Patent Description:
Pulsed light can be used for performing hair or skin treatment such as cosmetic hair removal. The light pulse is generated using sources such as lamps, light bulbs, light emitting diodes or lasers. It penetrates the skin and is absorbed, e.g. in the root of the hair. The temperature of the root of the hair consequently rises. The growth of the hair is inhibited if the temperature rise is sufficiently high. This process is known as selective photothermolysis.

Light-based treatment devices, such as intense pulsed light (IPL) devices, photo epilation devices, skin rejuvenation devices, phototherapy devices or pain relief devices, often use incoherent light for skin or hair treatment. For example, IPL technology uses light from e.g. a halogen, e.g. Xe, flash lamp at a relatively low fluence (up to <NUM>. 5J/cm2) (as compared to professional devices, for permanent photoepilation, that use fluences in excess of 10J/cm2), and relatively high beam divergence (e.g. compared to lasers).

<CIT> discloses a laser skin treatment device for laser induced optical breakdown of hair or skin tissue. A beam scanning system scans the beam using a rotated prism which implements a lateral shift to the beam. A focusing system at the output side of the beam scanning system focuses the incident light beam into a focal spot in the tissue.

In contrast to treatment devices where optical fibers are used as waveguides to guide light to a target (skin), in devices using prism-based light waveguides, the treatment light needs to be bent at relatively large angles (e.g. <NUM> degrees) to be guided effectively to the skin. The inventors of the present invention have recognized that it is not always possible to achieve such guidance in the latter. For example, as shown in <FIG>, light rays may bypass reflection at the prism, so that they are incident at incorrect angles in the waveguide. Moreover, since some rays are reflected and others not, there is a nonuniform angular and spatial distribution of the light beam/treatment light in the device. Such rays are not effectively directed to the target. Furthermore, due to the incoherent light source characteristics of the device, the emitted light is diffuse and characterized by a wide range of propagation angles. It is an object of the invention to provide an optical assembly to effectively guide such diffuse light using a prism-based optical waveguide, ensure uniformity of the treatment light, and in turn improve device treatment efficiency. It is a further object of the invention to reduce light leakage while guiding the light through the waveguide.

Another problem, as shown in <FIG>, is that while using prism-based waveguides, even after undergoing reflection in the prism, some incident light/rays may be redirected towards the treatment source. This may happen when light rays are incident on a sub-optimal position on the reflective surface of the prism, e.g. on an upper part of the prism hypotenuse. It is another object of the invention to provide an optical assembly which increases the flux of incident light directed towards the target by reducing such back propagation of light.

Additionally, prior to treatment, it is desirable to obtain characteristics (e.g. pigmentation) of the skin/target positioned adjacent to a device treatment aperture via which the treatment light pulses are applied to the skin. Other aspects like detection of skin contact, hair count or displacement and motion of the device are equally desirable. For example, if no skin contact or an unsafe skin tone is detected, the device is prevented from flashing. It is yet another object of the invention to provide an optical assembly which facilitates incorporation of further optical elements which can carry out these functions. Embodiments not falling within the scope of the claims, such as methods for therapeutic treatments, do not from part of the invention and are shown for illustrative purposes only.

According
to an aspect, an optical assembly for use in a skin treatment device is provided. The optical assembly comprises a light source, a first prism and first and second guiding elements with bound/enclosed reflective faces disposed opposite to or facing each other. The first prism includes a first surface, a second surface inclined with the first surface and a third surface adjoining the first and the second surfaces. The first guiding element is arranged to guide the light transmitted from the light source through the first surface of the first prism to its third surface. The second guiding element is further arranged to receive through the second surface of the first prism, the light reflected from the third surface of the first prism and output the received light for illuminating a target/body part (skin). The first surface and the second surface of the first prism are separated from the first guiding element and the second guiding element, respectively, by a refractive index interface. In other words, there exists a material which is different from the prism material, in contact with each of the first surface and the second surface. During use, the first and second surfaces each act as a total internal reflection surface by being disposed in contact with a medium having a refractive index less than a refractive index of the first prism. The first and second surfaces of the first prism may be disposed in contact with e.g. the material of the adjacent guiding element having a refractive index less than the refractive index np of the first prism. According to another aspect, a method is provided for performing a cosmetic or non-therapeutic treatment of the target using the optical assembly.

According to an aspect, the third surface of the first prism or a surface of the second guiding element is coated, at least partially, with a reflective coating e.g. on an outer side. According to an aspect, the first light guiding element and/or the second light guiding element is a total internal reflection (TIR) guiding element.

The third surface of the first prism may further be in contact with a medium of lower refractive index (air or a reflective coating). When the first or the second guiding element acts as a TIR element, the reflective faces of the first light guiding element and/or the reflective faces of the second guiding element are disposed in contact with air (medium of lower refractive index).

According to an aspect, a light exit face of the first guiding element and/or a light entry face of the second guiding element are separated by a predetermined gap from the first surface of the first prism and the second surface of the first prism, respectively. The gap further comprises a dielectric material, wherein the dielectric material has a lower refractive index than a refractive index of the first prism. The gap may further comprise metallic, glass and /or ceramic particles.

According to an aspect, the optical assembly further comprises a second prism having a first surface and second surface inclined with each other and a third surface adjoining the first and the second surfaces, wherein the third surface of the second prism is removably attached or fused to a portion of the third surface of the first prism or a reflective surface of the second guiding element, and such that the first surface of the second prism is disposed substantially parallel to the second surface of the first prism. The second surface of the second prism may comprise a reflective coating, e.g. on its outer side. The third surface of the second prism may further include a deformable layer such as a transparent silicone layer. The second surface of the second prism may be connected to a movable actuator.

According to an aspect, the optical assembly further comprises an imaging element for imaging the target through the first surface of the second prism. The imaging element may be mounted on the first surface or another suitable component of the optical assembly for this purpose.

According to an aspect, there is provided a light filter and/or an insulating window in the optical assembly. A cooling member is further provided in thermal contact with the first prism.

According to an aspect, a device comprising the above-mentioned optical assembly is provided, which is suitable for treating a body part/skin of a user. According to an aspect, the second guiding element is disposed in a removable attachment of the device.

According to an aspect, a computer-implemented method for performing cosmetic or non-therapeutic treatment of skin is provided. The method comprises providing an optical assembly as mentioned, determining, based on at least one image obtained by an imaging element of the optical assembly whether or not to perform the treatment, and if yes, guiding light emitted by a light source of the optical assembly to the target for performing the treatment.

These and other aspects, and further advantages, will be apparent from and elucidated with reference to the embodiment(s) described herein.

The matters exemplified in this description are provided to assist in a comprehensive understanding of various exemplary embodiments of the present invention disclosed with reference to the accompanying figures.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the exemplary embodiments described herein can be made without departing from the scope of the claimed invention. In particular, combinations of specific features of various aspects of the invention may be made. An aspect or embodiment of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect or embodiment of the invention.

Further, the functionality associated with any particular means may be centralized or distributed, whether locally or remotely. It may be advantageous to set forth that the terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

The expression "at least one of A, B and C" means "A, B, and/or C", and that it suffices if e.g. only B is present.

A surface is defined herein to refer to the faces of various optical components. The skilled person imparts the same meaning to these terminologies.

The light emitted by a light source (one or more) for treatment purposes is referred to as "treatment light". The light-based treatment device may comprise further light sources for emitting light that is not used as treatment light.

