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Title:
LASER LIGHT SOURCE UNIT, AND METHOD FOR GENERATING LASER LIGHT FOR VEHICLES
Document Type and Number:
WIPO Patent Application WO/2019/105546
Kind Code:
A1
Abstract:
The invention relates to a laser light source unit for vehicles having a resonator (3) containing a first end mirror (4) and a second end mirror (5), between which an active laser medium (6) is arranged, and having a pump device (2) for generating a pump radiation (30) which can be introduced via the first end mirror (4) into the resonator (3), wherein the pump radiation (30) corresponds to a first wavelength and wherein the active laser medium (6) is configured such that laser light (1 1 ) of the first wavelength (30) and/or of a second wavelength (31 ) and/or of a third wavelength (32) can be radiated, wherein an intermediate mirror (9) and a third end mirror (10) assigned to the same are provided, wherein the intermediate mirror (9) is configured in such a way that the radiation (31 ) of the second wavelength (31 ) is reflected, and the radiation (32) of the third wavelength is transmitted, by means of said intermediate mirror, and wherein the third end mirror (10) is configured in such a way that the radiation (31 ) of the second wavelength is reflected, a color control module (8) is provided, which acts on the radiation (31 ) of the second wavelength and/or the radiation (32) of the third wavelength in such a way that an intensity of the stimulated emission of the radiation (31 ) of the second wavelength is adjusted to the radiation (32) of the third wavelength, or vice versa.

Inventors:
HANSEN JULIEN (DE)
PÖRTNER LUKAS (DE)
BABAEI HANIEH (DE)
Application Number:
EP2017/080846
Publication Date:
June 06, 2019
Filing Date:
November 29, 2017
Export Citation:
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Assignee:
HELLA GMBH & CO KGAA (DE)
International Classes:
H01S3/08; H01S3/082; H01S3/16; H01S3/06; H01S3/0941; H01S5/323
Foreign References:
US20030035447A12003-02-20
DE102015121693A12017-06-14
Other References:
MULLER S ET AL: "Dual wavelength and switchable laser operation of Pr 3+ :LiYF 4 crystals at 523 nm and 640 nm", LASERS AND ELECTRO-OPTICS EUROPE (CLEO EUROPE/EQEC), 2011 CONFERENCE ON AND 12TH EUROPEAN QUANTUM ELECTRONICS CONFERENCE, IEEE, 22 May 2011 (2011-05-22), pages 1, XP031954326, ISBN: 978-1-4577-0533-5, DOI: 10.1109/CLEOE.2011.5942436
MARTIN FIBRICH ET AL: "Power-scaling of Pr:YAlO 3 laser operating in CW regime at 747 nm and 720 nm wavelengths", PROCEEDINGS OF SPIE, vol. 8599, 22 February 2013 (2013-02-22), 1000 20th St. Bellingham WA 98225-6705 USA, pages 85991S, XP055493093, ISSN: 0277-786X, ISBN: 978-1-5106-1533-5, DOI: 10.1117/12.2001096
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Claims:
Laser light source unit, and method for generating laser light for vehicles

Claims

1. A laser light source unit for vehicles having a resonator (3) containing a first end mirror (4) and a second end mirror (5), between which an active laser medium (6) is arranged, and having a pump device (2) for generating a pump radiation (30) which can be introduced via the first end mirror (4) into the res- onator (3), wherein the pump radiation (30) corresponds to a first wavelength and wherein the active laser medium (6) is configured such that laser light

(11 ) of the first wavelength (30) and/or of a second wavelength (31 ) and/or of a third wavelength (32) can be radiated, characterized in that

- an intermediate mirror (9) and a third end mirror (10) assigned to the same are provided, wherein the intermediate mirror (9) is configured in such a way that the radiation (31 ) of the second wavelength is reflect- ed, and the radiation (32) of the third wavelength is transmitted, by means of said intermediate mirror, and wherein the third end mirror (10) is configured in such a way that the radiation (31 ) of the second wavelength is reflected,

- a color control module (8) is provided, which acts on the radiation (31 ) of the second wavelength and/or the radiation (32) of the third wave- length in such a way that an intensity of the stimulated emission of the radiation (31 ) of the second wavelength is adjusted to the radiation (32) of the third wavelength, or vice versa.

