WO2017134432A1

WO2017134432A1 - A propulsion device and system using interfering laser beams

Info

Publication number: WO2017134432A1
Application number: PCT/GB2017/050248
Authority: WO
Inventors: Douglas Robinson
Original assignee: Douglas Robinson
Priority date: 2016-02-02
Filing date: 2017-02-01
Publication date: 2017-08-10
Also published as: GB2531475B; GB2531475A; GB201601857D0

Abstract

A propulsion device (1) for use in an aerospace or other vehicle (2) comprising: a first laser beam (11); a second laser beam (12); and a field material (13) which is a source of a first electric field, wherein the first laser beam (11) and the second laser beam (12) are configured to interfere constructively within a superposition zone (16), the field material is located with respect to the superposition zone (16) such that a second electric field generated by the interference between the first laser beam (11) and the second laser beam (12) in the superposition zone (16) interacts with the first electric field to result in a force being applied to the field material (13), and the field material (13) is configured for coupling to at least part of the vehicle (2) for movement therewith.

Description

Title: A propulsion device and system using interfering laser beams Description of Invention

Embodiments of the present invention relate to a propulsion device and system for use in an aerospace or other vehicle (e.g. for use on land, at sea, etc.). Some embodiments are particularly advantageous in relation to aerospace vehicles.

Transportation is presently highly dependent on internal combustion engines, associated with which is the pollution they create in the atmosphere and depletion of limited resources of valuable fossil fuels.

Propulsion without propellants is also regarded as an essential development to overcome the severe limitations associated with current fuel-based propulsion systems, for future deep space missions (i.e. far beyond the Earth's atmosphere, for example).

There is a desire, therefore, to provide engines which do not rely on combustion.

Such dependencies are unsustainable and place severe limitations on our future means of transportation.

There is therefore an urgent need to replace current forms of propulsion to alleviate atmospheric pollution and the limited effectiveness that becomes increasingly intolerable with altitude.

Accordingly, embodiments of the present invention seek to alleviate one or more problems associated with the prior art. Accordingly, an aspect of the present invention provides a propulsion device for use in an aerospace or other vehicle comprising: a first laser beam; a second laser beam; and a field material which is a source of a first electric field, wherein the first laser beam and the second laser beam are configured to interfere constructively within a superposition zone, the field material is located with respect to the superposition zone such that a second electric field generated by the interference between the first laser beam and the second laser beam in the superposition zone interacts with the first electric field to result in a force being applied to the field material, and the field material is configured for coupling to at least part of the vehicle for movement therewith.

The first laser beam and the second laser beam may be substantially counter- propagating beams.

The propulsion device may include a first laser device operable to emit the first laser beam and a second laser device operable to emit the second laser beam. The first laser device and the second laser device may be spaced apart and operable to emit the first and second laser beams in opposing coaxial directions.

The propulsion device may include more than two laser devices, each of which is operable to emit an additional laser beam.

The more than two laser devices may all lie on a single plane.

The propulsion device may include a beam splitter configured to split the first laser beam to form two or more laser beams of the same phase and frequency, and which are coherent. The propulsion device may include one or more light modification elements so as to alter one or more of the laser beams.

The field material may be spaced apart from the superposition zone.

The field material may lie in a plane which is parallel with the plane in which the laser beams lie. The field material may be an electret material.

The first and second laser beams may be substantially continuous beams. Another aspect provides an aerospace vehicle including a propulsion device. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates a vehicle including a propulsion system according to some embodiments of the invention;

Figure 2 illustrates a propulsion device in accordance with some embodiments of the invention;

Figure 3 illustrates a propulsion device in accordance with some embodiments of the invention;

Figure 4 illustrates a beam combiner for use in a propulsion device in accordance with some embodiments of the invention; Figure 5 illustrates a beam splitter for use in a propulsion device in accordance with some embodiments of the invention; Figure 6 is a vector diagram for the energy flow (or Poynting vector), the electric field, and the magnetic field in counter-propagating laser beams in accordance with embodiments of the invention; Figure 7 shows a general arrangement of a propulsion device (in block form) in accordance with some embodiments; and

Figure 8 shows a propulsion device in accordance with some embodiments.

Embodiments of the present invention include a propulsion device 1 , see figures 1 , 2, 3, and 7 for example.

The propulsion device 1 may be mounted with respect to a vehicle 2. The vehicle 2 could take a number of different forms and may be an aerospace vehicle such as a spacecraft or aircraft. The vehicle 2 may be configured to travel through open space (which may include interstellar space, interplanetary space, and/or orbital space around a planet, or the like). In some embodiments, however, the vehicle 2 may be configured for atmospheric travel (i.e. travel within the atmosphere of a planet). The vehicle 2 may be an aircraft, a land vehicle, or a boat/ship for example.

The vehicle 2 may be configured to carry a crew or may be an unmanned vehicle - which may include an artificial satellite, a probe, or an exploration vehicle.

The propulsion device 1 may be configured to drive movement of the vehicle 2 in space (or atmosphere) and may be a main drive engine of the vehicle 2 (i.e. an engine configured to provide a main driving force to move the vehicle 2 along its trajectory) or may be a manoeuvring engine of the vehicle 2 (i.e. an engine primarily concerned with altering the trajectory of the vehicle 2).

