DE102008029776B4 - Fiber laser arrangement - Google Patents

Abstract

Fiber laser arrangement (17) with:
a fiber laser or fiber amplifier (3) having a first fiber (3b) with laser-active material, the fiber laser or fiber amplifier (3) providing a laser beam (9, 3a) at a fiber output of the first fiber (3b),
characterized,
that at the fiber output in the axial direction, a solid-state laser amplifier (24) for amplifying the laser beam (9, 3a) is provided
and that an optical deflection device (22) is provided, which directs the pump radiation (5) on the first fiber (3b) to the laser amplifier (24) to the laser amplifier (24) for amplifying the laser beam (9, 3a) To make available.

Description

The The invention relates to a fiber laser array with a fiber laser or fiber amplifier, having a first fiber with laser active material, wherein the Fiber laser or fiber amplifier provides a laser beam at a fiber exit of the first fiber. Such fiber lasers are known, for example, from E. Snitzer et al., Conf. at Optical Fiber Sensors, New Orleans, 1988, contribution PD5.

For many Applications are miniaturized lasers desirable or even necessary the pulsed laser radiation with pulse widths of a few ns and pulse energies in the range of several mJ, such as long-range Laser measuring systems, for material fine machining or for excitation optically non-linear processes. The required pulse powers typically range from about 100 kW to more than one MW. According to P. Peuser, N. P. Schmitt "Diode Pumped Solid state laser ", Springer Verlag, 1995, diode-pumped solid-state lasers are particularly suitable for this purpose. The invention also deals with such miniaturized laser systems.

Especially advantageous for practicable laser systems is when the coupling with the Supply and control electronics over a several meters long Fiber connection can be made.

In Recently, pulsed fiber lasers or fiber amplifier assemblies have been used developed, characterized by a very compact design and a high beam quality distinguished. E. Snitzer et al., Conf. on optical fiber sensors, New Orleans, 1988, contribution PD5 describe that by applying the so-called double-core fiber the performance can be increased considerably could. These fibers are made of high purity quartz glass with a laser-active single-mode core, which is doped with lanthanide ions and of a multimode core for the pump radiation is surrounded. The pump light couples over the entire fiber length from the pump light core into the laser-active core over and there stimulates the laser process.

As in J.A. Alvarez-Chavez et al., Opt. Lett. 25 (2000) 37, could the achievable output through the development the so-called LMA fibers (Large Mode Area) are further increased, which is an enlarged mode field diameter having.

In more recently, the photonic crystal fibers have been developed which may allow further scaling of the pulse energy. Further Details are P. Russel, Science 299 (2003) 358 and J. Limpert et al., Optics Express 12 (2004) 1313 removable.

however reach the maximum, reliably achievable Pulse energies for many applications are not enough. This limit several basic physical Process the pulse energies in the range of a few mJ. These Processes are primarily ASE (so-called Amplified Spontaneous Emission), stimulated Brillouin scattering, Stimulated Raman scattering and self-focusing. This will be in individual in F.D. Teodoro et al., Opt. Lett. 27 (2002) 518 and in R.L. Farrow et al., Opt. Lett. 31 (2006) 3423.

In the DE 199 33 231 A1 A method and apparatus for converting optical pulses through optical parametric gain media into ultrashort optical pulses is disclosed. In this case, a fiber laser arrangement is described with Faserverstäker, is provided in the downstream of a solid state laser amplifier in the axial direction.

From the DE 196 21 461 C2 is a laser system with laser materials with low depolarization known. The laser system is designed as an oscillator amplifier system, which is followed by a phase conjugator. The laser beam is reflected with inverted wavefront on the phase conjugator. This eliminates phase noise and improves beam quality.

The DE 198 28 154 A1 discloses multimode fiber based single mode amplifiers and compressors. In this case, multimode optical waveguides with a large fiber cross section are used in an optical amplifier system for generating high peak powers and pulse energies.

at known fiber lasers and fiber amplifier arrangements are due of the small fiber cross-section in ns pulse mode extremely high intensities, so that scaling the pump power eventually destroys the fiber.

task The invention is a miniaturized fiber laser configuration with one over so far known miniaturized fiber laser arrays considerably expanded To realize pulse power range.

