Device and method for particle testing

Abstract

A particle testing device (100) is configured for studying particles in a fluid medium, the particle testing device comprising: a waveguide device (10), the waveguide device comprising a hollow optical waveguide (11), the hollow optical waveguide having an input end (12) and an output end (13); an irradiation device (20), the irradiation device comprising a laser source (21), the laser source being arranged to optically capture at least one particle at the input end (12) of the optical waveguide (11) and to propel the particle through the optical waveguide (11) towards its output end (13); and a measurement device (30), the measurement device being arranged to sense the at least one particle in the optical waveguide (11), wherein the measurement device (30) is arranged to measure the optical transmission of the optical waveguide (11). Furthermore, a particle testing device is described.

Description

Technical Field

[0001] The present invention relates to a particle testing device for studying particles in a fluid medium, for example a gas or liquid environment, in particular using the detection of particles propelled in a hollow gas or liquid filled optical waveguide. Furthermore, the present invention relates to a particle testing method for studying particles in a fluid medium. Applications of the present invention are suitable, for example, in the field of environmental or material research or for monitoring chemical or physical processes. Background Art

[0002] In this specification, reference is made to the following prior art, which illustrates the technical background of the present invention, and related technologies:

[0003] [1] RS Gao et al., Aerosol Science and Technology 47, 137–145 (2013);

[0004] [2] Met One Instruments:

[0005] https: / / metone.com / indoor-controlled-environments / controlled-environments / model-804-handheld-particle-counter / ;

[0006] [3] X.-C. Yu et al., Light: Science and Applications 7, 18003 (2018);

[0007] [4] S. Unterkofler et al., Journal of Biophotonics 1, 10 (2012);

[0008] [5] OA Schmidt et al., Journal of the Optical Society 37, 91 (2012);

[0009] [6] F. Benabid et al., Optical Society Letters 10, 1195 (2002);

[0010] [7] EP 2 835 674 A1;

[0011] [8] WO 2006 / 110749 A3;

[0012] [9] US 8 552 363 B2; and

[0013]

[10] US 2009 / 0175586 A1.

[0014] It is known that due to the increasing pollution of the environment with pollutants such as fine dust and other particles generated by technological processes (especially traffic), there is a growing need to detect and study particles in the air (e.g. in the atmosphere). In addition, there is also interest in detecting particles in the local environment (e.g. in a closed room or reaction vessel). A wide range of particle sensing methods are known, including optical measurements, in which particles are detected based on their interaction with light.

[0015] FIG6 (Prior Art) schematically shows two examples of known optical measurements, including free-space scattering-based detection and waveguide scattering-based detection. Free-space scattering-based detection ( FIG6A , see, e.g., [1]) employs a probe laser 20 ′ and a photodetector 30 ′ arranged in a sample chamber. Particles 1 ′ passing through the laser beam path 10 ′ between the probe laser 20 ′ and the photodetector 30 ′ partially scatter the laser beam, so that the number of particles in the air can be counted.

[0016] Although the system of FIG. 6A has been well established and is commercially available [2], the free-space configuration may have the following disadvantages. First, particles of the same size may pass through the laser beam of the detection laser 20 (which typically has a Gaussian intensity profile) at different locations along the profile, resulting in different amounts of scattered light. Therefore, this method can only count the number of particles, but cannot accurately determine the particle size. In addition, the particles need to be delivered to the sample chamber via a carefully aligned gas jet to ensure overlap with the laser beam. Any misalignment that causes a deviation in the point at which the particle 1' passes through the laser beam path 10' will increase the uncertainty of the measurement.

[0017] For detection based on waveguide scattering ( FIG. 6B , see, for example, [ 3 ]), a tapered waveguide 11 ′ is arranged between a probe laser 20 ′ and a photodetector 30 ′. The laser beam is coupled into the tapered waveguide 11 ′. Particles 1 attached to the outer surface of the waveguide 11 ′ interact with the evanescent field of the guided mode and thus scatter a portion of the light which may be detected as a transmission drop at the photodetector 30 ′.

