188 results about "Laser optics" patented technology

The invention relates to the technical field of optical processing, and discloses an imaging depth adjustable laser optical processing system, which comprises a laser emission unit, an optical conduction unit, a spectral domain optical coherence tomography imaging unit, a laser galvanometer scanning unit, an indication light imaging unit, an image processing display unit and a control unit, according to the spectral domain optical coherence tomography imaging system, time scanning of high output wavelength is realized by utilizing a wavelength scanning mode that the scanning telescopic rotating module drives the spectral domain optical coherence tomography imaging system, and position information or image information of a sample from the surface to the interior is provided in real time in combination with an image processing technology; the three-dimensional galvanometer scanning unit scans the position of a sample in real time and records the position and orientation information of a scanning point at the same time, real-time image information and different depths, widths and axial positions of the sample are scanned at the same time, the focusing depth and wavelength of an imaging laser beam and the focusing position and energy of the scanning laser beam are fed back and adjusted, and the laser beam is positioned to the sample for machining.

An optical device includes: a first optical system; and a second optical system. The first optical system includes a first light splitting device configured to split measurement light emitted from a first light source into a first measurement light and a second measurement light and then mix the split measurement light, a first mirror configured to add a first modulation signal by being moved in an entering direction of the first measurement light and reflecting the first measurement light, a second mirror configured to reflect the second measurement light, and a first light receiving device configured to receive the measurement light including a sample-derived signal and the first modulation signal and output a first light receiving signal. The second optical system includes a second light source configured to emit laser light, an optical modulator configured to add a second modulation signal to the laser light, and a second light receiving device configured to receive the laser light including a displacement signal generated by reflection on the first mirror and the second modulation signal and output a second light receiving signal.

The invention relates to the field of optical elements, in particular to a coating method of a high-precision intense laser optical lens. The film coating method comprises the following steps: step 1, substrate pretreatment; step 2, surface activation; 3, a preparation stage; step 4, coating treatment; and step 5, post-processing. According to the method disclosed by the invention, the problems of adhesive force, uniformity, damage resistance and the like of a traditional method in strong laser lens coating are solved through fusion of double-plasma cooperation and a self-adaptive gradient composite coating technology. The method provided by the invention can be used for customized production for different laser scenes, and is suitable for high-end fields such as high-energy laser industry, quantum calculation, infrared imaging and the like.

The invention discloses a miniature camera and laser common-caliber optical system and a use method, and relates to the field of laser optical instruments. The problem that an existing multi-band common-caliber optical system cannot achieve integration, multi-functionalization and miniaturization at the same time is solved. The miniature camera and laser common-aperture optical system comprises a zoom optical lens group, a beam expanding telescope group, an electromagnetic galvanometer, a spectroscope, a fast reflecting mirror and a laser light source. The laser converging zoom optical lens group and the fine tracking imaging branch are respectively connected with the zoom cam lens cone and the fine tracking lens cone, the beam expanding telescope group is connected with the antenna frame, and the electromagnetic galvanometer, the spectroscope and the reflector are all connected with respective bases. The optical axis collinear coupling design is adopted among the components, it is ensured that a laser path and an image path are completely overlapped, and high-precision image guide striking control is achieved. The small mobile platform is suitable for industrial precision machining and rapid identification, high-precision tracking and laser precise striking of short-range dynamic targets.

A laser annealing system and a laser annealing method are provided. A laser annealing system for annealing a thin film by irradiating the thin film on a substrate with a pulsed laser light, the laser annealing system comprising: a laser device for outputting the pulsed laser light; an optical system that irradiates the thin film with pulse laser light; and a processor that performs control to irradiate the same portion of the thin film with the pulsed laser light by performing burst irradiation in which a burst period in which the pulsed laser light is continuously irradiated and a suppression period in which the irradiation of the pulsed laser light is suppressed are repeated.