These The object is achieved by a fiber laser arrangement with the features of attached Claim 1 solved.

advantageous Embodiments of the invention are the subject of the dependent claims.

advantageous Uses of the fiber laser array according to the invention are the subject of the secondary claim.

According to the invention Radiation of a fiber laser or a fiber amplifier a laser amplifier introduced, in the axial direction close to the fiber output of the laser active Material provided fiber of the fiber laser or fiber amplifier arranged is and amplifies the radiation of the fiber laser or fiber amplifier.

In order to with a high degree of miniaturization, a large amount of pump energy in the laser amplifier guided can be, is further provided an optical deflection device, passing the pump radiation past the first fiber to the laser amplifier. By the deflection, the pump radiation can accordingly be prepared to increase the efficiency in the laser amplifier. Especially the pump radiation can be focused into the laser crystal.

in the Following is this provided with laser active material fiber of Fiber laser or fiber amplifier as "first Fiber ".

Of the laser amplifier preferably has an amplifier crystal on. The amplifier crystal is more preferably antireflective at its two end surfaces for the laser radiation coated, so high throughput and high gain for the laser radiation to reach.

Further is preferred for the laser amplifier used a longitudinal pumping configuration. Longitudinal pumps in the direction of being reinforced Laser beam has proved to be particularly effective, allowing a high efficiency can be achieved. It is also characterized by a longitudinal Pump configuration reached a particularly high degree of miniaturization.

According to one Another embodiment of the invention is an optical pump source provided for emitting pump radiation for the laser amplifier, so that the laser amplifier - preferably essentially in the same direction - both for receiving the Laser beam and the pump radiation is formed. To the Pumping radiation with high transmission through the entrance surface of the gain crystal to enter, this entrance surface is in addition to an anti-reflective coating for the Laser radiation also antireflecting designed for the pump radiation.

Over a appropriate choice of wavelength the pump radiation to adapt to the absorption spectrum of the amplifier crystal may have a predetermined inversion density distribution in the reinforcing crystal be generated.

According to preferred Embodiments of the invention is laser radiation from a fiber laser or from a fiber amplifier by means of specially arranged optical lenses arranged in an axially, longitudinally fiber-pumped solid-state laser amplifier coupled, so that in a miniaturized configuration power amplified laser radiation with high beam quality is produced with a high efficiency.

• a) Vorverstärker für einen DIRCM-Laser („directed infrared counter measures”)
• b) Miniaturisierter Basislaser für optisch nichtlineare Prozesse
• c) Flugzeuggetragene, miniaturisierte Lidar-Systeme
• d) Laserzündung in Motoren
• e) Roboter-getragene Laser

This provides a particularly advantageous integrated fiber laser solid state laser amplifier arrangement. Advantageous applications are:

• a) Preamplifier for a DIRCM laser ("directed infrared counter measures")
• b) Miniaturized base laser for optically non-linear processes
• c) Aircraft-borne miniaturized lidar systems
• d) laser ignition in motors
• e) robot-borne lasers

embodiments The invention will be explained in more detail with reference to the accompanying drawings. In this shows:

1 a first embodiment of a fiber laser array with laser amplifier;

1a a detail of a fiber laser array of 1 usable pump radiation guide combined with a fiber laser or fiber amplifier;

2 a second embodiment of the fiber laser array;

2a a schematic representation of a usable in the second embodiment pump radiation guide with the fiber laser / fiber amplifier combined therewith;

2 B a schematic detail view of a usable in the second embodiment beam combination;

2c an alternative embodiment of a combined with the fiber laser / fiber amplifier Pumpstrahlungsleiteinrichtung; and

3 A third embodiment of a fiber laser array.

In the 1 . 2 and 3 are three embodiments of a fiber laser array 17 with a fiber laser or fiber amplifier 3 and one in the axial direction behind a fiber output of the fiber laser / fiber amplifier 3 arranged laser amplifier 24 shown. pump radiation 5 from a pump source 20 is via a Pumpstrahlungsleiteinrichtung 21 to the laser amplifier 24 directed. An optical deflection device 22 is to collimacy ren and focusing the pump radiation 5 intended. The optical deflection device 22 has a collimator lens 6 . 6a and a focusing lens 8th . 8a for the pump radiation 5 on.