Further, although the method may be performed at home, it goes without saying that the method may also be practically exploited in an industrial setting, for example, in commercial salons.

The term "user" used herein may be used to refer also to the person using the device, and not necessarily the target whose skin is treated.

The term "guiding element" encompasses any element having sufficient dimensions (length, width or height equal to or different from one another) which can guide light. These elements may be elongated, and have shapes such as rectangular, square, triangular (e.g. a prism), trapezoid, planar, curved or a hybrid of planar and curved (e.g. plano-concave) and the like. Guiding elements <NUM> and <NUM> may further comprise fully or partially bound surfaces (faces).

<FIG> show top cross-sectional views of optical arrangement <NUM> according to an exemplary embodiment of the invention. The arrangement can be positioned inside a skin or hair treatment device, such as the IPL device.

The optical arrangement <NUM> comprises light source <NUM> which can generate light for illuminating and thus treating target <NUM>. The light source <NUM> can generate light pulses of any suitable or desired wavelength (or range of wavelengths) and/or intensities. For example, the light source <NUM> can generate visible light, infra-red (IR) light and/or ultraviolet (UV) light. In an embodiment, the arrangement comprises multiple light sources <NUM>. Each light source <NUM> can comprise any suitable type of light source, such as one or more light emitting diodes (LEDs), a (Xenon) flash lamp, one or more lasers (e.g. laser diodes, VCSELs), etc. The light source(s) <NUM> can provide light pulses with spectral content in the <NUM>-<NUM> nanometre (nm) range for a duration of around <NUM> milliseconds (ms), as these wavelengths heat melanin in the hair and hair root by absorption, which puts the hair follicles in a resting phase, preventing hair regrowth. These wavelengths further enable a contrast in absorption between the hair and surrounding dermis and ensure that light is minimally absorbed by the latter. In an embodiment, light source <NUM> is a broadband light source which emits light in a broad spectrum of wavelengths or frequencies.

The optical arrangement further comprises a prism (first prism <NUM>) which is arranged to receive the light emitted from the light source <NUM>. First prism <NUM> comprises a first surface <NUM>, a second surface <NUM> inclined with the first surface <NUM> and a third surface <NUM> adjoining the first <NUM> and the second <NUM> surfaces. The geometry of a prism, e.g. that the prism includes more surfaces than those exemplified in the drawings, is well-known to those skilled in the art. In an embodiment, the first surface <NUM> and the second surface <NUM> may be two orthogonal surfaces of a right-angled prism, preferably, a right-angled isosceles prism, and the third surface <NUM>, the oblique surface (hypotenuse) which connects the orthogonal first surface <NUM> and the second surface <NUM>. This prism configuration results in a light path which is bent by <NUM> degrees, i.e. the angle between the first surface <NUM> and the second surface <NUM>. Other prism configurations result in light bending angles corresponding to the angle between their respective first surface <NUM> and the second surface <NUM>. First prism <NUM> may be made of material with a suitable refractive index np.

Guiding elements <NUM> and <NUM> are further illustrated in <FIG> as part of the optical assembly <NUM>.

For example, guiding element <NUM> may comprise surfaces 121a, 121b, 122a and 122b, where surfaces 121a and 121b face each other on opposite sides of the first guiding element <NUM>, e.g. on opposite sides of an axis L through the light source <NUM>, the first guiding element <NUM> and the first prism <NUM>. Surfaces 122a and 122b face each other on another two opposite sides of the guiding element <NUM> and extend perpendicular to said axis. Surfaces 121a and 121b are further bound (closed) surfaces. Hence, surfaces 122a and 122b enclose the guiding element <NUM> from opposite directions. Surfaces 121a, 121b, 122a and 122b may be regarded as top, bottom and two side surfaces of the first guiding element <NUM> herein.

The first guiding element <NUM> is disposed between the light source and the first prism <NUM> such that the light emitted from the light source <NUM> is guided therethrough to the first surface <NUM> of the first prism <NUM>. Air may be present as medium between light source <NUM> and the first guiding element <NUM>, so that the light emitted from the light source <NUM> travels through air (refractive index n=<NUM>) to the first guiding element <NUM>. Opposite facing side surfaces/faces 122a and 122b act as light entry and light exit faces, respectively, for light emitted from the light source <NUM>. Edge 123a separating top surface 121a and side surface 122b of the first guiding element <NUM> may be positioned to be flush with edge 114a separating first surface <NUM> and third surface <NUM> of the first prism <NUM>. Edge 123b separating bottom surface 121b and side surface 122b of the first guiding element <NUM> may be positioned to be flush with edge 114b separating first surface <NUM> and second surface <NUM> of the first prism <NUM>.

Similarly, bound surfaces 131a and 131b face each other on opposite sides of the second guiding element <NUM> e.g. on opposite sides of an axis L' through the second guiding element <NUM> and the first prism <NUM>. Hence, surfaces 131a and 131b enclose the guiding element <NUM> from opposite directions. The second guiding element <NUM> is arranged to receive, through the second surface <NUM> of the first prism <NUM>, the light reflected from the third surface <NUM> of the first prism and output it for illuminating and thereby treating the target <NUM> (body part e.g. skin or hair, of a user). Light incident on bound surfaces 131a and 131b is reflected by these surfaces towards the treatment aperture. Depending on the dimensions of the first guiding element <NUM> and the second guiding element <NUM>, multiple reflections may occur at 121a, 121b and 131a, 131b. Such reflections are not excluded herein.

In the embodiment of <FIG>, opposite facing surfaces 132a and 132b which extend perpendicular to axis L' act as light entry and light exit faces, respectively, for light reflected from the third surface <NUM> of the first prism <NUM>. Surfaces 131a, 131b, 132a and 132b may be regarded as side, top and bottom surfaces of the second guiding element <NUM> herein. In an embodiment, e.g. as shown in <FIG>, surfaces 131a and 131b may simply face each other at an inclination, i.e. without being parallel to each other. In this case, surface 131a may bisect axis L' and be adjoined to surface 131b which is parallel to axis L'. Surface 132a may connect surfaces 131a and 131b, so that the second guiding element <NUM> takes the shape of a prism. Hence, it is not essential for guiding element <NUM> to comprise surface 132b. Here, surface 131b acts as the light exit face, as shown in <FIG>.

Edge 133a separating side surface 131a and top surface 132a of the second guiding element <NUM> may be positioned to be flush with edge 114b separating first surface <NUM> and second surface <NUM> of the first prism <NUM>. Edge 133b separating side surface 131b and top surface 132a of the second guiding element <NUM> may be positioned to be flush with edge 114c separating second surface <NUM> and third surface <NUM> of the first prism <NUM>.

As a result of bound top and bottom surfaces 121a and 121b of guiding element <NUM> and side surfaces 131a and 131b of guiding element <NUM>, both the treatment light emitted from light source <NUM>, and that reflected from the third surface <NUM> of the first prism <NUM> are confined to the interior of the respective guiding element, reducing losses due to beam divergence. This in turn increases the amount of light flux incident on the target <NUM>. The bound surfaces of guiding elements <NUM> and <NUM> are further reflective (e.g. made of metal, glass), so that any diverging treatment light is reflected by the bound surfaces and (re)-guided towards the first surface <NUM> of the first prism <NUM> or towards the treatment aperture to target <NUM>, further increasing the amount of light flux incident on the target <NUM>.

