WO2021205177A1

WO2021205177A1 - Apparatus and method for sterilisation of pathogens

Info

Publication number: WO2021205177A1
Application number: PCT/GB2021/050867
Authority: WO
Inventors: Graeme Peter Alexander MALCOLM; Gareth Thomas MAKER; Nils HEMPLER
Original assignee: M Squared Lasers Limited
Priority date: 2020-04-09
Filing date: 2021-04-08
Publication date: 2021-10-14
Also published as: GB202005334D0; GB2593930A

Abstract

A laser system and method for generating a continuous-wave, tuneable optical output field having a wavelength between 200 nm and 300 nm is disclosed. The laser system comprising: a continuous-wave, narrow-linewidth, tuneable optical field source employed to generate a first output field. The first output field is arranged to propagate thorough the first enhancement cavity frequency double to generate a first frequency doubled output field. The first frequency doubled output field is then arranged to propagate thorough a second enhancement cavity frequency double to generate a second frequency doubled output field which acts as an output field for the laser system. The laser system thus provides a frequency-agile, high power and spectrally pure light source across the UVC the region of the electromagnetic spectrum which makes it a flexible and efficient source for the sterilisation or decontamination of pathogens.

Description

Apparatus and Method for Sterilisation of Pathogens The present invention relates to the field of sterilisation of pathogens and other microbiological contaminants. In particular, a spectrally pure, tuneable, high-power laser system is disclosed which finds specific application in the sterilisation of pathogens. A pathogen is the term used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. A pathogen is sometimes referred to as an infectious agent. It is known in the art that C-band ultraviolet light (UVC) has very high germicidal effects, see for example the paper by Kim et al. entitled “Using UVC Light-Emitting Diodes at Wavelengths of 266 to 279 Nanometers To Inactivate Foodborne Pathogens and Pasteurize Sliced Cheese" , Applied Environmental Microbiology, 1 January 2016; Volume 82(1), pages 11 to 17, (see doi: 10.1128/AEM.02092-15). UVC refers to light in the region of the electromagnetic spectrum between 200 nm and 280 nm. A large body of work exits that demonstrates the sterilisation effects of UVC on a wide range of pathogens such as Influenza, Tuberculosis, E. Coli, S.Typhimurium and L. Monocytogenes, see for example the paper by Welch et al. entitled “Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases”, Scientific Reports (2018), Volume 8.2752, pages 1 to 7, (see https://doi.org/10.1038/s41598-018-21058-w).

The UVC light sources known in the art primarily rely on the employment of mercury lamps, light emitting diodes (LEDs) or fixed-wavelength, solid-state lasers. All of these UVC light sources have limitations such as low output power, lack of wavelength agility or lack of practicality which make them less than ideal for their use in the sterilisation of pathogens. As a result, light sources known in the art are limited in the speed and efficacy at which they can complete the desired sterilisation process.

Summary of Invention

It is therefore an object of an embodiment of the present invention to provide an improved UVC light source that obviates or at least mitigate the foregoing disadvantages of the UVC light sources known in the art.

According to a first aspect of the present invention there is provided a laser system for the sterilisation of pathogens, the laser system comprising: a continuous-wave, tuneable optical field source, and an optical frequency conversion system wherein a first output field generated by the continuous-wave, tuneable optical field source is arranged to propagate thorough the optical frequency conversion system to provide a continuous-wave, tuneable optical output field of the laser system having a wavelength between 200nm and 300 nm.

The laser system provides a frequency-agile, high-power and spectrally pure light source across the UVC the region of the electromagnetic spectrum which makes it a flexible and efficient source for the sterilisation or decontamination of pathogens. The tunability of the laser system enables an operator to carefully select the operating wavelength of the output field of the laser system thus allowing optimisation of the sterilisation or decontamination process while reducing the risk to humans and other organic organisms.

Preferably, the first output field has a narrow-linewidth, i.e. a linewidth of 1 GHz or less.

