AT506600B1 - ARRANGEMENT FOR THE OPTICAL REINFORCEMENT OF LIGHT PULSES - Google Patents

Description

Austrian Patent Office AT506 600 B1 2009-10-15

Description [0001] The invention relates to an arrangement for the optical amplification of light pulses.

Optical amplification by optical pumping, e.g. with intense pump pulses in the range of 10 ns to 50 ns, and stimulated emission caused thereby is used more and more in both the scientific and the technical field.

The main problem with direct optical amplification to high energies is the occurrence of parasitic nonlinearities (high B integral) which limit energy scalability.

One approach to providing high power in a amplifying optical element is the "Chirped Pulse Amplification" method. Thereby the spectrum of a short laser pulse, e.g. diffracted at a sequence of diffraction gratings and in this way the pulse is stretched in time. The now significantly longer pulse can be relatively easily amplified with conventional crystals and the amplified pulse can be compressed again with the aid of a second sequence of diffraction gratings. The energy of the pulse remains almost unchanged, resulting in a much higher pulse power. Due to nonlinearities in the gain, the achievable powers are limited in this case as well. To counteract this, the beam and amplifier crystal cross sections were increased. The achievable gain power but are also set here by the maximum thermal capacity of the amplifier crystal limits.

Another improvement has been made with the "Tilted Pulse Amplification". however, the application of diffraction gratings does not allow for practical implementation.

Furthermore, the so-called "Divided Pulse Amplification" has been introduced. (DPA) proposed to run through which stacks of birefringent crystals. Here there is the disadvantage that these stacks or the crystals become exponentially thicker with each pulse division, so that the material-technical limit is reached quickly.

The object of the invention is therefore to provide an arrangement for the optical amplification of light pulses, which can be realized with structurally simple means and manages without the excessive use of non-linear material in the amplifier chain.

According to the invention, the arrangement for optical amplification of light pulses comprises a light source for emitting light pulses, a Sagnac interferometer ground loop with an input / output coupling unit which is connected to the light source to divide each transmitted light pulse into two light pulses and couple them in opposite directions into the Sagnac interferometer ground loop and which input / output coupling unit is adapted to decouple the split light pulses in opposite directions as recombined light pulses after passing through the Sagnac interferometer ground loop, Optionally at least one with respect to the Sagnac interferometer ground loop subordinate Sagnac interferometer loop, which is connected in the Sagnac interferometer ground loop, wherein the at least one subordinate Sagnac interferometer loop in turn each one towards this subordinate Sagnac-I [0010] and at least one optical amplifying element which may be interleaved within the Sagnac interferometer ground loop or within the at least one subordinate Sagnac interferometer loop, which may be interleaved as often as desired with other subordinate Sagnac interferometer loops. Loop or the other subordinate Sagnac interferometer loops is arranged at an asymmetric position in order to be traversed by the split light pulses at least once separated in the opposite direction of [0011]. The invention thus employs a Sagnac interferometer as the basic building block for achieving a pulse division, wherein the temporal separation of the two counter-pulses divided in this way passes through the optical amplification element each different distances between the input / output coupling unit and the optical amplifying element is achieved. This is made possible by the asymmetric arrangement of the optical amplifying element in the Sagnac interferometer ground loop or one of the other subordinate Sagnac interferometer loops.

In this case, the reinforcing element can be traversed several times by the divided light pulses.

In other words, to reduce the peak power generated in the optical amplification in the optical amplifying element, the light pulse coupled via the input / output coupling unit is divided and divided by the Sagnac interferometer fundamental loop having different path length the optical amplifying element is sent in the forward and in the reverse circuit to be recombined in the input / output coupling unit.

A further reduction in the loading of the optical gain element results when the one or more subordinate Sagnac interferometer loops are inserted into the Sagnac interferometer ground loop, so that the divided pulses are each divided again.

An embodiment of the invention may be that the optical amplifying element is a laser crystal, wherein the laser crystal may be an isotropic laser crystal. In this way, appreciable optical amplification can be achieved within certain application limits. By using a plurality of Sagnac interferometer loops nested in accordance with the invention, the optical gain can be correspondingly increased without exceeding the maximum allowable peak power for the optical gain element.