The multi-element (therefore including multiple refractive interfaces) optical assembly comprising the first prism <NUM> (e.g. a solid prism), the first guiding element <NUM> and the second guiding element <NUM> creates refractive index variations/differences at surfaces <NUM> and <NUM> of the first prism <NUM>. Light rays 10a, 10b, 10c and 10d are shown for illustration purposes in <FIG>. Each light ray transmitted from light source <NUM> enters the first prism <NUM> through first surface <NUM> (where it is refracted) and is reflected by third surface <NUM>, before passing the second surface <NUM> of the first prism <NUM> (where it is refracted again) towards the target <NUM>. Light ray 10a may further be indirectly incident on the third surface <NUM> via reflection at second surface <NUM>. In an embodiment described below, this reflection may arise from TIR at the second surface <NUM>. After reflection at the third surface <NUM>, light ray 10d may further reach second surface <NUM> indirectly via reflection at the first surface <NUM>. In an embodiment described below, this reflection may arise from TIR at the first surface <NUM>. Because the rays entering the first prism <NUM> through first surface <NUM> are reflected by the third surface <NUM> and transmitted through the first prism <NUM> via the second surface <NUM>, light leakage in the optical assembly <NUM> is reduced. Consequently, the flux of incident light directed towards the target <NUM> is increased. Due to said optical path of the treatment light, spatial and/or angular uniformity is further maintained.

In an embodiment, third surface <NUM> of the first prism <NUM> further includes a reflective coating R, so that treatment light which is incident on the third surface suffers minimal transmission losses while being reflected by the surface.

The first guiding element <NUM> and the first prism <NUM> may be disposed in contact (and hence edges 123a, 114a and edges 123b, 114b are both flush and in contact with each other), as shown in <FIG>, or be disposed at a separation from one another as shown in <FIG>. Similarly, the second guiding element <NUM> and the first prism <NUM> may be disposed in contact (and hence edges 133a, 114b and edges 133b, 144c are both flush and in contact with each other), or be disposed at a separation from one another.

In an embodiment, side surfaces 122a and 122b of first guiding element <NUM>, and top and bottom surfaces 132a, 132b of second guiding element <NUM> may further be open or closed.

With open side surfaces/faces 122a and 122b, first guiding element <NUM> is essentially a hollow guiding element/waveguide so that the first surface <NUM> is disposed in contact with air (any fluid) as medium separating the first prism <NUM> and the light source <NUM>. Similarly, with open top and bottom surfaces 132a, 132b, second guiding element <NUM> is essentially a hollow guiding element so that the second surface <NUM> is disposed in contact with air (fluid) as the medium separating the first prism and the treatment aperture of the device. Treatment light may still be confined between the bound surfaces of the first and the second guiding elements <NUM> and <NUM> as indicated. The hollow guiding element allows for an optical assembly <NUM> with reduced weight, and thus making a device <NUM> incorporating the optical assembly <NUM> lighter. In practical implementations, such a hollow guiding element may be a pipe with reflective inner surfaces. These surfaces typically comprise a metallic layer (e.g. a layer which is deposited on a transparent substrate or a metallic foil by vacuum techniques).

Alternately, the first guiding element <NUM> and second guiding element <NUM> may be a hollow element with closed/bound side surfaces/faces 122a, 122b of first guiding element <NUM>, and bound top and bottom surfaces 132a, 132b of second guiding element <NUM>. In an implementation, such a guiding element may be a a closed pipe with reflective surfaces. In this case, for example, side surface 122b of first guiding element <NUM> and top surface 132a of second guiding element <NUM> may be disposed at a distance from the first surface <NUM> and the second surface <NUM> of the first prism <NUM>, respectively.

With closed/bound side surfaces 122a,122b of first guiding element <NUM>, and bound top and bottom surfaces 132a, 132b of second guiding element <NUM>, first guiding element <NUM> and second guiding element <NUM> may be a solid with appropriate refractive indices n<NUM> and n<NUM>, where n<NUM> is the same as or different from n<NUM>. The refractive indices n<NUM>, n<NUM> of the first and the second guiding elements <NUM>, <NUM>, and np of the first prism <NUM> may be further chosen to allow total internal reflection of light (TIR) within the first guiding elements <NUM>, the second guiding element <NUM> and the first prism <NUM>, to further minimize transmission losses (light leakage) in the optical assembly <NUM>. Preferably, the solid guiding element may be made of transparent material with a sufficiently high refractive index to guide the angular distribution of the beam generated by the light source <NUM>.

TIR occurs when a light ray 10a (or 10b-d) propagating in the first guiding element <NUM> made of a material e.g. a solid with certain refractive index (e.g. glass, n1=<NUM>) strikes top surface 121a or bottom surface 121b which acts as boundary between the solid with higher refractive index and air having a lower refractive index (n=<NUM>) (said surfaces are disposed to be in contact with air) at an angle larger than a critical angle θc (measured with respect to an axis/normal extending perpendicular to the top 121a or bottom 121b surface of the first guiding element <NUM>). In this case, the light ray is entirely reflected at surfaces 121a and 121b. As a result of TIR, light transmission losses at the reflective surfaces of the first guiding element <NUM> are further reduced.

TIR may further occur when the light ray 10a propagating in the first prism made of a solid (e.g. glass, np=<NUM>) strikes surface <NUM>, <NUM> or <NUM> which acts as boundary between the solid with higher refractive index and a medium (e.g. air, resin, solid) having a lower refractive index at an angle larger than a critical angle θc (measured with respect to an axis/normal extending perpendicular to the respective surface of the first prism). In this case, the light ray is entirely reflected at surfaces <NUM>, <NUM> and <NUM>.

In an embodiment, the refractive index n<NUM> of the first guiding element <NUM> may be less than refractive index np of the first prism <NUM>, to satisfy the above-mentioned TIR condition.

Assuming a ray 10d which is reflected by third surface <NUM> of the first prism <NUM> is incident on the first surface <NUM> of the first prism <NUM> and satisfies TIR condition, this light ray is total internally reflected at first surface <NUM> and hence coupled back to the prism towards the treatment aperture. This reduces instances when a ray, after reflection by the third surface <NUM>, leaks out of the first prism <NUM> into the first guiding element <NUM> through first surface <NUM>. As a result of TIR at first surface <NUM>, such light is redirected to surface <NUM> which either transmits the light further or reflects it to surface <NUM> depending on the angle of incidence of such light. Further, when guided towards the first prism <NUM>, the light ray 10a, 10b, 10c or 10d is not total internally reflected at the surface 122b.

The arrangement therefore reduces back coupling of the light to the first guiding element in a direction towards the treatment source <NUM>, and in turn improves the uniformity of the treatment light and increases the amount of light directed to the skin.

In another embodiment, the refractive index n<NUM> of the second guiding element <NUM> may be less than refractive index np of the first prism <NUM>.

Assuming a ray 10a which originates from first surface <NUM> of the first prism <NUM> is incident on the second surface <NUM> of the first prism <NUM> and satisfies TIR condition, this light ray (10a) is total internally reflected at second surface <NUM> to the third surface <NUM> of the first prism <NUM>, which can then be further reflected by the third surface <NUM>.