Most preferably the optical frequency conversion system comprises a first frequency doubler wherein the first output field is arranged to propagate through the first frequency doubler. Most preferably the optical frequency conversion system further comprises a second frequency doubler wherein a first frequency-doubled output field generated by the first frequency doubler is arranged to propagate thorough the second frequency doubler. Optionally, the first frequency doubler comprises a first enhancement cavity frequency doubler. Optionally, the second frequency doubler comprises a second enhancement cavity frequency doubler. Most preferably the first continuous-wave, tuneable optical field source is tuneable between 800 nm and 1200 nm. Preferably the first continuous-wave, tuneable optical field source comprises a Ti:Sapphire laser. Preferably the frequency doubler comprises an LBO (Lithium Triborate (LiB₃0₅)) crystal. Most preferably the first frequency doubler generates the first frequency doubled output field having a wavelength between 400 nm and 600 nm. Preferably the second frequency doubler comprises a BBO (Beta Barium Borate (BaB₂0₄)) crystal. Preferably the optical output field of the laser system has a linewidth of less than 500 kHz. Optionally the optical output field of the laser system has a linewidth of less than 100 kHz. In a further alternative the optical output field of the laser system has a linewidth of less than 10 kHz. Most preferably the optical output field of the laser system has a power between an 0.05 and 0.5 Watts. According to a second aspect of the present invention there is provided a method for generating a continuous-wave, tuneable optical output field having a wavelength between 200 nm and 300 nm for the sterilisation or decontamination of a pathogen, the method comprising: - generating a first continuous-wave, tuneable optical field; and - frequency converting the first output field. Preferably frequency converting the first output field comprises frequency doubling the first output field to generate a first frequency-doubled output field.

Preferably frequency converting the first output field further comprises frequency doubling the first frequency-doubled output field.

Most preferably the first generated continuous-wave, tuneable optical field is tuneable between 800 nm and 1200 nm.

Most preferably the frequency doubling the first output field comprises generating the first frequency-doubled output field having a wavelength between 400 nm and 600 nm.

Preferably the generated continuous-wave, tuneable optical output field has a linewidth of less than 500 kHz. Optionally the generated continuous-wave, narrow-linewidth, tuneable optical output field has a linewidth of less than 100 kHz. In a further alternative the generated continuous-wave, narrow-linewidth, tuneable optical output field has a linewidth of less than 10 kHz.

Most preferably the generated continuous-wave, tuneable optical output field has a power between an 0.05 and 0.5 Watts.

Embodiments of the second aspect of the present invention may comprise features to implement the preferred or optional features of the first aspects of the invention or vice versa.

According to a third aspect of the present invention there is provide a method of sterilising or decontaminating an object contaminated by one or more pathogens the method comprising generating a continuous-wave, tuneable optical output field having a wavelength between 200nm and 300 nm in accordance with the second aspect of the present invention.

Most preferably the method of sterilising or decontaminating an object comprises selecting the operating wavelength of the continuous-wave, tuneable optical output field.

