EP3994772A1

EP3994772A1 - Monolithic pulse compressor and associated adjustment method

Info

Publication number: EP3994772A1
Application number: EP20734688.3A
Authority: EP
Inventors: Dominik Bauer; Aleksander BUDNICKI; Raphael SCELLE; Michael Scharun
Original assignee: Trumpf Laser GmbH
Current assignee: Trumpf Laser Se
Priority date: 2019-07-02
Filing date: 2020-06-22
Publication date: 2022-05-11
Also published as: US20220120993A1; WO2021001185A1; CN114144948A; DE102019209649A1

Abstract

In a pulse compressor (1) having a plurality of optical components (2-4), at least one of which is a diffraction grating (3), according to the invention at least one of the optical components (2-4) is fastened to the base plate (6) by means of at least three intermediate elements (5a-5c) which are laser-welded to one another, a first and a second intermediate element (5a, 5b) being fastened to the base plate (6) and a third intermediate element (5c) being fastened to the optical component (2-4). The joint surfaces (7b) of the first and the second intermediate element (5a, 5b) abutting the third intermediate element (5c) and the joint surface (8b) of the third intermediate element (5c) abutting the first and the second intermediate element (5a, 5b) are curved. At least the laser-welded joint surfaces of the at least one optical component (2-4), of the intermediate elements (5a-5c) and of the base plate (6) are formed from materials in which the difference between their coefficients of thermal expansion is less than 10e-6/K.

Description

Monolithic pulse compressor and associated adjustment process

The invention relates to a pulse compressor with several optical components, of which at least one is a diffraction grating, and also to a method for adjusting and securing at least one optical component of the pulse compressor.

Pulse compressors are used in the so-called chirped pulse amplification (CPA) to generate laser pulses with maximum pulse peak powers up to the petawatt range. Such high peak powers cannot be generated directly by laser beam sources, since the laser's amplifier media would usually be destroyed by non-linear optical effects, among other things. There- Before being amplified, laser pulses are temporally stretched in pulse stretchers, where their peak pulse power is reduced, and then pass through an amplifier medium. After amplification, the laser pulses are compressed and now have a correspondingly higher power density.

Due to the high intensities that occur, compressors typically consist of free jet components. In the case of grating compressors based on diffraction gratings, the laser light is typically diffracted four times. For example, there are designs with a single grid over which the laser light passes four times, with two grids (e.g. Treacy compressor) and with four grids.

The optical components of the compressor are typically held and adjusted with mechanical holders. Very large stretching and compression factors are required to generate high pulse energies. For lasers based on CPA technology, this requires a very high optomechanical stability of the pulse compressor, which is difficult to achieve with mechanical holders.

The present invention is therefore based on the object of further increasing the optomechanical stability in a Pulskom pressor of the type mentioned above.

According to the invention, this object is achieved in a first variant of the invention in that at least one of the optical components is fastened to the base plate by means of at least two laser-welded intermediate elements, one, first intermediate element with the base plate and the other, second intermediate element with the optical Component are attached, or vice versa, and where one of the joining surfaces of the intermediate elements as a bearing recess and the other joining surface is curved, in particular convexly curved or spherical segment-shaped, at least the laser-welded joining surfaces of the at least one optical component, the base plate and the intermediate elements are formed from materials in which the difference in their coefficient of thermal expansion is less than 10e ^{_6 / K.} The coefficient of thermal expansion is understood to mean the thermal coefficient of linear expansion or the coefficient of linear thermal expansion. In a second variant of the invention it is provided that at least one of the optical components is fastened to the base plate by means of at least three intermediate elements welded to one another, a first and a second intermediate element being fastened to the base plate and a third intermediate element to the optical component, or vice versa, and wherein the joining surfaces of the first and second intermediate element resting on the third intermediate element and / or the joining surface of the third intermediate element resting on the first and second intermediate element are curved, and that at least the laser-welded joining surfaces of the at least one optical component, the Base plate and the intermediate element are formed from materials in which the difference in their coefficients of thermal expansion is less than 10e ^{_6 / K.}

According to the invention, the at least one optical component, the base plate and / or the at least one intermediate element are attached to a monolithic optical assembly without adhesive, in particular laser-welded, for example by means of USP (ultrashort pulse) welding with laser pulses in the range of a few picoseconds or less. The materials can be, for example, sapphire, BK7 or Zerodur, all of which have a coefficient of expansion less than 10e ^{6 / K.} The use of such materials prevents the occurrence of thermally induced stresses within the assembly and results in high thermal stability of the assembly and thus in high optomechanical stability of the pulse compressor. This in turn enables higher stretch factors and higher pulse energy scalings. Before the laser welding, the optical components of the pulse compressor are precisely adjusted to one another and then laser-welded to one another in this adjustment position.