A first embodiment of the fiber laser arrangement 17 will be referred to below with reference to 1 and 1a described. 1a shows details of the Pumpstrahlungsleiteinrichtung 21 that with the fiber laser / fiber amplifier 3 combined while in 1 the entire fiber laser array 17 is shown.

In the first embodiment of the fiber laser array 17 according to 1 and 1a is essentially a first fiber 3b Fiber laser formed with laser active material 3 or fiber laser amplifiers in the center of a fiber bundle 4b which has several second fibers 4 for the pump radiation 5 having. Accordingly, the fiber bundle leads 4b pump radiation 5 of one or more diode laser beam sources which generate pump radiation for the solid state laser amplifier. To generate this pump radiation 5 is at least a first diode laser 1 , preferably in the form of a high-power diode laser. For pumping / exciting the fiber laser / fiber amplifier 3 is at least a second diode laser 2 intended.

The through the at least one first diode laser 1 generated pump radiation 5 is via the optical deflection 22 directed. The optical deflection device 22 is in the illustrated embodiments by a suitable collimator-focusing lens assembly with the collimator lens 6 and the focusing lens 8th educated. The collimator focusing lens assembly directs the as pump radiation 5 used diode laser radiation from the at least one first diode laser 1 at the first fiber 3b the fiber laser or the fiber amplifier 3 past and forms them in the axial direction in a solid-state laser amplifier crystal 10 of the laser amplifier 24 from.

The amplifier crystal 10 is antireflective to the laser beam at its two end faces 9 of the fiber laser / fiber amplifier 3 coated and is at its entrance surface additionally antireflective for the pump radiation 5 coated.

The wavelength of the pump radiation 5 is the absorption spectrum of the booster crystal 10 (Solid state laser crystal), so that a certain inversion density distribution in the amplifier crystal 10 arises.

The collimator lens 6 has a first passage 26 on. The focusing lens 8th has a second passage 28 on. These passages 26 . 28 serve to the first fiber 3b or the laser beam 9 unaffected by the optical deflection device 22 down to near the amplifier crystal 10 introduce. The two passages 26 . 28 are in the embodiment by central through holes in the lenses 6 . 8th educated.

Next becomes a lens 7 smaller diameter at the end of the first fiber 3b for beam shaping of the laser beam 9 used. The one with the help of this little lens 7 at the fiber end in the amplifier crystal 10 imaged beam of Faserla sers / fiber amplifier 3 is in the optically pumped amplifier crystal 10 amplified when this solid-state laser amplifier material to the emission wavelength of the fiber laser / fiber laser amplifier 3 is adjusted. Accordingly, an amplifier material is selected whose cross-section for stimulated emission at the wavelength of the laser beam 9 has a high value.

By appropriate adjustment can thereby be an optimal spatial overlap of the laser beam 9 with the inversion volume. This is a holder 7a for the lens 7 provided, which can be fine-adjusted. The holder 7a for the lens is designed such that the largest possible proportion of the pump radiation 5 at the lens 7 over, especially through the bracket 7a through, can be conducted. For example, an annular element with radial webs is provided for this purpose.

by virtue of The applied here longitudinal pump geometry is a great efficiency reached. Details of the advantages of the longitudinal pumping geometry are in P. Peuser, N.P. Schmitt: "Diode Pumped Solid State Lasers", Springer Publisher, 1995 described.

