GB2541804A

GB2541804A - Beam dumper for particle counter

Info

Publication number: GB2541804A
Application number: GB1613801.8A
Authority: GB
Inventors: Choi Ki-Bong; Chong Eu-Gene; Jeong Young-Su
Original assignee: Agency for Defence Development
Current assignee: Agency for Defence Development
Priority date: 2015-08-28
Filing date: 2016-08-11
Publication date: 2017-03-01
Anticipated expiration: 2036-08-11
Also published as: GB201613801D0; KR101580932B1; GB2541804B

Abstract

A beam dumper for a particle counter includes an installation plate 207; a detector 203 mounted on the plate, comprising a photodiode 290 which receives excitation light; a housing 210 assembled with the detector, arranged in the path of non-scattering light of the excitation light, with a chamber 211 that guides the nonscattering light; a control circuit that measures intensity of the non-scattering light on the photodiode, calculates beam loss generated due to the optical path to detect actual intensity of the excitation light, and controls the intensity of the excitation light; a beam guide 205 with a beam stopper 230 that prevents a portion of the non-scattering light from returning to a condensation-inducing path, a beam dumper lens 270; and a beam hole structure 201 into which non-scattering light reflected from the photodiode is guided.

Description

BEAM DUMPER FOR PAlRTICLE COUNTER BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to technology of a beam dumper and, more particularly, to a beam dumper that is used for a particle counter that detects weak fluorescent light and scattering light that are generated due to interaction between a single fine particle and a light beam of a light-emitting diode (LED) , the beam dumper being capable of preventing stray light from affecting performance of a particle counter by reducing or eliminating the stray light that is generated by lenses, instruments, filters, or the like. The present invention further relates to a beam dumper that monitors optical alignment or intensity of a light beam of a light-emitting diode (LED) serving as a light source and controls the light source, for the purpose of reliable and stable measurement.

Description of the Related Art

The intensity of scattering light along to a fine particle depends on a reflective index of a particle, a wavelength of a light beam, an intensity of a light beam, and the like. However, the intensity of scattering light is very weak compared to a principal ray. Therefore, if a particle counter is not designed to block or eliminate stray light that scatters from the principal ray, the stray light becomes background noise that obstructs detection of scattering light and fluorescent light. A light-emitting diode serving as a light source has a large beam divergence angle that leads to a large light-emission area and is aims at cutting off/reducing signals which are be noise sources gegenerated from the light source in spite of any causes, in comparison with a laser. Therefore, it generates a large amount of stray light compared to a laser that emits a small-diameter beam and has good straight traveling ability. Therefore, a light source has to be designed to increase a good signal-to-noise ratio (SNR) in consideration of a beam-forming optical system, a measurement area, and a beam dumper. A typical beam dumper has a conical shape and is coated with an anti-reflective material. Even with this structure, typical beam dumpers cannot perfectly prevent reflection of light and thus produce stray light. For this reason, it is currently difficult to measure a weak fluorescence signal. Specifically, when detecting a weak signal such as scattering light and fluorescent light that are generated due to interaction between a micrometer-sized particle and a light beam of a light-emitting diode using a particle counter, design and manufacturing technology for attenuating stray light generated by a beam-forming unit, an optical chamber, and a beam dumper are critical factors to improve performance of a particle counter. That is, it is important to reduce stray light using a beam dumper so that stray light rarely enters a particle counter.

According to a related art, a detector that detects the intensity of a light beam of a light source such as a laser diode or a light-emitting diode is assembled with a light source, thereby measuring the intensity of light that is reflected by an optical system such as a lens or filter installed in front of the light source as well as the intensity of a principal ray. Therefore, it is difficult to obtain accurate actual intensity of a light beam of a light source using a conventional particle counter.

When a light-emitting diode, which has a larger beam divergence angle and a larger size than a laser and is difficult to form a small beam width, is used as an excitation light source, intensities of scattering light and fluorescent light that are generated when a light beam of the light source is emitted to a particle are very weak. Therefore, it is necessary to minimize influence of noise in detecting scattering light and fluorescent light.

