Optical trapping of airborne particles using dual counter-propagating hollow conical beams
Inventors
Assignees
United States Department of the Army
Publication Number
US-11016280-B1
Publication Date
2021-05-25
Expiration Date
2040-03-10
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Abstract
Embodiments of the present invention are directed to systems and methods for trapping and holding airborne particles, for further measurement and characterization. In the various embodiments, an optical trap is provided which generates and uses dual hollow conical beams to trap and hold absorbing and non-absorbing, spherical and irregularly shaped, liquid and solid airborne particles. The optical trap may include: a light source for generating a beam of light; optics for shaping and forming a hollow conical beam having a ring geometry from the beam of light; a trapping region where a particle can be present to be trapped; a first parabolic reflector configured to focus an inner portion of the hollow conical beam to a first focal point in the trapping region; and a second parabolic reflector configured to focus an outer portion of the hollow conical beam to a second focal point in the trapping region.
Core Innovation
Embodiments of the present invention are directed to systems and methods for trapping and holding airborne particles using an optical trap that generates and uses dual counter-propagating hollow conical beams. The optical trap can trap and hold absorbing and non-absorbing, spherical and irregularly shaped, liquid and solid airborne particles in air. The apparatus includes a light source that generates a beam of light, optics that shape and form a hollow conical beam with a ring geometry, a trapping region where particles can be trapped, and two parabolic reflectors. The first parabolic reflector focuses an inner portion of the hollow conical beam to a first focal point in the trapping region, while the second focuses an outer portion to a second focal point in the trapping region.
The problem solved by the invention addresses the difficulties in trapping airborne particles in air, as compared to trapping particles in a liquid or on a substrate. Conventional optical trapping requires overcoming stronger scattering forces, gravity, and air turbulence, usually requiring very high numerical aperture optics to produce sufficient gradient force. Existing single-beam hollow beam traps struggled to trap transparent particles with high trapping efficiency, especially those with high refractive indices. The invention overcomes these limitations by employing dual counter-propagating hollow conical beams that can trap both absorbing and transparent particles with improved efficiency and robustness, including particles of various shapes and states.
This dual-beam trap configuration is capable of trapping particles at multiple configurations of the focal points: at either focal point individually, at both focal points when separated by some distance, at a position where both focal points coincide, or between the focal points. The optical trap includes moveable stages allowing adjustment of the positions of the two focal points. The use of parabolic reflectors with relatively large numerical apertures enables strong focusing of the hollow beams, enhancing trapping forces while maintaining a working distance that minimizes contamination and allows integration with other optical characterization techniques. Numerical simulations and experimental results confirm enhanced trapping efficiency, robustness, and extended capacity to trap particles with various refractive indices and sizes.
Claims Coverage
The patent includes three independent claims covering an optical trap, a particle detection and measuring system utilizing the trap, and a method for continuously sampling particles using the system. Their inventive features focus on the optical trap configuration, system integration, and continuous sampling methods.
Optical trap with dual parabolic reflectors focusing inner and outer portions of a hollow conical beam
An optical trap for trapping both absorbing and non-absorbing, spherical and irregularly shaped, liquid and solid airborne particles comprising a light source generating a beam of light, optics shaping the beam into a hollow conical beam having a ring geometry, a trapping region for particles, a first parabolic reflector focusing the inner portion of the hollow conical beam to a first focal point, and a second parabolic reflector focusing the outer portion of the hollow conical beam to a second focal point in the trapping region.
Particle detection and measuring system integrating the optical trap and particle detector
A particle detection and measuring system including the described optical trap for trapping particles, a particle detector configured to detect airborne particles approaching or within the trapping region, and a measurement device to measure at least one property of trapped particles. The system further includes configurations to trap approximately one particle at a time, sources to illuminate or excite trapped particles, measurement of various optical and spectroscopic properties, and an optical trap with an average trapping efficiency of at least 20% from continuous sampling.
Method for continuously sampling airborne particles with trapping, measuring and releasing
A method comprising delivering air with airborne particles toward a trapping region, detecting particles approaching or within the trapping region, trapping them with the optical trap, measuring properties of the trapped particles, and releasing them. The method can further determine parameters related to particle shape, size, refractive index, absorption, molecular structures, compositions, and chemical reactions based on measured properties.
The independent claims cover an optical trap using dual counter-propagating hollow conical beams focused by parabolic reflectors, a system integrating this trap with particle detection and measurement devices, and a method for continuous airborne particle sampling involving trapping, measuring, and releasing particles. The inventive features focus on the optical configuration enabling enhanced trapping efficiency, system integration for measuring particle properties, and automated continuous sampling techniques.
Stated Advantages
The dual counter-propagating hollow conical beam optical trap offers simplicity and flexibility with a single light beam source and minimal optics for dual-beam formation.
The optical trap provides high trapping efficiency for both transparent and absorbing airborne particles, achieving over 50% efficiency for transparent particles and nearly 100% for absorbing particles, surpassing conventional single-beam traps.
The system offers strong trapping robustness capable of resisting air turbulence and maintaining stable trapping of airborne particles.
The trapping configuration allows for a large numerical aperture focusing with a working distance that minimizes sample contamination and facilitates integration with spectroscopic characterization techniques.
The method supports continuous, automated trapping, measuring, and releasing of airborne particles, enhancing throughput and enabling real-time particle characterization.
Documented Applications
Laboratory in-vitro inspection and measurement of airborne particles using optical trapping.
Integration into airborne particle handling systems for continuous sampling and characterization.
Measurement of physical, chemical, and biological properties of single airborne particles including imaging, Raman spectroscopy, fluorescence, laser-induced breakdown spectroscopy, spark-induced breakdown spectroscopy, thermal emission, and light scattering.
Monitoring and identification of potentially harmful particles such as bacteria, spores, pollens, allergens, smoke, chemical or biological warfare agents, and pollutants in real-time.
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