GB2381752A

GB2381752A - Laser skin treatment device with control means dependent on a sensed property of the skin to be treated

Info

Publication number: GB2381752A
Application number: GB0126662A
Authority: GB
Inventors: Ezio Panzeri
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-06
Filing date: 2001-11-06
Publication date: 2003-05-14
Also published as: GB0126662D0

Abstract

A skin treatment device having a laser radiation source for delivering coherent radiation to skin to be treated, a sensor for sensing at least one property of the skin and a controller. The controller is operable to control the radiation emitted from the laser radiation source in response to the property or properties sensed by the sensor. Preferably, the radiation source comprises a pulsed laser diode and the controller is operable to control at least one of its energy, pulse width and pulse interval. The sensor may be a pigment sensor, preferably a single chip blue, red and yellow detector, a pH sensor or a temperature sensor. The device is particularly suitable for the removable of hairs from the skin. A method of treating skin with laser radiation comprises sensing at least one property of the skin and delivering laser radiation to the skin according to the sensed property or properties.

Description

TREATMENT OF SKIN USING LASER RADIATION This invention relates to the field of skin treatment using laser radiation.

It is known to use laser radiation to remove unwanted features such as skin marks, surface capillaries and, in particular, hairs from epidermis.

With respect to the removal of hairs, a hair follicle is a large. complex structure that is vertically oriented within the dermis. The dermal papilla, located in the deepest portion of the follicle 3 to 7 mm below the skin's surface, has traditionally been believed to be responsible for hair cycling and regrowth. It is now apparent that the middle and upper portions of the follicle also are able to support hair growth.

Therefore, to destroy a hair follicle effectively, two potential targets must be selected: 1 to 1.5 mm below the surface and 3 to 7 mm below the surface.

Similarly, the epidermal melanin is contained in melanosomes, which are minute in size relative to an entire hair follicle. By this reasoning, the follicles must be heated for much longer than the epidermis if it is to be injured.

While it is not possible with the market products to prevent the epidermal melanin from absorbing the incident radiation, by mean of cooling the epidermis as it is radiated, a thermal gradient is established between the melanosomes and their surrounding environment.

The melanosomes must cool quickly enough that they are not destroyed, while the deeper hair follicle is heated to the point of injury. One problem associated with a contact-cooling window in direct contact with the skin is the dermal sensorial stresses and the debris build up. Dermatological tissue accumulates on the contact window as treatment pulses are delivered. The window must be periodically wiped in order to preserve the window from local, intense overheating that thermally and mechanically stresses the window and causes pitting.

All of the commercially available lasers/pulsed non-coherent light systems are bulky, extremely expensive and sometime ineffective towards total depilation, they use one of four wavelengths: 694 nm (ruby), 755 nm (alexandrite) 810 nm (diode) or 1,064 nm (Nd: YAG).

Current choices include various 694-nm long-pulse ruby lasers (Epilaser, Epitouch, Chromos 694), 755-nm alexandrite devices (Epitouch ALEX, Photogenica LPIR, GentleLASE), an 800-nm diode laser (Lightsheer), an intense pulsed xenon flashlamp light source with wavelengths ranging between 550 and 1200 nm (Epilight), and 1064-nn Nd : YAG lasers, a long-pulse laser (CoolGlide), another used in conjunction with a topical carbon suspension (Softlight), and a third high-power Q-switched Nd : YAG (Medlite IV).

The ruby, alexandrite, and diode lasers and the high-intensity pulsed light sources have been used for several years. While the data are somewhat confusing, in the vast majority of users, the alexandrite and diode lasers seem to produce 70% to 80% permanent reduction in the number of hairs in a given anatomic region after at least three treatments. However, there is no current instrument that has the most power to deliver through a large spot size for the longest time, and that is really low cost (market prices start from $25,000 US and up to $150,000 US).

None of the lasers of pulsed coherent light devices is highly effective against blonde, silver. or white hair.

The ruby laser was the first to be used in this fashion, and is still popular. It produces the shortest wavelength and is the most effective device for treating patients with red and lighter-coloured hair. It also is most susceptible to scatter within the dermis and a large spot size (at least 1 cm) is required to achieve sufficient penetration into the skin. Some of the early ruby lasers had spot sizes significantly less than 1 cm, and thus were less effective than today's models. The hairs that return do so lighter in colour and finer in diameter, and are thus clinically less noticeable than before treatment. The ruby laser may produce slightly less reduction in number of hairs, but is more effective against lighter-coloured hair.