[0018] In contrast to the technique of FIG. 6A , detection based on waveguide scattering can both count the number of particles and determine the size of the particles. However, when applying the technique of FIG. 6B , the following disadvantages may occur. After a long period of operation, the continuous attachment of particles to the tapered waveguide 11 'will severely reduce the transmission of the waveguide 11 ' and, therefore, the sensing capability of the waveguide. Even without particle attachment, the tapered waveguide will degrade over time. Therefore, the total lifetime of the device is strictly limited. In addition, for reproducible measurements, it must be ensured that the particles attach to a predefined area of ​​the waveguide. As a further limitation, the drop in fiber transmission occurs only at the moment when the particle attaches to the waveguide 11 '. Therefore, the system is very sensitive to any external perturbations with similar characteristics (e.g., laser intensity or photodetector noise), thereby increasing the fault detection rate.

[0019] Further optical measurements using optical waveguides are described in [4] to [7] and

[10] , where particles move within the waveguide under gas or liquid filling conditions. In [4], biological cells in liquid suspension are trapped in a hollow fiber at a certain distance from the fiber inner wall. The cells are analyzed by complex Doppler velocimetry. According to [5] or

[10] , particles are trapped in a dual-beam trap formed by counter-propagating Gaussian laser beams and the particles are moved in an air-filled hollow-core photonic crystal fiber by moving the dual-beam trap. Similarly, in [6], particles are manipulated in air-filled hollow fibers using laser tweezers. According to [7], particles in optical fibers are used as sensor elements for detecting environmental conditions. The optical measurements of [4] to [7] and

[10] allow the detection of particle properties. However, since the methods for manipulating and sensing particles are very complex, there are great limitations in practical routine applications, such as when studying particles in air. According to

[10] , a transmission measurement is proposed which is achieved by adding another solid waveguide which interacts with the hollow waveguide in an orthogonal direction. This allows sensing of particle properties in a restricted manner only.

[0020] The manipulation of particles in optical fibers has also been described with reference to optical chromatography systems ([8]) and systems for sorting particles in fluid media ([9]). However, these systems do not allow the study of particles in a gas environment, in particular the determination of their number or size.

[0021] Purpose of the Invention

[0022] The object of the present invention is to provide an improved particle testing device and / or method for studying particles in a fluid medium (such as a gas or liquid environment) that avoids the limitations and disadvantages of conventional techniques. Specifically, the particle testing device and / or method should be able to sense particles while reducing the complexity of the device configuration, improving reliability, improving accuracy, extending the device life and / or expanding applications (e.g., conventional applications in environmental or other technical process-related testing). For example, the particle testing device should be able to count particles with improved accuracy and determine particle size and / or sense further particle characteristics. Summary of the invention

[0023] These objects are solved by a particle testing device and / or a particle testing method comprising the features of the independent claims. Advantageous embodiments and applications of the invention are defined in the dependent claims.

[0024] According to a first general aspect of the present invention, the above objects are solved by a particle testing device for studying particles in a fluid medium (such as a gas or liquid environment), the particle testing device comprising a waveguide device, an irradiation device and a measurement device. The term "particle testing" refers to sensing at least one particle characteristic of particles contained in a gas sample (gas or vapor sample) or a liquid sample.

[0025] The waveguide device comprises a hollow, straight or curved optical waveguide extending longitudinally from a first end to a second end. With respect to at least one particle introduced into and output from the optical waveguide, the first end and the second end are respectively referred to as an input end and an output end. The optical waveguide is a hollow waveguide which is in a gas or liquid filled state, that is, the internal hollow space of the optical waveguide comprises any gas or vapor or liquid that allows at least one particle to be transmitted through the optical waveguide, for example, a gas or vapor or liquid sample from a volume to be measured. Preferably, the optical waveguide is a hollow core photonic crystal fiber (HC-PCF) capable of accommodating gas or vapor or liquid. Alternatively, other types of hollow optical waveguides capable of guiding light, like other hollow optical fibers, may also be used. Preferably, the core diameter of the optical waveguide is selected in the range of 5 μm to 50 μm, in particular in the range of 10 μm to 20 μm.