In an embodiment, the third surface <NUM> of the first prism <NUM> may be disposed in contact with air to allow TIR at the third surface <NUM> at certain angles of incidence. It may further be coated with a reflective coating R (e.g. a metallic layer) which ensures that most rays in the angular distribution of the beam generated by lamp <NUM> are reflected, independent of a TIR condition being satisfied at surface <NUM>. In an embodiment, the reflective coating may be made of a material with a lower refractive index than the first prism. Furthermore, TIR occurs when the light ray 10a (or 10b -10d) propagating in the second guiding element <NUM> made of a solid (e.g. glass, n1=<NUM>) strikes side surface 131a or 131b which acts as boundary between the solid with higher refractive index and air having a lower refractive index (n=<NUM>) (said surfaces are disposed to be in contact with air) at an angle larger than a critical angle θ c (measured with respect to an axis/normal extending perpendicular to the side surface of the second guiding element <NUM>). In this case, the light ray is entirely reflected at surfaces 131a and 131b. As a result of TIR, light transmission losses at the reflective surfaces of the second guiding element <NUM> are further reduced. In case of a hollow first <NUM> and/or second <NUM> guiding element with air in contact with the first surface <NUM> and the second surface <NUM> of the first solid prism <NUM>, the refractive index restriction for TIR is implicitly achieved.

In addition to guiding treatment light which is directly emitted by light source <NUM> towards the target, the optical assembly <NUM> also guides light scattered off the target and coupled back into the device via the treatment aperture. The optical assembly <NUM> guides such light through the second guiding element <NUM> to the first prism <NUM> and further to the first guiding element <NUM> in a similar manner as the treatment light.

A (parabolic) reflector <NUM> may be arranged behind the light source <NUM> to redirect such light back through the first guiding element <NUM>, the first prism <NUM> and the second guiding element <NUM> to the target <NUM>. The radius of curvature of reflector <NUM> is sufficiently large to collect the back-scattered light and reflect it towards the first guiding element <NUM>. The reflector <NUM> further functions to redirect treatment light emitted by light source <NUM> which is propagated in a backward direction.

As shown in <FIG>, the first guiding element <NUM> and the first prism <NUM> may be separated by a predetermined gap G. In such cases, the light exit face 122b of the first guiding element <NUM> and the light entry face 132a of the second guiding element <NUM> are separated by gap G from the first surface <NUM> and the second surface <NUM>, respectively, of the first prism. This is an embodiment to introduce the aforementioned refractive index variation at surfaces <NUM> and <NUM> of the first prism <NUM>.

Assuming that TIR occurs at surfaces 121a and 121b of the first guiding element <NUM>, and surfaces 131a and 131b of the second guiding element <NUM>, and that rays are reflected at the third surface <NUM> of the first prism (either by TIR or a reflective coating), each light ray 10a, 10b, 10c, 10d is refracted at side surface 122b of the first guiding element <NUM>, first surface <NUM> and second surface <NUM> of the first prism <NUM>, and surfaces 132a and 132b of the second guiding element. Light rays 10a, 10b,10c and 10d are incident on the third surface of the first prism <NUM> and reflected therefrom before being incident on its second surface <NUM> or first surface <NUM> and into the second guiding element <NUM>, so that the treatment light is homogenous and light leakage is minimized. Since TIR occurs at surfaces 121a and 121b of the first guiding element <NUM>, the third surface <NUM> of the first prism <NUM> and surfaces 131a and 131b of the second guiding element <NUM>, light leakage is minimized at both the first and second guiding elements <NUM> and <NUM> and the first prism <NUM>.

Leakage may occur at the gaps separating the light exit face 122b of the first guiding element <NUM> and the first surface <NUM> of the first prism <NUM>, and the light entry face 132a of the second guiding element <NUM> and the second surface <NUM> of the first prism <NUM>. However, this leakage can be minimized by reducing the size of gaps G, e.g. a size <<NUM> micrometers, preferably <NUM>-<NUM> micrometers, more preferably <NUM>-<NUM> micrometers.

Although according to <FIG>, the gaps G between the light exit face 122b of the first guiding element <NUM> and the first surface <NUM> of the first prism <NUM>, and the light entry face 132a of the second guiding element <NUM> and the second surface <NUM> of the first prism <NUM> are shown to be equal, these may also be different.

In an embodiment, the gap G further comprises a dielectric material <NUM>. Examples of dielectrics are air (n=<NUM>), resin, oil etc. To allow TIR at surfaces <NUM> and <NUM> of the first prism <NUM>, the dielectric material has a lower refractive index than a refractive index of the first prism <NUM>. With air (n=<NUM>) in contact with the first surface <NUM> and the second surface <NUM> of the first solid prism <NUM> (np><NUM>), the refractive index restriction for TIR is implicitly achieved. In this embodiment, the refractive indices n<NUM> and n<NUM> of the first guiding element <NUM> and the second guiding element <NUM> may be smaller, equal to or larger than the refractive index np of the first prism <NUM>.

When TIR occurs at surfaces <NUM> and <NUM> of the first prism <NUM> interfacing to a medium (air, resin) with lower refractive index, an evanescent wave (field) is generated adjacent to surfaces <NUM> and <NUM> of the first prism <NUM> in the less dense medium (e.g. in gap G). This is shown in <FIG>. The intensity of the evanescent wave decays exponentially from the respective surface into the gap. To prevent the evanescent wave from coupling to the first and the second guiding elements <NUM> and <NUM>, it is desirable to choose the size of gap G to be sufficiently large (e.g. several micrometers) to allow decay of the evanescent wave in the gap G.

In a preferred embodiment, the gap G is chosen to be <NUM>-<NUM> micrometers, preferably <NUM>-<NUM> micrometers to reduce light leakage as well as allow decay of the evanescent wave within the gap.

Gap G may further comprise metal, glass and/or ceramic particles dispersed therein. This is illustrated in <FIG>. Such microparticles may be comprised of materials such as TiO<NUM>, Al<NUM>O<NUM>, and AlN, and may have sizes of <NUM> to several tens of micrometers. Particles of such materials are thermally resistant, and mechanically strong which in turn results in a mechanically stable gap. Further, they do not absorb light in the relevant wavelength range for photoepilation. Therefore, the effect on light transmission and thus the hair or skin treatment is negligible. A minimal coverage of first surface <NUM> and the second surface <NUM> of the first prism <NUM> with microparticles, e.g. <<NUM>%, is sufficient to achieve said technical effect.

The first guiding element <NUM> and the second guiding element <NUM> may be attached to the first prism <NUM> by methods such as molding, by means of (polymer) resins with refractive indices similar to the guiding elements, or via contacting first and second surfaces <NUM> and <NUM> of the first prism <NUM> with surfaces 122b of the first guiding element <NUM> and 133b of the second guiding element <NUM> ensuring snug fit between the first guiding element <NUM>, the first prism <NUM> and the second guiding element <NUM>. The first prism <NUM> can be held in place by attaching the third surface <NUM> to a part of housing of the device <NUM> using suitable attachment means, e.g. with the aid of resin, or mechanically clamping a top (viewed parallel to plane of <FIG>) surface <NUM> of the first prism <NUM>.

Although <FIG> show optical assembly <NUM> with solid first and second guiding elements <NUM> and <NUM> each separated from the first prism <NUM> by gap G, as shown in <FIG> and <FIG>, any combination of arrangements of optical assembly <NUM> is possible according to the invention. Hence, the above discussed embodiments in relation with <FIG> can be combined without restriction in any of the disclosed embodiments <FIG> and <FIG>.

