DE3221150A1 - Dye laser device pumped in the longitudinal direction - Google Patents

Description

Dye laser device pumped lengthways

The invention relates to a longitudinally pumped dye laser device according to the preamble of claim 1.

Longitudinally pumped dye laser devices are known which differ from transversely pumped dye lasers differentiate. An advantage of the longitudinally pumped or longitudinally pumped dye laser arrays or laser devices versus the cross-directionally pumped dye lasers is the possibility of exceptional to use thin layers of the dye solution and thus to generate short output pulses. All of these - known for a long time - are pumped lengthways Arrangements are either very expensive or have a large number of optical components, which in turn are critical Require alignment. In the publication "Topics in Applied Physics ", Vol. 1, Dye Laser by

F. P. Schafer, 2nd edition, 1977, are different lengthways pumped dye laser arrays shown on page 39. In all of these arrangements the output radiation runs, exiting the dye laser cell in the same direction and is essentially colinear with the

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Input pump beam. To create a resonator cavity and to convert the input beam into the output beam suppress, it is necessary to cover the surfaces of the cavity with expensive dielectrics, with multilayer mirrors that selectively transmit a desired radiation wavelength to coat. The surface that the input pump jet must be relatively transparent to light at the wavelength of the input pump beam, and the surface at the opposite and exiting end region of the cavity should have a dielectric coating with a high reflectivity or a high degree of reflection for the wavelength of the pump beam. At wavelengths of the laser radiation, on the other hand, the input surface through which the pump beam must pass can have a high reflectivity, and the surface, from which the laser radiation emerges must have a lower reflectivity in order to enable that some of the dye laser radiation can escape from the cavity of the optical resonator.

Another longitudinally pumped dye laser device is known from "H. Salzmann and H. Strohwald, Physics Letter, 57 A (1976), 41". There is an arrangement there Shown with a laser medium - dye solution sandwiched between a mirror surface and a prism is provided. The entering pump beam is reflected onto the prism surface by a first mirror and broken down into the dye solution where laser activity or suggestion takes place. The resulting laser radiation passes through the prism, emerges from the Prism at a different place than the pump beam enters, and is refracted so that it goes into free space and is reflected in the desired direction by a second mirror. The arrangement of a prism in the optical path of a cavity for a dye laser has long been known, for example from US-PS 3 873 941, column 2, lines 24 to 36. Furthermore, an arrangement according to the Salzmann publication is required

and Strohwald that the first and second mirrors are independent of each other for proper optical alignment need to be adjusted.

From a publication by G. Veith and A. J. Schmidt in "OpticsCommunication", Vol. 30, Number 3, published September 1979, is a cross-directionally pumped dye laser device known whose output beam is through a longitudinally pumped amplifier cell is reinforced. The medium in the amplifier cell is excited to a level below the threshold required for the occurrence of laser radiation is required. The dye laser pulse to be amplified enters the amplifier cell and causes excited emission to occur in the amplifier cell. From this process results in the amplification of the dye laser pulse.

In the amplifier section with said construction, a single lens was used to focus the excitation beam on the To focus the amplifier cell and to collect the amplified pulse emerging from the cell. A second Lens was used to direct the dye laser pulse to be amplified to the opposite side of the amplifier cell to focus opposite the side from which the beam exits to excite the dye solution. As the dye laser pulse to be amplified enters the amplifier cell from the opposite side of the cell occurs as the amplified pulse exits, it is evident that no mirror may be used to reflect the amplified pulse to the first lens. Special precautionary measures must be taken to ensure a good spatial overlap between the focussing area or the focal zone of the area to be amplified Dye laser pulse and the gain zone. This is due to the fact that the Dye laser pulse the amplifier cell from the opposite Side of the cell enters when the beam

enters the cell to stimulate the dye solution. Since it is also necessary to make the amplifier cell long enough so that an adequate gain factor can be achieved, the alignment problems are further exacerbated.