[0026] The irradiation device comprises a laser source arranged for focused irradiation of the input end of the optical waveguide, in particular for optically trapping at least one particle at the input end, introducing at least one trapped particle into the optical waveguide, and propelling the particle along the optical waveguide towards its output end. The irradiation device is arranged for focused irradiation of the input end of the optical waveguide, preferably only from one side of the optical waveguide. The laser source preferably has a wavelength in the range of 400 nm to 2 μm, particularly preferably a wavelength in the visible or NIR wavelength range, and the laser source may comprise a continuous wave laser source or a pulsed laser source. The measuring device is arranged for optically sensing at least one particle in the optical waveguide.

[0027] In the case of the device according to the invention, the measuring device is arranged for measuring the optical transmission of the optical waveguide, preferably within a time interval comprising at least one particle moving through the optical waveguide. The inventors have found that the presence of at least one particle in the optical waveguide causes a scattering of the light field propagating in the optical waveguide, thereby affecting the optical transmission of the optical waveguide in a specific way and allowing at least one particle characteristic to be provided. The measuring device is arranged for sensing the light propagation through the optical waveguide. The measurement of the optical transmission comprises any type of sensing of the amplitude and / or amplitude variation of the light field travelling along the longitudinal extension of the optical waveguide. Preferably, the measuring device is suitable for measuring a time function of the optical transmission. The at least one particle characteristic obtained by the device of the invention is derived from the measured optical transmission and comprises, for example, the number of particles, the size of the particles and / or the refractive index of the particles.

[0028] According to a second general aspect of the present invention, the above-mentioned object is solved by a particle testing method for studying particles in a fluid medium (such as a gas or liquid environment), which particle testing method includes the following steps: providing a sample containing at least one particle at a hollow optical waveguide having an input end and an output end; optically capturing at least one particle at the input end of the optical waveguide and propelling the particle through the optical waveguide toward the output end using a laser source of an irradiation device; and sensing at least one particle in the optical waveguide.

[0029] In terms of the method according to the invention, at least one particle is sensed by measuring the optical transmission of the optical waveguide, in particular the optical transmission along the longitudinal extension of the optical waveguide, while advancing the at least one particle through the optical waveguide to obtain at least one particle characteristic. Preferably, the particle testing method is implemented using the particle testing device of the first general aspect of the invention.

[0030] Advantageously, the limitations of conventional techniques can be avoided by the present invention, i.e. coupling a laser beam from a laser source into an optical waveguide, preferably a hollow core fiber. The laser source is configured so that the laser beam has a sufficiently high optical power to capture particles in front of the end face of the waveguide input end and then propel the particles along the hollow core of the waveguide. The optical power can be selected according to the application conditions, for example by simulating the interaction of expected particles with the laser beam in a gas or liquid sample. In particular, measuring the optical transmission includes detecting the transmission drop and its duration using a measuring device (e.g., its photodetector). Therefore, at least the number of particles can be accurately counted and the particle size (particle sizing) can be determined. In particular, the flight time of the particles traveling through the waveguide can be obtained. The number of particles can be used as a qualitative measure to characterize the sample. Alternatively or in addition, the particle density in the sample can be derived based on the number of counted particles and reference data, in particular taking into account the conditions under which the particles are provided at the input end of the optical waveguide (e.g., in the housing) (see below).

[0031] Preferably, the optical waveguide is designed to meet the following criteria. First, the optical waveguide preferably guides the laser beam with low transmission loss, i.e., the transmission loss of the optical waveguide in the absence of particles is low enough so that the transmission change caused by the presence of particles can be sensed. Second, the modal area of ​​the optical waveguide is preferably small enough to capture the particles in front of the fiber end face. Third, by selecting a suitable core diameter and transmission characteristics of the optical waveguide according to the particle diameter and material (refractive index) of the optical waveguide, the amount of scattered light preferably provides an optimized size resolution on the photodetector.

[0032] Compared to existing particle counting and sizing techniques, the system of the present invention specifically provides the following advantages.