The invention relates to a multi-beam space angle positioning device and a using method, and belongs to the technical field of laser optics, the multi-beam space angle positioning device comprises a main positioning plate and a secondary positioning plate which are coaxially arranged, a plurality of main positioning holes are formed in the main positioning plate, and the number of the main positioning holes is equal to that of laser beams; a plurality of main positioning holes are formed in the main positioning plate, the arrangement shape formed by the plurality of main positioning holes is the same as the arrangement shape of the plurality of laser beams focused to the same target spot, a plurality of secondary positioning holes are formed in the secondary positioning plate, and the number of the secondary positioning holes and the arrangement shape formed by the plurality of secondary positioning holes are the same as those of the main positioning holes; according to the multi-beam laser positioning device, the positioning problem in the application of the multi-beam laser technology in the prior art can be solved, the multi-beam positioning requirements of different space angles are met, and the multi-beam laser positioning device is simple in structure and suitable for table-board type or small-sized optical machine instruments.

The invention provides a Faraday sheet performance measurement and polarization imaging system and method, and relates to the technical field of optical testing. The system comprises a light source system, an optical research platform, a polarizer, a first analyzer, a microscopic imaging system and an image acquisition system, the light source system is used for emitting laser; the optical research platform is used for arranging a to-be-measured Faraday sheet and generating a magnetic field; the microscopic imaging system comprises an eyepiece and an objective lens, and the image acquisition system comprises an image acquisition mechanism; in the first propagation direction of the laser, the light source system, the polarizer, the Faraday piece to be measured, the objective lens, the first polarization analyzer, the eyepiece and the image acquisition mechanism are sequentially arranged. According to the Faraday piece performance measurement and polarized light imaging system, the laser polarization state is accurately controlled, the polarization direction change is accurately detected, and the amplification and focusing functions of a microscopic imaging system are combined, so that the accuracy and comprehensiveness of the performance test of the Faraday piece adopting a magneto-optical film are improved, and the test cost is reduced.

The invention belongs to the technical field of water-jet guided laser processing, and relates to a water-jet guided laser optical mode water beam correction method, which comprises the following steps of: 1, constructing a triangular geometrical relationship; 2, arranging measuring points and sensors; 3, establishing three-dimensional space coordinates; 4, designing a control system; 5, calculating a deviation angle; 6, adjusting a control algorithm; 7, signal processing and data transmission; 8, performing cooperative control on the correction process; 9, the water-light debugging process is completed, and water-guided laser machining is carried out; according to the invention, the triangulation principle and reasonable arrangement are utilized, the water beam deviation angle can be measured with high precision, the theoretical precision reaches a sub-degree level, the measurement error is small under various interferences, and reliable data are provided for correction; therefore, the correction precision is high, and the machining precision requirement can be met.

The utility model relates to an air-cooled optical fiber laser, belongs to the field of lasers, and aims to solve the problems of complex structure and large occupied space of the existing optical fiber laser. The air-cooled optical fiber laser comprises a shell, a pumping source, an optical assembly, a first optical fiber disc, a second optical fiber disc, a gain optical fiber and a cooling fan, and the shell is provided with a containing cavity; the pumping source is positioned in the accommodating cavity and is used for emitting laser; the optical assembly is used for amplifying and outputting the laser emitted by the pumping source; the first optical fiber disc is arranged opposite to the pumping source; the second optical fiber disc and the first optical fiber disc are arranged at an interval, the second optical fiber disc and the first optical fiber disc are both provided with fiber winding grooves, and the pumping source and the optical assembly are both located between the second optical fiber disc and the first optical fiber disc; the gain optical fiber is arranged in the fiber coiling groove; and the cooling fan is fixedly connected with the shell. As the pumping source and the optical assembly are both located between the second optical fiber disc and the first optical fiber disc, the air-cooled optical fiber laser is simplified in structure, and the occupied space is reduced.

A print engine of an additive manufacturing system includes a print station configured to hold a removable cartridge. A laser engine including a frame can be positioned to hold at least one removable field replaceable unit that includes at least some laser optics or patterning optics. An optical alignment system can be attached to at least one of the print station or the laser engine to align the field replaceable unit with respect to the removable cartridge.

The invention provides a laser processing device and method, and the device comprises a laser device which is used for emitting laser; the optical system comprises a collimating lens, a shaping lens and a focusing lens, the laser is collimated and amplified by the collimating lens and then enters the shaping lens, the incident laser is converted into a flat-topped light spot from a Gaussian light spot by the shaping lens, and the flat-topped light spot is positioned on a bonding interface by moving the position of the focusing lens; the displacement table system comprises a longitudinal displacement table and a horizontal displacement table, and the longitudinal displacement table is used for driving the focus lens to move synchronously, so that the flat-topped light spot is located on a bonding interface; the horizontal displacement table is used for driving the heterogeneous bonding material to move synchronously so as to realize that the flat-topped light spot scans the whole bonding interface; the in-situ observation system is used for obtaining light spot images of the surface and the bonding interface at at least one height measurement point; and the processing control system is used for obtaining the moving distance of the focus lens according to the light spot image of the height measurement point so as to adjust the position of the focus lens. According to the method, the bonding interface can be optimized.

