RU2603819C2 - Optoacoustic lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to spectroscopy of condensed media and photoacoustic analysis of materials. Optoacoustic lens has an acoustic line with annular piezoelectric transducer at its one end, acoustic lens at its other end and point-to-point cylindrical channel in the central part and optical fibre placed in the cylindrical channel, as well as an adapter equipped with side nozzle for introduction of an immersion liquid. One end of the adapter is fixed in the channel at the side of the piezoelectric converter, and the second end is equipped with a sealing sleeve for sealing the optical fibre. Channel diameter and inner diameter of the adapter exceed the diameter of the optical fibre at value facilitating passage of an immersion liquid from the nozzle to acoustic lens.

EFFECT: providing an immersion liquid supply directly to the scanning region through the channel in the acoustic line of optoacoustic lens simplified design, possibility to vary the depth of probing and focusing zone of the laser radiation during examination.

4 cl, 4 dwg

Description

The invention relates to the field of condensed matter spectroscopy and photoacoustic analysis of materials and can be used as a lens of devices for photoacoustic visualization of microobjects and non-destructive testing of the surface and surface layer of materials in medicine, biology, nanotechnology and industry.

In known implementations, photoacoustic lenses have a multicomponent system of mirrors, prisms, lenses, or combinations thereof for focusing laser radiation, which complicates their design and manufacturing process. Also, in the known lens designs there is no system for adjustable focusing of laser radiation in the research process, which is of interest for volumetric analysis of the structure of the sample or for the detection of defects. In addition, for all known optical-acoustic lenses, it is necessary either to use a bath with immersion liquid or to apply a layer of immersion liquid to the scanning area before starting work. The use of the bath limits the use of such lenses in the study of samples at an angle to the horizon, samples with complex geometry, and also complicates the process of studying biological tissues in animals (immersion of the studied area of the animal in the bath requires its anesthesia.

In the case when the area under consideration is located in the area of the respiratory tract, a special air supply system is additionally required (articles: “Noninvasivelaser-induced photoacoustic tomography for structural and functional invivo imaging of the brain / Xueding Wang, YongjiangPang, Geng Ku, Xueyi Xie, George Stoica & Lihong V. Wang // Nature Biotechnology. - 2003, Vol. 21, pp. 803-806; Simultaneous Molecular and Hypoxia Imaging of Brain Tumors In Vivo Using Spectroscopic Photoacoustic Tomography / Meng-LinLi, Jung-TaekOh, XieX., Ku. G., WeiWang, ChunLi, Lungu. G., Stoica. G., Wang, LV // Proceedings of the IEEE.-2008, Vol. 96, Is. 3, pp. 481 - 489. doi: 10.1109 / JPROC. 2007.913515; Biomedical photoacoustic imaging / PaulBeard // Interface Focus.-2011, Vol. 1, pp. 602-631, doi: 10.1098 / rsfs.2011.0028), in addition, is absent in zmozhnost supply antireflective agents directly into the research area (which can be combined with the immersion liquid), which may significantly reduce the scan depth. Applying a layer of immersion fluid to the scan area requires special properties from immersion fluid, especially when working at an angle to the horizon, examining tissue in animals, and also when examining significant surface areas.

In the proposed invention, the laser focusing system is easy to manufacture and allows you to adjust the focus of the laser radiation in the research process (change the sounding depth). The immersion liquid in the proposed device is fed through a cylindrical channel in the sound duct of the optoacoustic lens (by using a special adapter), which allows the lens to be used in studies of samples at an angle to the horizon, samples with complex geometry and allows you to locally explore areas on the body of animals without using an immersion bath liquid.