[0033] The measurement of optical transmission is a relatively simple, well-established measurement technique, particularly allowing the use of a single photodetector (such as a photodiode) and providing a compact device configuration.

[0034] The optical force generated by the laser beam captures the particles and aligns them close to the core center of the optical waveguide so that the particles can pass through the entire optical waveguide, especially the HC-PCF, without being attached to the inner core wall. Therefore, the particle test device provides the functions of particle counting and sizing without being affected by any waveguide degradation. Therefore, the life of the particle test device is not limited.

[0035] The particles to be sensed are aligned with the core center of the optical waveguide by optical forces, making their trajectories within the core highly predictable. This provides the advantage that the same amount of light is scattered from particles of the same material and the same size. Thus, the system of the invention provides a particle sizing function with high accuracy and fully reproducible results.

[0036] The use of an optical waveguide allows the particle to pass through it for a finite duration given by the speed at which it travels. Thus, as the time window increases, the transmission in the measurement device decreases, making the system robust to external perturbations.

[0037] The travel time (time of flight) of a particle through the core of an optical waveguide depends on its size and refractive index, allowing the system to provide additional information about the particle's properties.

[0038] The use of optical waveguides and the presence of optical trapping forces greatly reduce or even avoid the requirement for alignment of the particle jet relative to the fiber.

[0039] Particle testing can be expanded to include single or multiple laser sources and combined with hollow core optical fiber arrays to further increase the detection area and efficiency of particle testing.

[0040] Finally, the present invention has a variety of applications including air or water pollution monitoring and / or indoor particle monitoring.

[0041] According to a preferred embodiment of the invention, the particle testing apparatus further comprises an analysis device coupled to the measuring device and arranged to provide at least one particle characteristic. The analysis device is adapted to receive an output signal of the measuring device representing the optical transmission of the waveguide device and to provide at least one particle characteristic based on the output signal. Thus, the analysis device is preferably a computer running software that calculates at least one particle characteristic from the measured optical transmission based on a predetermined model.

[0042] Particularly preferably, the analysis device is adapted to provide at least one of the number of particles, the size of the particles, the mass of the particles and the refractive index of the particles as at least one particle characteristic. In addition or alternatively, the analysis device is adapted to provide at least one particle characteristic based on the measured particle induced change of the optical transmission. Advantageously, the analysis of the optical transmission is facilitated. In the latter case, according to a particularly preferred embodiment of the present invention, the analysis device is adapted to provide at least one particle by analyzing the duration, amplitude and / or waveform of the measured particle induced change of the optical transmission. Advantageously, analyzing the output signal of the photodetector may include applying a model that assigns the measured value of the transmission drop during particle propagation and / or the duration of the transmission drop and / or the time shape of the transmission drop to the occurrence of the particle and the size of the particle, thereby allowing particle counting and sizing. The model may be based on calibration data collected using reference particles with known particle characteristics and / or based on numerical simulations.

[0043] According to a particularly preferred embodiment of the present invention, the laser source is arranged for the following two operations: illuminating the optical waveguide to optically capture and propel at least one particle; and measuring the optical transmission of the optical waveguide. Therefore, the laser source can be provided as a measurement light source for the measurement device. Advantageously, since the laser source realizes a dual function, the provision of an additional measurement light source can be avoided by this embodiment, thereby further reducing the complexity of the configuration.

[0044] Alternatively, the measuring device for measuring the optical transmission may include a measuring light source, such as a measuring laser source, which is additionally provided to the laser source for optically capturing and propelling at least one particle. The output emissions of the capturing and propelling laser source and the measuring light source may be superimposed at the input end of the optical waveguide, for example using a beam splitter component. Providing separate sources for capturing and propelling or measuring the optical transmission may have advantages in adapting the sources to their functions. For example, the laser source for capturing and propelling at least one particle may have higher power and higher noise than a measuring light source for measuring the optical transmission having less power and noise. Therefore, the signal quality of the measured transmission may be improved while improving the reliability of capturing and propelling the particles.