Preferably at least some, in particular all of the optical components of the pulse compressor are attached to the base plate by means of at least two or three intermediate elements which are laser-welded to the optical component and / or to the base plate, at least the laser-welded joining surfaces of the optical components, the base plate and the intermediate elements are made of materials in which the difference in their thermal expansion coefficient is less than 10e ^{_6 / K.} In a preferred embodiment, at least one of the optical components is made entirely of the same, non-absorbing material, in particular quartz glass or crystal. Alternatively, however, the laser-welded joining surface of at least one of the optical components can also be formed on a substrate of the optical component that is laser-welded to the base plate and / or to the intermediate elements. The optical element can be, for example, a reflective diffraction grating, the substrate of which is provided with a reflective coating. Accordingly, the base plate and the intermediate elements can each be made entirely of the same material, in particular made of quartz glass or crystal.

Particularly preferably, all optical components are fastened to the base plate in each case by means of the intermediate elements, which in turn are laser-welded to the optical component and / or to the base plate. Using the intermediate elements, the optical components can be precisely aligned on the base plate before they are attached, e.g. by moving and / or tilting them.

For a large-area contact of the optical component on the intermediate element or the intermediate element on the base plate, the intermediate element is preferably in contact with a flat joining surface on the optical component or on the base plate.

For a tilt adjustment of an optical component, according to the invention, the optical component is attached to the base plate by means of at least two intermediate elements welded to one another. One, first intermediate element is laser-welded to the base plate and the other, second intermediate element to the optical component, or vice versa. The joining surface of the one-piece or multi-part first intermediate element, which rests on the second intermediate element, is designed as a e.g. Align intermediate elements in a desired tilted position before laser welding.

For a height and tilt adjustment of an optical component, according to the invention, the optical component is fastened to the base plate by means of at least three interconnected, in particular laser-welded, intermediate elements. A first and a second intermediate element are attached to the base plate and a third intermediate element to the optical component, in particular laser-welded, or vice versa. The joining surfaces of the first and the second intermediate element and / or the joining surface of the third inter mediate element that rests on the first and second intermediate element are curved. By changing the distance between the first and second intermediate element, the height of the third intermediate element, and consequently also the distance between the optical component and the base plate, can be varied. Advantageously, the joining surfaces of the first and second intermediate elements resting on the third intermediate element are each formed as an inclined surface and the joining surface of the third intermediate element resting on the first and second intermediate element are convexly curved, in particular semi-cylindrical.

For a stable welded connection, the optical components, the intermediate elements and the base plate are laser-welded to one another over the entire length of their joining line, if possible.

The invention also relates to a method for adjusting and securing at least one optical component of a pulse compressor, which has several optical components, of which at least one is a diffraction grating, on a base plate of the pulse compressor by means of two intermediate elements, where one of the joining surfaces of the intermediate elements as Bearing recess and the other joining surface are curved, in particular convexly curved or spherical segment-shaped, with the following process steps:

Laser welding of the first intermediate element on the base plate and the second intermediate element on the optical component; - Adjustment of the optical component in a desired tilted position with respect to the base plate by rotating the joining surfaces that lie against one another; and

- Laser welding of the two intermediate elements to one another in the desired tilted position;

or with the following process steps:

- Laser welding of the second intermediate element to the optical component;

- Adjustment of the optical component in a desired tilted position relative to the first intermediate element by rotating the abutting joint surfaces;

- Adjustment of the optical component on the base plate in a desired position relative to the base plate; and

- Laser welding of the first intermediate element to the base plate in the desired position,

wherein at least the laser-welded joining surfaces of the at least one optical component, the base plate and the intermediate elements are formed from materials in which the difference in their coefficients of thermal expansion is less than 10e- ^{6 / K.}

In an alternative variant of the method, the invention relates to a method for adjusting and securing at least one optical component of a pulse compressor, which has several optical components, at least one of which is a diffraction grating, on a base plate of the pulse compressor by means of three intermediate elements, the third being The joining surfaces of the first and the second intermediate element resting against the intermediate element and / or the joining surface of the third intermediate element resting against the first and second intermediate element are curved, with the following process steps:

- Placing a first and a second intermediate element on the base plate and laser welding a third intermediate element on the optical component, or vice versa;

- Adjustment of the optical component in a desired tilted position relative to the base plate by turning the on the first and second intermediate element ment adjacent third intermediate element and / or adjusting the optical component in a desired flea position relative to the base plate by changing the distance between the first and the second intermediate element; and

- Laser welding of the first and the second intermediate element on the base plate and on the third intermediate element in the desired tilted or flea position,

Further advantages and advantageous configurations of the subject matter of the invention emerge from the description, the claims and the drawings.