2. The laser light source unit according to Claim 1 , characterized in that the in- termediate mirror (9) is arranged on the optical axis (7) of the active laser medium (6) and the third end mirror (10) is arranged outside the optical axis (7) of the active laser medium (6).

3. The laser light source unit according to Claim 1 or 2, characterized in that

- the first end mirror (4) and the second end mirror (5) are configured to be highly transmissive for the radiation (30) of the first wavelength,

- the first end mirror is configured (4) to be highly reflective for the radia- tion (32) of the third wavelength, and

- the second end mirror is configured (5) to be partially reflective for the radiation (31 ) of the second wavelength and the radiation (32) of the third wavelength.

4. The laser light source unit according to any one of Claims 1 to 3, character- ized in that the color control module (8) is arranged in the optical path of the radiation (31 ) of the second wavelength and/or the radiation (32) of the third wavelength.

5. The laser light source unit according to any one of Claims 1 to 4, character- ized in that the radiation (31 ) of the second wavelength and/or the radiation (32) of the third wavelength passing through the color control module (8) is/are reduced or enhanced by rotating the color control module (8).

6. The laser light source unit according to any one of Claims 1 to 5, character- ized in that the color control module (8) comprises a birefringent medium or a polarizing filter or a neutral density filter.

7. The laser light source unit according to any one of Claims 1 to 6, character- ized in that the active laser medium (6) consists of a praseodymium-doped yttrium lithium fluoride crystal material and that the pump device (2) has a laser diode that radiates the pump radiation (30) of a blue wavelength as the first wavelength.

8. The laser light source unit according to any one of Claims 1 to 7, character- ized in that the first end mirror (4) has a planar configuration and the second end mirror (5) has a spherical configuration.

9. A lighting apparatus for vehicles having a laser light source unit (1 ) according to any one of Claims 1 to 8, having an upstream optical unit in the radiation direction (A) of the same for generating a predefined light distribution.

10. A method for generating laser light (11 ), wherein a pump radiation (30) is coupled from outside via a first end mirror (4) into a resonator (3) having an active laser medium (6) and is decoupled at a second end mirror (5) of the same as laser light (11 ) with a predefined wavelength or with a predefined wavelength range, characterized in that

- a radiation (31 ) of a second wavelength generated in the active laser medium (6) is exclusively deflected at an intermediate mirror (9) out of the optical path of the pump radiation (30) in the direction of a third end mirror (10) arranged at a distance (a) from the optical path of the pump radiation (30), at which third end mirror the radiation (31 ) of the second wavelength is reflected in the direction of the intermediate mirror (9), and

- a radiation (32) of the third wavelength generated in the active laser medium (6) is transmitted at the intermediate mirror (9) in the direction of the first end mirror (4) or in the direction of the second end mirror (5).

Description:
Laser light source unit, and method for generating laser light for vehicles

The invention relates to a laser light source unit for vehicles having a resonator con- taining a first end mirror and a second end mirror, between which an active laser me- dium is arranged, and having a pump device for generating a pump radiation which can be introduced via the first end mirror into the resonator, wherein the pump radia- tion corresponds to a first wavelength and wherein the active laser medium is config- ured such that laser light of the first wavelength and/or of a second wavelength and/or of a third wavelength can be radiated.

The invention further relates to a lighting apparatus for vehicles.

The invention further relates to a method for generating laser light, wherein a pump radiation is coupled from outside via a first end mirror into a resonator having an active laser medium and is decoupled at a second end mirror of the same as laser light with a predefined wavelength or with a predefined wavelength range.

A laser light source unit for vehicles is known from DE 10 2015 121 693 A1 , which has a resonator having a first end mirror and a second end mirror, wherein an active laser medium is arranged between the two end mirrors. The active laser medium is acted upon by means of a pump radiation emitted by a pump device, wherein the pump ra- diation penetrates through a first end mirror into the resonator. The opposite second end mirror consists of multiple mirror segments which have such layer thicknesses that radiation of particular wavelengths is stimulated in the active laser medium. For example, three mirror segments can be provided, wherein a first mirror segment stimulates radiation of a blue wavelength, a second mirror segment stimulates radia- tion of a green wavelength and a third mirror segment stimulates radiation of a red wavelength, so that a white laser light can be emitted by means of additive color mix- ing. The emission spectrum of the radiated laser light is fixed with the selection of the mirror segments at the second end mirror. The light color cannot be varied or altered. It is the object of the present invention to specify a laser light source unit or respective- ly a lighting apparatus as well as a method for generating laser light, so that coherent and polarized laser light of different light colors can be emitted from a laser cavity.