The invention relates to a coated high-laser-damage-threshold high-reflectivity laser optical element and a preparation method thereof.The preparation method of the coated high-laser-damage-threshold high-reflectivity laser optical element comprises the following steps that (1) a substrate is subjected to ultrasonic cleaning, then Ar plasma generated by an anode ion source is adopted for cleaning the substrate, and a pre-cleaned substrate is obtained; (2) alternately carrying out high-refraction layer coating and low-refraction layer coating on the surface of the pre-cleaned substrate obtained in the step (1) to obtain a coated substrate; and coating a protective layer on the surface of the obtained coated substrate to obtain the coated high-laser-damage-threshold high-reflectivity laser optical element. According to the method, before high-refraction layer coating and low-refraction layer coating are carried out, the Ar plasma generated by the anode ion source is adopted to clean the substrate, and the laser damage threshold value of the high-reflectivity laser optical element composed of the thin film and the substrate is remarkably increased.

A laser optics experiment kit comprises a puzzle-style baseplate; an adapter plate configured to releasably attach to the baseplate; a plurality of components configured to attach to the adapter plate and baseplate, including: a laser holder; a mirror mount assembly; a beamsplitter mount assembly; an iris mount assembly; a lens mount assembly; and a rotation plate assembly a baseplate; an adapter plate configured to directly attach to the baseplate; a plurality of adapter components configured to releasably attach in varying angular positions to the adapter plate, including: a mirror mount assembly; a beamsplitter assembly; an iris mount assembly; a lens mount assembly; and a viewing panel.

Laser welding device (1) for producing a welded joint (S) in the area of ​​a joint between at least two components (2, 3) by means of an emitted laser beam (LS) with - a laser scanner (4), having - at least one laser emitter (4.1) designed to emit laser radiation (L), and - at least one laser optic (4.2) designed to shape, direct and focus the emitted laser radiation (L) to form the laser beam (LS), - a measuring unit (4.3) which is designed, - to emit at least one measuring beam (MS) in such a way that it is guided to a predetermined point of impact on at least one of the components (2, 3), - to detect reflected components of the measuring beam (MS) and - to automatically determine depth data of the point of impact based on optical coherence tomography using measurement beam data (MD1 to MD3) determined from the reflected components, - a control unit (4.4) which is designed, - before welding, the measuring unit (4.3) is controlled so that it automatically scans a surface of the components (2, 3) in a grid-like scan movement using a measuring beam (MS), automatically determines geometric parameters of the components (2, 3) from depth data determined at the respective point of impact from measuring beam data (MD1), and stores the parameters as reference data in a database for different positions of the surface of the components (2, 3). - then, during welding, to control the laser scanner (4) so ​​that it directs the laser beam (LS) onto the surfaces of the components (2, 3) and at least partially melts the components (2, 3), and simultaneously to control the measuring unit (4.3) so that it automatically scans a generated melt (SM) using a measuring beam (MS) in a scanning motion and automatically determines depth data of a vapor capillary (DK) generated in the melt (SM) based on optical coherence tomography for different positions of the melt (SM) from measuring beam data (MD2), and - to compare the position-related depth data of the vapor capillary (DK) with the position-related reference data in a comparison process carried out simultaneously with or following welding, and to determine a position-related comparison depth of the vapor capillary (DK) in comparison to an initial state of the components (2, 3) existing before welding, wherein the measuring unit (4.3) is configured to emit at least one measuring beam (MS) into the at least one laser optic (4.2) in such a way that it is guided together with the laser beam (LS) to its point of impact.