Known portable device for photoacoustic microscopy, which is used to visualize biological tissues (patent US 2011/0201914 A1). The device contains a photoacoustic sensor (optoacoustic lens), which consists of a single or multicomponent piezoelectric transducer made in the form of an acoustic lens, a multicomponent and difficult to manufacture optical radiation focusing system (includes a high-precision lens system, a filter reflecting a baffle, an integrating camera, a diaphragm), electrical outlet, cylindrical beam housing. The optoacoustic lens is located in a hermetic bath (container) filled with immersion liquid. The base of the hermetic container bath is made of an optically and acoustically transparent membrane. Acoustic contact between the membrane and the test sample is achieved by immersing the sides of the container with the membrane in an immersion fluid.

The disadvantages of this optoacoustic lens are:

1) The complex design of the lens and, as a consequence, the complexity of its manufacture (in particular, the need to manufacture a high-precision and consistent system of lenses, mirrors, prisms, or a combination thereof to ensure focusing of laser radiation).

2) The lack of a system of adjustable focusing of laser radiation in the research process.

3) The need to use an airtight container bath with immersion liquid and immerse it in immersion liquid for acoustic contact between the sample and the ultrasonic sensor. This circumstance limits the scope of the device in question when studying samples at an angle to the horizon and ease of use. For example, to study biological tissues in animals (mice), it is necessary to immerse the test area in a bath, which requires anesthesia of the animal. In addition, if the area in question is in the area of the respiratory tract, a special air supply system is additionally required (articles: “Noninvasive laser-induced photoacoustic tomography for structural and functional invivo imaging of the brain / Xueding Wang, Yongjiang Pang, Geng Ku, Xueyi Xie , George Stoica & Lihong V Wang // Nature Biotechnology. - 2003, Vol. 21, pp. 803-806; Simultaneous Molecular and Hypoxia Imaging of Brain Tumors In Vivo Using Spectroscopic Photoacoustic Tomography / Meng-Lin Li, Jung-Taek Oh, Xie X ., Ku. G., Wei Wang, Chun Li, Lungu. G., Stoica. G., Wang, LV // Proceedings of the IEEE.-2008, Vol. 96, Is. 3, pp. 481 - 489. doi: 10.1109 / JPROC.2007.913515; Biomedical photoacoustic imaging / Paul Beard // Interface Focus.-2011, Vol. 1, pp. 602-631, doi: 10.1098 / rsfs.2011.0028).

A device for confocal photoacoustic microscopy is also known (patent US 8,454,512 B2). The device contains an optoacoustic cell (optoacoustic lens), which consists of a piezoelectric transducer, a multi-component system for focusing laser radiation (includes a high-precision system of lenses and prisms or mirrors, a micro-hole, a photodetector) in various variations, sound duct, acoustic lens. The role of the sound duct is performed by a rhomboid prism with a layer of silicone oil on one of the faces to reflect the acoustic signal.

The disadvantages of this design of the optoacoustic lens are:

1) The complexity of the design of the optoacoustic lens.

2) The complexity of manufacturing an optoacoustic lens, in particular

the need to manufacture a high-precision and consistent system of lenses, mirrors, prisms, or a combination thereof to ensure focusing of laser radiation.

3) The presence of reflections of the acoustic signal in the sound duct.

4) The use of a bath with immersion liquid for acoustic contact between the surface of the sample and the ultrasonic sensor limits the scope of the device in question when examining samples at an angle to the horizontal. Immersion bathtubs limit usability. For example, to study biological tissues in animals (mice), it is necessary to immerse the test area in a bath, which requires anesthesia of the animal. If the area in question is located in the area of the respiratory tract, then a special air supply system.

Closest to the claimed invention is an optoacoustic lens adopted for the prototype (US patent 5,381,695). The device comprises: a cylindrical sound duct, on one end of which an acoustic lens is made, on the surface of which or on the other end of the sound duct there is an acoustic piezoelectric transducer. A cylindrical channel is made in the center of the sound duct, in which an optical fiber is fixed for supplying light to the study area. An optical lens is fixed at the end of the optical fiber in the center of the acoustic lens, which allows focusing the light radiation at a desired distance.