The vehicle 2 may include a power source 21 which is configured to provide electrical power to one or more parts of the vehicle 2, including the propulsion device 1 .

The power source 21 may include any suitable source of electrical power for that vehicle 2 and may comprise a plurality of different power sources. For example, the power source 21 may include one or more solar panels and/or nuclear reactors (such as an isotope generator or isotope generators) and/or an energy storage system (such as a battery or capacitor, or a plurality of batteries or capacitors (the or each capacitor may be a supercapacitor)). Operation of one or more parts of the vehicle 2 may be controlled by a control system 22. The control system 22 may be configured to control the operation of the propulsion device 1 and/or the power source 21 , for example.

The propulsion device 1 is configured to receive electrical power from the power source 21 for use in its operation.

Embodiments of the propulsion device 1 are discussed in more detail with reference to figures 2 to 8. In some embodiments, with reference to figures 2, 3, 6, 7 and 8, for example, the propulsion device 1 includes a first 1 1 and a second 12 light beam (in this context, light meaning electromagnetic radiation and not limited to visible light). The first 1 1 and second 12 light beams of the propulsion device 1 are orientated with respect to each other such that they are configured to overlap (e.g. converge) at one or more points in space (where space in this context means the dimensions in which all things exist). The first and second light beams 11,12 may be produced from a single light source or from a first and a second light source 111,112, respectively. The or each light source 111,112 may be configured to receive electrical power from the power source 21 (directly or via another part of the propulsion device 1) and the electrical power may be used to power the operation of the or each light source 111,112 (including the emission of light).

In some embodiments, the second light beam 12 may be emitted from the same light source as the first beam 11 (i.e. both the first and second light beams 11,12 may originate from a single beam of light). The second light beam 12 may be split from the single beam of light by one or more optical elements and deflected (or otherwise guided) such that it overlaps the first beam 11 (i.e. the first beam 11 remains from the single light beam that the second beam 12 was deflected from). The single beam of light may be a beam of light which is, itself, produced by combining two or more beams (e.g. from multiple light sources) - as described herein.

In some embodiments, with reference to figure 2 as an example, the first and second light beams 11,12 may be emitted from a first and a second light source 111,112, respectively. The first and second light sources 111,112 may be arranged to lie on a single plane (and may be arranged coaxially with respect to each other, so that the first and second light beams 11,12 counter- propagate). There may be more than two separate light sources 111,112 provided; each of those light sources 111,112 may lie on a single plane (and the light sources 111,112 may be arranged in coaxial pairs, to provide counter- propagating pairs of beams 11 ,12) - as described herein.

The first and second light sources 111,112 may be light sources which are configured to emit light of substantially the same frequency. In some embodiments where there is a single light source, both the first and second light beams 1 1 ,12 are the same frequency (and may be phase- and frequency- locked with respect to one another). The light of the first and second light beams 1 1 ,12 may, therefore, be substantially monochromatic light. Both the first and second light beams 1 1 ,12 have respective beam axes. In some embodiments, the first and second light sources 1 1 1 ,1 12 may each be configured to emit a respective beam of light along respective beam axes.

The beam axes may be angled with respect to one another such that they cross or otherwise overlap in a desired location.

In some embodiments, the beam axes may be substantially parallel with each other and aligned with each other. Accordingly, the first light beam 1 1 may be directed towards the second light beam 12 and as such the first and second light beams 1 1 ,12 may be coaxial and travelling in opposing directions - i.e. the first and second light beams 1 1 ,12 may be counter-propagating beams 1 1 ,12. In some embodiments, such as depicted in figure 2 for example, the first light source 1 1 1 may emit light directly towards the second light source 1 12 and the two light sources 1 1 1 ,1 12 may be spaced apart from each other, in order to produce coaxial beams of light.

As will be appreciated, different orientations of the first and second light beams 1 1 ,12 may be used to provide the overlap at the desired location (which may be achieved, at least in part, by using different orientations of the two light sources 1 1 1 ,1 12). For example, the first and/or second light beam 1 1 ,12 may be emitted to propagate in one direction, then may be redirected. The first and/or second light beam 1 1 ,12 may be redirected once in order to arrive at the desired location, or may undergo more than one change of propagation direction to arrive at the desired location. Redirection may be achieved by, for example, directing the first and/or second light beam 1 1 ,12 towards one or more mirrors, and/or towards one or more polarizing gratings, or other examples of light redirection elements (such as a first 15c or second 15d light redirection element as shown in figure 7).

In some embodiments, a location where the first and second light beams 1 1 ,12 overlap may be referred to as being in a "superposition zone" 16 of the first 1 1 and second 12 light beams and, hence, also of the propulsion device 1 . In some embodiments in which the first and second light beams 1 1 ,12 are emitted as counter-propagating beams 1 1 ,12, without the need for redirection, the superposition zone 16 may be generally midway between the first light source and the second light source 1 1 1 ,1 12.