The laser annealing system includes: a laser system; and a laser annealing device, which irradiates a first pulse laser and a second pulse laser to an irradiated object, the laser annealing device includes: an irradiation optical system, which guides the first pulse laser and the second pulse laser to the irradiated object; a moving mechanism, which causes the irradiation positions of the first pulse laser and the second pulse laser to move relative to the irradiation position of the irradiated object; and a control unit, which controls the laser system so that the irradiated object is irradiated with the first pulse laser, and after the irradiation with the first pulse laser, the area of ​​the irradiated object irradiated with the first pulse laser is irradiated with the second pulse laser, the laser system includes: a laser oscillator, which outputs a pulse laser; an optical pulse stretcher, which stretches the pulse laser output from the laser oscillator; and a gate, which is arranged on a delay optical path of the optical pulse stretcher, and the control unit controls the output of the first pulse laser and the second pulse laser by controlling the opening and closing of the gate.

The invention relates to a method for surface treatment of a cylindrical housing (110) of an electrical energy storage device (100) made of metal by means of laser structuring, wherein the housing (110) has a housing shell (120) and an upper housing cover (111) surrounded by the housing shell (120) and a lower housing cover (112) surrounded by the housing shell (120), and the housing shell (120) is surface treated.According to the invention, during surface treatment, the housing (120) is guided in a holder (500) in a rotating manner such that a distance of a surface (130) of the housing shell (120) to a laser optics (200) emitting at least one laser beam (210) onto the surface (130), in particular a focus position of the laser optics (200), is kept constant and at least one structure (300, 310) is produced in the surface (130) surrounding the housing shell (120) by means of the at least one laser beam (210).

The application belongs to the technical field of laser optics, and particularly relates to a heat distortion resistant mirror seat for a high-power laser system; the mirror seat comprises a seat body, a plurality of convex bosses for limiting a mirror are arranged on the inner side wall of the seat body, a contact plate for bearing the mirror is arranged in the frame of the seat body, a group of heat dissipation fins are arranged on the bottom of the contact plate, flexible grooves and threaded holes are respectively arranged in the frame of the seat body at positions corresponding to the convex bosses, a flexible pressing ring is fixed to the top end of the seat body through the threaded holes and is used for pressing the mirror, mounting holes corresponding to the threaded holes are arranged on the flexible pressing ring, and a flexible groove of the pressing ring is arranged on the inner side of each mounting hole; the application is suitable for the working condition that the temperature of the mirror continuously rises, can effectively reduce the temperature level of the mirror, and effectively solves the mirror surface shape distortion problem caused by the fact that the mirror seat extrudes the mirror due to the mismatch of the thermal expansion coefficients of the mirror seat and the mirror.

The application relates to the technical field of optical processing, and discloses a laser optical processing system with adjustable imaging depth, which comprises a laser emission unit, an optical transmission unit, a spectral domain optical coherence tomography unit, a laser galvanometer scanning unit, an indicating light imaging unit, an image processing and display unit and a control unit. The wavelength scanning mode of the spectral domain optical coherence tomography system is driven by a scanning telescopic rotating module, time scanning of high output wavelength is realized, image processing technology is combined to provide position information or image information of a sample from a surface to an interior in real time, the position of the sample is scanned in real time by a three-dimensional galvanometer scanning unit, the position and directional information of a scanning point are recorded, the real-time image information of the sample is simultaneously scanned, different depths, widths and axial positions are realized, the focusing depth and wavelength of an imaging laser beam, the focusing position and energy of a scanning laser beam are adjusted and fed back, and the sample is positioned for processing.

A Raman fiber laser includes a pump light source, a reflective end mirror, a wavelength division multiplexer, a Raman gain fiber, and an output end mirror. The output end mirror is an ultra-low reflectance fiber Bragg grating. The reflective end mirror is connected to a reflective end of the wavelength division multiplexer. The pump light source is connected to an input end of the wavelength division multiplexer. One end of the Raman gain fiber is connected to a common end of the wavelength division multiplexer, and the other end of the Raman gain fiber is connected to the ultra-low reflectance fiber Bragg grating. The laser of the present invention can reduce loss of laser light at the reflective end mirror, thereby increasing laser light optical conversion efficiency and output power, and simultaneously achieving high time domain stability and extremely low coherence.

A laser interferometer includes: a laser light source configured to emit first laser light; an optical modulator including a vibration element that generates a vibration component in a direction intersecting an incident surface of the first laser light, and configured to modulate the first laser light by using the vibration element to generate second laser light including a modulation signal; a photodetector configured to receive the second laser light and third laser light that includes a sample signal generated by the first laser light being reflected by an object, and output a light reception signal; a demodulation circuit configured to demodulate the sample signal from the light reception signal based on a reference signal; and an oscillation circuit configured to operate using the vibration element as a signal source and output the reference signal to the demodulation circuit.