At each one of the second fibers 4 of the fiber bundle 4b may be a separate diode laser beam source - that is, a separate first diode laser 1 - be coupled, so that a total of high pump power is available. The from this fiber bundle 4b exiting pump radiation 5 is through the collimator lens 6 collimated. For example, the pump radiation passes 5 on the between the collimator lens 6 and the focusing lens 8th formed route 18 almost in parallel. In this way, a large proportion of the pump radiation passes 5 further radially outside the fiber laser / fiber amplifier 3 , leaving room for the lens inside 7 for blasting the laser 9 is created and still a high proportion of the pump radiation to the amplifier crystal 10 can be directed. After ßend the pump radiation 5 through the focusing lens 8th into the amplifier crystal 10 (Solid state laser amplifier crystal) imaged so that the laser beam 9 the fiber laser or the fiber amplifier 3 with a big gain as amplified laser beam 11 from the laser amplifier 24 emerges.

At the in 1a illustrated embodiment of the Pumpstrahlungsleiteinrichtung 21 is therefore the first fiber 3b of the fiber laser / fiber amplifier 3 with the fiber bundle 4b for the pump radiation 5 combined.

In the in the 2 and 2a illustrated second embodiment of the fiber laser array 17 is the first fiber 3b which are essentially the fiber laser or fiber amplifier 3 forms, in the center of a separate outer optical fiber, which is the second fiber 4 forms for the pump radiation. Such fiber structures can be produced according to the prior art.

If the fiber laser / fiber amplifier 3 on the one hand and the amplifier crystal 10 on the other hand have different pump wavelengths, a beam combination 12 for coupling both pumping radiations into those with the fiber laser / fiber amplifier 3 combined pump radiation guide 21 intended. This beam association 12 is in 2 B shown in more detail. In this case, the first pump radiation 13 for the laser amplifier and the second pump radiation 15 for the fiber laser / fiber amplifier 3 in a known manner by means of a dichroic mirror 14 united in a collinear ray. This combined beam is represented by means of a suitable optical lens arrangement - exemplified here by an optical lens 16 for pump beam injection - into the combined optical fiber 4a with the inner first fiber 3b and the second fiber provided annularly therearound 4 coupled. In this way, the second pumping radiation pumps the central first fiber 3b optically, and the first pump radiation 13 occurs as pump radiation 5 for the amplifier crystal 10 at the end of the fiber.

In the case when the fiber laser / fiber amplifier 3 and the laser amplifier 24 can be excited with the same wavelength, a correspondingly provided for pumping both devices pump radiation from a high-power diode laser source (it is sufficient here a first high-power diode laser for pumping both devices) in the axial direction in the fiber 4a coupled, so the fiber laser / fiber amplifier 3 with a smaller part of the pump radiation is optically pumped and the larger, remaining part of the pump radiation 5 for the excitation of the laser amplifier 24 is used.

At the in 2c shown further embodiment, the two optical fibers - first fiber 3b and second fiber 4 - arranged close to each other. In this case, the focusing lens 8th for the pump radiation 5 of the amplifier crystal 10 arranged slightly transversely shifted, so that the laser radiation 9 and the pump radiation 5 in the amplifier crystal 10 lie one above the other.

At the in 3 shown further embodiment of the fiber laser array 17 becomes the first fiber 3b of the fiber laser / fiber amplifier 3 itself used, at the same time the pump radiation 5 for the laser amplifier 24 respectively. The first fiber 3b acts accordingly as Pumpstrahlungsleiteinrichtung 21 , Again, pump radiation can 13 . 15 be used, which includes two different wavelengths, of which the second pump radiation 15 for excitation of the fiber laser / fiber amplifier 3 serves and the first pump radiation 13 to the absorption properties of the amplifier crystal 10 is adjusted. A smaller part of the pump radiation 13 . 15 is then absorbed in the doped fiber core, and the larger, remaining part leaves the fiber 3b and is called pump radiation 5 for pumping the amplifier crystal 10 used. In contrast to the previously described embodiments, however, then the fiber laser radiation 3a and the pump radiation 5 for the amplifier crystal 10 together with the lens arrangement of the optical deflection device 22 into the amplifier crystal 10 displayed. In this embodiment, therefore, is a collimator lens 6a and a focusing lens 8a provided which the two passages 26 . 28 do not have.

The described configurations may include, for example, an ytterbium-doped fiber laser or fiber amplifier 3 which emit radiation at the wavelength of the main junction of a neodymium laser at 1064 nm. As solid state laser amplifier materials for forming the amplifier crystal 10 Thus, the known Nd: YAG laser crystal or comparable solid-state laser crystals can be used.