When detecting a signal of a biological particle, an excitation light source that emits a light beam having a wavelength in the range of from 200nm to 450nm is used. In this case, when a light-emit ting diode based on silicon (Si) , aluminum nitride (AIN) , or gallium nitride (GaN) that have a large band gap is used, it is difficult in terms of technology to form a light beam with high intensity due to a large band gap. Therefore, development of a technology for reducing a noise signal is highly demanded.

Moreover, a small-size particle counter has to employ a light-emitting diode or a laser diode as a light source to realize low cost, low power consumption, and lightness. However, such a light source produces a relatively large amount of heat compared to other kinds of light sources, and the heat negatively affects emission of a light beam having stable intensity.

In order to solve this problem, various efforts have been made, for example, a temperature-indicator-controller (TIC) or a heat-sinking system has been applied to a metal printed circuit board (PCB). However, this solution has many disadvantages such as increases in weight of a system, power consumption, and cost. As for a small-size particle counter, even subtle change in intensity of a light beam of a light source heavily affects generation of an optical signal. Therefore, it is important to maintain stable and constant intensity of a light beam of a light source. For this reason, monitoring and automatic control on the intensity of a light beam of a light source are needed.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a beam dumper that is suitably used for a particle counter that measures intensities of scattering light and fluorescent light that are generated when a fine particle is irradiated with a light beam, in which the intensity of a light beam emitted from an excitation light source is measured and automatically controlled.

Another object of the present invention is to provide a beam dumper that maximally absorbs a light beam that passes through a chamber to minimize noise that enters a sensor that measures scattering light and fluorescent light, thereby increasing a signal-to-noise ratio (SNR) and maintaining stable and constant intensity of a light beam of a light-emitting diode. The beam dumper helps a particle counter to accurately measure a particle size and to count the number of particles. A further object of the present invention is to provide a beam dumper that prevents stray light from entering an optical chamber of a particle counter or a detection device that measures scattering light and/or fluorescent light, wherein the stray light is specifically attributable to the following: a light beam emitted from an excitation light source and introduced into the beam dumper, reflected light that is reflected from a surface of a photo diode that is a detector installed at the back of the beam dumper, and reflection and scattering in the beam dumper. That is, the beam dumper prevents stray light from undesirably entering a detector (for example, scattering detector or fluorescence detector) installed in an optical system, thereby preventing deterioration in accuracy of measurement. A further object of the invention is to provide a beam dumper that measures the intensity of a light beam of an excitation light source that has passed through an optical chamber to monitor actual intensity of a light beam of the excitation light source, thereby improving operation stability of an optical system. A further specific object of the invention is to provide a beam dumper that enables measurement of intensity of a light beam to which beam loss along an optical chamber or a lens is applied unlike a conventional technology in which a detector for detecting intensity of a light beam of a light source detects intensity of a light beam in a state in which an optical chamber is arranged next to a light source and a sample without consideration of beam loss. Therefore, the beam dumper enables monitoring of actual intensity of a light beam of an excitation light source, the actual intensity being actually irradiated onto a particle. A further object of the invention is to provide a beam dumper that enables an excitation light source to maintain stable and constant intensity of a light beam by supplementing a driving voltage of the excitation light source according to the intensity of the light beam of the excitation light which is measured through monitoring. A further object of the invention is to provide a beam dumper that enables monitoring of alignment of an optical axis with respect to an optical part, thereby improving operability of an optical system. A further object of the invention is to provide a beam dumper that enables simultaneous monitoring of intensity of a light beam of a light source and alignment of an optical part that selectively includes a light source unit, a nozzle unit, an optical chamber, and a lens unit because intensity of a light beam that is emitted from an excitation light source, passes a condensing lens and an optical chamber, and reaches the beam dumper is measured.