As far as the known systems work correctly, they are expensive, complicated and difficult to align and consist of many individual parts.

In contrast, it is the object of the invention to provide an in To provide longitudinally pumped dye laser device according to the preamble of claim 1, which is easy to align and has a simple structure.

This task is made possible by the distinguishing features of the Claim 1 solved.

A particular advantage results from the device according to the invention, which is economical and simple can be aligned. The device has an optical unit device, a container device, in which a laser medium dye solution can be received is, and a reflector device with which laser radiation can be reflected to the unit optical device. The dye solution is between the optical Unit device and the reflector device provided, and the reflector device adjoins the Dye solution. The optical unit device is arranged relative to the container device so that a Focusing a pump beam into the dye solution can take place, and the laser radiation, which from the Container device emerges, can be aligned in a substantially parallel beam.

Advantageous further developments result from the subclaims.

In one embodiment of the invention, the container device a front and a rear window, with the dye solution between the windows can be picked up and the reflector device behind the rear or rear window is arranged adjacent to this. In a further embodiment has the container device has a front window and a rear body region adjacent to the dye solution with the dye solution absorbable between the front window and the rear body area is. The rear body area has a reflector device with which laser radiation is applied the optical unitary device or the unitary, multiple-use optical device is reflectable.

Further advantages, features and details of the invention will become several in the following description Embodiments of the invention explained in more detail with reference to the accompanying drawing.

It shows:

1 shows a schematic view of a cross section through the dye laser device according to the invention; and

Fig. 2 is a view of a cross section through another embodiment of the dye laser device according to the invention.

in Fig. 1 is a cross-sectional view of one in the longitudinal direction pumped dye laser device 10 shown schematically. One entering the laser device 10 Pump beam or input pump beam 20 is through a unit optical device 30 on a Focused area containing a laser medium dye solution. The laser medium dye solution is in a container device 50, which is designed as a cavity, is provided. The focused pump beam excites

the laser medium dye solution to an excited state or stimulated level, which then goes to a low energy state or a lower level falls back and thereby stimulated or excited laser radiation in the paraffin solution results. A reflector device 60, which is designed as a reflector and is located behind the laser medium dye solution, reflects the laser radiation to the optical unit device 30. The from which the laser medium dye solution containing container device 50 exiting Laser radiation 70 is shown in FIG. 1. The same optical unitary device 30 that the pump beam 20 focused, also serves the purpose of the container device 50 emerging from the container device 50 containing the dye solution Align laser radiation in a substantially parallel beam 80.

The unit optical device 30 is such relative to the container device containing the dye solution 50 arranged that the pump beam 20 is focused in the laser medium dye solution, and the exiting laser radiation 70 is aligned in a substantially parallel beam 80. This arrangement provides an easily orientable longitudinally pumped dye laser device.

The container device 50 in which the laser medium dye solution can be received has an inexpensive one and simple structure. A front window 90 of the container device 50 allows the pump beam 20 to enter the laser medium dye solution, which is received in the container device, enters and excites it, and allows laser radiation from the container device 50 exits. In another embodiment of the invention, a rear window 95 is similar to the front Window 90 provided.

The cavity or the container device 50 can either

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designed to be a replenishing river the laser medium dye solution is enabled so that there is a flow essentially transverse to the direction of the pump jet 20; or the cavity or the container device 50 can be closed at both ends. With high pump energies and high repetition speeds, i.e., small pulse train intervals, or in a continuous mode it may be necessary for a Circulation of the laser medium dye solution.

It has been shown that in most cases it is sufficient to simply have a stationary and not refilled Use stock of laser medium dye solution. In this case the windows 90 and 95 are along their side surfaces and at least along their base surfaces so connected that a cavity for receiving the laser medium dye solution is formed. When recirculating flow is required, the windows become natural connected only along their side surfaces and the upper and lower end regions of the cavity are fitted with suitable connectors and piping to enable the solution to re-establish is filled.