The disadvantages of this device are:

1) The need to use a bath with immersion fluid or the use of special seals to prevent leakage of immersion fluid. This limits the scope of this solution.

2) The impossibility of tuning the depth of sounding and the focus area of the laser radiation during the experiment.

The technical result, the achievement of which the invention is directed, is:

1) Expanding the scope of application by providing the immersion fluid directly to the scanning area through the channel in the optical duct of the optoacoustic lens, which allows you to study samples at an angle to the horizon, samples with complex geometry, and also simplifies the process of studying biological tissues in animals (there is no need to immerse the studied areas of the animal in the bath and the introduction of a special air supply system).

2) Simplification of the design, since there is no need to use a bath with immersion liquid, seals.

3) The expansion of functionality, which is associated with the ability to change the sounding depth and the focus area of the laser radiation during the study due to a simple laser focusing system (changing the distance between the optical fiber and the optical lens), as well as by changing the caustics of the acoustic lens by changing the focal length coaxial multi-element converter.

The indicated technical result is achieved in that the optoacoustic lens comprising a sound duct with a piezoelectric ring transducer at one end thereof, an acoustic lens at its other end and a through cylindrical channel in the central part, the optical fiber placed in the cylindrical channel, according to the solution, comprises an adapter device provided with a lateral fitting for the introduction of immersion fluid, one end of the adapter is fixed in the channel from the side of the piezoelectric transducer, and W swarm end of the adapter is provided with a sealing sleeve for sealing the optical fiber, wherein the channel diameter and the inner diameter of the adapter to exceed the diameter of the fiber value allowing the passage of the immersion fluid from the union to the acoustic lens. An optical lens is fixed in the center of the spherical acoustic lens, and a gap is made between the lenses for supplying the immersion fluid from the cylindrical channel. An annular piezoelectric transducer is a coaxial multi-element structure, the elements of which are designed to be connected to a receiver or an electric signal source through separate phase shifters. A microtransfer device is attached to the sound duct, an optical fiber is attached to the movable part thereof, and the sleeve is configured to longitudinally move the optical fiber therein.

The invention is illustrated by drawings, where in FIG. 1 is a schematic representation of an optoacoustic lens; in FIG. 2 is a schematic illustration of an optoacoustic lens on the side of an acoustic lens; FIG. 3 is a schematic illustration of a transition device for the simultaneous introduction of optical fiber and the supply of immersion fluid; FIG. 4 - schematically shows a change in the focal length of an optical lens with a shift in the position of the optical fiber in the channel of the optoacoustic lens;

The positions in the drawings indicate:

1 - sound duct;

2 - channel;

3 - immersion fluid;

4 - optical fiber;

5 - source of immersion fluid;

6 - transition device;

7 - the case of the transition device with a side fitting;

8 - sealing sleeve;

9 - plate of lithium niobate;

10 - metal electrodes;

11 - an optical lens;

12 - mount optical lens;

13 - the investigated surface;

14 is a micro-moving device.

The optoacoustic lens (Fig. 1) contains a sound pipe 1 (for example, from dielectric single crystals: quartz, magnesium alloys, yttrium aluminum garnet, sapphire), which is, for example, a cylinder, parallelepiped or cone. In the central part of the sound duct, along its axis of symmetry, a cylindrical channel 2 is made, designed to bring the immersion fluid 3 into the study area. Also in the channel is placed optical fiber 4 for transmitting optical radiation. The diameter of the cylindrical channel in the sound duct exceeds the diameter of the optical fiber by an amount that ensures the passage of immersion fluid. In addition, the gap between the optical fiber and the surface of the cylindrical channel in the sound duct is configured to connect to the source of immersion fluid 5 by using a transition device 6. The transition device (Fig. 3) is provided with a side fitting 7 for introducing immersion fluid 3, one end of the transition device is fixed to a cylindrical channel of the sound duct, and the second end of the adapter is equipped with a sealing sleeve 8 for sealing the optical fiber 4, the inner diameter of the adapter being The diameter of the optical fiber is increased by an amount that ensures the passage of the immersion fluid from the side fitting into the cylindrical channel 2 of the sound duct. As an immersion liquid, for example, water, an ultrasound gel, castor oil, etc. can be used.