Within the superposition zone 16 the first and second light beams 1 1 ,12 interfere constructively. Therefore, within the superposition zone 16, the magnetic field components of each respective light beam 1 1 ,12 (each being an electromagnetic wave) cancel one another (i.e. sum to zero), and the respective electric field components are superposed (i.e. summed). In other words, the magnetic field of the light is substantially transformed into an electric field. Therefore, the electric field at a point within the superposition zone 16 (the "second electric field") is greater than would be the case for the electric field associated with a single such light beam 1 1 ,12.

This is understood to occur in accordance with the observations described in "On the superposition and elastic recoil of electromagnetic waves" by Dr Hans G. Shantz, Forum for Electromagnetic Research Methods and Application Technologies (FERMAT), Vol 4 No.2 Jul-Aug, 2014. This paper generally investigates the case of two electromagnetic waves travelling in opposing directions (i.e. counter-propagating), and states that superimposed and interfering waves give rise to momentary concentrations of static electric or static magnetic energy associated with the recoil and reflection of interfering waves from each other. Embodiments of the present invention seek to take advantage of this non-linear effect. Thus, when the first light beam 1 1 interferes with the second light beam 12 there is a momentary concentration of static electric field which is larger than the electric field associated with either the first or second light beam 1 1 ,12 (and may be larger than the two electric fields added together, which is understood to be due to the transformation of the magnetic field at that instant).

The vector diagram of figure 6 shows the electric (E) and magnetic (H) field vectors for the first and second light beams 1 1 ,12, along with the associated Poynting vectors (S). During constructive interference in the superposition zone 16, there is a resulting electric field (2E) which is also shown in figure 6, and no resulting magnetic field (H) or energy flow (S). A very similar vector diagram can be seen in figure 1 of "On the superposition and elastic recoil of electromagnetic waves" by Dr Hans G. Shantz, Forum for Electromagnetic Research Methods and Application Technologies (FERMAT), Vol 4 No.2 Jul- Aug, 2014, in relation to constructive interference in transmission lines, for example. Embodiments of the present invention use a similar effect to generate an electric field using constructive interference of the first and second light beams 1 1 ,12. Accordingly, as will be appreciated, constructive interference of the first and second light beams 1 1 ,12 is used by embodiments of the present invention to generate an electric field (2E) in the superposition zone 16 generally as shown in figure 6. In short, therefore, with reference to figure 3, embodiments may use first and second light beams 1 1 ,12 directed towards a superposition zone 16 which is positioned with respect to a field material 13.

More complex embodiments are envisaged in order to seek to provide one or more further advantages and some of these are described below. Accordingly, in some embodiments, the propulsion device 1 further includes one or more light modification elements 15 which may include one or more lenses, filters, deflection devices and/or gratings. The or each light modification element 15 is configured to modify a characteristic of a light beam received thereby.

With reference to figure 7 several different light modification elements are depicted which may also be used in other embodiments. Accordingly, a light modification element may be any one or more of a beam combiner 15a (e.g. a binary optic grating and/or a diffraction grating and/or an element for common cavity laser beam addition), a beam splitter 15b (e.g. a binary optic beam splitter), a light redirection element 15c,15d (e.g. a laser prism), or a collimator 15e (e.g. collimating binary optics). A light modification element may include one or more micro-lenses, for example.

In some embodiments, it may be advantageous to have only two light beams 1 1 ,12 which are coaxial with one another and traveling in opposing directions - i.e. counter-propagating. More than two light sources 1 1 1 ,1 12, which may be in an array, (and/or more than two light beams 1 1 ,12) may be used, however, to increase the power of such a system. In such embodiments, a beam combiner 15a may be provided (e.g. a common cavity, including a binary grating) as part of the propulsion device 1 to combine multiple light beams into a single beam (which may then be split using a beam splitter 15c downstream of the beam combiner 15a to form the first and second light beams 1 1 ,12) or to combine multiple light beams into the first and/or second light beams 1 1 ,1 2.

With reference to figure 4, therefore, a plurality of first or second light sources 1 1 1 /1 12 may be provided and each light source 1 1 1/1 12 of the plurality may be configured to direct a respective source light beam 1 1 a into the beam combiner 15a.

The beam combiner 15a is configured to combine this plurality of source light beams 1 1 a into a single light beam (for example, by use of a common cavity and a binary diffraction element, as proposed in "Coherent laser beam addition: an application of binary-optics technology" by J. R. Leger et al) which may then form one of the first and second light beams 1 1 ,12 or which may be split to form both the first and second light beams 1 1 ,12 (the latter being depicted in figure 7).

As will be appreciated, the single light beam output by the beam combiner 15a may be a coherent light beam (and more than one such coherent light beam may be generated within the propulsion device 1 ) which may be a phase- and frequency-locked beam. In the case of separate sources 1 1 1 ,1 12, the beams 1 1 ,12 may be mutually coherent (which may be achieved by use of a master oscillator coupled to all of the sources 1 1 1 ,1 12).

The first and second light beams 1 1 ,12 may therefore be produced from an array or from respective arrays of light sources 1 1 1 /1 12, for example a semiconductor laser array.