The invention relates to the technical field of solid lasers, and particularly provides a narrow-linewidth tunable dual-wavelength laser output system based on data driving, which comprises a pumping source, a resonant cavity, a data acquisition unit and a data receiving and driving device, a single gain medium, two F-P etalon and an F-P angle regulator are arranged in the resonant cavity, the inclination angles of the two F-P etalon are adjusted through an F-P angle adjuster so as to perform longitudinal mode selection and wavelength tuning on the output laser of the resonant cavity; a neural network screening model is arranged in the data receiving and driving device, the neural network screening model is used for learning the mapping relation between intracavity parameters and output laser optical parameters, and dual-wavelength simultaneous locking and line width prediction are achieved through dual-etalon collaborative mode selection and data driving of the neural network screening model. According to the invention, the complexity of the system is greatly simplified, and dual-wavelength, narrow-linewidth, high-stability, repeatable and automatic laser output regulation and control which cannot be achieved by a traditional architecture are realized functionally.

The present application relates to the technical field of geophysical exploration, in particular to a downhole three-component magnetic field sensing system based on atomic magnetometer. The downhole three-component atomic magnetic field sensor is connected with the optical fiber signal modem in the ground well logging vehicle through the armored photoelectric composite cable. The optical fiber signal modem is used for real-time demodulation of the three-component magnetic field signals and three-component attitude signals measured by the three-component atomic magnetic field sensor. The three-component atomic magnetic field sensor comprises a non-magnetic high-temperature packaging structure, a high-temperature-resistant atomic gas chamber module, a three-axis orthogonal laser optical system, a high-temperature-resistant photoelectric detection array, a power management module, a temperature sensor, a magnetic field solving and signal processing unit and a three-component optical fiber attitude sensor which are arranged in the non-magnetic high-temperature packaging structure. The three-component atomic magnetic field sensor adopts the atomic magnetometer measurement principle, combines the high-temperature-resistant materials and the optimized heat dissipation design, and can work stably in an environment of up to 200 DEG C.

The invention discloses a beta distribution-based composite aberration construction method, which relates to the technical field of laser optics and comprises the following steps of: constructing a non-ideal laser initial light field; generating a Zernike polynomial weight coefficient based on a beta distribution model; substituting the weight coefficient into the phase expression to form a composite aberration mode, and substituting the composite aberration mode into the non-ideal laser initial light field to obtain a non-ideal laser initial light field with composite aberration; repeating the steps, generating N groups of different weight coefficient combinations corresponding to N composite aberration scenes, simulating transmission evolution of laser in atmospheric turbulence by adopting a multi-layer phase screen method for each group of aberrations, and performing simulation calculation; a simulation result change rule is observed by changing parameters of the beta distribution model, and a parameter-light spot quality mapping relation is established. According to the method, the beta distribution model is introduced, a brand new technical path is provided for flexible construction and high-precision simulation of the composite aberration, and the reliability and efficiency of laser optical system design can be effectively improved.

The invention provides a stress measuring device for glass and an optical element. A light emitting unit is used for emitting laser; the optical element comprises a first surface and a second surface, the laser emission direction of the light emission unit faces the first surface, the second surface is in contact with to-be-detected glass, and the acquisition unit is used for acquiring scattered light and processing the scattered light into data signals; the processing unit is used for determining stress distribution in the to-be-detected glass according to the data signal; wherein a plurality of supporting pieces are arranged on the second surface. Therefore, the matched refractive index liquid can be arranged between the prism and the to-be-measured glass, air is expelled, refractive index deviation of laser passing through the three media is reduced, light loss caused by an interface is reduced, and meanwhile, the problem of inaccurate measurement caused by relative sliding of the to-be-measured glass during measurement due to the refractive index matching liquid is solved.