It can also be provided as a birefringent laser crystal, the laser crystal, with appropriate precautions must be taken to compensate for the influence of birefringence on the laser crystal passing through partial light pulses.

In addition, however, the optical amplifying element replaceable within the scope of the invention is not limited to amplification based on stimulated emission, which is why the optical amplifying element may be, for example, an optical parametric amplifier crystal.

The Sagnac interferometer ground loop may include one or more subordinate Sagnac interferometer loops that are completely traversed as part of the optical path of all sub-light pulses, again splitting into sub-light pulses.

This may be implemented in accordance with a further embodiment of the invention for a subordinate Sagnac interferometer loop, in that the Sagnac interferometer ground loop comprises a divide / recombine node, via which into the Sagnac interferometer ground loop the subordinate Sagnac interferometer loop so that the partial Sagnac interferometer ground loop passes through the split / recombine node in a first direction after passing through the subordinate Sagnac interferometer loop by splitting and recombining into the Sagnac interferometer loop. Basic loop and continue to travel in the first direction and the Sagnac interferometer ground loop in a second, opposite direction passing partial light pulses over the division / recombination node after passing through the subordinate Sagnac interferometer loop by splitting and recombining in the above re-enter the ordered Sagnac interferometer loop and continue through it in the second, opposite direction.

The dividing / recombining node can be formed by two polarizing beam splitters and a lambda-quarter element or a half-wave element or a Faraday rotator, which are connected via a polarizing beam splitter and a 2/20 Austrian Patent Office AT506 600 B1 2009-10-15 optical path are directly coupled together. In this way, the sub-light pulses entering the subordinate Sagnac interferometer loop can be redivided and recombined, after passing through, back into sub-light pulses, which then continue to travel through the Sagnac interferometer ground loop.

Similarly, the input / output coupling unit may comprise a quarter-wave element or a half-wave element or a Faraday rotator and a polarizing beam splitter, which are coupled directly to one another via an optical path. Thus, the function of the input / output coupling unit, which consists in splitting light pulses transmitted into the Sagnac interferometer ground loop and recombining part light pulses emerging from the loop, is easily ensured.

Alternatively, the input / output coupling unit may comprise a quarter-wave element or a Faraday rotator and two polarizing beam splitters, which are directly coupled together via an optical path.

The invention will be explained in detail with reference to the embodiments illustrated in the drawings. FIG. 1 shows a schematic representation of an embodiment of the optical amplification arrangement according to the invention; FIG. FIG. 2 shows a schematic illustration of a further embodiment of the arrangement according to the invention; FIG. Fig. 3 is a schematic representation of another embodiment of the arrangement according to the invention; 4 shows a schematic illustration of a further embodiment of the arrangement according to the invention; 5 shows a schematic representation of a further embodiment of the arrangement according to the invention; Fig. 6 is a schematic representation of another embodiment of the arrangement according to the invention; 7 shows a schematic representation of a further embodiment of the arrangement according to the invention; FIG. 8 is a schematic representation of a further embodiment according to the invention; FIG. 9 shows a schematic illustration of a further embodiment of the arrangement according to the invention; 10 shows a schematic representation of a further embodiment of the arrangement according to the invention; 11 shows a diagram of the spectral intensity of the amplified partial light pulses and of the recombined light pulse; 12 shows a schematic illustration of a further embodiment of the arrangement according to the invention; 13 shows a schematic representation of a further embodiment of the arrangement according to the invention, and [0038] FIG. 14 shows a representation of a further embodiment of the arrangement according to the invention.

Fig. 1 shows an arrangement for the optical amplification of light pulses with the aid of a Sagnac interferometer beam path. 3/20 Austrian Patent Office AT506 600 B1 2009-10-15 For this purpose, a light source 1 for emitting light pulses and a Sagnac interferometer ground loop 3 are provided, which are connected via an input / output coupling unit 2 coupled together. The input / output coupling unit 2 divides each light pulse (arrow 32) sent via an input 17 into two partial light pulses (arrows 30 and 31) and couples them into the Sagnac interferometer ground loop 3 in opposite directions.