[0045] Further specific advantages of the present invention may be obtained if the particle testing device has at least one of the following features. The irradiation device may include a first single-mode fiber having an input end and an output end. The input end of the first single-mode fiber is coupled to the output of the laser source. A first imaging lens (preferably a first gradient refractive index lens (GRIN lens)) is arranged at the output end of the first single-mode fiber for focusing the laser to the input end of the optical waveguide. Advantageously, this configuration improves the efficiency of relaying the laser beam from the laser source to the input end of the optical waveguide and capturing particles. Thus, for a given optical power, larger particles and / or particles with a lower refractive index can be captured, or, in order to capture particles of a specific size and refractive index, a smaller optical power can be used.

[0046] Additionally or alternatively, the measuring device preferably comprises a photodiode and a second single mode fiber having an input end and an output end. The output end of the second single mode fiber is coupled to the photodiode. A second imaging lens (preferably a second GRIN lens) is arranged at the input end of the second single mode fiber for collecting light from the output end of the optical waveguide into the second single mode fiber. Advantageously, by providing a photodiode with a second single mode fiber and a second imaging lens, the sensitivity of the transmission measurement can be increased. The use of a GRIN lens has particular advantages in terms of small size lenses.

[0047] According to another advantageous embodiment of the present invention, the particle testing device comprises a housing (test chamber) which accommodates an optical waveguide. The laser source and the photodetector of the measuring device are arranged outside the housing. A transparent window is arranged in the housing wall at the opposite side of the housing for coupling light from the laser source into the housing and coupling light transmitted through the optical waveguide to the outside of the housing. The optical waveguide is positioned in the housing, which is aligned with the transparent window but the input and output ends are at a certain distance from the transparent window. In addition, the housing is suitable for flow through operation, in which the gas or vapor or liquid sample to be tested flows through the housing. To this end, the supply section is arranged for supplying the sample to be studied into the housing, and the discharge section is arranged for guiding the sample to the outside of the housing. The use of the housing has special advantages in providing a protective environment, for example, protecting the capture of particles entering the optical waveguide from the influence of outflows (such as wind during environmental measurements), and / or preventing the sample to be tested from contaminating the measurement site.

[0048] As a further advantage, the particle test of the present invention has a wide range of applications including monitoring air pollution (eg in an atmospheric environment), monitoring gases from machines, particularly vehicles and / or monitoring the type and / or size of dust in an environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further advantages and details of the present invention are shown below, with reference to the accompanying drawings, which are schematically shown as follows:

[0050] Figure 1 : Features of a preferred embodiment of a particle testing device according to the present invention;

[0051] Figures 2 to 5 : Experimental results obtained using an embodiment of a particle testing method according to the present invention; and

[0052] Figure 6: Illustration of conventional optical measurement of airborne particles (prior art). DETAILED DESCRIPTION

[0053] Embodiments of the present invention are described below with particular reference to particle testing using HC-PCF. The present invention is not limited to this embodiment, but can be implemented using other hollow waveguide types such as capillaries, ARROW waveguides. The details of collecting and optionally further preparing the sample to be tested are not described, because the sample collection and preparation techniques themselves are known according to conventional analytical techniques. For example, the sample can be collected by sucking or collecting part of the air or other reaction gas or sample liquid from the environment or a closed space. The present invention is suitable for testing samples under gas or liquid conditions. Specifically, the liquid sample can be directly tested by guiding the liquid sample through an optical waveguide, or by converting the liquid sample into a gas state, for example using a medical nebulizer, while maintaining particles that may be present in the sample.

[0054] A single-channel embodiment of the particle testing device of the present invention is described in an exemplary manner. In practical applications of the present invention, a multi-channel embodiment of the particle testing device of the present invention may be provided, including a fiber array as described below.