Laser beam addition in this manner has been investigated in "Coherent laser beam addition: an application of binary-optics technology" by J. R. Leger et al, The Lincoln Laboratory Journal, Volume 1 , Number 2 (1988). This paper concludes that coherent laser beam addition offers the potential for extremely bright optical sources by combining the power from many individual lasers and presents several advantages that include resistance to failure because if one laser device fails there are several more that can still provide a beam of substantial power. The use of a binary grating, or another beam combiner 15a, and a plurality of light sources 1 1 1 ,1 12 (which may be in one or more arrays) to create a phase- and frequency-locked beam 1 1 /12 (for use as the first and/or second light beam 1 1 ,12), therefore, may provide increased power but also redundancy in relation to some embodiments. In some embodiments, the or each beam combiner 15a is associated with a respective one of a set of the first 1 1 1 or second 1 12 light sources and configured to modify the light emitted by that set of light sources 1 1 1 ,1 12. For example, there may be several light sources 1 1 1 ,1 12 on either side of the superposition zone 16, the outputs of which are combined together to produce two powerful first and second light beams 1 1 ,12. In this case, "either side" may refer to the physical location or to the location in relation to the flow path of the light from the sources 1 1 1 ,1 12 to the superposition zone or zones 16.

"Coherent laser beam addition: an application of binary-optics technology" by J. R. Leger et al, The Lincoln Laboratory Journal, Volume 1 , Number 2 (1988), also discusses three requirements for providing high radiance from a laser array: that the lasers must be mutually coherent (i.e. phase- and frequency- locked to one another), the phase relationship must be adjusted so that they have the maximum power along the optical axis, and the wavefront emanating from the array must be modified to produce quasi-uniform exit aperture illumination. Embodiments of the present invention may use such techniques to provide high radiance from a laser array (e.g. an array of light sources 1 1 1 /1 12) providing the first and second light beams 1 1 ,12. In some embodiments, all of the light sources 1 1 1 ,1 12 (of which there may be more than two) are arranged in order to produce light beams 1 1 ,12 in opposing (i.e. counter-propagating) pairs around a common superposition zone 16 (and this may be achieved by the light sources 1 1 1 ,1 12 also being arranged in opposing pairs around a common superposition zone 16 in some embodiments). In some embodiments, there may be a plurality of light sources 1 1 1 ,1 12 with multiple groups of light sources 1 1 1 ,1 12 producing light beams 1 1 ,12 associated with respective different superposition zones 16 (and so the light sources 1 1 1 ,1 12 may be associated with different superposition zones 16). The light sources 1 1 1 ,1 12 may, in some embodiments, be laser devices which are each configured to output a laser beam - i.e. coherent light. As will be appreciated, the light sources 1 1 1 ,1 12 are examples of emitters of electromagnetic radiation (e.g. in the form of respective beams). This electromagnetic radiation may be at a frequency at or above the terahertz range (i.e. 300 GHz to 3 THz). This electromagnetic radiation may be at a frequency in the visible light range (i.e. may be between 400THz and 800THz), or in the X-ray range (i.e. at a higher frequency than visible light, up to the exahertz region of the electromagnetic spectrum), for example. Electromagnetic radiation may be of a frequency which is less than the gamma ray range of the electromagnetic spectrum (i.e. at a frequency below around 10 or 30 EHz (exahertz)). .

In embodiments, therefore, the light sources 1 1 1 ,1 1 2 may be sources of coherent light in the form of respective beams and may be in-phase with each other.

The present inventor has discovered that quantum cascade lasers (QCLs) may be particularly suitable for use in some embodiments because they are relatively stable. The present inventor deduced that they are also suitable for other high precision environments such as the one described herein. QCLs are understood to be intrinsically stable against optical feedback and this is beneficial in some embodiments - in which a first and a second light source 1 1 1 ,1 12 (which may be each be part of a respective array of light sources 1 1 1 /1 12) may be arranged to produce light beams 1 1 ,12 opposing each other (and may, themselves, be arranged to oppose each other). The light sources 1 1 1 ,1 12 are configured to output light which is linearly polarised.

In some embodiments, as will be appreciated, the light sources 1 1 1 ,1 12, may be coupled to one or more integrated plasmonic out-couplers or one or more binary optic elements, which are configured to act on the output for the light sources 1 1 1 ,1 12 respectively.

So, in some embodiments, the first and second light sources 1 1 1 ,1 12 are configured to provide the first and second light beams 1 1 ,12 and may achieve this directly or via one or more light modification elements.

"Coherent laser beam addition: an application of binary-optics technology" by J. R. Leger et al, The Lincoln Laboratory Journal, Volume 1 , Number 2 (1988) also discusses grating splitting efficiency, and more particularly a design for a grating (i.e. an exemplary light modification element, and in particular an exemplary beam splitter 15b) to split a single beam into multiple beams having equal intensity, without a detrimental effect on efficiency. For example, binary phase-only structures to split a laser beam into a number of equal orders, N, are discussed. The document discusses aperture filling by coupled micro- cavities, which is well-suited for use with large two-dimensional semiconductor arrays in achieving high power densities. Some embodiments of the present invention may make use of such two-dimensional arrays (e.g an array of light sources 1 1 1 /1 12) to achieve high radiance beams, with high efficiency and reliability (which may be suitable for aerospace applications, for example).