In order to achieve this object, the invention in conjunction with the preamble of Claim 1 is characterized in that an intermediate mirror and a third end mirror assigned to the same are provided, wherein the intermediate mirror is configured in such a way that the radiation of the second wavelength is reflected, and the radiation of the third wave- length is transmitted, by means of said intermediate mirror, and wherein the third end mirror is configured in such a way that the radiation of the second wavelength is re- flected, a color control module is provided, which acts on the radiation of the second wavelength and/or the radiation of the third wavelength in such a way that an intensity of the stimulated emission of the radiation of the second wavelength is adjusted to the radiation of the third wavelength, or vice versa.

According to the invention, a resonator is provided, which not only has a first end mir- ror and a second end mirror, between which an active laser medium is arranged, so that a stimulated emission can be generated. In addition, the resonator has an inter- mediate mirror and a third end mirror, by means of which radiation of a predefined second wavelength or third wavelength can be divided spatially from the additional radiation so that this divided radiation can be additionally stimulated. In addition, the resonator has one or more color control modules which act(s) on the pump radiation or respectively the stimulated radiation of the second wavelength and third wavelength in such a way that radiation of a predefined wavelength or respectively wavelength spectrum (in the case of white light color or other mixed colors) is decoupled by means of the second end mirror. The intermediate mirror and the third end mirror vir tually form part of an additional resonator so that, together with the main resonator, a polychromatic emission of radiation of a first wavelength, of a second wavelength and radiation of a third wavelength can be simultaneously decoupled from a laser cavity along an optical axis of the same. A light color of the emitted laser radiation can be effected through additive color mixing of the pump radiation of the first wavelength and the radiation of other wavelengths. The at least one color control module determines the spectral components of the emitted laser radiation, wherein, for example, by means of additive color mixing of blue, red and green radiation, white light can be generated for a predefined light distribution in the vehicle or a particular light color for, by way of example, a“welcome light scenario”. The invention makes possible a poly- chromatic or monochromatic emission of light of multiple different wavelengths from a single laser cavity in a simple way. As a result, different color light signatures can ad- vantageously be generated in a space-saving manner, so that the range of variation of a lighting design is increased. The laser light source unit advantageously has a rela- tively high luminance, in particular when emitting laser radiation of a white light color, so that the radiated light can, in particular, be conveyed via glass fibers. Since the la- ser light source unit radiates polarized light, a predefined light distribution can be real- ized with little effort in a vehicle headlight in combination with an upstream liquid crys- tal panel in an efficient manner that saves installation space. It is, in this case, advan- tageous that the resolution to be achieved is substantially higher than in the case of conventional matrix-LED headlights. Compared with the known laser light source units which have previously been used in headlights, the cooling effort required for the laser light source unit according to the invention is substantially lower, since the heat gen- eration is constant irrespective of the emitted laser radiation spectrum.

According to a preferred embodiment of the invention, the intermediate mirror is ar- ranged on the optical axis of the active laser medium, and the third end mirror is ar- ranged outside the optical axis of the active laser medium. A partial radiation of the radiation stimulated in the active laser medium is therefore spatially separated. While the first end mirror reflects the radiation of the third wavelength (preferably red radia- tion), the third end mirror reflects radiation of a second wavelength (preferably green radiation). The intermediate mirror virtually serves as a beam splitter, since it acts re- flectively for the radiation of the second wavelength (green radiation) and transmis- sively for the radiation of the third wavelength (red radiation). Since both the radiation of the second wavelength and of the third wavelength are decoupled by means of the same second end mirror, a polychromatic emission can simultaneously take place from a single laser cavity. According to a preferred embodiment of the invention, the first end mirror and the sec- ond end mirror are configured to be highly transmissive for a radiation of a first wave- length (for example, blue radiation). Laser light of a white light color can advanta- geously be hereby emitted through additive color mixing with the second end mirror which is configured to be partially reflective for the radiation of the second wavelength and of the third wavelength.