[0055] according to Figure 1 , an embodiment of a particle testing device 100 comprises: a waveguide device 10, which is provided by a straight or curved HC-PCF 11, having an input end 12 and an output end 13; an irradiation device 20, which has a laser source 21; a first optical fiber 22 and a first GRIN lens 23; and a measurement device 30, which has a photodiode 31 or another type of photodetector. For a practical example, the core diameter of the HC-PCF 11 is 10μm to 20μm. Preferably, the length of the HC-PCF 11 is selected so that the travel time of the particle is longer than the duration required for the transmission change at the beginning and end of the transmission drop caused by the particle, and the length is, for example, 5cm. For example, the laser source 21 is a fiber laser or a fiber-coupled diode laser with an emission wavelength of 1064nm and an output power of 500mW, providing an optical field power of about 400mW at the focus produced by the first GRIN lens 23 at the input end 12. The laser source 21 may be coupled to a measuring device 30 and / or an analyzing device 40, for example for adjusting the power of the laser beam according to the waveform of the optical transmission and thus adjusting the propulsion speed of the particles through the HC-PCF 11 (loop control).

[0056] The measuring device 30 is connected to an analyzing device 40 for analyzing the output signal of the photodiode 31. The analyzing device 40 is shown as a separate component, for example provided by a computer coupled to the photodiode. Alternatively, the functionality of the analyzing device 40 may be provided by a portion of the measuring device 30, for example, a control computer that controls the operation of its photodetector (such as the photodiode 31). Therefore, the separate analyzing device 40 may be considered an optional feature of the particle testing apparatus 100.

[0057] The HC-PCF 11 is arranged in a housing 50 having a housing wall with two transparent windows 51 made of, for example, glass. Preferably, the housing wall is made of an airtight and liquid-tight material such as plastic or metal. The housing 50 is provided with a supply section 52 and a discharge section 53. The supply section 52 comprises, for example, a supply pipe (partially shown) or any other opening connected to the space to be inspected. The sample containing particles is guided into the housing 50 via the supply pipe. In order to drive the flow through the housing 50, the discharge section 53 comprises a pump that draws gas out of the housing 50. The pump can be coupled to the measuring device 30 and / or the analyzing device 40, for example, for adjusting the flow rate of the sample through the housing 50 according to the number of particles present in the sample (loop control).

[0058] The particle testing device 100 provides a system that is preferably capable of counting and sizing particles (e.g., particles in the air or particles in an environmental water sample), which consists of a laser source 21, a HC-PCF 11, and a photodiode 31. The particulate matter will enter the housing 50 through a supply section 52 and leave from another supply section with the help of a pump. This supports a constant gas flow or vapor flow within the housing 50. The laser beam generated by the laser source 21 captures the particles at the input end 12 of the HC-PCF 11, and the laser beam is coupled into the core of the HC-PCF 11 and propels the particles along the fiber core of the HC-PCF 11. Within the HC-PCF 11, the particles captured at the input end 12 are held in an optical trap extending perpendicularly to the longitudinal direction of the optical waveguide. Propulsion is achieved by the irradiation pressure effect of the laser field in the HC-PCF 11.

[0059] Each particle 1 scatters a portion of the guided core light, the amount of scattered light depending on the particle size and refractive index, enabling real-time counting of the number of particles as well as measurement of particle size by monitoring the fiber transmission via a photodiode 31. The use of the HC-PCF 11 has the particular advantage that particles can be aligned and propelled in the hollow core by optical forces, so that particle counting can be achieved in a non-degradable manner, providing an unlimited device lifetime, while the particle size can be accurately determined, for example, as described below. The design of the HC-PCF 11 and the wavelength of the laser source 21 are selected so that the capture and guidance of the particles 1 within the core is efficient, while the amount of scattered light from the particles 1 provides an optimized size resolution on the photodiode 31. The transmitted laser beam of the laser source 21 is collected in the photodiode 31, which is connected to a computer for data analysis as is the analysis device 40.

[0060] For a multi-channel embodiment of the particle testing apparatus (not shown) of the present invention, a plurality of HC PCFs are arranged, for example, Figure 1 As shown, each HC PCF has a core diameter and transmission characteristics optimized for a specific particle type. Each HC-PCF is provided with a separate laser source having a wavelength selected for the particle type to be detected using the associated fiber. Advantageously, the multi-channel embodiment of the particle testing device facilitates the detection of a greater number of different particle types in a mixture of particles in a sample.