In order to accomplish the objects of the present invention, according to one aspect, there is provided a beam dumper that enables measurement of intensity of a light beam emitted from an excitation light source and automatic control of the intensity of the light beam of the excitation light source. The beam dumper is suitably used for a particle counter that measures intensities of scattering light and fluorescent light that are generated when a light beam is irradiated onto a fine particle.

The beam dumper includes: an installation plate 207; a detector 203 that is mounted on the installation plate 207 and receives a light beam of an excitation light source; a housing 210 that is assembled with the detector 203 and has a chamber 211 therein that is arranged along an optical path of nonscattering light of the light beam of the excitation light source; a photo diode 290 that is arranged in the chamber 211 and outputs non-scattering light in a position that is on the optical path of the non-scattering light introduced into the chamber; and a control circuit 120 that measures the intensity of the light beam, calculates beam loss along the optical path to obtain actual intensity of a light beam of the excitation light source, and controls the intensity of a light beam of the excitation light source according to the actual intensity.

The housing 210 and the detector 203 may be assembled to be inclined so that the non-scattering light introduced into the chamber 211 of the housing 210 is reflected in a direction that is not parallel with an optical path of the non-scattering light and thus the non-scattering light is dumped. A beam guide unit 205 may be arranged in the chamber 211 and on the optical path of the non-scattering light. A beam hole structure 201 may be formed in the chamber and may guide non-scattering light that is reflected by the surface 420 of the detector 203 into a hole and dumps the guided nonscattering light.

The beam guide unit 205 may include a condensing lens 320 that condenses the non-scattering light guided into the chamber 211 of the housing 210 so that the non-scattering light is focused on the surface of the detector and has a condensation-inducing path 410 therein, in which the condensation-inducing path 410 causes the non-scattering light that is condensed to be focused on the surface of the detector by the condensing lens 320 to propagate toward the surface 420 of the detector without interference.

The beam hole structure 201 may have a recess 430 that is recessed and inclined in a direction that is not parallel with a central axis of the condensation-inducing path so that the non-scattering light which is guided into the beam hole structure 201 cannot return to the condensation-inducing path.

The beam guide unit 205 may further include a beam stopper 230 that is arranged on the condensation-inducing path and prevents a portion of the reflected non-scattering light from returning to the condensation-inducing path.

The beam hole structure 201 may have a bent surface that is bent one or more times.

An inside surface of the beam hole structure may be coated with an anti-reflection coating.

The beam stopper 230 may be arranged between the detector 203 and a window.

The beam dumper lens 270 may be formed by coating a silica lens with an anti-reflection coating and/or micro/nano scale pattern formation to minimize production of stray light.

According to the present invention, as for a device that simultaneously measures scattering light and fluorescent light that are generated due to interaction between a particle and a light source, it is possible to minimize stray light that returns to a highly sensitive detector such as a photomultiplier tube that is a sensor for measuring intensities of scattering light and fluorescent light, thereby improving a signal-to-noise ratio (SNR).

In addition, another advantage of the present invention is to measure intensity of a light beam of an excitation light source, which has passed through an optical chamber, and thus stably maintains constant intensity of the light beam of the excitation light source. For this reason, it is possible to accurately and precisely measure information of a fine particle that interacts with the light beam of the excitation light source, thereby improving accuracy in analysis.