According to a further development of the invention, the color control module is ar- ranged in the optical path of the radiation of the second wavelength and/or of the third wavelength. If the color control module is located in the optical path of the radiation of the second wavelength, the stimulated emission (avalanche effect) of this radiation can be adjusted. If the color control module is located in the optical path of the radia- tion of the third wavelength, the stimulated emission (avalanche effect) of this radiation can be adjusted. Two color control modules can also be used in order to control both wavelengths simultaneously with respect to each other. For example, if the color con- trol module is arranged in the optical path of the radiation of the second wavelength, an adjustment can be made to the radiation of the third wavelength and, if the color control module is arranged in the optical path of the radiation of the third wavelength, an adjustment to the radiation of the second wavelength can be made, so that two continuous types of radiation which have different wavelengths can be emitted simul- taneously.

According to a further development of the invention, the color control module is con- figured as a birefringent medium or as a polarizing filter. This can advantageously re- duce the radiation by altering the phase relation or by filtering a particular direction of polarization of the radiation passing through the color control module.

According to a further development of the invention, the active laser medium is formed from a praseodymium-doped yttrium lithium fluoride crystal material. The pump device has a laser diode that radiates the pump radiation of a blue wavelength. The active laser medium makes it possible to stimulate radiation of the second wavelength (green radiation) and of the third wavelength (red radiation), so that by means of additive col- or mixing with the radiation of the first wavelength (blue radiation), which is caused by the laser diode, light of a white light color can be radiated.

According to a development of the invention, at least one of the end mirrors is planar or spherical, wherein all end mirrors of the resonator can also be shaped as planar or spherical end mirrors. In a particularly preferred embodiment, the first end mirror is flat and the second and third mirror are spherical. A particularly simple adjustment of the end mirrors can thus be achieved, in order to achieve a particularly stable resonator, which thereby satisfies the best reflection properties.

In order to achieve the object, the lighting apparatus has the features of Claim 9. An upstream optical unit for generating a predefined light distribution in a headlight can, for example, comprise a liquid crystal panel, the pixels of which can be individually controlled so that, for example, a dynamic full beam distribution with dimmed regions can be generated in the light distribution in order to avoid dazzling other road users.

In order to achieve the object, a method according to the invention has the features of Claim 10. Advantageously, a radiation of a particular wavelength can be deflected out of the optical path of the pump radiation and then deflected back in by means of an intermediate mirror and a third end mirror. As a result, two separate optical paths are created for radiation of a different wavelength. In particular, a polychromatic emission of multiple wavelengths can be advantageously provided from a single laser cavity.

One embodiment example of the invention will be explained in greater detail below with reference to the drawings, wherein:

Fig. 1 shows a schematic construction of a laser light source unit according to the invention, and

Fig. 2 shows a representation of an emission spectrum of the active laser medi um. A laser light source unit 1 according to the invention is preferably used in vehicles, in particular in headlights, for generating predefined light distributions. Alternatively, the laser light source unit 1 can also be used in other lights for identification inside or out- side the vehicle, or for other purposes.

The laser light source unit 1 has a pump device 2 for generating a pump radiation 30. The pump device 2 can comprise a laser diode that emits light of a first wavelength in order to form the pump radiation 30 (blue light).

Furthermore, the laser light source unit 1 has a resonator 3 which is assigned to the pump device 2. The resonator 3 has a first end mirror 4 on one side facing the pump device 2 and a second end mirror 5 on a side facing away from the pump device 2. An active laser medium 6 is arranged between the first end mirror 4 and the second end mirror 5 which, in the present embodiment example, consists of a praseodymium- doped crystal material, namely praseodymium-doped yttrium lithium fluoride crystal material (Pr 3+ : YLF). The first end mirror 4 serves as a coupling-in mirror for the pump radiation 30. The first end mirror 4 has, for example, a planar configuration. The sec- ond end mirror 5 serves as a decoupling mirror of the laser light source unit 1 for de- coupling the light in the radiation direction A. This has a spherical configuration in this embodiment example.

The radiated pump radiation 30 is coupled into the resonator 3 via the first end mirror 4 and is focused by means of lenses, which are not shown, onto the active laser me- dium 6.