[0061] Particle characteristics can be obtained from transport measurements, as described below using Figure 1 Specifically, the number of particles and the particle size can be obtained by measuring, for example, Figures 2 to 5In general, particle counting and sizing is based on detecting intensity drops and particle flight times (transmission times) collected using transmission signals and preliminary calibration or reference measurements. Analyzing the output signal of the photodetector includes analyzing at least one of the transmission drop caused by the particle, the duration of the transmission drop, and the temporal shape of the transmission drop. Since the propagation time of a particle through a waveguide is typically less than 1 second, hundreds of particles can be sensed per minute.

[0062] Figure 2 The time transmission traces collected using the photodiode 31 for polystyrene particles of different sizes in air are shown, including particles of diameter 625nm (curve A), 1μm (curve B), and 2μm (curve C). It is observed that the 2μm polystyrene particles have the highest drop in transmission intensity, followed by 1μm and 625nm, thus indicating that larger particles scatter more of the laser guided mode. In addition, larger particles have shorter flight times because larger particles travel faster within the hollow fiber 11. Although particles of the same size produce slightly different transmission drop and flight time values, the measured optical transmission provides a clear distinction between particle sizes, as shown in FIG. Figure 3 and Figure 4 As shown, Figure 3 and Figure 4 Histograms of the intensity drop and flight time for different particle sizes are shown.

[0063] Figure 5 Detecting the presence of more than one particle in a hollow fiber 11 is shown in , which plots the transmission signal collected when two 1 μm polystyrene particles propagate through the fiber 11 simultaneously, one after the other. Here, a single polystyrene particle is first captured, showing its first sharp intensity drop (A). As the particle propagates through the fiber, a second particle is also captured and propelled into the fiber before the previous particle leaves. This can be seen by the second sharp intensity drop after the first sharp intensity drop (B). Once the first particle leaves the fiber, the second sharp intensity drop returns to the first sharp intensity drop (C), and then returns to the uncaptured initial transmission state (D) after the second particle also leaves the fiber. The intensity drop and flight time can be well derived from these data.

[0064] The features of the invention disclosed in the above description, the drawings and the claims are of great significance for implementing the invention in its various embodiments, either alone or in combination or in sub-combination. The invention is not limited to the preferred embodiments described above. Various variants and derivatives are also possible using the concept of the invention and therefore fall within the scope of protection. Furthermore, the invention also claims the subject matter and features of the dependent claims independent of the features and claims cited in the dependent claims.

Claims

1. A particle testing device (100), the particle testing device being configured to study particles in a fluid medium, the particle testing device comprising: - a waveguide device (10), comprising a hollow optical waveguide (11), the hollow optical waveguide having an input end (12) and an output end (13), - an irradiation device (20) comprising a laser source (21) arranged to optically capture at least one particle at the input end (12) of the optical waveguide (11) and to propel the particle through the optical waveguide (11) towards its output end (13), and - a measuring device (30) arranged for sensing the at least one particle in the optical waveguide (11), It is characterized in that - the laser source (21) is arranged for focused irradiation of the input end of the optical waveguide from only one side of the optical waveguide for optically capturing and propelling the at least one particle by irradiation pressure effect of the laser field and as a light source for the measuring device (30) for measuring the optical transmission of the optical waveguide (11), - the laser source has a sufficiently high optical power to capture the particle in front of the end face of the waveguide input end and then propel the particle along the hollow core of the waveguide, - the measuring device (30) comprises a single photodetector arranged to sense the at least one particle in the optical waveguide (11) by measuring the optical transmission of the optical waveguide (11) along its longitudinal extension, and - an analysis device (40) coupled to the measuring device, wherein the analysis device is arranged to provide at least one particle characteristic, wherein - said analyzing means are adapted to provide said at least one particle characteristic based on an output of said measuring means, - the analyzing device is adapted to provide the at least one particle characteristic based on at least one of the duration, amplitude and waveform of the measured particle induced change in optical transmission.

2. The particle testing device according to claim 1, wherein - the analysis device (40) is adapted to provide at least one of particle number, particle size, particle mass and particle refractive index as the at least one particle characteristic.