In what way the Sagnac interferometer ground loop 3 is realized, e.g. with a circular guided glass fiber line (FIG. 12) or with an optical path deflected by means of mirrors is not subject to any restrictions within the scope of the invention. In the schematic diagram according to FIG. 1, no suitable devices are shown at the deflection points of the optical path; be realized by mirror elements.

A suitable light source 1 is, for example, a light source which emits ultrashort light pulses with a duration of 10 ps to 50 ps and a repetition frequency of 1000 Hz.

The one partial light pulse, symbolized by arrow 30, thereby passes through the Sagnac interferometer ground loop 3 in the clockwise direction, while the other partial light pulse according to arrow 31 lapses them in the counterclockwise direction.

After the partial light pulses have passed through the Sagnac interferometer ground loop 3, they meet again in the input / output coupling unit 2, which is suitable, the divided light pulses as a recombined light pulse, the in Fig. 1 by Arrow 33 is indicated to decouple again. This recombined light pulse is optically amplified and therefore appears at the output 18 with a higher intensity than the light pulse sent into the input 17.

In order to achieve the optical amplification, an optical amplifying element 4, e.g. may be formed by a laser crystal 5, arranged within the Sagnac interferometer ground loop 3 at an asymmetric position to be traversed by the split light pulses at least once in the opposite direction in the opposite direction. However, the optical amplifying element is not limited to the principle of amplification based on stimulated emission, but it may be e.g. also find an optical parametric amplifier crystal application, with which a parametric amplification is performed.

In this context, the term asymmetric position means all positions that are appreciably offset from the symmetrical position 89, so that a temporal separation of the divided light pulses in the optical amplification element 4 results.

As can be seen from Fig. 1, therefore, within the Sagnac basic loop 3 for geometric reasons, the path to the optical amplifying element 4 for the circulating in the clockwise light pulse 30 longer than for the counterclockwise rotating light pulse 31. On this Way, the one light pulse arrives later in the optical gain element 4 as the opposite and a temporal separation when passing through the optical gain element is achieved.

Fig. 2 shows an equivalent arrangement in which the light input and output takes place in the reverse manner.

3 shows a further embodiment of the arrangement according to the invention, in which the principle according to the invention is realized by in the Sagnac interferometer ground loop 3 is arranged with respect to this subordinate Sagnac interferometer loop 3 ', wherein the divided by the light source 1 in the Sagnac interferometer ground loop 3 light pulse is divided into two partial light pulses 30, 31 whose path continued within the Sagnac interferometer ground loop 3 in the subordinate Sagnac interferometer loop 3 ' becomes.

Upon entry into the subordinate Sagnac interferometer loop 3 ', each of the 4/20 Austrian Patent Office AT506 600B1 2009-10-15

Sagnac interferometer ground loop 3 coming partial light pulse 30, 31 again divided into two opposing, ie a total of four light pulses 300, 310, which pass through the subordinate Sagnac interferometer loop 3 'in opposite directions, and then again to each to recombine a light pulse which exits the Sagnac subordinate interferometer loop 3 'and continues its path in the Sagnac interferometer ground loop 3 to return to the input / output coupling unit 2.

In the embodiment according to FIG. 3, the optical amplifying element 4 is arranged at an asymmetric position within the subordinate Sagnac interferometer loop 3 'such that four time-shifted partial light pulses pass through the optical amplifying element 4.

The subordinate Sagnac interferometer loop 3 ', in turn, may include a subordinate Sagnac interferometer loop (not shown in FIG. 3) which may be interleaved as often as desired with further subordinate Sagnac interferometer loops.

For the purpose of transferring between the Sagnac interferometer ground loop 3 and the subordinate Sagnac interferometer loop 3 ', the Sagnac interferometer ground loop 3 has a split / recombine node 8, via which the subordinate Sagnac interferometers Loop 3 'is connected in the Sagnac interferometer ground loop 3 so that the Sagnac interferometer ground loop 3 in a first direction (arrow 30) passing through partial light pulses via the division / recombination node 8 after passing through the subordinate Sagnac interferometer loop 3 're-enter into the Sagnac interferometer ground loop 3 by splitting and recombining, and continue in the first direction, passing the Sagnac interferometer ground loop 3 in a second, opposite direction (arrow 31) ) passing through the partial / recombination node 8 after passing through the subordinate Sagnac interferometer loop 3 'by up divide and recombine into the superordinate Sagnac interferometer loop 3 and continue through it in the second, opposite direction.