The document discusses beam splitting in order to distribute a single feedback beam evenly amongst lasers in an optical system. Some embodiments of the present invention may use such techniques, however, to split, or redistribute, one or both of the first and second light beams 1 1 ,12 to form respective pluralities of beams, which may be equal order beams (e.g. having one or more identical or substantially identical properties). These techniques may be used in embodiments including the one or more light modification elements (e.g. such as embodiments discussed herein and using a binary grating, configured to act as a beam splitter 15b).

In some embodiments, the propulsion device 1 may further include one or more other light modification elements, in particular a beam splitter 15b, associated with one or both of the first and second light beams 1 1 ,12. The or each light beam 1 1 ,12 may be split by a light modification element, and in particular a beam splitter 15b, to form respective sets of multiple mutually coherent first and second beams 1 1 ,12 (i.e. first and second sets of mutually coherent beams 1 1 ,12). A coherent first or second beam 1 1 ,12 may propagate in the same direction as the first or second light beam 1 1 ,12 from which that coherent first or second beam 1 1 ,12 originated. Therefore, the propagation direction of the mutually coherent first beams 1 1 resulting from the splitting of the first light beam 1 1 may be away from the first light source 1 1 1 (or plurality of first light sources 1 1 1 , which may be in an array), and may be in the direction of the superposition zone 16.

The propagation direction of the mutually coherent second beams 12 resulting from the splitting of the second light beam 12 may be away from the second light source 1 12 (or plurality of second light sources 1 12, which may be in an array), and may be in the direction of the superposition zone 16.

Such embodiments may result in sets of coherent first and second beams 1 1 ,12 being directed towards the superposition zone 16 (or, in this case, zones 16); each set including a respective beam from a pair of beams, such that a set includes a coherent beam corresponding with a coherent beam from the other set. Similarly, a set of coherent first beams or second beams 1 1 ,12 may propagate in a direction at an angle to the axis of propagation of the first and/or second light beam 1 1 ,12 from which the coherent beam 1 1 ,12 originated, such a coherent beam may be redirected. Redirection may be achieved by, for example, directing the coherent beam towards a mirror, or a polarizing grating, or the like (i.e. a light modification element, and in particular a light redirection element 15c, 15d).

However, in some embodiments, a single beam is directed to the beam splitter 15b which splits that single beam into the first and second beams 1 1 ,12, each of which is then directed towards the superposition zone 16 (directed by a waveguide, for example). Of course, as will be appreciated, one or more other light modification elements may be located downstream (in the light flow path) of the beam splitter 15b and upstream (in the light flow path) of the superposition zone 16 in order to provide the required respective orientation of the two light beams 1 1 ,12 at the superposition zone 16. These one or more other light modification elements may include one or more light redirection elements 15c,15d, for example a mirror or a polarizing grating. Figure 5 shows a light modification element (and in particular a beam splitter 15b) for splitting the first light beam 1 1 into the set of coherent first beams 1 1 . This set of coherent beams 1 1 may be referred to as a first set of coherent beams to designate the set as originating from the first light beam 1 1 . The beam splitter 15b may be a combination of optical elements. The combination of optical elements may include a beam splitter 15b, for example a binary grating to split the first light beam 1 1 . The combination of optical elements may include a light redirection element 15c, for example a mirror or a polarizing grating. Although Figure 5 shows splitting and redirecting the first light beam 1 1 , it should be understood that a similar or identical method may also be used on the second light beam 12 (and to generate a second set of coherent beams 12.

Equally, as described above, the beam splitter 15b shown in figure 5 could be used to split a single light beam into the first and second light beams 1 1 ,12.

In embodiments in which coherent first and second sets of light beams 1 1 ,12 are produced, the coherent first and second sets of light beams 1 1 ,12 may be arranged such that one beam resulting from the splitting of the first light beam 1 1 and one beam resulting from the splitting of the second light beam 12 may be identifiable as a pair of beams having one or more of the same characteristics as the light beams 1 1 ,12 as herein described. In particular, these beams may be opposing co-axially aligned light beams. These beams may be counter-propagating beams. These beams may be arranged in opposing pairs such that a superposition zone 16 is defined for the interference of the pair or pairs of counter-propagating beams. Pairs of first and second beams 1 1 ,12 (or be they part of a set or otherwise) may be arranged such that a common superposition zone 16 is defined. For example, a first axis along which a first pair of beams 1 1 ,12 counter-propagate may intersect a second axis along which a second pair of beams 1 1 ,12 counter-propagate, and the superposition zone 16 defined for the first pair may be the same superposition zone 16 defined for the second pair. There may be multiple pairs of counter-propagating beams 1 1 ,12, arranged such that a common superposition zone 16 is formed; for example the pairs of beams 1 1 ,12 may propagate radially inwardly towards a central superposition zone 16. There may be more than one superposition zone 16 defined for a system in which there is more than one pair of beams 1 1 ,12. There may be one superposition zone 16 associated with one pair of beams 1 1 ,12 and another superposition zone 16 associated with another pair of beams 1 1 ,12, for example. Two or more superposition zones 16 may be located generally in the same plane. A superposition zone 16 may be a two-dimensional zone in which superposition may occur.