In addition, a further advantage of the present invention is to supplement a driving voltage of a light source according to the intensity of the light beam of the excitation light source that is measured through monitoring, thereby maintaining stable and constant intensity of the light beam of the excitation light source. Further, it is possible to constantly monitor status change of the excitation light source, alignment of an optical axis, contamination of an optical chamber, and change of an optical part attributable to vibration, thereby improving operation stability of an optical system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a light control system according to one embodiment of the present invention, the diagram illustrating the concept of control on the intensity of a light beam of an excitation light source; FIG. 2 is a cross-sectional view of a beam dumper of FIG. 1; FIG. 3 is a block diagram illustrating an optical path of a light beam of an excitation light source according to one embodiment of the present invention; and FIG. 4 is a cross-sectional view illustrating a beam hole structure that absorbs a light beam according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of the present invention, specific examples of which are illustrated in the accompanying drawings and described below, since the embodiments of the present invention can be variously modified in many different forms. While the present invention will be described in conjunction with exemplary embodiments thereof, it is to be understood that the present description is not intended to limit the present invention to those exemplary embodiments. On the contrary, the present invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments that may be included within the spirit and scope of the present invention as defined by the appended claims.

Throughout the drawings, the same reference numerals will refer to the same or like parts.

It will be understood that, although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

For instance, a first element discussed below could be termed a second element without departing from the teachings of the present invention. Similarly, the second element could also be termed the first element.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Hereinbelow, a beam dumper for monitoring an optical axis of a particle counter and for measuring the intensity of a light beam according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings . A particle counter typically analyzes an optical signal that is generated due to interaction between a fine particle in air and a beam and obtains information of particle size, concentration of particles, presence or absence of biological particles, or the like. Specifically, a particle counter is a device employing an induced fluorescence technology. It irradiates a fine particle with a light beam of a specific wavelength and measures intensity of scattering light that is scattered from the fine particle and intensity of weak fluorescent light. Recently, as for the particle counter, induced fluoresce technologies that use a relatively cheap UV light-emitting diode rather than an expensive laser have been developed.

Generally, in the process of condensing a light beam emitted from a light source on a focus, light that is generated due to multiple reflections of light on the surface of a lens, scattering of light from a filter, diffused reflections of light, or diffractions of light, does not propagate along the designed optical path but propagates in many directions. This light is collectively called stray light. FIG. 1 is a block diagram of a light control system 100, the diagram illustrating the concept of control on the intensity of a light beam of an excitation light source. With reference to FIG. 1, when a light beam is emitted from a light source 110, a beam dumper 130 absorbs the light beam and a control circuit 120 measures the intensity of the light beam using the beam dumper 130, compares the measured intensity and preset intensity, and adjusts the intensity of the light beam emitted from the light source 110. FIG. 2 is a cross-sectional view of the beam dumper 130 of FIG. 1. With reference to FIG. 2, the beam dumper 130 includes: an installation plate 207; a detector 203 that is mounted on the installation plate 207 and receives a light beam emitted from an excitation light source; a housing 210 that has a chamber 211 therein, the housing 210 being assembled with the detector 203 and arranged on an optical path of non-scattering light of the light beam of the excitation light source to guide the non-scattering light, and a light source output detector that is arranged in the chamber, measures the intensity of the non-scattering light that passes along the optical path of the non-scattering light that is introduced into the chamber, detects actual intensity of the light beam of the excitation light source to which optical loss is applied, and monitors alignment of an optical axis. A beam guide unit 205 includes a beam dumper lens 270, a second retainer 260 that fixes the beam dumper lens 270, a fixing ring 240 that surrounds and fixes the second retainer 260 and the beam dumper lens 270, a beam stopper 230 that prevents a portion of the non-scattering light from returning to a condensation-inducing path, and a first retainer 250 that fixes the beam stopper 230.

The detector 203 includes a photo diode 290 and a photo diode cell 220 that includes the photo diode 290. The photo diode 290 operates based on a phenomenon in which electromotive force is generated when light is irradiated to a PN junction of a semiconductor. The detector 203 may include an avalanche photo diode (APE) instead of the photo diode 190. The photo diode 290 receives a light beam of the excitation light source 110 and performs light detection.

The detector 203 is fixed to the surface of the housing using a screw 291. Instead of the screw, a bolt and nut, or an adhesive may be used as the fixing means.

The beam stopper 230 is arranged in the condensation-inducing path to prevent a portion of reflected non-scattering light from returning to the condensation-inducing path. The condensation-inducing path is formed in the chamber 211 of the housing 210.

