy consumption, as well as small footprint and various precisely tuned wavelengths.
The laser principle described according to the invention has the following great advantage over conventional gas lasers:
Because of the wavelength-oriented excitation by, for example, an additional light source, the laser emits only the desired wavelengths and its modes, which is generally not possible with gas-filled mixed-light or white-light lasers. Thus with an argon laser, for example, the undesired contribution must be filtered out with prisms, color filters or coated mirrors, which represents a loss of effective power in operation relative to the power expended. This further results in severe heating as well as higher laser power consumption.
A further advantage of the invention or of the preferred kind of gas laser pumping as described consists in the possibility of much faster modulation, which, for example at 4.31818 MHz modulation, makes possible an image resolution of 640×400 points, which results for example in an image sequence of 25 frames. Under corresponding conditions, only 256 colors could be reproduced in the prior art. Of course these are not absolute limits, since with the fast LEDs now commonly available or with other faster semiconductors it is entirely possible to get better resolution and greater color depth. Still a further advantage due to the low power dissipation lies in the more compact construction and thus lower manufacturing cost.
The presumed principle is based on the idea that the following happens in the laser tube filled with gas mixture:
The imposition of a high voltage brings the atoms or molecules present in the gas mixture from a lower to a higher energy level. The high voltage is selected so that the electrons are shortly to drop back to a lower energy level. Here the voltage is known to depend on the temperature, tube length, pressure, and gas employed. Now, by means of the light sources placed around the inner tube (the use of LEDs is proposed according to the invention, for example, as depicted in
In general, light is attenuated by absorption rather than amplified upon passage through a medium. The reason is that at thermal equilibrium a larger number of atoms are in the low energy state, so that absorption dominates over emission. An essential condition for laser amplification is population inversion, that is, a condition in which more atoms are at a higher energy level than at the lower one. Such an inversion is effected by the supply of optical (electromagnetic) power (as in the helium-neon laser).
This means, first, that if a high voltage just up to the level at which electrons drop back from the higher to a lower energy level is imposed (high voltage on the glass tube anode/cathode), then in order to trigger the dropping back, photons of one or a variety of wavelengths are introduced into the inner laser tube via one or a plurality of initiating source(s) (LED, etc.), and in this way dropping back with the emission of a photon is commenced, which in turn triggers an avalanche effect in the gas mixture and commences the stimulated optical oscillation and then leads to amplified electromagnetic radiation emission through the output coupler (laser beam). A 720 nm LED triggers only photons of the same wavelength.
By way of clarification it is noted here that even if a laser (a He—Ne laser) must be initiated just once and afterward is “self”-excited, and only an operating voltage is still present. An example is a He—Ne laser tube manufactured by Meles Griot, which requires an initiating voltage of, say, 1.6 EV1 and afterward falls back to an operating voltage of 200 V. Translator's Note: Thus in the original; error for kV?
When a gas laser is used, argon-CO2 or other mixed-gas lasers can be used for example as white-light lasers or so-called mixed-light or chromatic lasers. This means that most of the visible wavelengths can arise or be excited therein, the wavelength of the light source necessarily, of course, coinciding with one of the wavelengths to be excited in the laser arrangement.
The invention is now explained in greater detail by way of example and with reference to the appended Drawings, in which:
In the laser arrangement schematically illustrated in
According to the invention it is now proposed to arrange additional light sources along inner laser tube 3, such as for example LEDs 25, by means of which the laser beam proper is initiated.
The laser proposed according to the invention is operated in the following manner:
First, a determination is made of the high voltage at which the laser beam is initiated. Now the voltage is reduced to, for example, a value just below the initiating voltage, so that the laser is not initiated. In order to initiate the laser, light sources such as LEDs 25 are used, these having a power such that initiation of the laser is enabled.