In addition, a color control module 8 as well as an intermediate mirror 9 of an addition- al resonator 13 are arranged along an optical axis 7 of the laser light source unit 1 , which extends along a direction of the pump radiation 30 and between the first end mirror 4 and the second end mirror 5. A third end mirror 10 of the additional resonator 13 is located outside the optical axis 7. The intermediate mirror 9 is arranged oriented towards the optical axis 7 in such a way that a radiation with a predefined wavelength is deflected at a deflection angle f with respect to the laterally arranged third end mir- ror 10. The deflection angle f in the present embodiment example is equal to 90°. In the present embodiment example, the color control module 8 is arranged between the first end mirror 4 and the active laser medium 6 or respectively the intermediate mirror 9 of the additional resonator 13. The intermediate mirror 9 is arranged between the first end mirror 4 or respectively the color control module 8 and the active laser medi- um 6. According to an alternative embodiment of the invention (not shown), the inter- mediate mirror 9 and/or the color control module 8 can also be arranged between the active laser medium 6 and the second end mirror 5. Another additional color control module can also be positioned between the intermediate mirror 9 and the third end mirror 10.

The emission cross-section of the active laser medium 6 as a function of the wave- length is shown in Fig. 2. Thanks to a corresponding stimulated emission, the laser light source unit 1 is therefore in a position to emit laser light 11 of a white light color in the radiation direction A. The white laser light 11 substantially consists of radiation 30 of a first wavelength (blue radiation), radiation 31 of a second wavelength (green radi ation) and radiation 32 of a third wavelength (red radiation).

Fig. 1 shows the spectral radiation components 30, 31 , 32 which, by means of additive color mixing, generate the white or any other mixed color of laser light 11. The blue pump radiation 30 serves to excite the active laser medium 6 which is to be used for the generation of the green radiation 31 and the red radiation 32.

The first end mirror 4 and the second end mirror 5 are configured to be highly trans- missive for the radiation of the first wavelength (blue radiation). In this way, it is en- sured that the blue radiation 30 can be decoupled as a component of the laser light 11 from the laser light source 1 by means of the second end mirror 5. The first end mirror 4 is configured to be highly reflective for the radiation of the third wavelength (red ra- diation) so that the excited red radiation 32 is constantly reflected in the direction of the second end mirror 5. The second end mirror 5 is configured to be partially reflec- tive for the radiation 32 of the third wavelength (red radiation) so that the red radiation 32 can be decoupled from the laser light source unit 1 , To this end, the second end mirror 5 has a reflectance in the range of 96% to 100%.

The first end mirror 4 has a transmittance in the range of 100% or just below 100% (close to 100%) for the first wavelength 30.

The first end mirror 4 has a reflectance of 100% or just below 100% (close to 100%) for the radiation 32 of the third wavelength.

The intermediate mirror 9 is configured to be transmissive with respect to the radiation 32 of the third wavelength (red radiation), the transmittance for this wavelength is preferably 100% or respectively just below 100% (close to 100%). With respect to the radiation 31 of the second wavelength (green radiation 31 ), the intermediate mirror 9 is configured to be highly reflective, for example, a reflectance of 100% or just below 100%. The intermediate mirror 9 is configured in such a way that the radiation 31 of the second wavelength is exclusively reflected to the side, and indeed at the right an- gle of deflection f to the third end mirror 10. The third end mirror 10 is configured to be highly reflective with respect to the radiation 31 of the second wavelength (reflec- tance of 100% or just below 100%) so that the green radiation 31 is reflected back to the intermediate mirror 9.

Since the second end mirror 5 is configured to be partially reflective for the radiation 31 of the second wavelength and the radiation 32 of the third wavelength, preferably equally partially reflective, and indeed in the range of 96% to 100% of reflectance, the laser light 11 can be generated by additive color mixing of the blue radiation 30, the green radiation 31 and the red radiation 32.