The diode lasers have become extremely popular because they are smaller and more portable. The longer wavelength penetrates deeply into the dermis and patients with darker skin types may be treated with a greater margin of safety due to the decreased absorption by melanin at longer wavelengths.

The Nd : YAG laser is the most recent addition to the list of devices used for laserassisted hair removal. Its longer wavelength makes it even safer for treating patients with

darker skin and preliminary data suggest that it is at least as effective as the shorter- wavelength lasers.

Finally, high-intensity pulsed non-coherent light sources also have been used to achieve hair removal. These devices use a series of filters to deliver a broad range of wavelengths selectively. Due to the fact that they are not actually lasers, they are considered class II medical devices as opposed to the class IV designation assigned to lasers. This has a significant practical implication in that regulations regarding the operation of a class II device are typically far less stringent than those with a class IV device are. Data on the pulsed light sources varies, but most investigators find these devices somewhat similar to the ruby laser in terms of effectiveness.

Laser-assisted hair removals are transient in nature and are related to pigmentary changes. Hypopigmentation, hyperpigmentation, epidermal blistering and/or crusting, scarring, and regrowth of hair have all been reported.

Patients who are tanned must not be treated due to an unacceptably high risk of epidermal injury. With a small spot size, such as 1 mm, the current market products have more scatters off the skin than with a larger linear emitting area and therefore the light cannot penetrate as deeply, in addition the thermal epidermal stress is greater. Larger spot size also affords better epidermal protection because a given therapeutic result is achieved with less energy using a larger emitting window.

Laser-assisted hair removal has become a widely accepted treatment for an otherwise difficult problem. As long as patients are selected and treated appropriately, post-treatment satisfaction is extremely high. The application of some powerful machines requires surgeons to perform cosmetic or refractive laser-assisted hair removal.

As we said wavelength, pulse duration, spot size, and flux are the parameters to consider for a laser or light source for hair removal and none of the lasers or pulsed light devices is highly effective against blonde, silver or white hair.

The cause for light hair pigmentation-colour is the melanin ; such melanin is the main key to reach total hair removal.

In summary, the treatment of skin to remove such things as hairs, surface capillaries or skin marks using lasers, can be problematic, as in order for these things to be removed a certain amount of energy needs to be absorbed by them, however, the

absorption of too much energy by the surrounding skin can cause it to become damaged. Furthermore, the amount of energy that is absorbed by the skin is dependent on different properties of the skin, such as skin pigmentation, skin temperature, melanin and PH and will therefore vary from person to person.

In accordance with a first aspect of the present invention there is provided a skin treatment device comprising: a laser radiation source for delivering coherent radiation to skin to be treated; a sensor for sensing at least one property of said skin; and a controller operable to control laser radiation emitted by said laser radiation source in response to said at least one property sensed by said sensor.

By providing a sensor and controller along with the treatment device, the laser radiation that is emitted can be controlled in accordance with properties of the skin that affect radiation absorption and thus dose to the unwanted feature can be increased whilst reducing the radiation dose to the surrounding area.

Preferably, said laser radiation source comprises a pulsed laser diode.

A new Microstack technology pulsed laser diodes are relatively small, portable and cheap and yet can provide a fairly high intensity spot.

In preferred embodiments said controller is operable to control at least one of, energy. pulse width, and pulse interval of said pulsed laser diode.

Control of pulsed energy, its duration and frequency each second are important as in the removal of hair, for example, the hair as energy carrier must not be allowed to cool or burn between pulses, if the bulb is to be killed. Whereas the epidermis must be allowed to cool if it is not to be damaged. Thus, pulsed Energy its duration and frequency should be chosen with these two parameters in mind. The thickness of the hair effects hair cooling time, whereas epidermis cooling time is fairly constant, a sensor is therefore helpful in setting the correct pulse and interval duration for a particular hair follicle.

