High-brightness addressable solid laser area array chip

Abstract

The invention provides a high-brightness addressable solid laser area array chip, and relates to the technical field of laser technology and application. The high-brightness addressable solid laser area array chip comprises first units arranged in an array, each first unit comprises a plurality of vertical cavity surface emitting semiconductor lasers arranged in an array, and the number of the vertical cavity surface emitting semiconductor lasers in each unit is the same or different; the driving module is configured to drive the first units in the preset area to emit light and drive the preset number of vertical cavity surface emitting semiconductor lasers in the first units in the preset area to emit light so as to output pump light in a preset shape; and the modulation unit is configured to perform gain and / or modulation processing on the received pump light so as to output addressing laser with the same shape as the preset shape of the pump light. A high-brightness laser light source can be obtained by integrating the VCSEL area array and the laser modulator, and the laser light source is used as an addressing light source, so that accurate long-distance laser addressing, detection, information transmission and the like can be realized.

Description

Technical Field

[0001] The present disclosure relates to the field of laser technology and application technology, and more specifically, to a high-brightness addressable solid-state laser array chip. Background Art

[0002] Brightness and addressing methods are key factors in determining laser detection distance and accuracy. Traditional laser systems generally lack flexible control mechanisms to quickly change the shape or direction of the laser beam, and the pump light usually needs to go through a complex shaping and transmission coupling system when generating laser light, which results in a complex laser system and a single illumination form. Therefore, high-power vertical-cavity surface-emitting semiconductor lasers (VCSELs) are currently used as detection light sources. However, they have low pulse peak power, poor beam quality, wide emission spectrum linewidth, large divergence angle, and low emission brightness, making it difficult to meet the application requirements of long distance, high precision, and multiple scenarios. Summary of the Invention

[0003] In view of this, the present disclosure provides a high-brightness addressable solid-state laser array chip, which can solve at least one of the above technical problems.

[0004] The present disclosure provides a high-brightness addressable solid-state laser array chip, comprising: first units arranged in an array, each first unit comprising a plurality of vertical cavity surface emitting semiconductor lasers arranged in an array, the number of vertical cavity surface emitting semiconductor lasers in each unit being the same or different; a driving module configured to drive the first units in a predetermined area to emit light and to drive a predetermined number of vertical cavity surface emitting semiconductor lasers in the first units in the predetermined area to emit light, so as to output pump light of a predetermined shape; and a modulation unit configured to perform gain and / or modulation processing on the received pump light to output addressing laser light of the same predetermined shape as the pump light.

[0005] According to an embodiment of the present disclosure, the array arrangement of the first units includes a one-dimensional array arrangement, and the driving module includes: one-dimensionally arranged driving circuit units, and one driving circuit unit drives one first unit.

[0006] According to an embodiment of the present disclosure, the array arrangement of the first unit includes a two-dimensional array arrangement, and the driving module includes: a two-dimensionally arranged driving circuit unit, a driving circuit unit in a first direction and a driving circuit unit in a second direction correspondingly driving one first unit, wherein the first direction and the second direction intersect.

[0007] According to an embodiment of the present disclosure, the predetermined shape includes a one-dimensional linear distribution, a two-dimensional array distribution, or a preset non-uniform distribution.

[0008] According to an embodiment of the present disclosure, the modulation unit includes: a gain medium configured to amplify received pump light to output oscillating laser light as addressing laser light, wherein an absorption spectrum of the gain medium matches a spectrum of the pump light.

[0009] According to an embodiment of the present disclosure, the modulation unit includes: a gain medium for amplifying the received pump light to generate oscillating laser light; and a Q-switched medium for saturating and bleaching the oscillating laser light to output pulsed laser light as the addressing laser light.

[0010] According to an embodiment of the present disclosure, the modulation unit includes: a nonlinear laser medium for performing nonlinear frequency conversion on received pump light to output frequency-converted laser light as the addressing laser light.

[0011] According to an embodiment of the present disclosure, the modulation unit includes: a gain medium for amplifying the received pump light to generate an oscillating laser; a Q-switched medium for saturating the oscillating laser and bleaching it to generate a pulsed laser; and a nonlinear laser medium for performing nonlinear frequency conversion on the received pulsed laser to output a frequency-converted pulsed laser as an addressing laser.

[0012] According to an embodiment of the present disclosure, the gain medium includes a first dielectric film layer and a second dielectric film layer, and the first dielectric film layer and the second dielectric film layer form a solid laser resonant cavity to generate oscillating laser.