The method of sterilising or decontaminating an object may comprise shaping the continuous-wave, tuneable optical output field. The object may comprise an object in a solid, gaseous or liquid phase. The object may comprise a surface, a volume of air, a food product, food packaging, clothing or personal protective equipment (PPE). The volume or air may be contained with an air conditioning system. Embodiments of the third aspect of the present invention may comprise features to implement the preferred or optional features of the first or second aspects of the invention or vice versa. Brief Description of Drawings Aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following drawings in which: Figure 1 presents a schematic representation of a laser system in accordance with an embodiment of the present invention. Figure 2 presents schematic diagram of a narrow-linewidth laser employed within the laser system of Figure 1 ; Figure 3 presents schematic diagram of a frequency doubling cavity employed within the laser system of Figure 1 ; and Figure 4 presents a tuning curve of the output field of the laser system of Figure 1 . In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of embodiments of the invention. Detailed Description A laser system 1 , in accordance with an embodiment of the present invention will now be described with reference to Figure 1. In particular, Figure 1 presents a schematic representation of the laser system 1 that can be seen to comprise an optical pump source 2, a continuous-wave, narrow-linewidth, tuneable optical field source 3, a first frequency doubler in the form of a first enhancement cavity frequency doubler 4 and a second frequency doubler in the form of a second enhancement cavity frequency doubler 5. In the presently described embodiment the continuous-wave, narrow-linewidth, tuneable optical field source 3 is the applicant’s proprietary SolsTiS^® laser platform which is a ThSapphire laser, a schematic representation of which is presented in Figure 2. The continuous-wave, narrow-linewidth tuneable source 3 can be seen to comprise a laser cavity 6 that exhibits a bow-tie ring cavity geometry defined by a first mirror 7, a second mirror 8, a dual piezo-actuated mirror 9 (of the type described within UK patent number GB 2,499,471 B) and an output coupler 10 all of which are located within a mechanically stable housing 11 . Located within the cavity 6 is a Ti:Sapphire gain medium 12 (between the first 7 and second 8 mirrors); an optical diode 13 (between the first 7 and the dual piezo- actuated 9 mirrors); a birefringent filter (BRF) 14 (between the second mirror 8 and the output coupler 10); and an air-spaced etalon 15 (between the piezo-actuated mirror 9 and the output coupler 10). It is a combination of the ring cavity geometry and the optical diode 13 that forces the laser cavity 6 to operate in a unidirectional manner, resulting in a travelling intracavity optical field 16 that removes the detrimental effects of spatial-hole burning within the gain medium 12. Given that the optical absorption within ThSapphire occurs over a broad wavelength range from ~400nm to ~600nm, the gain medium 12 can be optically pumped by a pump field 17 generated by any commercially available continuous-wave “green” laser 2 e.g. a 532 nm diode pumped solid-state laser source. Pumping of the gain medium 12 preferably takes place through the second mirror 8. In the presently described embodiment the pump field 17 has a power of 20 Watts. In order to tune the wavelength of a laser output field 18, the intracavity BRF 14 is employed. The BRF 14 introduces a wavelength-dependent loss into the cavity 6, and wavelength tuning is accomplished by rotation of the BRF 14. The BRF 14 provides a relatively rapid but coarse wavelength adjustment. In the absence of any further linewidth narrowing techniques the laser output 18 exhibits a linewidth of ~8 GHz.

The introduction of the air-spaced etalon 15 to the laser cavity 6 acts to further narrow the linewidth operation of the laser 3. This is because the air-spaced etalon 15 introduces a spectral loss into the cavity 6 that has a narrower transmission bandwidth than that exhibited by the BRF 14. By electronically adjusting the spacing of the air-spaced etalon 15 the laser output field 18 can also be finely tuned. Long-term single mode operation for the laser cavity 6 can also be achieved through the electronic servo locking of the intracavity air-spaced etalon 15, a technique known to those skilled in the art. This technique involves locking the peak of the air-spaced etalon’s 15 transmission function to the nearest cavity 6 longitudinal mode (within the capture range of the servo loop) by dithering the spacing of the air-spaced etalon 15. In the absence of any further linewidth narrowing techniques, the laser output field 18 exhibits a linewidth of ~5 MHz.

The dual piezo-actuated mirror 9 comprises first and second piezoelectric crystals. The thickness of the second piezoelectric crystal is less than the thickness of the first piezoelectric crystal. With this arrangement the dual piezo-actuated mirror 9 provides a means for maintaining a single longitudinal mode operation as the laser frequency is tuned since accurate control of the first, thicker piezoelectric crystal of the duel piezo-actuated mirror 9 allows the cavity length to be changed precisely, and to match the single oscillating longitudinal cavity mode frequency as the cavity length is tuned. With the air- spaced etalon 15 peak lock circuit engaged, the peak transmission of the air-spaced etalon 15 is then kept locked to this oscillating longitudinal mode frequency (to within the capture range of the locking circuit), even as this frequency is tuned by the dual piezo- actuated mirror 9. The combination of the first and second piezoelectric crystals of the dual piezo-actuated mirror 9 can also be employed to lock the laser cavity to an external reference cavity (not shown) which reduces the laser line width further. In the presently described embodiment, the narrow-linewidth tuneable laser 3 is arranged to generate a laser output field 18 at wavelength of 910 nm having a linewidth around ~5 kHz and a power of 5.7 Watts.