Micro-right-angled tubes or cuvettes, which z. B.

are made of quartz or different types of glass are particularly useful for forming the container device 50 with their front window 90 and rear window 95 proven. Such commercially available cuvette with micro-precise right angles with a thickness of the major surfaces of 0.2 mm as a window and a clearance between the windows of either 0.2 mm or 0.5 mm have been found to be satisfactory and proven economical to use. Each of the main surfaces of the micro-right-angled tubular Container material has a reflectivity or

°° a degree of reflection of approximately 4% at the wavelengths of the pump beam 20 and the laser radiation 70.

Of course, the strength of the two windows and

the clear width between the windows in one wide Area can be selected so that the total thickness is sufficient to generate laser radiation.

A reflector device 60 or reflector is behind the laser medium dye solution and adjacent to it arranged. The reflector device 60 serves to reflect the laser radiation to the optical unit device 30. It is not necessary that the reflector Device 60 adjoins the laser medium dye solution, however, it is desirable that this be arranged sufficiently close to the area of laser activity, so that the laser radiation is reflected to the optical unit device 30 so that it is in an im substantially parallel beam 80 can be aligned.

In one embodiment of the invention, the reflector device is 60 arranged immediately behind the rear window of the container device 50. In another Embodiment may have the rear surface of the rear window 95 with either aluminum or silver be coated so as to produce a reflector. Of course, the rear window 95 can Container device 50 is replaced by a rear body portion 110 having a reflective surface with which laser radiation can be reflected to the optical unit device 30. That other cavity or container device 100 in which the laser

0 medium dye solution can be absorbed is shown in FIG. 2. The front surface 112 of the rear body region 110 can be provided with a reflective surface, with which the laser radiation can be reflected to the optical unit device. Alternatively, the rear surface 114 of the rear body region 110 can be provided with a reflective surface 116. It goes without saying that in this case the rear body region 110 should essentially

be transparent to the wavelengths of both the pump beam and the laser radiation, so that the laser radiation can be reflected by the reflective surface 116 to the unit optical device. It it is also possible to arrange the reflective surface in the rear body area 110, provided that that at least the portion of the rear housing surface between the reflective surface and the dye solution is essentially transparent or permeable to the wavelengths of the pump beam and the Laser radiation is.

Many possible types of reflective surfaces can be used can be used if they work as good reflectors at the wavelength of the laser radiation. One either surface coated with aluminum or silver has proven successful. Because the strong energy both the pump beam and the laser radiation can destroy the reflector, he can with a suitable protective layer, for example magnesium fluoride, provided to reduce the damage. A dielectric mirror can also be used.

Various commercially available dyes can be prepared in special solutions to suit a desired Application can be selected, the solution being determined by the desired wavelength of the laser radiation will. The concentration of the dye solution can be adjusted by diluting the dye in a suitable solvent can be set. The desired concentration is usually a function of the layer thickness of the in the container device 50 contained dye solution. In tests it has proven to be advantageous adjust the concentration of the dye solution so that only about 20% of the radiation of the pump beam is the rear Reach the window or the rear surface of the container device.

The input pump beam 20 is the output beam of a other laser. The output beam of a nitrogen gas laser and the output beam is either a longitudinally pumped or a transversely pumped dye laser has been used on an experimental basis. The only requirements are that / 3 is the wavelength of the pump beam is compatible with the absorption characteristics of the laser medium dye solution, and that the pump beam a sufficient energy density in the laser medium dye solution generated to a sufficiently large population inversion or an inverted energy state in the Generate laser medium dye solution and thus create excited laser radiation. The pump beam 20 is aligned by the unit optical device 30 to provide high pump energy density in the laser medium dye solution to reach. A plano-convex lens is shown in FIG. 1 as a unitary optical device 30 shown. However, a biconvex can be used, as shown by dashed lines in FIG. 1 is, or a meniscus lens or convex-concave lens 130, as shown in FIG. The pump jet As shown in FIG. 1, 20 enters the center region of the lens. This is not a strict one The requirement, however, results in a less distorted focus area in the laser medium dye solution occurs as if the pump beam 20 at outer regions of the optical unit device 30 in this entry. The lens 30 is preferably made of quartz, since normal glass tends to block the pump beam and the laser

"^ to weaken or attenuate radiation.