[0013] The high-brightness addressable solid-state laser array chip provided in accordance with the embodiments of the present disclosure has at least the following beneficial effects:

[0014] This embodiment independently controls the number of VCSELs emitting light in the first unit, enabling brightness adjustment and improved emission luminance. Several VCSELs are arranged in zones with specific one-dimensional or two-dimensional periods. Circuitry then drives each zone individually, enabling controllable alternating illumination of one or more zones to meet the requirements of pumping the solid-state laser gain medium and achieve one-dimensional or two-dimensional addressing.

[0015] By integrating the modulation device with the first unit, not only high-brightness, addressable, good beam quality and narrow linewidth laser output is achieved, but also the size and weight of the laser are significantly reduced, the stability and reliability of the laser are improved, and it is cost-effective and easy to mass-produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0017] Figure 1 The structure diagram of the laser array chip according to the embodiment of the present disclosure is schematically shown;

[0018] Figure 2 Schematically shows a schematic diagram of a first unit of a one-dimensional arrangement according to an embodiment of the present disclosure;

[0019] Figure 3 Schematically shows a schematic diagram of a second unit of a two-dimensional one-periodic arrangement according to an embodiment of the present disclosure;

[0020] Figure 4 Schematically shows a schematic diagram of a second unit of another two-dimensional periodic arrangement according to an embodiment of the present disclosure;

[0021] Figure 5 Schematically shows a schematic diagram of a one-dimensionally arranged driving module according to an embodiment of the present disclosure;

[0022] Figure 6 A schematic diagram schematically illustrates an oscillating laser used as an addressing laser according to an embodiment of the present disclosure;

[0023] Figure 7 Schematically illustrates the embodiment of the present disclosure using Figure 2 Schematic diagram of addressing of the structure shown in a;

[0024] Figure 8 Schematically illustrates the embodiment of the present disclosure using Figure 3 Schematic diagram of addressing structure;

[0025] Figure 9 Schematically illustrates the embodiment of the present disclosure using Figure 4 Schematic diagram of addressing structure;

[0026] Figure 10 Schematically illustrates the embodiment of the present disclosure using Figure 5 Schematic diagram of the addressing structure. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may be implemented without these specific details. In addition, in the following description, descriptions of well-known systems and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0028] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0029] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0030] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0031] Compared to traditional high-power edge-emitting semiconductor lasers (EELs), vertical-cavity surface-emitting semiconductor lasers (VCSELs) offer higher beam roundness and temperature stability. However, single-tube VCSELs have low luminous power and a single illumination method, making them incapable of addressing complex scenes.

[0032] Based on this, the present invention arranges several VCSEL tubes in a specific one-dimensional / two-dimensional periodic partition, and then drives each area separately through a circuit to achieve controllable regional or multi-region alternating light emission to meet the needs of pumping solid laser gain media.

[0033] Figure 1 The schematic diagram shows the structure of the laser array chip according to the embodiment of the present disclosure.

[0034] Figure 2 A schematic diagram of a first unit of a one-dimensional arrangement according to an embodiment of the present disclosure is schematically shown.

[0035] Figure 3 The figure schematically shows a second unit of a two-dimensional periodic arrangement according to an embodiment of the present disclosure.

[0036] Figure 4 The figure schematically shows a second unit of another two-dimensional periodic arrangement according to an embodiment of the present disclosure.

[0037] like Figure 1 A in the middle is a front view of the laser array chip of this embodiment. Figure 1 Figure b is a side view of the laser array chip of this embodiment. This embodiment discloses a high-brightness addressable solid-state laser array chip, comprising: a first unit I arranged in an array, a driving module II, and a modulation unit C.

[0038] The first units I are arranged in an array, each of which includes a plurality of vertical cavity surface emitting semiconductor lasers arranged in an array, and the number of vertical cavity surface emitting semiconductor lasers in each unit is the same or different.

[0039] The driving module II is configured to drive the first unit in the predetermined area to emit light and drive a predetermined number of vertical cavity surface emitting semiconductor lasers in the first unit in the predetermined area to emit light, so as to output a continuous wave or nanosecond or sub-nanosecond high peak power pulse pump light of a predetermined shape.

[0040] The modulation unit C is configured to perform gain and / or modulation processing on the received pump light to output an addressing laser having the same predetermined shape as the pump light.

[0041] In the disclosed embodiments, the arrayed first units I and driver modules II together form a VCSEL array. By driving the first units within a predetermined area to emit light, the number of light-emitting units and their area can be dynamically allocated as needed, meeting complex application scenarios. Simultaneously driving a predetermined number of VCSELs to emit light allows for brightness gradient adjustment.