The beam dumper lens 270 having a focal distance of about 25 mm is installed in front of the beam dumper 130 so that a light beam emitted from the excitation light source 110 installed in the chamber 211 can pass through the beam stopper 230. The focal distance is determined according to the distance between a beam hole structure 201 and the detector 203 and an inclination angle (= about 15°) 209 of the detector 203. The beam stopper 230 blocks stray light that is a portion of a principal ray that passes the focus of the beam stopper 230. Herein, the stray light is light introduced in a direction in which the light cannot reach the detector.

The principal ray passes the beam dumper lens 270, is reflected by the detector 203, reaches the entrance of a hole with a focal distance of 25mm, and is finally attenuated in the hole of the beam hole structure. That is, the detector 203 is structured to be inclined. With this inclination, a portion of an incident light beam that is not absorbed by the detector 203 is reflected to propagate toward the beam hole structure and is then absorbed in the beam hole structure. Therefore, even though a portion of a light beam is reflected, the reflected light does not return to an optical chamber. In this case, the beam hole structure may have a hole that is inclined by an inclination angle of about 30° with respect to the detector 203 and has a depth of about 21.7 mm and a diameter of about 5 mm.

The detector 203 is arranged to be inclined, thereby reflecting the principal ray toward the beam hole structure. At this point, the reflected light is absorbed by the hole in the beam dumper so that the reflected light does not return to the optical chamber.

The inside surface of the chamber 211 of the beam dumper 130 and the inside surface of the beam hole structure 201 are black-coated or are made of graphite, a metal alloy, or a metal mat (oxide) for effective absorption of a light beam.

In addition, the detector 203 is attached to measure the intensity of the principal ray introduced into the beam dumper 130, thereby monitoring the intensity of the light beam of the light source and enabling the intensity of the light beam to be stable and constant. The stable and constant intensity of the light beam guarantees the sufficient intensity of scattering light which indicates the size of a particle. Therefore, accuracy in particle size measurement is guaranteed.

In addition, it is possible to monitor misalignment of an optical axis attributable to vibration and changes in the intensity of a light beam attributable to contamination or shortened lifespan of a light-emitting diode, and to notify a user of the problems. FIG. 3 is a view illustrating an optical path of a light beam of an excitation light source. With reference to FIG. 3, a light beam emitted from an excitation light source 360 passes an optical chamber, is condensed by the beam dumper lens 270, and reaches the photo diode 290. A light beam 301 reflected by the surface 420 of the detector is guided to an aspheric reflector 350. Next, the light beam that has passed through the aspheric reflector 350 then passes a spherical reflector 340 and is focused on a predetermined spot. When the amount of light is measured at the predetermined spot on which the light beam is focused, actual intensity to which beam loss along the optical chamber or the lens is applied can be measured.

The inclination of the surface 420 of the detector may be about 15°, the focal distance of the beam dumper lens 270 serving as a focusing lens may be about 25 mm, and the diameter cp of the light beam at the photo diode 290 may be about 6.0 mm. FIG. 4 is a cross-sectional view illustrating the beam hole structure that absorbs a light beam, according to one embodiment of the present invention. With reference to FIG. 4, the beam hole structure 201 has a recess 430 that is recessed in a direction that is not parallel with a central axis of the condensation-inducing path 410. Therefore, non-scattering light that is guided into the beam hole structure cannot return to the condensation-inducing path.

The beam hole structure may have a bent surface that is bent one or more times and the inside surface of the beam hole structure is coated with an anti-reflection coating.

According to one embodiment of the present invention, the beam dumper is structured to enable measurement of the intensity of a light beam of a light source while increasing an signal-to-noise ratio when detecting the intensity of a light beam of a light-emitting diode as well as detecting a weak signal that is generated when a light beam of the excitation light source 110 is irradiated onto a fine particle.