Advantageously, a newly approach against the other devices in the market is a pulse width of said pulsed laser diode of between 0. 5ns and 100ns. These pulse widths have been found to be the most effective to our scope.

In preferred embodiments said controller is operable to control flux emitted by said laser radiation source. The amount of flux influences the permanency of the hair

removal, in addition to affecting skin damage, this therefore should be controlled in accordance with readings from the sensor (s).

Preferably. said controller is operable to control beam size of said laser radiation source. The beam size affects the amount of energy delivered to a particular area and as such is another important factor in the energy delivered to the unwanted feature and that delivered to surrounding skin.

In preferred embodiments said sensor comprises a pigment sensor operable to sense the pigmentation of epidermis and/or hair under treatment. The amount of laser radiation absorbed by the skin and hair depend to a large extent on their pigmentation or colour. Thus, in order to target the radiation at the unwanted feature, the pigmentation of the feature and the surrounding area should be considered.

Advantageously, said pigment sensor comprises a single chip blue, red and yellow detector. Such a detector is effective, small and relatively inexpensive.

In preferred embodiments, said sensor comprises a PH sensor, this sensor indicates whether the skin under test is over dry and within the correct melanin values or not.

The temperature of the skin and in particular, any variations in its temperature, may provide an indication of how much radiation is being absorbed by the surrounding skin. Thus, in preferred embodiments, said sensor comprises a temperature sensor operable to sense the temperature of said skin.

Preferably, said pulsed laser radiation source comprises a MICROSTACKMultiple Epitaxially Stacked Emitters InGaAs/GaAs.

The laser diode used for this particular application uses Pulsed Microstack Laser Diode technology, which for the first time been adapted to a hair epilator and a skin rejuvenation device (Esfoliator). With the Microstack laser technology, that includes multiple epitaxially stacked emitters in a plastic package. low cost is gained, due to the physical reliability of strained InGaAs/GaAs material. Making this laser diode has been found to be relatively inexpensive, 5 to 20 times the less the market products and particularly well adapted for hair removal and skin treatment.

Finally the High power diode large-optical-cavity structure allow a larger laser- emitting surface covering more skin area in shorter operational time with a lateral laser aperture of between zum and 250um, preferably 20ovum. A lateral laser aperture of 200m gives a beam divergence (FWHM) of 6 X 34 .

Compared with the traditional laser in the market mentioned herein the Microstack technology has high power in such small surface, (5 mm diode standard case) with a ranging emission from 3 W to 50 W Peak Power with a wavelength ranging from 780 nm to 980, pulse width of 100ns and a average 10 KHz frequency. Others do not reach either 10 Hz.

Preferably, said pulsed laser radiation source is encased in a plastic package.

If we have to use metal laser diode packages, the case will be electrically connected to the discharge voltage. This requires careful design consideration to isolate the laser package from the surrounding environment which is often grounded. This also presents an electrical shock hazard if handling the laser and driver is necessary during open bench testing. In our case the diode has plastic package then it is very safe from all the aspect covering shock hazard, high temperature emission and electromagnetic compatibility with EC regulation.

Preferably, said laser radiation source comprises a further laser radiation source, said two laser radiation sources having different wavelengths and working in parallel upon said skin under treatment.

By using two lasers in paralleL the one with the longer wavelength can be used to target deeper parts of the epidermis while the shorter wavelength laser can be targeted at things nearer the surface. Advantageously, said controller is operable to control laser radiation emitted by said two laser radiation sources in response to at least one property sensed by said sensor. The use of two lasers in conjunction with the sensor may in some embodiments enable the device to be used in such a way that the flux at different depths is controlled with reference to the natural skin cooling, so that there is no need to switch off the laser pulses.

Preferably, said controller comprises a microprocessor.

In preferred embodiments said device further comprises an optical block, said optical block comprising an entry surface arranged to receive radiation emitted by said laser radiation source and an emitting window arranged to emit said radiation.

The use of an optical block in this way, helps reduce losses and provides a robust and compact optical unit. Furthermore, many pulsed laser diodes are capable of tremendous peak optical power output and accordingly demand the practice of eye-safe procedures. This is especially true when the laser is removed from an apparatus such that the bare laser diode is visible. The optical power density near the device can be very hazardous to the eye. That is not the case using the embodiment optical block.