An embodiment equivalent to Fig. 3 is shown in Fig. 13.

Fig. 4 shows an embodiment of the inventive arrangement with a Sagnac interferometer ground loop 3, in which the reinforcing element 4 is arranged as an optically isotropic laser crystal 70 in an asymmetrical position. The beam path within the Sagnac interferometer ground loop 3 is set up so that each partial light pulse passes through the laser crystal 70 twice (twice-pass) before both partial light pulses in the input / output coupling unit 2 close again be recombined a light pulse.

In the embodiment according to FIG. 4, the input / output coupling unit 2 is composed of a half-wave element 20 and a polarizing beam splitter 21. The half-wave element 20, which is e.g. is realized by a half-wave plate causes a rotation of the polarization of the incident, linearly polarized light pulse by 45 degrees. The polarizing beam splitter 21 following in the beam direction splits the light pulse into a reflected s-polarized partial light pulse and a transmitted p-polarized partial light pulse, whereby the p-polarized partial light pulse first passes through the laser crystal 70 due to the path difference and only then the s-polarized partial light pulse. The second pass is in the same order. Thus, for each transmitted light pulse, the input / output coupling unit 2 couples two counter-propagating partial light pulses into the Sagnac interferometer ground loop.

After complete passage, the two counter-rotating partial light pulses are recombined in the input / output coupling unit 2 again to an outgoing light pulse. An inserted into the beam path birefringence phase compensator 22, which lies with its major axes parallel to the p and s polarization, provides the required phase correction. FIG. 11 shows the spectral intensity for the p-polarized and the s-polarized partial light pulses after their amplification and the spectral intensity of the recombined partial light pulse at the output 18 , which corresponds to the sum of the two partial intensities.

Fig. 5 shows a further embodiment of the arrangement according to the invention, in which the laser crystal 5 is formed by an - intrinsically or thermally induced birefringent laser crystal 71, which is arranged asymmetrically in the Sagnac interferometer ground loop 3.

Here, the input / output coupling unit 2 is constituted by a polarizing input-output beam splitter 28, a quarter-wave element 29, and the polarizing beam splitter 21, which are coupled to each other via an optical path. Lamda quarter element 29, e.g. a quarter-wave plate can also be replaced by a Faraday rotator that rotates the polarization by 45 degrees.

The input-output beam splitter 28 allows a p-polarized light pulse transmitted from the light source 1 to pass unhindered to the subsequent quarter-wave element 29, where the light pulse is split into two mutually polarized partial light pulses p and s, which have a retardation of a quarter-wavelength. The polarizing beam splitter 21 following in the direction of incidence couples the p-part light pulse counterclockwise and the s-part light pulse clockwise into the Sagnac interferometer base loop 3. After passing through the birefringent laser crystal 71 twice, the pT eil light pulse is converted by a half-wave element 23 into an s-polarized partial light pulse, which then reflects back at the polarizing beam splitter 21 in the direction of the quarter-wave element 29 becomes.

In contrast, the sT eil light pulse is already converted before passing through the laser crystal 71 by means of the half-wave element 23 to a pT eil light pulse to undistracted after passing through the laser crystal 71 twice to be passed through the polarizing beam splitter. Both partial light pulses decoupled from the Sagnac interferometer ground loop 3 are recombined in the quarter-wave element 29 to form an amplified light pulse with s polarization and guided to the output 18 via reflection at the input-output beam splitter 28. Since the birefringent laser crystal 71 is traversed by all the p-polarization partial light pulses, the influence of the birefringence is compensated.

Below, a variant of the invention will be explained with reference to the embodiment shown in Fig. 14, in which instead of the quarter-wave element 29, a Pockels cell and a lambda half-element is used.