The laser radiation becomes the optical one through the reflector Unit device 30. As shown in Fig., The container device 50 and the Reflector 60 aligned slightly obliquely to one another, so that the laser radiation emerging from the container device 50 is slightly non-colinear with the pump beam 20. The emerging laser radiation 70 is divergent and

is aligned or aligned in a substantially parallel beam 80 by the optical unit device 30. collected. When the unit optical device 30 is arranged so that the pump beam 20 into the laser medium c When the dye solution is focused, the diverging laser radiation emanating from the cavity 50 emerges, collected in a substantially parallel beam. It is advantageous to use the container device 50 and the mirror, reflector device 60, a little

jQ at an angle so that the essentially

parallel beam 80 can be separated from the pump beam 20 can. A prism 120 can then be positioned so that the substantially parallel beam 80 is intercepted and projected in a desired direction. It goes without saying that a mirror can be used instead of the prism 120 be used. Of course, it is also possible for the cavity 50 and the mirror 60 not to be inclined

align. Without inclination, the emerging laser radiation 70 runs in a direction towards the pump beam 20 colinear orbit. A dielectric mirror can be used to highlight the substantially parallel beam 80 to separate from the pump beam 20.

In the case of a non-obliquely aligned cavity and reflector, the axis is the unitary optical device 30 substantially normal to the front surface of the cavity or container device 50. In the case of an obliquely inclined cavity and reflector, as shown in Fig. 1, the axis lies optical unit device 30 at an angle relative to one of the front window 90 of the container device 50 normal axis. Two points of view arise

in choosing this angle. Since the unit optical device is limited in size, it follows that that the laser radiation which emerges from the container device 50 does not impinge on the optical device would if the angle was too big. Furthermore, if the angle is too large, the pump beam cannot laser activity

generate in the container device, as explained in more detail in US-PS 38 73 941. Has an angle of about 6 ° has been found to be satisfactory in tests and shows that the substantially parallel beam 80 of the pump beam 20 is separated.

The distance between the unit optical device 30 and the container device 50 is substantially the same the focal length of the optical device 30. Two aspects arise in the selection of the desired ones Focal length of the optical device 30. As a sufficiently high energy density in the laser medium dye solution is required, the focal length of the unit optical device not be too big, as a long focal length results in a greater expansion of the focal point and thus leads to a lower energy density, which may not be sufficient for laser activity in of the container device 50 to generate. Although most of the laser radiation emitted from the container device passes to the optical unit device 30, a certain amount of super-radian occurs Radiation in an almost spherical, i.e. spherical, radiation direction from the container device. These Super-radiant or over-radiating radiation arises from the spontaneous emission of the at a high energy level excited dye solution is undesirable and should not be picked up by the optical unit device 30 bzv /. be aligned. If the optical unit device 30 is too close to the container device 50 30 is ordered, an undesirably high proportion of these super-radiant laser radiation collected. Therefore, it is desirable to ensure that the focal length of the optical unit device 30 has a sufficient length so that an insignificant proportion of the overexposed

"° Radiation is collected. If the focal length is too small is used, too high an energy density is generated in the housing 50 and so a high percentage of the undesired superradian impulses generated.

Non-critical alignment steps are required for the construction of the dye laser device pumped in the longitudinal direction. The pump beam 20 is directed to fall on the surface of the unit optical device 30. The distance between the unit optical device 30 and the cavity 50 is visually adjusted so that a well-defined focal area exists in the laser medium dye solution. The container device 50 and mirror 60 may be tilted slightly IQ so that the pump beam 20 and the resulting substantially parallel beam 30 are separated from one another.