As can be seen from Figure 1 , laser output field 18 is arranged to propagate thorough the first enhancement cavity frequency doubler 4, a schematic representation of which is presented in Figure 3. The applicant’s proprietary SolsTis® ECD-X is a suitable example of such an enhancement cavity frequency doubler 4.

The first enhancement cavity frequency doubler 4 can be seen to comprise a Brewster- angle cut crystal 19 formed from LBO (Lithium Triborate (LiB₃0₅)) located within a ring cavity defined by a first mirror 20, an output coupler 21 , an input coupler 22 and a second mirror 23 . The first enhancement cavity frequency doubler 4 employs resonant enhancement to convert the output frequency of the laser output field 18 to produce a first frequency-doubled output field 24. In the presently described embodiment, the first frequency doubled output field 24 has a wavelength of 455 nm and a power of 2.4 Watts.

As can be seen from Figure 1 , the first frequency doubled output field 24 is then arranged to propagate thorough the second enhancement cavity frequency doubler 5. The applicant’s proprietary SolsTis® ECD-Q is a suitable example of such an enhancement cavity frequency doubler 5, a schematic representation of which is again provided by Figure 3.

The second enhancement cavity frequency doubler 5 is identical to the first enhancement cavity frequency doubler 4 except for the fact that in the second enhancement cavity frequency doubler 5 the Brewster-angle cut crystal 19 is formed from BBO (Beta Barium Borate (BaB₂0 )). The second enhancement cavity frequency doubler 5 therefore employs resonant enhancement to convert the output frequency of the first frequency doubled output field 24 to produce a second frequency doubled output field 25. In the presently described embodiment, the second frequency doubled output field 25, which acts as the output field for the laser system 1 , has a wavelength of 227.5 nm and a power of 0.5 Watts.