One of the end surfaces of the sound duct is made normal to the axis of symmetry of the sound duct. An annular piezoelectric transducer and an adapter 6 are located on this surface. An annular piezoelectric transducer can be made of a ferroelectric or piezoelectric plate located between metal electrodes, for example, plate 9 (for example, lithium niobate (LiNbO ₃ )), located between two metal (for example, silver ) electrodes 10. Also, the piezoelectric transducer may be a coaxial multi-element structure, the elements of which are connected with an electric signal source through separate phase shifters.

The opposite end of the lens (Fig. 2) is made in the form of an acoustic (for example, spherical) lens, in the center of which there is a hole in a cylindrical channel (the axis of the hole coincides with the axis of symmetry of the ring acoustic transducer and acoustic lens) and an optical lens 11 of spherical symmetry (made from natural or synthetic materials that are transparent in the appropriate range of optical radiation, such as quartz). Between the lenses there is a gap for supplying immersion fluid from a cylindrical channel. The optical lens is mounted on the sound duct, (for example, in three places at an angle of 120 °) 12 through the use of glue or mandrel. Changing the focus of the optical radiation to the test surface 13 is made by changing the distance between the end surface of the optical fiber 4 and the optical lens 11. The light radiation emerging from the optical fiber has a spherical front. In this regard, the focusing area behind the optical lens depends on the distance between the output end of the optical fiber and the optical lens. The position of the optical fiber is changed by moving it in the cylindrical channel of the sound pipe 2 with the help of a micro-moving device 14, which is rigidly connected to the sound pipe.

The essential features of the claimed invention:

1. The first essential feature of the invention is that on the side of the flat end of the sound duct there is a transition device having an opening for introducing optical fiber at the end end and a side fitting for introducing immersion liquid, the channel diameter and the inner diameter of the transition device exceeding the diameter of the optical fiber by an amount that provides the passage of immersion fluid from the nozzle to the acoustic lens.

2. The second distinguishing feature is that an optical lens is fixed in the center of the spherical acoustic lens, while a gap is made between the lenses for supplying the immersion fluid from the cylindrical channel.

3. The third distinguishing feature is that the piezoelectric transducer is a coaxial multi-element (at least two rings) structure, the elements of which are connected to the receiver / source of the electrical signal through separate phase shifters. In this case, the coaxially located elements of the transducer can be separate ring transducers, each of which has its own sublayer (lower electrode), a superlayer (upper electrode) and a piezoelectric layer located between two electrodes. In such an implementation, each of the elements is connected to the generator through its own phase shifter via a two-wire line. In another implementation, all elements have a common lower electrode (sublayer) and a common piezoelectric layer, and each element has separate upper electrodes (layers), so that all elements are connected to the generator by one common electrode (for example, a sublayer), and each element is connected to the generator through a separate phase extender by means of the second of the electrodes supplying energy (for example, a layer). In addition, the ratios of the outer and inner diameters of each ring, as well as the gap between the rings, are calculated on the basis of ensuring: 1) the conditions of focusing in a given region of the test sample; 2) the maximum ratio of the amplitudes of the zero and first lobes in the radiation pattern of the converter.

4. The fourth distinguishing feature is that a micromoving device is attached to the sound duct, an optical fiber is attached to the moving part thereof, and the adapter sleeve is capable of longitudinally moving the optical fiber in it. The presence of a micro-moving device allows tuning to the focus of the optical radiation supplied by the optical fiber.

Optoacoustic lens works as follows.