These Fiber laser or fiber amplifier are preferably in the emission wavelength range of the InGaAs diode laser while Nd: YAG preferentially pumped with GaAIAs diode lasers is excited at 807 nm. Other versions are thulium or Holmium-doped fiber lasers and crystals can be realized, which in the 2 μm wavelength range emit.

The fiber laser arrays described above 17 can be used in principle for the amplification of short fiber laser pulses as an arrangement for the power scaling of continuous or quasi-continuous fiber laser radiation or even single-frequency laser radiation when the fiber laser / fiber amplifier 3 is executed accordingly.

By the measures described is achieved that the radiation - laser beam 9 , Fiber la serstrahlung 3a - A fiber laser or a fiber laser amplifier in a miniaturized arrangement is so amplified that a power-scaled laser beam 11 With high beam quality, the power range of short pulse fiber lasers or short pulse fiber amplifiers, as known in the art, is greatly expanded.

1

first Diode laser (high-power diode laser for amplifier crystal)

2

second Diode laser (for Fiber laser / fiber amplifier)

3

Fiber laser / fiber amplifier

3a

Fiber laser radiation

3b

first fiber

4

second Fiber (for Pump radiation)

4a

combined optical fiber with fiber laser / fiber amplifier

4b

fiber bundles

5

pump radiation

6

collimator lens (for pump radiation)

6a

collimator lens

7

lens (for fiber laser / fiber amplifier)

7a

bracket for lens

8th

focusing lens (for pump radiation)

8a

focusing lens

9

laser beam

10

crystal amplifier

11

amplified laser beam

12

beam combiner

13

first Pump radiation (for Laser amplifier)

14

dichroic mirror

15

second Pump radiation (for Fiber laser / fiber amplifier)

16

optical Lens for Pumpstrahleinkopplung

17

Fiber laser arrangement

18

route

20

pump source

21

Pumpstrahlungsleiteinrichtung

22

optical deflecting

24

laser amplifier

26

first passage

28

second passage

Claims (23)