Frequency tuning of the output field 25 generated by second enhancement cavity frequency doubler 5 can be achieved by tuning the wavelength of laser output field 18 and by simultaneously rotating the Brewster-angle cut crystals 19 of the first frequency doubler 4 and the second frequency doubler 5 about their respective axis 26. This rotation of the Brewster-angle cut crystals 19 allows for maintenance of the required phase-matching conditions required for the second harmonic generation processes to take place within the first enhancement cavity frequency doubler 4 and the second enhancement cavity frequency doubler 5. Figure 4 presents a tuning curve of the output field 25 of the laser system 1 when the narrow-linewidth tuneable laser 3 is scanned between 820 nm and 1000 nm and the Brewster-angle cut crystals 19 of the first frequency doubler 4 and the second frequency doubler 5 are appropriately rotated about their respective axis 26. As can be seen from Figure 4 the laser system 1 produces an output field 25 of several hundred milliwatts of power across the UVC the region of the electromagnetic spectrum. The linewidth of the output field 25 matches that of the narrow-linewidth tuneable laser 3, in the presently described embodiment this linewidth is around ~5 kHz. As a result of the laser systems 1 superior performance, when compared with those system known in the art based on the employment of mercury lamps, light emitting diodes (LEDs) or fixed-wavelength solid-state lasers, the laser system provides sterilisation efficacy that are orders of magnitude greater than the known prior art systems. The tunability of the laser system 1 also enables an operator to carefully select the operating wavelength of the output field 25 thus allowing optimisation of the sterilisation or decontamination process while reducing the risk to humans and other organic organisms. The physical nature of the laser system 1 means that it can easily be employed to sterilise or decontaminate objects contaminated with a wide range of pathogens such as Influenza, Tuberculosis, E. Coli, S.Typhimurium and L. Monocytogenes in the solid, gaseous or liquid phase. A particular application of the laser systeml is in the sterilisation or decontamination of objects, including surfaces and a volume of air, contaminated with the Covid-19 virus. The high-quality of the output field 25 emitted by the laser system 1 can easily be shaped and thus allows configurations of large spot size or line scan decontamination. As known in the art, low doses of UVC radiation of only 2 mJ/cm² are enough to eradicate influenza A. At this dose, the present laser system 1 can be employed to decontaminate an area of 5 square meters in less than 1 minute. The high power of the output field 25 thus enables the sterilisation or decontamination of significantly larger surface areas, at greater speeds and efficacy, compared to traditional prior art solutions. The laser system 1 has been demonstrated to exhibit an increase in germicidal efficacy of 150,000 times when compared to other light sources such as mercury lamps and LEDs. In addition to the removal of surface contamination, the illumination of air by the output field 25 can be employed to kill Influenza when airborne. It has previously been shown that at deep UVC the radiation is safe for humans. The laser system 1 , can therefore be employed to create ‘light curtains’ that generate germ free zones in hospitals and isolation areas to increase overall safety. Alternative ways of deployment could be in the use of sterilising circulating air in air- conditioning units. Similarly, the laser system 1 could be employed for the sterilisation of food products e.g. cheese, food packaging, clothing, including personal protective equipment (PPE). The above embodiments have been described with a TkSapphire laser being employed as the a continuous-wave, narrow-linewidth, tuneable optical field source 3. It will however be appreciated by those skilled in the art that alternative continuous-wave, narrow-linewidth, optical field sources may be employed as the continuous-wave, narrow-linewidth tuneable source 3, e.g. other solid state lasers or optical parametric oscillators (OPOs) as long as they are tuneable between 800 nm and 1200 nm so as to allow the output field 25 to be tuned between 200 nm and 300 nm. As will also be appreciated by the skilled reader, the combined effects of the first enhancement cavity frequency doubler 4 and the second enhancement cavity frequency doublet 5 is to provide an optical system that frequency quadruples the laser output field 18. Other optical systems which frequency quadruple the laser output field 18 may be employed in alternative embodiments. A laser system and method for generating a continuous-wave, tuneable optical output field having a wavelength between 200nm and 300 nm is disclosed. The laser system comprising: a continuous-wave, narrow-linewidth, tuneable optical field source employed to generate a first output field. The first output field is arranged to propagate thorough the first enhancement cavity frequency double to generate a first frequency doubled output field. The first frequency doubled output field is then arranged to propagate thorough a second enhancement cavity frequency double to generate a second frequency doubled output field which acts as an output field for the laser system. The laser system thus provides a frequency-agile, high power and spectrally pure light source across the UVC the region of the electromagnetic spectrum which makes it a flexible and efficient source for the sterilisation or decontamination of pathogens.

Throughout the specification, unless the context demands otherwise, the terms “comprise” or “include”, or variations such as “comprises” or “comprising”, “includes” or “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

Furthermore, reference to any prior art in the description should not be taken as an indication that the prior art forms part of the common general knowledge.