Precisely the wavelength that is to be selected from the mixed light of the laser is excited in the laser tube by the wavelength emitted by the LEDs. Because of the laser arrangement, which, governed by the spacing of both mirrors 11 and 13 and the gas mixture used, permits only a limited number of wavelengths, the wavelength of the light source must naturally correspond to one of these selected wavelengths. If for example the spacing between the mirrors is 1 meter, then the wavelength of the light-emitting diodes must exhibit a value of, for example, 100 nm, 200 nm, etc., as well as ½ or any wavelength divisible into this meter, since otherwise no excitation at all is possible.
Arranged in front of each of respective caps 7 and 9 are two reflecting mirrors 11 and 13, which must be arranged at a precisely specified spacing and plane-parallel to each other. For the adjustment of the spacing and plane-parallelism, mirror 11 on cap 7 is arranged with a special holder 15, which is additionally illustrated in enlarged view and in detail in
Further, on cap 9 there is a connection 19 for the imposition of the high voltage, the connection at the opposite end of tube 5 being effectable via arms of holder 15, which are fabricated for example from a highly conductive material. Additional metallic framing 12 around mirror 11 makes it possible to generate a uniform high-voltage field.
Arranged in the interior of tube 5, which is manufactured for example from a quartz glass, are LEDs 25, which are rigidly arranged on corresponding boards. LEDs 25 are so oriented relative to inner laser tube 3 as to enable an optimal illumination or excitation of the gas or mixture.
The position of light-emitting diodes 25 is better illustrated with reference to FIG. 3, which depicts a cross section through tube 5 along line K-K. Connections 21 and 23, protruding laterally from cap 9, are provided for powering the LEDs.
In an arrangement illustrated in
Because only one wavelength need be excited in the laser tube in order to generate a certain monochromatic color beam, the laser arrangement according to the invention can be operated at a lower power, which naturally also leads to less evolution of heat. Thus cooling such as is used when operating conventional lasers may become unnecessary, or only minimal cooling of lower power and smaller size may be necessary, as appropriate.
As has already been noted,
As already noted, the precise adjustment of the output coupler arranged in cap 7 is to be explained in greater detail with reference to
In
Similarly to the embodiment of
The remaining components of the laser arrangement of
A mercury vapor lamp or a white-light source or other suitable radiation source can for example be employed as light source 47. Instead of frequency doubling, of course, a frequency filter can be arranged in order to filter out one or a plurality of wavelengths specifically.
In
One or a plurality of sensor(s) 39 is/are provided on the tube for acquiring or determining the gas mixture present in the tube, the pressure, etc. Connected ahead of charging fitting 38 is a mixing battery 80 for mixing various gases, which are stored in various gas tanks 81. Finally, an outlet valve or pressure relief valve 82 is provided on valve fitting 37.
According to the laser arrangement as illustrated in
The laser arrangements described with refrence to
An interesting use of the laser arrangement as proposed in the invention is image projection with a laser projector. In laser arrangements customarily used for image projection at present, at least three laser-beam generators are used in each case, namely to generate a red light laser, a green light laser and a blue light laser (RGB=red, green, blue). The beams are subsequently merged and the laser beam so generated is deflected, for example by a polygon scanner, so that horizontal lines are written. When a line has been written, a second mirror deflects the beam one line downward. This can also be implemented with just one mirror (polygon) that is movable in both axes. In this way the whole image is written at length. The principle is fully correspondent to the cathode-ray tube, as it is known from a television receiver. According to the invention, one single laser-beam arrangement as proposed by the invention can be employed instead of the abovementioned three laser-beam generators, which makes possible a considerable simplification and, in association therewith, a reduction in the cost of such an arrangement.
Further uses are for example the generation of certain laser effects, light shows, the use for illumination purposes, for research. Further embodiments are for example medical lasers having high power, low energy consumption, as well as small footprint and various precisely tuned wavelengths. Again, a further application is in so-called depilation devices, in which the desired wavelengths for the removal of hairs are first determined or measured with color filters, in order that the laser can be adjusted to the optimal wavelength or wavelengths. This kind of laser is also best suited to the removal of tattoos and the treatment of melanomas.
Number | Date | Country | Kind |
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06 008 989.3 | Apr 2006 | EP | regional |