[0042] The solid-state laser emitted by this array chip has the same emission array distribution as the VCSEL array laser. This high-brightness two-dimensional solid-state laser array serves as the addressing laser. Detectors (such as single-photon avalanche photodiode arrays) activate the area corresponding to the VCSEL array to receive reflected light from the target, enabling precise addressing. The integrated assembly of the modulation unit and the VCSEL array eliminates the need for separate optical components such as lenses, mirrors, and optical waveguides to guide and control the transmission and coupling of pump light. This solid-state laser array chip offers advantages such as high brightness, one- and two-dimensional addressability, high efficiency, and chip-scale size. This effectively overcomes the practical bottlenecks of limited detection range and low accuracy caused by the low peak pulse power, poor beam quality, wide emission linewidth, large divergence angle, and low emission brightness of high-power VCSEL lasers. It also has broad applications in 3D sensing, optical communications, laser printing, and medical imaging.

[0043] For example, Figure 2 As shown in a, the first units are closely arranged in a one-dimensional uniform arrangement. Each first unit is provided with a preset number of single-tube VCSELs, and the number of VCSELs in each unit can be the same or different. The required first units can be lit as needed, or the first units in a preset area can be lit in a time sequence as needed.

[0044] You can also Figure 2 As shown in b, the first units are arranged alternately and at intervals, and the required first units can be lit up as needed or the first units in a preset area can be lit up in a time sequence as needed.

[0045] You can also Figure 3 As shown, the first units are closely arranged in a two-dimensional uniform pattern. Each first unit is equipped with a preset number of single-tube VCSELs, and the number of VCSELs in each unit can be the same. The first units can be illuminated as needed, or the first units in a predetermined area can be illuminated sequentially as needed. For example, the first units in the intersecting rows and columns are driven to emit light by driver modules A2 and B2.

[0046] You can also Figure 4 As shown, the first units are closely arranged in a two-dimensional uniform arrangement, each first unit is provided with a preset number of VCSELs, and the number of VCSELs in each unit can be different. The required first units can be lit as needed, or the first units in a preset area can be lit in a time sequence as needed.

[0047] According to the embodiments of the present disclosure, one-dimensional or two-dimensional addressing can be achieved, and the brightness of the addressing light source is adjustable, which can be widely used in fields such as 3D sensing, optical communication, laser printing, and medical imaging.

[0048] Furthermore, the modulation unit and the VCSEL array can be tightly combined and assembled using bonding, gluing, matching liquid, direct close arrangement and other methods.

[0049] Figure 5 The figure schematically shows a one-dimensional arrangement of driving modules according to an embodiment of the present disclosure.

[0050] like Figure 5 As shown, this embodiment discloses that the array arrangement of the first units includes a one-dimensional array arrangement, and the driving module includes: one-dimensionally arranged driving circuit units, and one driving circuit unit drives one first unit accordingly.

[0051] Furthermore, the array arrangement of the first units includes a two-dimensional array arrangement, and the driving module includes: two-dimensionally arranged driving circuit units, a driving circuit unit in a first direction and a driving circuit unit in a second direction respectively driving one first unit, wherein the first direction and the second direction intersect.

[0052] Furthermore, the driving mode of the first unit may include common cathode design, planar electrode design, separate current drive, etc., which can realize alternating lighting of different regions or multiple regions, and the output pump light is continuous wave or nanosecond / sub-nanosecond high peak power pulse laser output.

[0053] In the embodiments of the present disclosure, Figure 5As shown, a driving module drives a first unit; and in a two-dimensional array arrangement, a first unit is driven by a driving circuit unit in a first direction and a driving circuit unit in a second direction, so that each first unit is independently controlled, and regional or alternating light emission can be achieved.

[0054] According to an embodiment of the present disclosure, the predetermined shape includes a one-dimensional linear distribution, a two-dimensional array distribution, or a preset non-uniform distribution.

[0055] In the embodiments of the present disclosure, a pump light of a predetermined shape can be set as needed to meet complex scene addressing.

[0056] Figure 6 A schematic diagram schematically shows oscillating laser light as addressing laser light according to an embodiment of the present disclosure.

[0057] Figure 7 Schematically illustrates the embodiment of the present disclosure using Figure 2 Addressing diagram of the structure in a.

[0058] like Figure 6-Figure 7 As shown, the modulation unit of this embodiment includes: a gain medium C1, which is configured to amplify the received pump light to output oscillating laser light as the addressing laser, wherein the absorption spectrum of the gain medium matches the spectrum of the pump light.

[0059] Furthermore, the gain medium includes a first dielectric film layer R1 and a second dielectric film layer R2 , and the first dielectric film layer R1 and the second dielectric film layer R2 form a solid laser resonant cavity to generate an oscillating laser L1 .