The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1) A laser system for the sterilisation of pathogens, the laser system comprising: a continuous-wave, tuneable optical field source, and an optical frequency conversion system wherein a first output field generated by the continuous-wave, tuneable optical field source is arranged to propagate thorough the optical frequency conversion system to provide a continuous-wave, tuneable optical output field of the laser system having a wavelength between 200 nm and 300 nm. 2) A laser system as claimed in claim 1 wherein the first output field has a linewidth of 1 GHz or less. 3) A laser system as claimed in either claim 1 or 2 wherein the optical frequency conversion system comprises a first frequency doubler and the first output field is arranged to propagate through the first frequency doubler. 4) A laser system as claimed in claim 3 wherein the optical frequency conversion system further comprises a second frequency doubler and a first frequency-doubled output field generated by the first frequency doubler is arranged to propagate thorough the second frequency doubler. 5) A laser system as claimed in either of claims 3 or 4 wherein the first frequency doubler comprises a first enhancement cavity frequency doubler. 6) A laser system as claimed in either of claims 4 or 5 wherein the second frequency doubler comprises a second enhancement cavity frequency doubler. 7) A laser system as claimed in any of the preceding claims wherein the first continuous- wave, tuneable optical field source is tuneable between 800 nm and 1200 nm. 8) A laser system as claimed in any of the preceding claims wherein the first continuous- wave, tuneable optical field source comprises a Ti:Sapphire laser. 9) A laser system as claimed in any of claims 3 to 8 wherein the first frequency doubler comprises an LBO (Lithium Triborate (UB305)) crystal. 10) A laser system as claimed in any of claims 3 to 9 wherein the first frequency doubler generates the first frequency doubled output field having a wavelength between 400 nm and 600 nm. 11) A laser system as claimed in any of claims 4 to 10 wherein the second frequency doubler comprises a BBO (Beta Barium Borate (BaB204)) crystal. 12) A laser system as claimed in any of the preceding claims wherein the optical output field of the laser system has a linewidth of less than 10 kHz. 13) A laser system as claimed in any of the preceding claims wherein the optical output field of the laser system has a power between an 0.05 W and 0.5 Watts. 14) A method for generating a continuous-wave, tuneable optical output field having a wavelength between 200 nm and 300 nm suitable for sterilisation or decontamination of a pathogen, the method comprising: -generating a first continuous-wave, tuneable optical field; and - frequency converting the first output field. 15) A method for generating a continuous-wave, tuneable optical output field as claimed in claim 14 wherein frequency converting the first output field comprises frequency doubling the first output field to generate a first frequency-doubled output field. 16) A method for generating a continuous-wave, tuneable optical output field as claimed in claim 15 wherein frequency converting the first output field further comprises frequency doubling the first frequency-doubled output field. 17) A method for generating a continuous-wave, tuneable optical output field as claimed in any of claims 14 to 17 wherein the first generated continuous-wave, tuneable optical field is tuneable between 800 nm and 1200 nm. 18) A method for generating a continuous-wave, tuneable optical output field as claimed in any of claims 15 to 17 wherein frequency doubling the first output field comprises generating the first frequency-doubled output field having a wavelength between 400 nm and 600 nm.

19) A method for generating a continuous-wave, tuneable optical output field as claimed in any of claims 14 to 18 wherein the generated continuous-wave, narrow-linewidth, tuneable optical output field has a linewidth of less than 10 kHz.

20) A method for generating a continuous-wave, tuneable optical output field as claimed in any of claims 14 to 19 wherein the generated continuous-wave, narrow-linewidth, tuneable optical output field has a power between an 0.05 W and 0.5 Watts.

21) A method of sterilising or decontaminating an object contaminated by one or more pathogens the method comprising generating a continuous-wave, tuneable optical output field having a wavelength between 200nm and 300 nm in accordance with the method of any of claims 14 to 20.

22) A method of sterilising or decontaminating an object contaminated by one or more pathogens as claimed in claim 21 wherein the method comprises selecting the operating wavelength of the continuous-wave, tuneable optical output field.

23) A method of sterilising or decontaminating an object contaminated by one or more pathogens as claimed in either of claims 21 or 22 wherein the method comprises shaping the continuous-wave, tuneable optical output field.

24) A method of sterilising or decontaminating an object contaminated by one or more pathogens as claimed any of claims 21 to 23 wherein the object may comprise an object in a solid, gaseous or liquid phase.

25) A method of sterilising or decontaminating an object contaminated by one or more pathogens as claimed in any of claims 21 to 24 wherein the object comprises a surface, a volume of air, a food product, food packaging, clothing or personal protective equipment (PPE). 26) A method of sterilising or decontaminating an object contaminated by one or more pathogens as claimed in claim 22 wherein the volume or air is contained with an air conditioning system.