The invention discloses a frequency-variable light source capable of covering a vacuum ultraviolet band based on a frequency conversion system, and belongs to the technical field of laser optics and nonlinear optics. The device comprises an infrared or visible light wave band laser, an optical frequency conversion device, an amplitude and pulse adjusting device, a frequency selection resonant cavity, a higher harmonic module and a light source output coupling module. A frequency converter and a wavelength selection resonant cavity are added behind a laser source, so that the original single-frequency light is converted into other wavelengths through frequency conversion, then the light is converted into an ultraviolet band through a higher harmonic method, and a light source with any adjustable frequency in a vacuum ultraviolet band range is realized. By means of a method of adopting a nonlinear crystal, an inflatable photonic crystal fiber and a higher harmonic module, broadband spectrum frequency conversion operation is implemented, and a vacuum ultraviolet wave band covered after final frequency conversion reaches the range of 100-300 nm. By adding an amplitude and pulse width adjusting device behind the wavelength selection resonant cavity, the pulse width adjustment of the generated laser can be realized.

The application provides an objective refraction system and method of refractive state, comprising: a laser light source emitting three beams of blue laser, green laser and infrared laser, an optical beam splitter splitting the three beams into a reference light path and a measurement light path; a plane mirror reflecting the reference light path back to the original path and being received by an interference measurement device; a light adjusting device refracting the measurement light path to realize range measurement of a measurement object, the refracted measurement light path being reflected back to the original path by the measurement object and then being received by the interference measurement device; then, the interference measurement device obtains an interference measurement signal according to the incident measurement light path and the reference light path, a data processing device obtains refractive factor data of the measurement object according to the interference measurement signal, and obtains refractive refraction data of the measurement object according to the refractive factor data. The application can realize the ophthalmic examination that can be completed by multiple devices through one measurement, can quickly understand the real state of the eyeball and judge the myopia condition, and improves the myopia examination efficiency.

A handheld laser trimming and welding device can include a handheld laser trimming and welding wand and a nozzle. The nozzle can extend from the handheld laser trimming and welding wand to a distal portion, and the nozzle can have an aperture on the distal portion. The distal portion of the nozzle can be configured to optically communicate a laser to the distal portion of the nozzle and fluidically communicate a pressurized gas to the distal portion of the nozzle.

The present application relates to a thermal-optical characteristic measurement system and method, in particular to a thermal-optical characteristic comprehensive measurement system and method of a high-power laser optical lens, which is used to solve the problems of scene limitation, single information acquisition and lack of mutual inspection means in the measurement of the thermal-optical characteristic of a high-power laser system by using a laser focal point analyzer. The thermal-optical characteristic comprehensive measurement system of the high-power laser optical lens comprises a laser light source, a first rotating high-reflection mirror, a second rotating high-reflection mirror and a control computer, wherein the laser light source comprises a high-power laser light source and a low-power laser light source, which are perpendicular to each other and intersect. The present application realizes the consistency of the optical paths of the high-power laser and the low-power laser in the lens measurement area by using the first rotating high-reflection mirror and the second rotating high-reflection mirror, realizes the common optical axis of the two optical paths in the measurement process, and reduces the error of the measurement system.

A method of laser-based high temperature mechanical property characterization comprising the steps of providing a mechanical test frame and chamber, loading a specimen in the mechanical test frame in the chamber, providing a laser, aligning the laser, sealing the chamber, evacuating 5 the chamber and optionally backfilling with a prescribed atmosphere, turning on the laser, applying mechanical loading to the specimen in the mechanical test frame, utilizing a load cell and a non-contact video extensometer, synchronizing the output of the load cell and non-contact video extensometer, and tracking the strain in the specimen. A device for laser-based high temperature mechanical property characterization comprising a vacuum chamber with a laser 10 transmissible window and viewing window, a vacuum pump, a uniaxial tensile system inside the vacuum chamber, a thermocouple inside the vacuum chamber, laser optics inside the vacuum chamber, a function generator, a laser source, an IR camera, and a video camera.

A catheter for debulking of an undesired deposit from an inner surface of at least one of a blood vessel wall and a stent located in a blood vessel, the catheter having a tip section comprising: circumferentially-directed laser optics; and a circular-action cutter, wherein said circumferentially-directed laser optics is configured to transmit laser radiation for modifying an area of the undesired deposit thereby preparing said area for penetration of said cutter, wherein said cutter is configured to cut through said modified area and thereby debulk at least a part of the undesired deposit. In addition, a catheter for pacemakers and ICD (Implantable Cardioverter Defibrillator) lead extraction is disclosed.