[0060] In the embodiments of the present disclosure, Figure 7 As shown, a VCSEL array 1 with controllable zone emission or multiple alternating zones emits VCSEL pump light 2 using a one-dimensional arrangement of zones. The spectral lines of the VCSEL pump light 2 emitted by the VCSEL array 1 match the absorption lines of the laser gain medium C1. The laser gain medium C1 absorbs the VCSEL pump light 2 and provides gain to the oscillating laser light L1. A dielectric film R1 is coated on the surface of the laser gain medium C1 facing the VCSEL array pump laser 1. This film R1 provides high transparency to the VCSEL pump light 2 and high reflection to the oscillating laser light L1. A dielectric film R2 is coated on the surface of the laser gain medium C1 facing away from the VCSEL array pump laser 1. This film R2 provides high reflection to the VCSEL pump light 2 and a certain transmittance to the oscillating laser light L1. Dielectric films R1 and R2 form a solid-state laser resonant cavity, which generates the oscillating laser light L1. The oscillating laser light L1 serves as an addressing laser to scan and detect objects at a certain distance, achieving one-dimensional addressability.

[0061] Furthermore, the laser gain medium may be a single piece of single substance, a composite bonded or glued laser crystal, laser glass, laser ceramic, laser optical fiber, nano laser medium, etc.

[0062] Figure 8 Schematically illustrates the embodiment of the present disclosure using Figure 3 Schematic diagram of the addressing structure.

[0063] like Figure 8 As shown, the modulation unit of this embodiment includes: a gain medium C1 for performing amplification on the received pump light to generate oscillating laser light; and a Q-switched medium C2 for performing saturation absorption and bleaching on the oscillating laser light to output pulsed laser light as addressing laser light.

[0064] In the embodiment of the present disclosure, the VCSEL array 1 emits VCSEL pump light 2 in a two-dimensional arrangement of regions. The absorption spectrum of the laser gain medium C1 can be well matched to the wavelength of the VCSEL pump light 2. A dielectric film layer R1 is coated on the surface of the laser gain crystal C1 facing the VCSEL array pump laser 1. The dielectric film layer R1 is highly transparent to the VCSEL pump light 2 and highly reflective to the Q-switched oscillating laser L2. The laser gain medium C1 is bonded to the Q-switched medium C2. The surface of the Q-switched medium C2 facing away from the laser gain medium C1 is coated with a dielectric film layer R3. The dielectric film layer R3 is highly reflective to the VCSEL pump light 2 and has partial transmittance to the Q-switched laser L2. The Q-switched medium C2 performs nonlinear saturation absorption and bleaching on the Q-switched laser L2, thereby generating a high-peak power pulsed laser. The dielectric film layer R1 and the dielectric film layer R3 form the resonant cavity of the passively Q-switched laser. The laser gain medium C1 provides the starting gain for the resonant cavity. After the Q-switching medium C2 modulates the intra-cavity loss of the resonant cavity, the passively Q-switched pulse laser output is realized. The passively Q-switched pulse laser scans and detects objects at a certain distance, realizing two-dimensional addressability.

[0065] Furthermore, the Q-switching medium may be a saturable absorber crystal, or any Q-switching medium that has a certain saturable absorption and bleaching effect on the wavelength of the laser emitted by the laser gain material.

[0066] Figure 9 Schematically illustrates the embodiment of the present disclosure using Figure 4 Schematic diagram of the addressing structure.

[0067] like Figure 9 As shown, the modulation unit of this embodiment includes: a nonlinear laser medium C3, which is used to perform nonlinear frequency conversion on the received pump light to output frequency-converted laser light as the addressing laser light.

[0068] In the embodiment of the present disclosure, the VCSEL array 1 emits VCSEL pump light 2 in a two-dimensional arrangement of regions as pump light with nonlinear frequency variation. The nonlinear laser medium C3 performs nonlinear frequency conversion on the VCSEL pump light 2 and generates frequency-variable laser light L3.

[0069] Furthermore, nonlinear laser media include inorganic nonlinear optical materials, organic nonlinear optical materials, metal organic complex nonlinear optical materials, and organic / inorganic hybrid materials, among which inorganic nonlinear optical materials include: KDP-type nonlinear crystals, KTP-type nonlinear crystals, borate nonlinear crystals, semiconductor materials, perovskite-type crystals, glass nonlinear optical materials, etc.; organic nonlinear optical materials include: organic low-molecular nonlinear optical materials, polymer nonlinear optical materials, etc.

[0070] Figure 10 Schematically illustrates the embodiment of the present disclosure using Figure 5 Schematic diagram of the addressing structure.