The studied object is placed in the focus area of the optoacoustic lens. To ensure acoustic contact between the sample and the optoacoustic lens, an immersion liquid is supplied through an adapter and a cylindrical channel in the optoacoustic lens. Pulse laser radiation is supplied through the input end of the optical fiber. Laser light passing through the optical fiber, incident on the optical lens, which focuses the radiation on the studied object. A change in the focusing of radiation (Fig. 4) is achieved by changing the distance between the output end of the optical fiber, where the optical radiation has a certain divergence, and the optical lens. The laser radiation energy is absorbed by the sample material (inhomogeneity in the sample under study), causing local heating and expansion of the sample (thermoelastic effect) with a duration proportional to the laser pulse duration. This local expansion, in turn, excites a pulsed acoustic wave. An acoustic impulse propagates in the studied object and is reflected from the interfaces. Spherical acoustic waves, propagating through the immersion liquid, fall on the surface of the acoustic lens, where they are converted into plane waves propagating through the sound pipe to the piezoelectric transducer, which transforms the acoustic signal into an electromagnetic one. The lens moves in two coordinates in a plane perpendicular to the direction of propagation of the laser beam using a scanning system.

After processing the received acoustic signal in the visualization unit, we obtain an image of the object under study.

The present invention is illustrated by a specific example of execution, which, however, is not the only possible, but clearly demonstrates the possibility of achieving the desired technical result. The optoacoustic lens contains a quartz sound duct, which is a cylinder, 20 mm high and 10 mm in diameter. A cylindrical channel with a diameter of ~ 0.8 mm is coaxially made in the sound duct. The channel contains optical fiber with a diameter of the central quartz core of 50 μm. One of the end surfaces of the sound duct is made normal to the axis of the sound duct. An annular piezoelectric transducer is located on this surface, which is a plate of lithium niobate (LiNbO ₃ ) placed between two silver electrodes, one of which serves as a bonding layer between the sound duct and the piezoelectric. The opposite end of the lens is made in the form of a spherical acoustic lens with a radius of 11 mm. In the center of the acoustic lens there is an opening of a cylindrical channel and an optical lens made of quartz in the form of a sphere with a diameter of ~ 0.6 mm. The gap between the lenses is ~ 0.2 mm. The optical lens is fixed to the sound duct through the use of glue. The immersion liquid (water) is fed into the gap between the optical fiber and the channel wall in the sound duct through a transition device having a sealing sleeve at the end end for introducing the optical fiber and a side fitting for introducing the immersion liquid.

The proposed design solution of the optoacoustic lens does not exclude the use of the optoacoustic lens without an optical lens or only with the supply of immersion liquid.

Claims (4)

one . An optoacoustic lens comprising a sound duct with an annular piezoelectric transducer at one end thereof, an acoustic lens at its other end and a through cylindrical channel in the central part, an optical fiber located in a cylindrical channel, characterized in that it comprises an adapter equipped with a lateral fitting for introducing an immersion liquid , one end of the adapter is fixed in the channel from the side of the piezoelectric transducer, and the other end of the adapter is provided with a seal guide bushing for sealing optical fiber, wherein the channel diameter and the inner diameter of the adapter to exceed the diameter of the fiber value allowing the passage of the immersion fluid from the union to the acoustic lens. 2. The optoacoustic lens according to claim 1, characterized in that an optical lens is fixed in the center of the spherical acoustic lens, and a gap is made between the lenses for supplying the immersion fluid from the cylindrical channel. 3. The optoacoustic lens according to claim 1, characterized in that the annular piezoelectric transducer is a coaxial multi-element structure, the elements of which are designed to connect to a receiver or source of an electric signal through separate phase shifters. 4. The optoacoustic lens according to claim 1, characterized in that a micromoving device is attached to the sound duct, an optical fiber is attached to the movable part thereof, and the sleeve is configured to longitudinally move the optical fiber therein.

Images