<FIG> shows an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM> and first guiding element <NUM> and second guiding element <NUM> being hollow waveguides, so that air is in contact with the first surface <NUM> and the second surface <NUM> of the first prism <NUM>.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, first guiding element <NUM> and second guiding element <NUM>, where the first guiding element <NUM> is a hollow waveguide so that air is in contact with the first surface <NUM> of the first prism <NUM> and the second guiding element <NUM> is a solid with surface 132a disposed in contact with the second surface <NUM> of the first prism <NUM>. The refractive index n<NUM> of the second guiding element <NUM> may be less than the refractive index np of the first prism <NUM>, as shown in <FIG>.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, first guiding element <NUM> and second guiding element <NUM>, where the second guiding element <NUM> is a hollow waveguide so that air is in contact with the second surface <NUM> of the first prism <NUM> and the first guiding element <NUM> is a solid with surface 122b disposed in contact with the first surface <NUM> of the first prism <NUM>. The refractive index n<NUM> of the first guiding element <NUM> may be less than the refractive index np of the first prism <NUM>, as shown in <FIG>.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, solid first guiding element <NUM> and solid second guiding element <NUM>, where the surface 122b of the first guiding element <NUM> is disposed in contact with the first surface <NUM> of the first prism <NUM> and the surface 132a of the second guiding element <NUM> is disposed in contact with the second surface <NUM> of the first prism <NUM>. The refractive index n<NUM> of the first guiding element <NUM> and refractive index n<NUM> of the second guiding element <NUM> may be less than the refractive index np of the first prism <NUM>, as shown in <FIG>. <FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, a solid first guiding element <NUM> and a hollow second guiding element <NUM>, where the first guiding element <NUM> is separated from the first surface <NUM> of the first prism <NUM> by gap G comprising a dielectric <NUM> (air, resin etc.) and the second surface <NUM> of the first prism <NUM> is disposed in contact with air. The refractive index n<NUM> of the first guiding element <NUM> may be less than, the same as or greater than the refractive index np of the first prism <NUM>. In <FIG>, refractive index n<NUM> is shown to be equal to refractive index np.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, a hollow first guiding element <NUM> and a solid second guiding element <NUM>, where the second guiding element <NUM> is separated from the second surface <NUM> of the first prism <NUM> by gap G comprising a dielectric <NUM> (air, resin etc.) and the first surface <NUM> of the first prism <NUM> is disposed in contact with air. The refractive index n<NUM> of the second guiding element <NUM> may be less than, the same as or greater than the refractive index np of the first prism <NUM>. In <FIG>, refractive index n<NUM> is shown to be equal to refractive index np.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, a solid first guiding element <NUM> and a solid second guiding element <NUM>, where the first guiding element <NUM> is separated from the first surface <NUM> of the first prism <NUM> by a (polymer) resin 15a and the second guiding element <NUM> is also separated from the second surface <NUM> of the first prism <NUM> by a (polymer) resin 15b. The refractive index n<NUM>, n<NUM> of the first and second guiding element <NUM>, <NUM>, respectively, may be less, the same as or greater than the refractive index np of the first prism <NUM>. In <FIG>, refractive indices n<NUM> and n<NUM> are shown to be equal to refractive index np. The refractive indices nr1, nr2 of the polymer resins 15a, 15b may be less than the refractive index np of the first prism <NUM>. Further, nr1 may be the same as or different from nr2.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, a solid first guiding element <NUM> and a solid second guiding element <NUM>, where the first guiding element <NUM> is disposed in contact with the first surface <NUM> of the first prism <NUM> and the second guiding element <NUM> is separated from the second surface <NUM> of the first prism <NUM> by a resin 15b. The refractive index n<NUM> of the first guiding element <NUM> may be less than the refractive index np of the first prism <NUM>. The refractive indices nr2 of the resin 15b may be less than the refractive index np of the first prism <NUM>. The refractive index n<NUM> of the second guiding element <NUM> may be less than, the same as or greater than the refractive index np of the first prism <NUM>. In <FIG>, refractive index n<NUM> is shown to be equal to refractive index np.

<FIG> is an exemplary embodiment of optical assembly <NUM> comprising a solid first prism <NUM>, a solid first guiding element <NUM> and a solid second guiding element <NUM>, where the first guiding element <NUM> is separated from the first surface <NUM> of the first prism <NUM> by gap G comprising air as the dielectric and the second guiding element <NUM> is disposed in contact with the second surface <NUM> of the first prism <NUM>. The refractive index n<NUM> of the second guiding element <NUM> may be less than the refractive index np of the first prism <NUM>. The refractive index n<NUM> of the first guiding element <NUM> may be less than, the same as or greater than the refractive index np of the first prism <NUM>. In <FIG>, refractive index n<NUM> is shown to be equal to refractive index np. Assuming the medium between light source <NUM> and the first guiding element has a refractive index np, in embodiments where the first surface <NUM> and the second surface <NUM> of the first prism <NUM> are disposed in contact with a solid, the refractive index np of the first prism <NUM> to satisfy TIR conditions in the optical assembly <NUM> may be calculated with respect to refractive indices n<NUM> of the first guiding element <NUM> and n<NUM> of the second guiding element <NUM> as follows. <MAT> <MAT>.

For example, in the embodiment of <FIG>, assuming that the light emitted from the light source <NUM> travels through air to the first guiding element <NUM>, and the first guiding element <NUM> and the second guiding element <NUM> are made of standard optical glass, n<NUM>= <NUM>, n<NUM>=n<NUM>=<NUM>, so that the requirement for the prism material is np≥ <NUM>. Such a refractive index can be realized in glass.

In embodiments where the first surface <NUM> and the second surface <NUM> of the first prism <NUM> are disposed in contact with air, the refractive indices n<NUM> of the first guiding element <NUM> or n<NUM> of the second guiding element <NUM> in the above equation are replaced by <NUM>, i.e. <MAT>.

The top surface <NUM> of the first prism <NUM> and the bottom surface (not shown) are disposed typically in contact with air or mechanically clamped e.g. by metal clamps, which does not influence the external refractive index and the refractive index relation between the components of the optical assembly <NUM>.

In embodiments where the first surface <NUM> and the second surface <NUM> of the first prism <NUM> are disposed in contact with a resin, the refractive index np of the first prism <NUM> to satisfy TIR conditions in the optical assembly <NUM> may be calculated with respect to refractive indices nr<NUM> of the polymer resin 15a and nr<NUM> of the polymer resin 15b is calculated as: <MAT> <MAT>.

For example, in the embodiment of <FIG>, assuming that the light emitted from the light source <NUM> travels through air to the first guiding element <NUM>, and the material of the resins 15a and 15b are chosen as <NUM> (resins with n<<NUM> are equally applicable), n<NUM>= <NUM>, nr1=nr2=<NUM>, so that the requirement for the prism material is np≥ <NUM>. Such a refractive index can be realized in glass (e.g. Schott N-SF4) or optical plastic (e.g. polymers with thianthrene moieties).

The above embodiments show optical assembly <NUM> comprising a single first guiding element <NUM> between the first prism <NUM> and the light source <NUM>, and a single second guiding element <NUM> between the first prism <NUM> and the treatment aperture (not shown). In an embodiment, a further light guiding element (not shown) may be disposed between the first prism <NUM> and the light source <NUM>. The further light guiding element may be located adjacent to or integrated within the first guiding element <NUM> and may be hollow or a solid with bound reflective top surfaces flush with surface 121a of the first guiding element <NUM>. Similarly, a further light guiding element may be disposed between the first prism <NUM> and the treatment aperture. There is no restriction to the number of further guiding elements. By using further light guiding elements, the diffuse treatment light (with different propagation angles) is further collimated between the light source <NUM> and target <NUM>.