With respect to the radiation 31 of the second wavelength, the intermediate mirror 9 and the third end mirror 10 as well as the second end mirror 5 form the additional res- onator 13, which ensures that the radiation 31 of the second wavelength can be de- coupled as a spectral component of the laser light 11. The color control module 8 can have a birefringent medium or a polarizing filter, by means of which radiation 32 of the third wavelength passing through them can be ad- justed to the radiation 31 of the second wavelength. In the present exemplary embod- iment, the radiation 32 of the third wavelength is adjusted with respect to the degree of the generated avalanche effect such that the enhancement, i.e. the avalanche effect of the green radiation 31 , corresponds to the enhancement of the red radiation 32. In this way, all three basic components RGB which are necessary for the white laser light 11 can be generated by means of stimulated emission of the two wavelengths 32 and 31 as well as with the blue radiation 30.

According to an alternative embodiment (not shown) of the invention, the color control module 8 can also be arranged within an optical path of the green radiation 31 , for example between the intermediate mirror 9 and the third end mirror 10. In this way, the intensity of the green radiation 31 could be adjusted to the intensity of the red ra- diation 32. Consequently, according to one construction of the laser light source unit 1 according to the invention, not only can the color control module 8 be arranged be- tween the first end mirror 4 and the intermediate mirror 9, but also additionally or al- ternatively between the intermediate mirror 9 and the third end mirror 10.

In the present exemplary embodiment, the color control module 8 brings about a re- duction in the radiation by altering the phase relation (in the case of a birefringent ma- terial) or by filtering a particular direction of polarization (in the case of a polarizing filter) of the radiation 32 passing through the color control module 8.

In the present exemplary embodiment, the color control module 8 is configured as a birefringent crystal plate which is located at a Brewster angle to the optical axis 7. The color control module 8 has a rigid configuration - like the other components of the la- ser light source unit 1 , but can be rotated or turned about the optical axis.

Different spectrally-dependent optical paths are provided according to the invention. While the optical path for the radiation 32 of the third wavelength runs linearly between the first end mirror 4 and the second end mirror 5, the optical path of the radiation 31 of the second wavelength is arranged in an angular form. Instead of the right-angled deflection angle cp, an acute or obtuse deflection angle f can also be provided. It is essential that the radiation 31 of the second wavelength is guided out of the optical path of the radiation 32 of the third wavelength, or vice versa.

An optical unit (not shown) for forming the lighting apparatus is arranged in the radia- tion direction (A) before the laser light source unit 1. The optical unit has, for example, a liquid crystal panel having a number of pixels which are arranged in the manner of a matrix and which are individually controllable. A predefined light distribution, for exam- pie a low-beam light distribution, can be adjusted by controlling the pixels. To this end, the pixels of the liquid crystal panel are mapped by means of a subordinate lens unit into the area in front of the vehicle. If necessary, a traffic area capturing unit can be provided, which supplies sensor data regarding the existence and the location of an- other traffic object in the area in front of the vehicle. Depending on the current location of this traffic object, the pixels of the liquid crystal panel can then be controlled so that the region of the generated light distribution, in which the traffic object is located, is not illuminated and, therefore, a glare suppression region of the light distribution is gener- ated. This glare suppression region can be adapted to the altered relative position of the traffic object with respect to the vehicle, so that the entire area in front of the vehi- cle is illuminated with the exception of the glare suppression region, in which the traffic object is currently located (glare-free full beam distribution).

The third end mirror 6 is arranged at a distance a from the optical path of the blue ra- diation 30 and the red radiation 32.

The color control module 8 can also be configured such that it absorbs the radiation 32 of the third wavelength, so that said spectral component is not available for the la- ser light 11. If necessary, an additional color control module (not shown) can also be arranged for the radiation 31 of the second wavelength and/or of the first wavelength inside or outside the resonator 3, so that the radiation 30 of the first wavelength and/or the radiation 31 of the second wavelength can be absorbed and is therefore not avail- able for the radiated laser light 11. In this way, laser light 11 of a red or blue or green color or any other mixed color can be radiated, for example, for a welcome light func- tion.

An additional lens device is preferably provided in the radiation direction A behind the liquid crystal panel for enlarging and for further blending the laser light 11 radiated by the laser light source unit 1.

List of reference numerals

1 Laser light source unit

2 Pump device

3 Resonator

4 1 st end mirror

5 2 nd end mirror

6 Active laser medium

7 Optical axis

8 Color control module

9 intermediate mirror

10 3 rd end mirror

11 Laser light

13 Additional resonator

30 Pump radiation

31 Radiation

32 Radiation a Distance

A Radiation direction f Deflection angle