Fiber laser arrangement ( 17 ) comprising: a fiber laser or fiber amplifier ( 3 ), which is a first fiber ( 3b ) with laser-active material, wherein the fiber laser or fiber amplifier ( 3 ) at a fiber exit of the first fiber ( 3b ) a laser beam ( 9 . 3a ), characterized in that at the fiber output in the axial direction of a solid-state laser amplifier ( 24 ) for amplifying the laser beam ( 9 . 3a ) is provided and that an optical deflection device ( 22 ) is provided, the pump radiation ( 5 ) on the first fiber ( 3b ) over to the laser amplifier ( 24 ) leads to the laser amplifier ( 24 ) for amplifying the laser beam ( 9 . 3a ) to provide. Fiber laser arrangement according to claim 1, characterized in that the laser amplifier ( 24 ) an amplifier crystal ( 10 ), which at its two end faces antireflecting the laser radiation ( 9 . 3a ) is coated. Fiber laser arrangement according to one of the preceding claims, characterized in that an optical pump source ( 20 ) for emitting pump radiation ( 5 ) for the laser amplifier ( 24 ) is provided, wherein the laser amplifier ( 24 ) both for receiving the laser beam ( 9 . 3a ) as well as the pump radiation ( 5 ) is adapted to the laser beam ( 9 . 3a ) in longitudinal pump configuration. Fiber laser arrangement according to claim 2 and claim 3, characterized in that the amplifier crystal ( 10 ) at its entrance surface additionally antireflective for the pump radiation ( 5 ) is trained. Fiber laser arrangement according to one of claims 3 or 4, characterized in that the wavelength of the pump radiation ( 5 ) the absorption spectrum of the amplifier crystal ( 10 ) is adjusted to a predetermined inversion density distribution in the amplification crystal ( 10 ) to create. Fiber laser arrangement according to one of the preceding claims, characterized in that the optical deflection device ( 22 ) a collimator lens device for collimating the pump radiation ( 5 ) such that the pump radiation ( 5 ) runs over a defined distance substantially parallel or quasi parallel. Fiber laser arrangement according to claim 6, characterized in that the collimator lens device comprises a collimator lens ( 6 . 6a ) or acting as a collimator lens entrance surface of a lens block. Fiber laser arrangement according to one of claims 6 or 7, characterized in that the deflection device ( 22 ) at least one passage ( 26 . 28 ) for the first fiber ( 3b ) and / or for one by the deflection ( 22 ) unaffected passage of the laser beam ( 9 ) Has. Fiber laser arrangement according to one of claims 7 to 8, characterized in that at the fiber output a lens ( 7 ) for beam shaping of the laser beam ( 9 ) is provided, whose diameter is formed such that the deflection device ( 22 ) the pump radiation ( 5 ) can guide past it. Fiber laser arrangement according to one of claims 3 to 9, characterized in that the first fiber ( 3b ) substantially parallel and centric to the pump radiation ( 5 ) is arranged. Fiber laser arrangement according to one of claims 2 to 10, characterized in that the pump source ( 20 ) a pump radiation guide device ( 21 ) for guiding the pump radiation ( 5 ) having. Fiber laser arrangement according to claim 11, characterized in that the pump radiation guiding device ( 21 ) around the first fiber ( 3b ) is arranged around. Fiber laser arrangement according to claim 11 or 12, characterized in that the pump radiation guiding device ( 21 ) at least one second fiber ( 4 ) for guiding the pump radiation ( 5 ) having. Fiber laser arrangement according to claim 12 and 13, characterized in that a fiber bundle ( 4b ) of a plurality of second fibers ( 4 ) around the first fiber ( 3b ) is arranged around. Fiber laser arrangement according to claim 12 and 13, characterized in that the first fiber ( 3b ) inside the second fiber ( 4 ) is arranged and / or formed. Fiber laser arrangement according to claim 12, characterized in that the first fiber ( 3b ) and the second fiber ( 4 ) are guided closely adjacent to each other in parallel. Fiber laser arrangement according to claim 11, characterized in that the pump radiation guiding device ( 21 ) through the first fiber ( 3b ) is formed, through which the pump radiation ( 5 ). Fiber laser arrangement according to claim 17, characterized in that the fiber laser or fiber amplifier ( 3 ) by a second pump radiation ( 15 ) is excitable, which has a different wavelength to the first pump radiation ( 5 . 14 ) has for the laser amplifier, wherein the two pumping radiation ( 15 ; 5 . 14 ) via a beam union ( 12 ), in particular with a dichroic mirror ( 14 ), combined and into the first fiber ( 3b ) are coupled. Fiber laser arrangement according to claim 17, characterized in that the fiber laser or fiber amplifier ( 3 ) by pump radiation having the same wavelength as the pump radiation ( 5 ) for the laser amplifier ( 24 ) is excitable, wherein the common pump radiation into the first fiber ( 3a ) is coupled so that a smaller part of the pump radiation power for exciting the fiber laser or fiber amplifier ( 3 ) is usable and a larger part for exciting the laser amplifier ( 24 ) is usable. Fiber laser arrangement according to one of claims 3 to 19, characterized in that the pump source ( 20 ) at least one, preferably a plurality of first diode lasers ( 1 ) having. A fiber laser array according to claim 20 and claim 13, characterized in that the plurality of second fibers ( 4 ) for conducting through a plurality of the first diode lasers ( 1 ) generated pump radiation ( 5 ) serves. Fiber laser arrangement according to one of the preceding claims, characterized in that a second diode laser ( 2 ) for exciting and / or pumping the fiber laser or the fiber amplifier ( 3 ) is provided. Use of a fiber laser array ( 17 ) according to one of the preceding • as a preamplifier for a DIRCM laser ("directed infrared counter measures"), • as a miniaturized base laser for optically non-linear processes, • for miniaturized LIDAR systems, in particular in or on aircraft, • as a miniaturized laser transmitter for space applications , • For laser ignition in motors or • As a robot-borne laser.