<FIG> show various schematics of optical assembly <NUM> further comprising an optical filter <NUM>. As mentioned, light source <NUM> may emit light comprising multiple wavelengths ("incoherent/white light", non-monchromatic). For example, Xenon flash lamps are capable of generating intense light within a spectral range from ultra-violet to infrared, i.e. from lower than <NUM> to as high as <NUM>. Wavelengths below <NUM> are aborbed by hemoglobins in the blood, potentially causing discomfort and side-effects, so it is preferred that this light is filtered out. Furthermore, in case of high voltages produced on outer surfaces of light source <NUM>, an electrical insulator may be needed in device <NUM> for protection against electrical hazards. To prevent unwanted radiation from being guided to the target while using device <NUM>, and/or provide electrical insulation, a suitable filter is used in device <NUM>.

In <FIG>, filter <NUM> is shown mounted above surface 132a of the second guiding element <NUM>, proximal to the treatment aperture (not shown). Gap G, filled with either air or another dielectric with a suitable refractive index (nr<np), between the filter <NUM> and the second surface <NUM> of the first prism <NUM> allows for TIR at the second surface <NUM> of the first prism <NUM>. The filter <NUM> may have a larger cross-section than the second guiding element <NUM> in order to provide better electrical insulation (e.g. by increasing electrical creepage distance of the insulator). To accommodate gap G in an optical assembly <NUM>, embodiments with filter <NUM> may include a larger (total) spacing between the second surface <NUM> of the first prism <NUM> and the second guiding element <NUM>. In this embodiment, the filter <NUM> also functions as an insulator.

As a result of the prism-based optical assembly <NUM> which positions light source <NUM> and the treatment aperture (not shown) adjacent to target <NUM> in non-coaxial directions, e.g. at <NUM> degrees with respect to each other as shown in the above embodiments, filter <NUM> (e.g. optical filter) can alternately be positioned adjacent to or integrated with the first guiding element <NUM> (<FIG>). Such optical assembly <NUM> offers more flexibility for incorporating additional imaging elements e.g. a camera in the line of sight of the target, e.g. along axis L' in <FIG> or perpendicular to L' as shown in <FIG>, additional insulator components etc. <FIG> shows a transparent insulating window (e.g. made of glass) <NUM> sandwiched between the second surface <NUM> of the first prism <NUM> and the surface 132a of the second guiding element <NUM>. The optical window <NUM> may be disposed adjacent to and/or substantially parallel to the second surface <NUM> of the first prism <NUM>. Depending on the refractive index of the window, a gap G may or may not be present between the window <NUM> and the second surface <NUM> of the first prism <NUM>. The window <NUM> provides electrical insulation at the exit of the the device <NUM> near the treatment aperture. To accommodate gap G in the optical assembly <NUM>, embodiments with window <NUM> may comprise a larger (total) spacing between the second surface <NUM> of the first prism <NUM> and the second guiding element <NUM>.

In another embodiment, the optical window <NUM> or the filter <NUM> may be disposed adjacent to and/or substantially parallel to the first surface <NUM> of the first prism <NUM>.

<FIG> show schematics of optical assembly <NUM> wherein filter <NUM> is disposed in the first prism <NUM>. In <FIG>, filter <NUM> is shown disposed entirely in the first prism <NUM> (e.g. by using doped glass as the prism material). In this case, in addition to guiding light from light source <NUM> to the treatment aperture, the first prism <NUM> also acts as the optical filter. While filter <NUM> blocks undesired light wavelengths, it is transparent to light wavelengths for treatment. The person skilled in the art knows how to choose a suitable filter which fulfils both purposes.

In this embodiment, the third surface <NUM> of the first prism <NUM> may be in thermal contact with a cooling member <NUM> (e.g. heat sink), so that the filter can be effectively cooled. This in turn protects the user of the device <NUM> from heat emitted by filter <NUM> during device operation. Furthermore, since the heat is efficiently channelled to the cooling member <NUM>, filter <NUM> itself has a lower temperature (value<<NUM>). A wider selection of polymer materials, which can withstand the lower temperatures, can then be used for manufacturing the filter.

The filter <NUM> may be disposed in contact with a reflective coating R on the third surface <NUM> of the first prism <NUM>, and the cooling member then attached to the reflective coating R.

<FIG> shows that filter <NUM> may be disposed partially in the first prism <NUM>, an outer surface of the filter <NUM> coexisting with the third surface <NUM> of the first prism <NUM>. Light from the light source <NUM>, when guided to the third surface <NUM> of the first prsim <NUM>, first passes through the optical filter <NUM>. As a result, the light gets filtered to remove the unwanted optical wavelengths before reaching the target upon being reflected by the third surface <NUM>. It is desirable that the refractive index of the filter <NUM> is similar to the refractive index of the first prism <NUM>. This reduces light reflections at the prism-filter interface so that all incident treatment light is transmitted to the third surface <NUM> through the optical filter <NUM>. Between the light source <NUM> and the target (skin or hair), all light passes the filter <NUM> twice, travelling towards the third surface <NUM>, and travelling away from it upon being reflected. Due to this increased optical path length, the filter layer can be (less than) half the thickness of a traditional pass-through filter (e.g. < <NUM>). As shown in <FIG>, the outer surface of filter <NUM> (and the third surface <NUM> of the first prism <NUM>) may be disposed in contact with a cooling member <NUM> through a reflective coating R on the third surface <NUM>, to further improve the cooling efficiency of the filter.

Alternately, filter <NUM> may be simply disposed on the third surface <NUM> of the first prism <NUM> (not shown) as a coating. In embodiments 5d or 5e, the filter <NUM>, the reflective coating R and the cooling member <NUM> may be cut through to allow light from an imaging element disposed proximal to the cooling member <NUM> to travel through the first prism <NUM> to the target/skin.

<FIG> shows the schematic of optical assembly <NUM> comprised within a light-based treatment device <NUM>. Optical assembly <NUM> may be housed in a main body (shown in <FIG>) of device <NUM>. The device <NUM> may include at least one attachment <NUM>, and the second guiding element <NUM> may alternately be disposed in the attachment <NUM> of device <NUM> for guiding the light output from the first prism <NUM> to the target <NUM>.

The optical assembly <NUM> of <FIG> further comprises a second prism <NUM> (e.g. having a right triangular shape) mounted on the third surface <NUM> of the first prism <NUM>. The second prism <NUM> comprises a first surface <NUM> and second surface <NUM> inclined with each other and a third surface <NUM> adjoining the first <NUM> and the second <NUM> surfaces. The refractive index np' of the second prism <NUM> may be similar to the refractive index np of the first prism <NUM>.

As mentioned, the third surface <NUM> of the first prism <NUM> (on its outer side) may further include a reflective coating R. The third surface <NUM> may be either fully or partially coated using this coating R.

The third surface <NUM> of the second prism <NUM> can be removably attached or fused to an uncoated portion of the third surface <NUM> of the first prism <NUM>. Further, the first surface <NUM> of the second prism <NUM> may be disposed substantially parallel to the second surface <NUM> of the first prism <NUM> (perpendicular to axis L'). The second surface <NUM> of the second prism <NUM> may further include a reflective coating R' (R' = or ≠ R) so that treatment light which leaks into the second prism <NUM> and is incident on the second surface <NUM> suffers minimal transmission losses at the surface. As a result of the coating, any light reaching the surface <NUM> of the second prism <NUM> is reflected into the first prism <NUM> for recycling. Recycling allows treatment light from light source <NUM> reflected off various surfaces (e.g. skin, optical components of the device) to be used again for treatment.