[0071] like Figure 10 As shown, the modulation unit of this embodiment includes: a gain medium C1, a Q-switched medium C2 and a nonlinear laser medium C3.

[0072] The gain medium C1 is used to amplify the received pump light to generate oscillating laser light.

[0073] The Q-switched medium C2 is used to perform saturation absorption and bleaching on the oscillating laser to generate pulsed laser.

[0074] The nonlinear laser medium C3 is used to perform nonlinear frequency conversion on the received pulse laser to output frequency-converted pulse laser as the addressing laser.

[0075] In the embodiment of the present disclosure, the VCSEL array pump laser 1 emits the VCSEL pump light 2 in a top emission manner, and the absorption spectrum of the laser gain medium C1 can be well matched with the wavelength of the VCSEL pump light 2 .

[0076] A dielectric film layer R1 is coated on the surface of the laser gain crystal C1 facing the VCSEL array laser 1, which emits regional or multi-region alternating light. This layer provides high transparency for the VCSEL pump light 2 and high reflection for the Q-switched laser light L2. The laser gain medium C1 is bonded to the Q-switched medium C2. The surface of the Q-switched medium C2, facing away from the laser gain medium C1, is coated with a dielectric film layer R3. This layer highly reflects the VCSEL pump light 2 and partially transmits the Q-switched laser light L2. The Q-switched medium C2 saturates and bleaches the Q-switched laser light L2, generating high-peak power pulsed laser light. The dielectric films R1 and R3 form the resonant cavity of a passively Q-switched laser. The laser gain medium C1 provides the initial gain for the resonant cavity, which oscillates the laser light. After the Q-switched medium C2 modulates the intracavity losses of the resonant cavity, passively Q-switched pulsed laser output is achieved. The Q-switched oscillation laser L2 serves as fundamental frequency light, and the nonlinear laser medium C3 performs nonlinear frequency conversion on the Q-switched oscillation laser L2, thereby generating a frequency-converted pulse laser L4.

[0077] Those skilled in the art will appreciate that various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, even if such combinations or combinations are not explicitly described in this disclosure. In particular, various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0078] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A high-brightness addressable solid-state laser array chip, characterized in that: include: First units arranged in an array, each of the first units comprising a plurality of vertical cavity surface emitting semiconductor lasers arranged in an array, the number of vertical cavity surface emitting semiconductor lasers in each unit being the same or different; The driving module is configured to drive the first unit in a predetermined area to emit light and drive a predetermined number of vertical cavity surface emitting semiconductor lasers in the first unit in the predetermined area to emit light, so as to output pump light of a predetermined shape. The modulation unit is configured to perform gain and / or modulation processing on the received pump light to output an addressing laser having the same predetermined shape as the pump light.

2. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The array arrangement of the first units includes a one-dimensional array arrangement, and the driving module includes: The driving circuit units are arranged in one dimension, and one driving circuit unit drives one first unit accordingly.

3. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The array arrangement of the first units includes a two-dimensional array arrangement, and the driving module includes: The driving circuit units are arranged in two dimensions, and a driving circuit unit in a first direction and a driving circuit unit in a second direction drive one first unit respectively, wherein the first direction and the second direction intersect.

4. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The predetermined shape includes a one-dimensional linear distribution, a two-dimensional array distribution, or a preset non-uniform distribution.

5. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The modulation unit includes: A gain medium is configured to amplify the received pump light to output oscillated laser light as the addressing laser light, wherein an absorption spectrum line of the gain medium matches a spectrum line of the pump light.

6. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The modulation unit includes: A gain medium, configured to amplify the received pump light to generate oscillating laser light; The Q-switched medium is used to perform saturation absorption and bleaching on the oscillating laser to output pulsed laser as addressing laser.

7. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The modulation unit includes: The nonlinear laser medium is used for performing nonlinear frequency conversion on the received pump light to output frequency-converted laser light as the addressing laser light.

8. The high-brightness addressable solid-state laser array chip according to claim 1, characterized in that: The modulation unit includes: A gain medium, configured to amplify the received pump light to generate oscillating laser light; A Q-switched medium, used for performing saturation absorption and bleaching on the oscillating laser to generate pulsed laser; The nonlinear laser medium is used for performing nonlinear frequency conversion on the received pulse laser to output frequency-converted pulse laser as addressing laser.

9. The high-brightness addressable solid-state laser array chip according to claim 5, characterized in that: The gain medium includes a first dielectric film layer and a second dielectric film layer, and the first dielectric film layer and the second dielectric film layer form a solid laser resonant cavity to generate oscillating laser.

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