The features mentioned above and those listed below can also be used individually or collectively in any combination. The embodiments shown and described are not to be understood as a conclusive list, but rather have an exemplary character for describing the invention. Show it:

Figs. 1 a, 1 b schematically shows a pulse compressor according to the invention in one

Top view from above (Fig. 1 a) and in a perspective Seitenan view (Fig. 1 b);

2 shows a three-part substructure for the optical components of the in

Fig. 1b shown pulse compressor;

Figs. 3a, 3b a two-part substructure for the optical shown in Fig. 1b

Components of the pulse compressor in the assembled state (Fig. 3a) and in a single part representation (Fig. 3b); and

Figs. 4a, 4b a further substructure, not according to the invention, for the optical components of the pulse compressor shown in FIG. 1b in the assembled state (FIG. 4a) and in a single-part representation (FIG. 4b). The pulse compressor 1 shown in FIG. 1 is designed as a so-called Treacy compressor with two diffraction gratings 2, 3 and with a prism 4. These optical components 2-4 are each fastened to a preferably transparent base plate 6 by means of three intermediate elements 5a-5c. The three optical components 2-4, the intermediate elements 5a-5c and the base plate 6 can all be made of the same, non-absorbent material, in particular quartz glass, or of different materials in which the difference in their thermal expansion coefficients is less than 10e ^{_6 / K} is to be formed. The different materials can be, for example, sapphire, BK7 or Zerodur, all of which have an expansion coefficient of less than 10e- ^{6 / K.} Before geous enough, the optical components 2-4, the intermediate elements 5a-5c and the base plate 6 are formed from materials that have a coefficient of thermal expansion less than 10e ^{_6 / K.}

As shown in FIG. 2, a first and a second intermediate element 5a, 5b each lie on the base plate 6 with a flat joining surface 7a, which is the lower in FIG.

The third intermediate element 5c rests against the optical component 2-4 with a flat joining surface 8a, the upper one in FIG. 2, and is laser-welded to the optical component 2-4. The joining surfaces 7b of the first and second intermediate element 5a, 5b resting on the third intermediate element 5c are designed as inclined surfaces and the joining surface 8b of the third intermediate element 5c resting on the first and second intermediate element 5a, 5b are semi-cylindrical. The adjacent intermediate elements 5a-5c are also laser-welded to one another.

Before the laser welding, the optical components 2-4 have been precisely adjusted to one another on the base plate 6 by means of the intermediate elements 5a-5c.

The first and second intermediate elements 5a, 5b can be moved with their flat joining surfaces 7a on the base plate 6 as desired and rotated about a vertical axis so as to align the optical components 2-4 to each other or to the base plate 6 correctly. By changing the distance d between the first and the second intermediate element 5a, 5b, the height distance of the third intermediate element 5c and thus also the height distance can be adjusted the optical component 2-4 to the base plate 6 can be varied. The two inclined surfaces 7b of the first and second intermediate element 5a, 5b form a pivot bearing in the form of a V-shaped groove for the semi-cylindrical joining surface 8b of the third intermediate element 5c, whereby the optical component 2-4 can be adjusted about both horizontal axes. By means of these degrees of freedom of adjustment, in particular the diffraction gratings 2, 3 can be adjusted in the direction of the optical axis to a certain optimal length position.

As soon as correctly adjusted, the optical components 2-4, the intermediate elements 5a-5c and the base plate 6 are laserver welded together in this adjustment position and form a monolithic optical assembly. The same material or the different materials with similar thermal expansion coefficients prevent the occurrence of thermally induced stresses within the assembly in the joint partners welded to one another and result in maximum thermal and thus optomechanical stability of the pulse compressor 1. This monolithic pulse compressor 1 enables higher stretching factors and higher pulse energy scalings because of its minimized misalignment.

The laser welding of two parts to be joined is preferably carried out by means of ultra-short pulse (USP) welding with laser pulses in the range of a few picoseconds or less, and ideally over the entire length of their joint line. In Fig. 2, the weld between the second and the third Zwischenele element 5c is denoted by 10.