In an alternate embodiment in which the second guiding element <NUM> is shaped as a prism as shown in <FIG>, the (e.g. third surface <NUM> of the) second prism <NUM> may be attached to an uncoated surface 131a (oblique surface/hypotenuse) of the second guiding element <NUM>, as shown in <FIG>. Surface 131a may comprise a full or partial reflective coating R. The first surface <NUM> of the second prism <NUM> may be disposed substantially parallel to the surface 131b of the second guiding element <NUM>. The second surface <NUM> of the second prism <NUM> may further include a reflective coating, like mentioned above with reference to <FIG>.

In the embodiments of <FIG>, an imaging element e.g. camera C may be further mounted on or adjacent to the first surface <NUM> of the second prism <NUM> for imaging the target (the body part). The second prism <NUM> is so arranged to function as a camera viewing port and entry for imaging light. In the embodiment of <FIG>, the imaging light is incident on and transmitted through the first surface <NUM> and the third surface <NUM> of the second prism <NUM> disposed on the uncoated portion of the third surface <NUM> of the first prism, through the second surface <NUM> of the first prism <NUM> and surfaces 132a and 132b of the second guiding element <NUM> and the attachment <NUM> to the target <NUM>. In the embodiment of <FIG>, the imaging light is incident (not shown) on and transmitted through the first surface <NUM> and the third surface <NUM> of the second prism <NUM> disposed on the uncoated portion of surface 131a of the second guiding element <NUM>, surface 131b of the second guiding element <NUM> to reach the target <NUM>. Although second prism <NUM> is disclosed as being attached to an uncoated portion of the reflective coating of the first prism or the second guiding element, this is merely a preferred feature.

Camera C may be mounted on another element of device <NUM> (e.g. mounted to housing of the device <NUM>), as long as it is suitably arranged to image the skin through the first surface <NUM> of the second prism <NUM>. Hence, its position in optical assembly <NUM> is not limited to the embodiments of <FIG>.

The inset in <FIG> shows a top view of the first surface <NUM> of the second prism <NUM>. The imaging light from the camera (e.g. using LEDs) may enter through light entry port(s) O to the target <NUM>. The reflected light from the target <NUM> which re-enters the camera through light exit port O' may be detected by the imaging element in the camera C.

The characteristics (e.g. skin pigmentation/skin tone) of skin adjacent to a device treatment aperture via which the treatment light pulses are applied to the skin can thus be obtained. The camera C may also be used for detection of skin contact, hair count or displacement and motion of the device. For example, if no skin contact or an unsafe skin tone is detected, the device is prevented from flashing. This also offers a cost advantage by not having to incorporate dedicated contact/skin tone/motion sensors in the device.

In case of configurations <FIG>, as mentioned, a cut through or a light channel (e.g. by using a suitable transmissive coating) may be further provided in the filter <NUM>, the cooling member <NUM> and the coating on first prism <NUM>, e.g. by leaving a part of the filter transparent to all visible light, a part of the surface <NUM> of the first prism <NUM> uncoated so as to allow passage of light from and to the imaging element C. The second prism <NUM> may be mounted on a section of the third surface <NUM> of the first prism <NUM> which is not covered by the cooling member <NUM>. In the embodiment of <FIG>, a further guiding element may be further be attached to surface 131b of the second guiding element <NUM> to guide the treatment light and imaging light to the target. Further, the different optical path of the imaging light in this embodiment makes the presence of the mentioned light channel non-essential.

The remaining aspects of the <FIG> and <FIG> embodiments are similar to those mentioned above and shall not be repeated here for sake of conciseness.

The embodiment of <FIG> can be combined with any of the optical assemblies disclosed in <FIG>, or any other multi-element assembly which can be used to overcome at least one of the technical problems mentioned above.

As mentioned, the third surface <NUM> of the second prism <NUM> can be removably attached or fused to an uncoated portion of the third surface <NUM> of the first prism <NUM> or to surface 131a of the second guiding element <NUM>. This is especially useful when an imaging element such as a camera C is comprised in the optical assembly <NUM>.

<FIG> have been shown in reference to the camera configuration of <FIG>. It can also be combined with the camera configuration described with reference to <FIG>.

As shown in <FIG>, the second surface <NUM> of the second prism <NUM> (which may be coated by reflective coating R') is connected to a movable actuator A. In a first operation mode, as shown in <FIG>, movement of actuator A causes second prism <NUM> to be arranged in contact with the first prism <NUM> (with its third surface <NUM>). The camera C then obtains image(s) of the target <NUM>. In this mode, the treatment light source <NUM> is switched off. In other words, this step is carried out before the treatment of the target using the light pulse.

The third surface <NUM> of the second prism <NUM> may further include an elastic/deformable layer AD, preferably a transparent silicone layer, which is brought in contact with the uncoated portion of the third surface <NUM> of the first prism <NUM>. The deformable layer enables the prisms to have good optical contact with each other. In an embodiment, the refractive index of the deformable layer is similar to the refractive indices np' of the second prism <NUM> and np of the first prism <NUM>. In this case, in the first operation mode as shown in <FIG>, movement of actuator A causes the second prism <NUM> to be arranged in contact with the first prism <NUM> (with its third surface <NUM>) via the deformable layer AD.

After the target characteristics is confirmed by camera C using the obtained image(s) and the target is determined safe for the light-based treatment by a controller (not shown in <FIG>), a second operation mode is initiated. In the second operation mode, as shown in <FIG>, movement of actuator A causes second prism <NUM> to be disconnected from/not in contact with the first prism <NUM>.

As a result of the second operation mode, an air gap is created between the third surface <NUM> of the first prism <NUM> and the deformable layer AD on the third surface of the second prism <NUM>. Due to the air gap, a high (prism <NUM>)-to-low (air) refractive index media interface is formed on the third surface <NUM>. As a result, a large fraction of the light from the light source <NUM> (and light reflected from the target <NUM> which is coupled to device <NUM>) is total internally reflected at the third surface <NUM> of the first prism <NUM>, without damaging leakage to the second prism <NUM> and camera C. In this embodiment, an air gap is used as an example, however, as clear from above, any fluid can be comprised in the gap as long as its refractive index allows TIR at the third surface <NUM> of the first prism <NUM>.

In this mode, optionally, the camera C may be disabled as shown in <FIG>. In combination with the retracted second prism <NUM>, the camera C is further protected from high intensity flashes of the light source <NUM>.

<FIG> shows a method for operating device <NUM> for cosmetic treatment according to an exemplary embodiment of the invention. Although described in reference to the structural arrangement of the imaging element as described in <FIG>, it is also applicable to that of <FIG>.

The method comprises providing the optical assembly <NUM> of any of the aforementioned embodiments. At least one image of the target <NUM> (either by the imaging element C or by an external imaging element/camera) is obtained to determine its suitability to treatment and thereby to determine whether to perform the treatment. If yes, the light emitted by a light source <NUM> of the optical assembly <NUM> is guided to the target for performing the treatment.

In more detail, in step <NUM>, device <NUM> (main body portion or attachment) is brought in contact with target <NUM> (skin) for treatment. In step <NUM>, it is determined whether contact is properly established between the device <NUM> and the target using a suitable skin contact sensor.