In some embodiments, a light modification element is provided which may be a collimator 15e, configured to create a collimated beam of light. The first and second beams 1 1 ,12 may be collimated by respective collimators 15e, for beam alignment. One or more collimators 15e may be used to create a local maximum at one or more locations within one superposition zone 16. There may be more than one light modification element (and in particular more than one collimator 15d).

The light modification element provided upstream of the superposition zone 16 may be configured to create concentrations of local maxima of the light within the superposition zone 16.

In some embodiments, a focusing element is provided instead of or in addition to the collimator 15e. This may be used to improve the effect of the operation of some embodiments of the invention and/or to concentrate the resulting electric field at one or more locations. This may increase the amplitude of the electric field at one or more locations. The electric field may be a quasi-static electric field.

The propulsion device 1 further includes a material 13 which generates or is otherwise a source of a first electric field, herein referred to as the "field material". The field material 13 may have a high surface charge density. This field material 13 may be a bound (i.e. trapped) charge carrier. In other words, the field material 13 may include a plurality of charged particles which are bound (i.e. trapped) within the confines of the material in such a manner that the material has and may sustain a substantially permanent electric field. The field material 13 may be a dielectric material and may be an electret material. An electret material is a material that has a quasi-permanent electric charge or dipole polarisation (and is generally thought of as the electrostatic equivalent of a permanent magnet). In some embodiments such as those with counter-propagating light beams 1 1 ,12, the field material 13 may be located such that it is substantially aligned with the superposition zone 16 (or with the plane in which two or more superposition zones 16 are defined) and offset from the beam axes - which, for counter-propagating beams 1 1 ,12, is a common beam axis. Accordingly, the field material 13 may be generally located along an axis which is transverse to the beam axes (preferably perpendicular) and which also intersects (or bisects) the superposition zone 16, this axis will be referred to herein as the "drive axis" (i.e. the drive axis is normal to a main plane of the field material 13, the main plane being a plane in which the largest part of the field material 13 lies).

In some embodiments (such as those with additional light beams or non- coaxial arrangements), the field material 13 may be spaced apart from the superposition zone 16.

The field material 13 may be provided as a plate of material 13 which extends through the main plane which is generally parallel with the beam axes (and, therefore, substantially perpendicular to the drive axis). The drive axis may, in some embodiments, pass through a generally central portion of the field material 13. In some embodiments, in which there are multiple superposition zones 16 (e.g. due to the use of multiple groups of light sources 1 1 1 ,1 12 or due to the there being sets of first and second light beams 1 1 ,12, as described herein), each superposition zone 16 may be associated with its own field material 13 or more than one superposition zone 16 may be associated with a common field material 13.

The field material 13 is located a predetermined distance from the beam axes in the region of the superposition zone 16 (in other words, a predetermined distance from a plane in which the first and second light beams 1 1 ,12 are located). This distance is such that the field material 13 and the electric field generated in the superposition zone 16 (i.e. by the quasi-static second electric field) may interact. Accordingly, therefore, the first and second electric fields interact. The predetermined distance may, in some embodiments, be linked to the size of the field material 13. For example, the width (e.g. the diameter) of the field material 13 may be approximately five times the predetermined distance. The field material 13 may, in these and some other embodiments, be positioned so that a central portion of the field material 13 is generally aligned with the superposition zone 16.

The first and second light beams 1 1 ,12 are arranged such that in the superposition zone 16, the electric fields of the first and second light beams 1 1 ,12 are of the same polarity and substantially aligned to intersect the field material 13.

As the field material 13 includes bound charges, the electric field generated in the superposition zone 16 (see figure 6, for example) will act on the bound charges and will, therefore, apply a force to those bound charges. The force may be a repulsive force. The bound charges may be bound surface charges within the field material 13. As the charges are bound (i.e. trapped) within the field material 13, movement of the charges is restricted within the material and a force will be translated through the field material 13. This force may be translated into motion of the vehicle 2, for example.

Professor Richard Feynman sought to explain discrepancies in momentum conservation for interactions involving charged particles and electric fields, and in doing so showed in his lectures (Vol. 1 , chapter 10-5, Relativistic Momentum) that Newton's third law does not apply (at least in conventional terms) to interactions between charged particles and electric fields, in which a force due to an interaction is mediated at the speed of light. The resulting force would be subject to delays; an 'action at a distance' force according to Professor Feynman. Thus, in embodiments of the present invention, the action and reaction of Newton's third law are, at least locally, decoupled through the use of electromagnetic waves (i.e. the first and second light beams 1 1 ,12).

Wave-particle duality allows a photon (i.e. a quantised wave-packet of light, for example in beams 1 1 ,12) which is a chargeless, massless, relativistic particle, to propagate in an electric field without perturbation, but also to interact (i.e. interfere) through the wave nature to produce a massless field which may impose a force on a massive material (i.e. the field material 13, and in turn, for example, a vehicle 2 with which a field material 13 is engaged).