Other than described above, one or more optical components 2-4 can also be welded to the base plate 6 directly, that is to say without intermediate elements. Also, the optical components 2-4 do not have to be made entirely of the same material, but it is sufficient if only the laser-welded substrate of the optical components 2-4 are made of materials in which the difference in their thermal expansion coefficients is less than 10e ^{_6 / K} in particular from the same material is formed. For example, the diffraction grating 2, 3 can be designed as a reflective diffraction grating with a substrate and a metallic coating applied to it. In an oscillator, for example in a mode-locked fiber laser, a seed pulse is generated (ps / fs), which is then stretched over time, for example via a fiber stretcher. This stretched pulse is amplified in an amplifier or an amplifier chain (rod, disc, slab or fiber) and then compressed in time with the help of the pulse compressor 1. The laser pulse 11 incident in the pulse compressor 1 is diffracted at the two reflective diffraction gratings 2, 3. Here, ver different wavelengths of the laser pulse 1 1 at different angles are bent ge, which results in a different optical path for the spectral components of the laser pulse 1 1. The time-compressed laser pulse 11 leaves the pulse compressor 1 with a correspondingly higher power density.

In FIGS. 3a, 3b shows a two-part substructure for the optical components 2-4 of the pulse compressor shown in FIG. 1b. The optical component 2-4 is attached to the base plate 6 by means of two laser-welded intermediate elements 15a, 15b, the one, first intermediate element 15a being laser-welded to the base plate 6 and the other, second intermediate element 15b to the optical component 2-4. The joining surface 17a of the first intermediate element 15a resting on the second intermediate element 15b is conical in the direction of the base plate 6 and the joining surface 17b of the second intermediate element 15b resting on the first intermediate element 15a is configured as a spherical segment. The abutting joining surfaces 17a, 17b form a pivot bearing to align the two intermediate elements 15a, 15b against each other - and thus the optical component 2-4 against the base plate 6 - in a desired tilted position before laser welding (double arrow 18). Instead of conical, the joining surface 17a can also be V-shaped, spherical cap-shaped or even as a circular bearing opening.

In FIGS. 4a, 4b shows a further substructure for the optical components 2-4 of the pulse compressor shown in FIG. 1b. The optical component 2-4 is fastened to the base plate 6 by means of a single intermediate element 15 which is laser-welded to the base plate 6 and to the optical component 2-4. The joining surface 17 of the intermediate element 15 resting on the base plate 6 is configured in the shape of a spherical segment and is pivotably mounted in a bearing recess 19 of the base plate 6 (double arrow 18). The abutting joint surfaces 6a, 17 of the base plate 6 and the intermediate element 15 form a pivot bearing in order to align the base plate 6 and the intermediate element 15 with one another in a desired tilted position before the laser welding. In order to form a linear joining contact, the bearing recess 19 can be designed conical, V-shaped or also as a circular bearing opening. In order to form a large-area joining contact, the bearing recess 19 can be designed in the form of a spherical cap.

Claims

1. Pulse compressor (1) with several optical components (2-4), of which at least one is a diffraction grating (2, 3),

characterized,

that at least one of the optical components (2-4) is attached to the base plate (6) by means of at least two laser-welded intermediate elements (15a, 15b), one, first intermediate element (15a) with the base plate (6) and the other, second intermediate element (15b) are attached to the optical component (2-4), or vice versa, and with one of the joining surfaces (17a, 17b) of the intermediate elements (15a, 15b) as a bearing recess and the other joining surface curved, in particular special convex curved or spherical segment-shaped, or at least one of the optical components (2-4) is attached to the base plate (6) by means of at least three intermediate elements (5a-5c) which are laser-welded to one another, a first and a second intermediate element (5a , 5b) are attached to the base plate (6) and a third intermediate element (5c) to the optical component (2-4), or vice versa, and the joining surfaces (7b) resting on the third intermediate element (5c) de s first and second intermediate elements (5a, 5b) and / or the joining surface (8b) of the third intermediate element (5c) resting on the first and second intermediate element (5a, 5b) are curved, and

that at least the laser-welded joining surfaces of the at least one optical component (2-4), the base plate (6) and the intermediate elements (5a-5c; 15a, 15b) are made of materials in which the difference in their coefficients of thermal expansion is less than 10e ^{_6 / K} is.

2. Pulse compressor according to claim 1, characterized in that at least some, in particular all optical components (2-4) of the Pulskom pressors (1) on the base plate (6) each by means of at least two or three intermediate elements (5a-5c; 15a, 15b) are attached, which are laser-welded to the optical component (2-4) and / or to the base plate (6), at least the laser-welded joining surfaces of the optical components (2-4 ), the base plate (6) and the Zwischenele elements (5a-5c; 15; 15a, 15b) are made of materials in which the difference in their thermal expansion coefficients is less than 10e ^{_6 / K.}

3. Pulse compressor according to claim 1 or 2, characterized in that at least the laser-welded joining surfaces of the optical components (2-4), the base plate (6) and the intermediate elements (5a-5c; 15a, 15b) made of the same material, in particular made of quartz glass or crystal.