! Laid out the basic description of the invention in the following figures are given for a specific example without restrictive character. One in cross section glass or micro-rectangular tubular container Quartz has a cavity with a front and a rear window, each 0.2 mm thick, and a clear one Width of 0.5 mm. A laser medium color

Rhodamine 6G substance solution in an approximately 8 χ 10 molar Solution in ethanol was made by a nitrogen gas laser with a power of 200 kilowatts for about 300 picoseconds stimulated with a repetition rate of 20 pulses per second. A plano-convex ouarz lens with a focal length of about 50.8 mm was used. An output laser radiation with a duration resulted no more than 75 picoseconds.

Claims (9)

Claims Dye laser device pumped lengthwise, thereby characterized in that an optical unit device (30), a container device (50) in which a Laser medium dye solution is absorbable, and a .. reflector device (60) are provided with which laser radiation (70 ^ to the optical unit device (30) can be reflected is that the dye solution between the optisehen Einfieitsvorrichtung (30) and the reflector device (60) is arranged so that the reflector device (60) is arranged in the immediate vicinity of the dye solution, and that the arrangement of the optical unit device (30) is provided in a relationship to the container device (50) with which a pump jet (20) into the dye solution focusable and the laser radiation (70) emerging from the container device can be directed into a substantially parallel beam (80). 2. Laser device according to claim 1, characterized in that that the container device (50) has a front window (90) and a rear window (95) that the dye solution between the front window (90) and the rear window (95) is provided, and that the reflector device (60) behind the rear window (95) has an adjoining reflector surface with which OFFICE 6370 OBERURSEL
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TEL. 06171 5684 «TELEX 4186343 rual d D (IKO 8050 FREISING " SC HNECGSTRASSE 3-5 TfX. O8161.'62O91 TH.EX 526547 p.iwa d BRANCH OFFICE 8.W0 PASSALI LUDWiGSTRASSE 2 TEL. 085136616 -TELEGRAM ADDRESSK PAWAMUC - POSTSCHECKMONCHfN 1360 32 802 ■ - TELECOPY: 08161/62096 (GROUP II - automat.) - Laser radiation (70) is reflectable to the optical unit device (30). 3. Laser device according to claim 1 / characterized in, that the container device (50) has a front window (90) and one adjacent to the dye solution rear body area (40) has that the dye solution between the front window (90) and the rear body region (40) is provided, and that the rear body region (40) the Having reflector device (60) with which laser radiation (70) to the optical unit device (30) is reflective. 4. Laser device according to claim 3, characterized in that the reflector device (60) on the rear Surface of the rear body area (40) is provided, and that the body area (40) is essentially transparent at the wavelengths of the pump radiation and the laser radiation. 5. Laser device according to one of claims 3 or 4, characterized in that the reflector device (60) on the front surface adjacent to the dye solution of the rear body area (40) is provided. 6. Laser device according to one of the preceding claims, characterized in that the optical unit device (30) is a plano-convex or a biconvex or a meniscus lens. 7. Laser device according to one of the preceding claims, characterized in that the axis of the Lens is disposed substantially perpendicular to the front surface of the container device (50), and that the distance between the lens and the container device (50) is substantially the focal length of the Lens is the same. 8. Laser device according to one of claims 1 to 6, characterized in that the axis of the lens is at an angle to an axis perpendicular to the front surface of the container device (50), the angle being provided so that the Laser radiation (5O) emerging from the container device through the optical unit device (30) is further aligned in a substantially parallel beam (80) and that the distance between the Lens and the container device (50) is substantially equal to the focal length of the lens. 9. Laser device according to one of the preceding claims, characterized in that the reflectivity or the reflectance of the windows (90, 95) are both for the wavelengths of the pump beam (20) and those of the laser beam (70) is less than 10%.