Accordingly, superposition and constructive interference between the first beam and the second beam 1 1 ,12 (where the beams 1 1 ,12 may be counter- propagating) may generate a quasi-static electric field. Interaction between the quasi-static electric field (the second electric field) and the electric field associated with the field material 13 (the first electric field) produces a force on the field material 13 without any expulsion of mass from the field material 13 or other part of the propulsion device 1 . If the second electric field is of the same polarity as the bound charges in the field material 13, the force is a repulsive force.

As will be understood, when the first and second light beams 1 1 ,12 propagate within the region of the first electric field, each respective beam 1 1 ,12 does not interact with the first electric field (as photons are chargeless). However, the second electric field interacts with the first electric field and this interaction is generally instantaneous, as the second electric field is formed by the interference of the first and second light beams 1 1 ,12. Therefore, the influence of the second electric field on the field material 13 is generally instantaneous and it is this interaction which applies a force on the field material 13 to drive movement of the propulsion device 1 .

In some embodiments, the first and second light beams 1 1 ,12 may be provided substantially continuously over a period of time - which may be the period of time in which the propulsion device 1 is configured to drive movement. The substantially continuous provision of the first and second light beams 1 1 ,12 seeks to ensure the replacement of electric field energy lost during the mutually repulsive reaction between the first and second fields so as to maintain a propulsive force acting on the field material 13.

In embodiments in which the electric field in the superposition zone 16 (i.e. the second electric field) has local maxima as a result of the use of one or more light modification elements, the distribution of bound charges within the field material 13 may be such that the bound charges are concentrated at the location of the local maxima in the electric field.

The field material 13 may be secured for movement with a frame 14 of the propulsion device 1 which is, in turn, secured for movement with the vehicle 2. Accordingly, the force acting on the field material 13 will be transmitted, in such embodiments, through the frame 14 of the propulsion device 1 to the vehicle 2 to cause the vehicle 2 to move through space (which may be in outer space or in an atmosphere, etc.).

Accordingly, the propulsion device 1 may be used to drive movement of the vehicle 2. The propulsion device 1 does not consume a propellant material but will, of course, require electrical power from the power source 21 in order to power the light sources 1 1 1 ,1 12.

Embodiments of the present invention also do not expel pollutants or the results of any combustion process. Accordingly, the operation of the propulsion device 1 of some embodiments is environmentally friendly.

In some embodiments, the first and second light sources 1 1 1 ,1 12 may comprise a first pair of such light sources of the propulsion device 1 . In some embodiments, there is a plurality of such pairs of light sources. These pairs of light sources may each be associated with a respective superposition zone 16. In some embodiments, these superposition zones 16 are spaced apart (and may act on respective portions of field material 13) but in other embodiments the superposition zones 16 are aligned along at least one axis and may be substantially superimposed with respect to each other. In some such embodiments, the plurality of superposition zones 16 is associated with a single portion of field material 13. In some embodiments, the pairs of light sources are arranged in a circular array with their respective light beams directed radially inwardly - each pair of light sources may direct their beams in the same plane or in different planes. This may, in some embodiments, result in a generally centrally located superposition zone 16.

The first and second light sources 1 1 1 ,1 12 may be configured to direct the first and second light beams 1 1 ,12 into a chamber of the propulsion device 1 . One or more light modification elements, for example one or more light redirection elements 15c,15d, may be configured to direct the first and second light beams 1 1 ,12 into a chamber of the propulsion device 1 . This chamber may define a volume into which the first and second light beams 1 1 ,12 are directed and in which is located the field material 13. In some embodiments, this volume is maintained substantially as a vacuum.

As will be appreciated, the propulsion device 1 forms part of a propulsion system 3 which may include other parts of the vehicle 2 too, such as the power source 21 and/or the control system 22. The vehicle 2 may take, as mentioned above, a number of different forms - with the propulsion device 1 providing a direct driving force for the movement of the vehicle 2 (be it a vehicle 2 configured for travel in space or in atmosphere). As will be appreciated, the operation of some embodiments of the invention does not require the moving parts within the propulsion device 1 . Therefore, in some embodiments, there is less noise generated through operation than might be the case for some conventional propulsion devices. With reference to figures 7 and 8, an embodiment is depicted which comprises an arrangement of the above described features of the propulsion device 1 . Various embodiments are described below with reference to these figures.

In some embodiments, the propulsion device 1 includes one or more light sources 1 1 1 /1 12 which may be arranged in a linear array or in a two dimensional array (such that there are multiple rows and columns of light sources 1 1 1 /1 12).

These one or more light sources 1 1 1 /1 12 are configured to direct light beams 1 1 /12 (which are source light beams 1 1 a within the context of figure 5) towards a beam combiner 15a (which may be common to all of the beams 1 1 /12, or for one or more sub-groups of the beams 1 1 /12). This beam combiner 15a is configured to combine the beams 1 1 /12 into one or more phase- and frequency-locked light beam and, in some embodiments, into a single phase- and frequency-locked light beam.