3. The particle testing device according to claim 1, comprising at least one of the following features: - the irradiation device (20) further comprises a first single-mode fiber (22) and a first gradient refractive index lens (23), the first single-mode fiber having an input end and an output end, wherein the input end of the first single-mode fiber (22) is coupled to the output of the laser source (21), and the first gradient refractive index lens is arranged at the output end of the first single-mode fiber (22) for focusing the laser light onto the input end of the optical waveguide (11), and The measuring device (30) comprises a photodiode (31), a second single-mode fiber (32) and a second gradient refractive index lens (33), wherein the second single-mode fiber has an input end and an output end, wherein the output end of the second single-mode fiber (32) is coupled to the photodiode (31), and the second gradient refractive index lens is arranged at the input end of the second single-mode fiber (32) for collecting light from the output end of the optical waveguide (11).

4. The particle testing device according to claim 1, wherein the waveguide device (10) further comprises: a housing (50) accommodating the optical waveguide (11) and having two transparent windows (51) arranged to couple light from the laser source (21) into the housing (50) and to couple light transmitted through the optical waveguide (11) out of the housing (50), wherein The housing (50) is adapted for flow-through operation, wherein a supply section (52) is arranged for supplying a sample containing particles into the housing (50) and a discharge section (53) is arranged for directing the sample out of the housing (50).

5. The particle testing device according to claim 1, wherein - The optical waveguide (11) is a hollow core photonic crystal fiber.

6. A particle testing method for studying particles in a fluid medium, the particle testing method comprising the following steps: - providing a sample comprising at least one particle at a hollow optical waveguide (11) having an input end (12) and an output end (13), - optically capturing the at least one particle at the input end (12) of the optical waveguide (11) and propelling the particle through the optical waveguide (11) towards the output end (13) using a laser source (21) of an irradiation device (20), and - sensing the at least one particle in the optical waveguide (11) using a measuring device (30), It is characterized in that - the laser source (21) is used for the following two operations: optically trapping the at least one particle; and irradiating the optical waveguide (11) to measure its optical transmission, wherein the laser source (21) provides focused irradiation of the input end of the optical waveguide from only one side of the optical waveguide for optically trapping and propelling the at least one particle by irradiation pressure effect of the laser field, and provides the light source of a measuring device (30) for measuring the optical transmission of the optical waveguide (11), - the laser source has a sufficiently high optical power to capture the particle in front of the end face of the waveguide input end and then propel the particle along the hollow core of the waveguide, - the measuring device (30) senses the at least one particle in the optical waveguide by measuring the optical transmission of the optical waveguide (11) along its longitudinal extension by means of a single photodetector, and, - providing at least one particle characteristic by analyzing the output of the measuring device (30), wherein the at least one particle characteristic is provided based on at least one of the duration, amplitude and waveform of the measured particle-induced change in optical transmission.

7. The particle testing method according to claim 6, comprising: - providing at least one of particle number, particle size, particle mass and particle refractive index as the at least one particle characteristic.

8. The particle testing method according to claim 6 or 7, comprising at least one of the following features: - obtaining said optical trapping of said at least one particle by illuminating said input end of said optical waveguide (11) with said laser source (21) via a first single mode fiber (22) and a first gradient index lens (23), and - Sensing of the at least one particle in the optical waveguide (11) is obtained by directing light transmitted through the optical waveguide (11) through a second gradient index lens (33) and a second single mode fiber (32) to a photodiode (31).

9. The particle testing method according to claim 6, comprising the following steps: - the optical waveguide (11) is arranged in a housing (50), the housing having two transparent windows, the two transparent windows being used to couple light from the laser source (21) into the housing (50) and to couple light transmitted through the optical waveguide (11) out of the housing (50), wherein - The housing (50) is suitable for flow-through operation.

10. The particle testing method of claim 6, wherein the sample is provided for at least one of the following operations: - monitor ambient air or water pollution, - monitoring of gas or liquid emissions from machinery or vehicles, and -Monitor the type and / or size of dust in the environment.

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