The beam dumper lens 270 is formed by coating a silica lens that can pass multiple wavelengths up to a UV ray of 200 nm with an anti-reflection coating to minimize generation of stray light. The beam dumper lens 270 is arranged in front of the beam stopper 230. The beam stopper 230 is arranged between a window and the detector 203 that detects the intensity of light and includes a photo diode. A field stop 310 blocks light that is reflected from the photo diode 290 toward an optical path fomed therein.

The detector 203 may be fixed to an inclined retainer. The detector 203 is structured to be inclined at an inclination angle of about 15° according to the embodiment of the invention. Because of this structure, an optical path is formed such that an incident light beam passes the beam dumper lens 270, is reflected by the detector 203, is re-reflected toward the beam hole structure 201 formed in the beam dumper, and is finally absorbed in the beam hole structure. As a result, the light beam is not returned to the optical chamber. Therefore, stray light undergoes multiple reflections and does not interfere with performance of a particle counter.

Claims

WHAT IS CLAIMED IS:

1. A beam dumper for a particle counter, comprising: an installation plate (207); a detector (203) that is mounted on the installation plate (207) and receives a light beam of an excitation light source; a housing (210) that is assembled with the detector (203), is arranged in an optical path of non-scattering light of the light beam of the excitation light source, and has a chamber (211) that guides the non-scattering light; a photo diode (290) that is arranged in the chamber (211) and outputs non-scattering light in a position that is on the optical path of the non-scattering light introduced into the chamber; and a control circuit (120) that measures intensity of the light beam, calculates beam loss along the optical path to detect actual intensity of the light beam of the excitation light source, and adjusts the intensity of the light beam of the excitation light source according to the actual intensity of the light beam of the excitation light source, wherein a beam guide unit (205) arranged in a preceding stage of the housing (210) includes a beam dumper lens (270), a second retainer (260) that fixes the beam dumper lens (270) , and a fixing ring (240) that surrounds and fixes the second retainer (260) and the beam dumper lens (270), the beam guide unit (205) further includes a beam stopper (230) that prevents a portion of the non-scattering light from returning to a condensation-inducing path, and a first retainer (250) that fixes the beam stopper (230), the condensation-inducing path (410) is formed such that non-scattering light that is condensed by the beam dumper lens (270) propagates toward a surface of the detector without interference, and a beam hole structure (201) is formed in the chamber of the beam dumper so that the non-scattering light reflected from a surface (420) of the detector (203) is guided into an inside of the beam hole structure, and the beam loss is measured causing the beam loss.

2. The beam dumper for a particle counter, according to claim 1, wherein the beam hole structure (201) has a recess (430) that is recessed with an inclination angle of 30° with respect to a central axis of the condensation-inducing path so that the non-scattering light guided into the beam hole structure does not return to the condensation-inducing path.

3. The beam dumper for a particle counter, according to claim 2, wherein in the beam hole structure (201) , the surface of the detector is inclined clockwise by an inclination angle of 15° with respect to a plane that is perpendicular to the condensation-inducing path so that the non-scattering light guided into the beam hole structure does not return to the condensation-inducing path.

4. The beam dumper for a particle counter, according to claim 1, wherein the beam hole structure (201) has a bent surface that is bent one or more times.

5. The beam dumper for a particle counter, according to claim 1, wherein an inside surface of the beam hole structure (201) is coated with an anti-reflection coating.

6. The beam dumper for a particle counter, according to any one of claims 2 to 5, wherein the non-scattering light is reflected and guided into the beam hole structure 201, passes an aspheric reflector (350) , passes a spherical reflector (340), and is finally focused on a predetermined spot, wherein the beam loss is measured at the predetermined spot on which the non-scattering light is focused.

7. The beam dumper for a particle counter, according to claim 1, wherein the beam dumper lens (270) is formed by coating a silica lens with an anti-reflection coating and/or micro/nano scale pattern formation, thereby minimizing production of stray light.