The phase- and frequency locked beam(s) are, subsequently, directed to a second light modification element. The second light modification element may be a beam splitter 15b (which may include a binary grating and/or one or more other optical elements) which is configured to split the one (or more) light beams from the first light modification element 15a into a plurality of light beams 1 1 ,12 - namely the first and second light beams 1 1 ,12 as described herein. This plurality of light beams 1 1 ,12 may be in the form of coherent light and may be in-phase. As will be appreciated, the combining and splitting of beams in accordance with some such embodiments, allows the power of multiple light sources 1 1 1 ,1 12 to be combined and for multiple beams of coherent light to be generated (which may all also be coherently in phase with each other).

The first and second light beams 1 1 ,12 may then be directed to a third light modification element, which may be a first light redirection element 15c and may be, for example, a laser prism or other optical element, configured to redirect the light beams 1 1 ,12 towards one or more fourth light modification elements, which may be respective second light redirection elements 15d, configured to redirect the light beams 1 1 ,12 towards the superposition zone 16.

The third and fourth light modification elements 15c,15d are configured to direct the light beams 1 1 ,12 to the desired location with respect to the superposition zone 16 and this may include directing the light beams 1 1 ,12 around one or more other parts of the device 1 . For example, the light beams 1 1 ,12 may be directed around the field material 13. The frame 14 may, as will be appreciated, be configured to allow the re-directed light beams 1 1 ,12 therethrough (e.g. around the frame 14 or through apertures at least partially defined by the frame 14). The third and fourth light modification elements 15c,15d may include a plurality of optical elements which may include one or more mirrors, lenses and the like. Whilst the light beams 1 1 ,12 reaching the superposition zone 16 are depicted as being directed through respective further light modification elements 15d (such as lenses), this is optional - these optional elements may be collimators 15e or focusing elements as described herein, for example.

The fourth light modification elements 15d are configured to be secured in a substantially fixed position with respect to the frame 14 and, hence, with respect to the field material 13. In some embodiments, the fourth light modification elements 15d are secured to the frame 14 itself.

In some embodiments, arrays of fourth light modification elements 15d are provided - see figure 8. In such embodiments, the third light modification element 15c (which may be one element or multiple elements) is configured to direct the light beams 1 1 ,12 to respective ones of the fourth light modification elements 15d. As will be understood, therefore, with regard to figure 7, there may be additional pairs of fourth light modification elements 15d located behind the depicted elements 15d. In some embodiments, a single fourth light modification element 15d is configured to receive and redirect multiple beams 1 1 ,12 generally simultaneously. In such embodiments, the first and second light beams 1 1 ,12 may include first and second sets of light beams 1 1 ,12 as described herein.

As can be seen in figure 8, the resulting arrays of fourth light modification elements 15d may provide a plurality of superposition zones 16 across a length of the field material 13. Again, the provision of the final light modification elements 15e is optional. In some embodiments, the second beam redirection elements 15d (which are also the fourth light modification elements 15d) may be binary optic beam transmission elements.

The propulsion device 1 may be a modular device, such that the vehicle 2 may include multiple propulsion devices 1 as described herein.

That electric forces are billions of times stronger than gravitational forces between masses is indicative of the huge potential and effectiveness of electric forces in propulsion applications.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

Claims

A propulsion device for use in an aerospace or other vehicle comprising:

a first laser beam;

a second laser beam; and

a field material which is a source of a first electric field, wherein the first laser beam and the second laser beam are configured to interfere constructively within a superposition zone,

the field material is located with respect to the superposition zone such that a second electric field generated by the interference between the first laser beam and the second laser beam in the superposition zone interacts with the first electric field to result in a force being applied to the field material, and

the field material is configured for coupling to at least part of the vehicle for movement therewith.

A propulsion device according to claim 1 , wherein the first laser beam and the second laser beam are substantially counter-propagating beams.

A propulsion device according to claim 1 or claim 2, wherein the device includes a first laser device operable to emit the first laser beam and a second laser device operable to emit the second laser beam.

A propulsion device according to claim 3, wherein the first laser device and the second laser device are spaced apart and operable to emit the first and second laser beams in opposing coaxial directions.

A propulsion device according to claim 3 or 4, wherein the propulsion device includes more than two laser devices, each of which is operable to emit an additional laser beam.

A propulsion device according to claim 5, wherein the laser devices are arranged such that the laser beams emitted by each laser device intersect at a common superposition zone.

A propulsion device according to claim 5, wherein the laser devices are arranged such that there are a plurality of superposition zones with at least two laser devices associated with each superposition zone.

A propulsion device according to any of claims 5 to 7, wherein the more than two laser devices all lie on a single plane.

9. A propulsion device according to any of the preceding claims, wherein the device includes a beam splitter configured to split the first laser beam to form two or more laser beams of the same phase and frequency, and which are coherent.

10. A propulsion device according to claim 9, wherein the beam splitter includes one or more diffraction gratings.

1 1 . A propulsion device according to any of the preceding claims, wherein the field material is spaced apart from the superposition zone.

12. A propulsion device according to claim 1 1 , wherein the field material lies in a plane which is parallel with the plane in which the laser beams lie.

13. A propulsion device according to any of the preceding claims in which the field material is an electret material.

14. A propulsion device according to any of the preceding claims, wherein the first and second laser beams are substantially continuous beams.

15. An aerospace vehicle including a propulsion device according to any preceding claim.