The embodiment shown in Fig. 6 realizes an asymmetrical arrangement of the birefringent laser crystal 71 with a single pass of the two partial light pulses with p and s polarization, by the same form of the input / output coupling unit 2 is achieved as in the embodiment of Figure 4. Here, by arranging a Faraday rotator 60 which causes rotation of the polarization direction by 45 ° in both directions, at the crossing center of the Sagnac interferometer branches and by arranging a half-wave element 61, 62 respectively in both directions of travel between the polarizing beam splitter 21 and the Faraday rotator 60 accomplishes that both the p-polarized sub-light pulse and the s-polarized sub-light pulse with p-polarization are passed through the birefringent laser crystal 71 to eliminate the influence of the birefringence ,

FIG. 7 shows an exemplary embodiment in which a Sagnac interferometer loop 3 'is connected to the Sagnac interferometer ground loop 3 according to FIG. 4. This corresponds to the arrangement as shown in Fig. 3.

Instead of the birefringence phase compensator 22, as used in the embodiment according to FIG. 4, a variable optical delay unit 50 occurs.

When entering the subordinate Sagnac interferometer loop 3 ', both the p-polarized sub-light pulse and the s-polarized sub-light pulse are transmitted via the half-wave Element 20 'again split into respectively two s and p-part light pulses, namely s1, s2' and pT, p2 ', which are guided through the optical amplifying element 4 by a polarizing beam splitter 41 and a mirror arrangement 42, 43, 44 be that all four partial light pulses pass through the reinforcing element 4 and are then reflected back and again passed through this, resulting in a total of eight passes. In order to simplify the beam path, the mirror 44 is embodied as a vertical V-retro reflector, from which the reflected beam emerges offset in height with respect to the beam entering it. Also, in the variable optical delay unit 50 ', such a mirror is used.

The half-wave element 51 rotates the polarization of the incident s-polarized sub-pulses sT s2 'by 90 degrees so that all the sub-light pulses pass through the reinforcing element 4 with p-polarization, and rotates the polarization of the amplified portion Light pulses pT, p2 'by 90 degrees to the s-polarization.

After the eight passes, the partial light pulses sT, s2 'and pT, p2' are recombined coming from the subordinate Sagnac interferometer loop 3 'in the polarizing beam splitter 21' and transmitted as partial light pulses s and p into the Sagnac. Interferometer ground loop 3 coupled, which they now go through to the end. The dividing / recombining node 8 is formed in this embodiment by the half lamb element 20 'and the polarizing beam splitter 21'.

Similarly, FIG. 8 shows an embodiment in which the Sagnac interferometer ground loop 3 has the subordinate Sagnac interferometer loop 3 ', and in turn another Sagnac subordinate interferometer loop 3 " is switched. The Sagnac interferometer ground loop 3 used is constructed with the components explained in connection with Figure 5, as well as the two subordinate Sagnac interferometer loops 3 ', 3 ". The beam path is shown simplified because of its complexity.

5, the embodiment variant shown in FIG. 9 is constructed, with the difference from FIG. 5, that at the transition between the Sagnac interferometer ground loop 3 and the subordinate Sagnac interferometer loop 3 ', the beam path of the s-polarized partial light pulse and the p-polarized partial light pulse via two separate beam splitters 28', which are directly connected to each other via an optical path 60, and subsequently via four further beam splitters 28 ", two of which are directly connected to each other via an optical path 60 ', are split. As shown schematically in Fig. 9, each additional subordinate Sagnac interferometer loop 3 ', 3 " a division of the intensity of the partial light pulses in half relative to the superordinate Sagnac interferometer loop.

A similar optical path as in the arrangements according to FIGS. 8 and 9 is selected in the embodiment according to FIG. Again, a Sagnac interferometer ground loop 3 and two Sagnac subordinate interferometer loops 3 ', 3 " is provided, with the number of split partial light pulses doubled from loop to loop, so that the asymmetrically arranged optical amplifying element 4 is traversed twice in total of eight partial light pulses.