If the device controller, based on the sensor output, determines that skin contact is not established with the device, a control signal is transmitted by the controller to an interface unit connected to a display in step <NUM>, which then informs the user to position device <NUM> in contact with the target <NUM>.

If the device controller, based on the sensor output, determines that skin contact is established with the device, in step <NUM>, a control signal is transmitted to activate actuator A of optical assembly <NUM>. The second prism <NUM> is then moved towards the (uncoated) portion of the third surface <NUM> of the first prism <NUM>, so that the deformable layer AD is in contact with said portion of the third surface <NUM>.

In step <NUM>, a control signal is transmitted to camera C of optical assembly <NUM>. The camera C then obtains image(s) of the target <NUM> (skin), to determine the suitability of the skin (target <NUM>) to the light-based treatment. Such suitability may be determined based on various skin characteristics information, e.g. skin pigmentation/tone, inferred from the image(s).

A dedicated skin contact sensor may be used for detecting contact with skin. Alternately, camera C can be used to detect skin contact. In this case, the controller transmits a control signal to activate camera C of optical assembly <NUM> in step <NUM>. The controller may transmit this signal upon its activation by user e.g. via the display. The camera C obtains image(s) of the skin to detect skin contact. Steps <NUM> and <NUM> may be combined in this case. The controller may then determine, based on an image focusing quality and/or sharpness, whether contact has been established with skin. The same or a different image may then be analyzed by the controller to determine suitability of the skin to the treatment in step <NUM>.

In step <NUM>, the controller determines whether the skin is suitable for treatment. If suitable, in step <NUM>, a control signal is transmitted to actuator A, to move the second prism <NUM> away from the uncoated portion of the third surface <NUM> of the first prism <NUM>, so that the deformable layer AD is disconnected from said portion of the third surface <NUM>. A control signal may further be transmitted to camera C so that it is disabled prior to triggering a treatment pulse from the light source <NUM>. Once the second prism is retracted (and the camera disabled), in step <NUM>, the control signal transmitted to the light source <NUM> controls the source <NUM> to emit the treatment light pulse.

In step <NUM>, if the controller determines that the skin is not suitable for treatment, a control signal is transmitted to an interface unit connected to a display in step <NUM>, which then informs the user to position device <NUM> on another target location. The method then resumes from step <NUM>, till the treatment procedure is completed by the user.

<FIG> shows device <NUM> according to an exemplary embodiment of the present invention.

The device <NUM> comprises a controller <NUM> that generally controls the operation of the apparatus <NUM> and enables the device <NUM> to perform the method and techniques described herein.

The controller <NUM> is configured to transmit a control signal to the light source <NUM>, so that the light source <NUM> emits light to be guided through the optical assembly <NUM> to target <NUM>. It is further configured to receive one or more images from an imaging element (e.g. camera C) and processes the image(s) to determine whether device <NUM> is in contact with target <NUM> (skin). It may alternately process a contact sensor output to determine whether device <NUM> is in contact with the target. The controller is further configured to activate actuator A so that the imaging element can obtain image(s) or be protected from the light emitted by light source <NUM>, and analyse the obtained image(s) to determine suitability of the skin to the light treatment. If contact is not established, or if the skin is determined to be unsuitable to treatment, the controller <NUM> transmits a signal to an interface unit <NUM> connected to a display <NUM>, which then informs the user to re-position device <NUM>. The controller <NUM> may further implment machine learning ML models such as a support vector machine, a decision tree, a random forest, an artificial neural network, a deep neural network or a convolutional neural network to perform any of the mentioned analyses or determinations.

The controller <NUM> can be implemented in numerous ways, with software and/or hardware, to perform the various functions described herein. The controller <NUM> may comprise one or more microprocessors or digital signal processors (DSPs) that may be programmed using software or computer program code to perform the required functions and/or to control components of the controller <NUM> to effect the required functions. The controller <NUM> may be implemented as a combination of dedicated hardware to perform some functions (e.g. amplifiers, pre-amplifiers, analog-to-digital convertors (ADCs) and/or digital-to-analog convertors (DACs)) and a processor (e.g., one or more programmed microprocessors, controllers, DSPs and associated circuitry) to perform other functions. Examples of components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, DSPs, application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), hardware for implementing a neural network and/or so-called artificial intelligence (AI) hardware accelerators (i.e. a processor(s) or other hardware specifically designed for AI applications that can be used alongside a main processor).

The controller <NUM> can comprise or be associated with a memory unit <NUM>. The memory unit <NUM> can store data, information and/or signals (including image(s)) for use by the controller <NUM> in controlling the operation of the device <NUM> and/or in executing or performing the methods described herein. In some implementations the memory unit <NUM> stores computer-readable code that can be executed by the controller <NUM> so that the controller <NUM> performs one or more functions, including the methods described herein. In particular embodiments, the program code can be in the form of an application for a smart phone, tablet, laptop, computer or server. The memory unit <NUM> can comprise any type of non-transitory machine-readable medium, such as cache or system memory including volatile and non-volatile computer memory such as random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM) and electrically erasable PROM (EEPROM), and the memory unit can be implemented in the form of a memory chip, an optical disk (such as a compact disc (CD), a digital versatile disc (DVD) or a Blu-Ray disc), a hard disk, a tape storage solution, or a solid state device, including a memory stick, a solid state drive (SSD), a memory card, etc..

The interface unit <NUM> may comprise transceivers which enable a data connection to and/or data exchange with other devices, including any one or more of servers, databases, user devices, and sensors. It can operate using WiFi, Bluetooth, Zigbee, or any cellular communication protocol (including but not limited to Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), LTE-Advanced, etc.). It may further comprise ciruitry to control any suitable input component(s), including but not limited to a keyboard, keypad, one or more buttons, switches or dials, a mouse, a track pad, a touchscreen, a stylus, a camera, a microphone, etc., and the user interface can comprise any suitable output component(s), including but not limited to a display unit or display screen, one or more lights or light elements, one or more loudspeakers, a vibrating element, etc..

It will be appreciated that a practical implementation of device <NUM> may include additional components to those shown in <FIG>.

Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent approximation surrounding that value. Also, unless otherwise specified, the dimensions mentioned herein are measured using common laboratory measurement techniques known to the skilled person.

Claim 1:
An optical assembly (<NUM>), for use in a skin treatment device, the optical assembly comprising:
a light source (<NUM>); and
a first prism (<NUM>) including a first surface (<NUM>), a second surface (<NUM>) inclined with the first surface (<NUM>) and a third surface (<NUM>) adjoining the first (<NUM>) and the second (<NUM>) surfaces; characterized in that the optical assembly further comprises:
a first guiding element (<NUM>) comprising enclosed reflective faces (121a, 121b) disposed facing each other, and arranged to guide the light transmitted from the light source (<NUM>), through the first surface (<NUM>) of the first prism; and
a second guiding element (<NUM>) comprising enclosed reflective faces (131a, 131b) disposed facing each other, and arranged to receive, through the second surface (<NUM>) of the first prism (<NUM>), the light reflected from the third surface (<NUM>) of the first prism and output the received light for illuminating the skin (<NUM>),
wherein the first surface (<NUM>) and the second surface (<NUM>) of the first prism (<NUM>) are separated from the first guiding element (<NUM>) and the second guiding element (<NUM>), respectively, by a refractive index interface and, during use, each act as a total internal reflection surface by being disposed in contact with a medium having a refractive index less than a refractive index (np) of the first prism (<NUM>).