4. Pulse compressor according to one of the preceding claims, characterized in that the at least one optical component (2-4), the base plate (6) and / or the intermediate elements (5a-5c; 15a, 15b) each completely made of the same material, in particular quartz glass or crystal is formed.

5. Pulse compressor according to one of claims 1 to 3, characterized in that the laser-welded joining surface of the at least one optical component (2-4) is formed on a substrate of the at least one optical component (2-4) that is connected to the Base plate (6) or with the intermediate elements (5a-5c; 15a, 15b) is laser-welded.

6. Pulse compressor according to one of the preceding claims, characterized in that the at least one intermediate element (5a-5c; 15a, 15b) with a flat joining surface (7a, 8a) on the optical component (2-4) and / or on the The base plate (6).

7. Pulse compressor according to one of the preceding claims, characterized in that the joining surfaces (7b) of the first and second intermediate elements (5a, 5b) resting on the third intermediate element (5c) each as an inclined surface and that of the first and second intermediate element (5c) adjacent joining surface (8b) of the third intermediate element (5c) are formed so as to be convexly curved.

8. Pulse compressor according to one of the preceding claims, characterized in that the optical components (2-4), the Zwischenele elements (5a-5c, 15a, 15b) and the base plate (6) are laser-welded to one another.

9. Pulse compressor according to claim 11, characterized in that the at least one optical component (2-4), the intermediate elements (5a-5c; 15a, 15b) and the base plate (6) each over the entire length of their joining line or surface are laser welded together.

10. A method for adjusting and securing at least one optical component (2-4) of a pulse compressor (1), which has several optical components (2-4), of which at least one has a diffraction grating (2,

3) is on a base plate (6) of the pulse compressor (1) by means of two intermediate elements (15a, 15b), one of the joining surfaces (17a, 17b) of the intermediate elements (15a, 15b) being a bearing recess and the other joining surface being curved, in particular convexly curved or spherical segment-shaped, are formed,

with the following process steps:

- Laser welding of the first intermediate element (15a) on the base plate (6) and the second intermediate element (15b) on the optical component (2-4);

- Adjustment of the optical component (2-4) in a desired tilt position relative to the base plate (6) by rotating the mutually abutting joining surfaces (17a, 17b); and

- Laser welding the two intermediate elements (15a, 15b) to one another in the desired tilted position;

or with the following process steps:

- Laser welding of the second intermediate element (15b) to the optical component's (2-4); - Adjustment of the optical component (2-4) in a desired tilted position relative to the first intermediate element (15a) by rotating the mutually adjacent joining surfaces (17a, 17b);

- Adjusting the optical component (2-4) on the base plate (6) in a desired position relative to the base plate (6); and

- Laser welding of the first intermediate element (15a) to the base plate (6) in the desired position,

wherein at least the laser-welded joining surfaces of the at least one optical component (2-4), the base plate (6) and the intermediate elements (15a, 15b) are made of materials in which the difference in their coefficients of thermal expansion is less than ^{10e_6 / K.}

11. A method for adjusting and securing at least one optical component (2-4) of a pulse compressor (1), which has several optical components (2-4), of which at least one has a diffraction grating (2,

3) is on a base plate (6) of the pulse compressor (1) by means of three intermediate elements (5a-5c), the joining surfaces (7b) of the first and second intermediate elements (5a, 5b) and / or the joining surface (8b) of the third intermediate element (5c) lying on the first and second intermediate element (5a, 5b) are curved, with the following process steps:

- Placing a first and a second intermediate element (5a, 5b) on the base plate (6) and laser welding a third intermediate element (5c) to the optical component (2-4), or vice versa;

- Adjustment of the optical component (2-4) in a desired tilted position with respect to the base plate (6) by rotating the third intermediate element (5c) resting on the first and second intermediate element (5a, 5b) and / or adjusting the optical component (2 -4) in a desired height relative to the base plate (6) by changing the distance (d) between the first and second inter mediate element (5a, 5b); and - Laser welding of the first and second intermediate elements (5a, 5b) on the base plate (6) and on the third intermediate element (5c) in the desired tilted or vertical position,

at least the laser-welded joining surfaces of the at least one optical component (2-4), the base plate (6) and the intermediate elements (5a-5c) are formed from materials in which the difference in their thermal expansion coefficients is less than ^{10e_6 / K.}