Fig. 14 shows an embodiment of the invention in which, in place of the variant shown in Fig. 8, instead of the quarter-wave elements 29, 29 ', 29 " each a half-wave Pockels cell 290, 290 ', 290 " and a half-lambda element 291, 29T, 291 " to be used. The Pockels cell 290, 290 ', 290 " rotates the polarization plane by 90 degrees when applying an electric field. The Pockels cell is on while the light pulses enter and is off as the light pulses exit, resulting in a 90 degree rotation of the polarization plane of the output signal relative to the input signal.

Alternatively, the Pockels cell may be turned off while the light pulses are on

Claims (9)

Austrian Patent Office AT506 600B1 2009-10-15 and be switched on while the light pulses escape. In other words, the state of the Pockels cell 290, 290 ', 290 " changed while the partial light pulses the respective Sagnac interferometer loop 3, 3 ', 3 " run through. 1. Arrangement for the optical amplification of light pulses, comprising: - a light source (1) for emitting light pulses, - a Sagnac interferometer ground loop (3) with an input / output coupling unit (2) with the light source (1) is connected to split each transmitted light pulse into two light pulses and to couple them in opposite directions in the Sagnac interferometer ground loop (3) and which input / output coupling unit (2) is suitable, the split light pulses after passing through the Sagnac interferometer ground loop (3) in opposite directions as coupled recombined light pulse, - optionally at least one with respect to the Sagnac interferometer ground loop (3) subordinate Sagnac interferometer loop (3 '. 3 "), which is connected in the Sagnac interferometer ground loop (3), wherein the at least one subordinate Sagnac interferometer loop (3 ', 3 ") may each include, in turn, a subordinate Sagnac interferometer loop which may be interleaved with other subordinate Sagnac interferometer loops as often as desired, and at least one optical gain element (4) within the Sagnac interferometer ground Loop (3) or within the at least one subordinate Sagnac interferometer loop (3 ', 3 ") or the further subordinate Sagnac interferometer loops is arranged at an asymmetric position to be temporally separated from the split light pulses in the opposite direction to go through at least once. 2. Arrangement for optical amplification according to claim 1, characterized in that the optical amplifying element (4) is a laser crystal (5). 3. Arrangement for optical amplification according to claim 2, characterized in that the laser crystal (5) is an isotropic laser crystal (70). 4. An optical amplification arrangement according to claim 2, characterized in that the laser crystal (5) is a birefringent laser crystal (71). An optical amplification device according to claim 1, characterized in that the optical amplifying element (4) is an optical parametric amplifier crystal (7). 6. Arrangement according to one of claims 1 to 5, characterized in that the Sagnac interferometer ground loop (3) has a division / recombination node (8) via which in the Sagnac interferometer ground loop (3) the subordinate Sagnac interferometer loop (3 ', 3 "), so that the sub-light pulses passing through the Sagnac interferometer ground loop (3) in a first direction are passed through the split / recombine node (8) after passing through the subordinate Sagnac -Interferometer loop (3 ', 3 ") by dividing and recombining in the Sagnac interferometer ground loop (3) to re-enter and continue in the first direction and the Sagnac interferometer ground loop (3) in passing a second, opposite direction, passing partial light pulses across the divide / recombine node (8) after passing through the subordinate Sagnac interferometer loop (3 ', 3 ") by splitting and recombining into the transitions To return, place the Sagnac interferometer loop (3) and continue in the second, opposite direction. 7. Arrangement according to claim 5, characterized in that the division / recombination node (8) by two polarizing beam splitter (21 ') and a quarter-wave element or a half-wave element (20') or a Faraday rotator formed is directly coupled to each other via an optical path. 8/20 Austrian Patent Office AT506 600B1 2009-10-15 8. Arrangement according to one of claims 1 to 7, characterized in that the input / output coupling unit (2) has a quarter-wave element or a half-wave element (20) or a Faraday rotator and a polarizing beam splitter (21), which are directly coupled together via an optical path. 9. Arrangement according to one of claims 1 to 7, characterized in that the input / output coupling unit (2) comprises a quarter-wave element or a Faraday rotator and two polarizing beam splitter, which via an optical path are directly coupled with each other. For this 11 sheets drawings 9/20