Preferably. said device further comprises a housing arranged to receive said optical block and said laser radiation source, said optical block being arranged within said housing such that in use said emitting window faces said skin to be treated, thereby providing a robust and easy to use device.

In preferred embodiments, said optical block comprises a lens for controlling the size of a beam of said emitted laser radiation and preferably, said optical block comprises a reflecting parabolic surface operable to focus a beam emitted by said laser radiation source into a collimated beam perpendicular to said emitting window.

This provides a defined beam area having a known flux that is therefore suitable for use in treating skin.

On the eyes safety point the optical block work in such a way that the emitted beam is collimated for the first 10 mm, with decay after that, making the system less hazardous, been classified under Class III A or even Class II B.

Making it available not only to Dermatologist, Skin Doctors or qualified Medical centres but also to Air dresser or Beauty Saloons.

Preferably, said flux emitted by said laser radiation source is between 1 and 60 J/cm2 and said wavelength of said laser radiation source is between 780nm and 980nm. These range values have been found to be particularly suitable for skin treatment and, in particular, hair removal.

In preferred embodiments, said pulsed laser radiation source comprises a plurality of laser emitters, preferably a plurality of diode emitters monolithically integrated within a single chip and electrically connected in series. A plurality of diode emitters

(preferably 2-3) monolithically integrated in a single chip are produced by continuous epitaxial growth of several laser zones on each other, separated by tunnel junctions. As they are electrically connected in series the output power is doubled or tripled by applying the same current as for the standard laser chip.

A further aspect of the present invention provides, a method of treating skin with laser radiation comprising the steps of : (i) sensing at least one property of said skin ; (ii) delivering laser radiation to said skin, wherein said delivered radiation is controlled in response to said at least one property sensed.

Embodiments of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which: Fig. I is a simplified 3-Dimensional view of a skin treatment device according to an embodiment of the present invention; Fig. 2 shows simplified side views of a skin treatment device with portions broken away to show laser emitted light from the optical block window in a perpendicular direction to the skin, according to an embodiment of the invention; Fig. 3 is a schematic representation of a skin treatment device optical block with laser diode package assembly, and a plan view of the optical block made according to an embodiment of the invention; Fig. 4 shows optical blocks positioned in antithesis one to the other and the diode case internal design; Fig. 5 is a simplified side view of hair follicles being treated with two optic block emitting windows each working at different skin levels, i. e. at depths of 1- ]. 5mm and 3- 7 mm ; Fig. 6 is a simplified side view of a skin treatment device according to an embodiment of the invention with portions broken away to show PH sensor position and related reference stick; Fig. 7 is a simplified side view of a skin treatment device according to an embodiment of the invention with portions broken away to show the colour skin detectors system an SMD-Chip with the emitting diode; Fig. 8 shows layout diagram of the laser diode driver and pulse generator; and

Fig. 9 shows driver photo with pin numbers and connection, schematic of pulse width variances.

A portable, miniaturised low cost skin treatment device according to an embodiment of the invention (see fig. 1 and 2), includes an ergonomic surface (3a) which is used to contact the skin (10) a housing (3) having at least one optical chamber block (1) for sequentially emitting a series of pulses of coherent light energy having a pulse duration in the range of Ins to 100 ns and a flux adjustable electronically between I J/cm2 to 60 J/cm2 upon the parameterised skin data. It is particularly well adapted for hair removal and skin resurfacing.

Figure 2 shows a radiation beam (la) of follicle damaging laser light as it is passing from an optical chamber (1) connected to the impulse laser (lb) (see fig 3) for transmitting through a recessed window (2) a series of pulses of coherent light energy to the skin. The optical block (1) preferably includes an entry surface facing one impulse laser diode (lob), one internal negative spherical lens (6), a reflecting parabolic optical lens element (7) and an emitting window (2). The optical block is attached to the body frame by means of four flexible hooks 7a (see fig. 2), where the hook receiving apertures 7a'are on the optical block (see fig. 3), easing the assembly or replacement. 7c are optical guides to monitor visually the pulse rate and the selected processes. 7b is a'L' shape guide that direct two ultra-bright SMD-LED's light to the back of the laser diode and optical block in order to make visible the emitted infrared pulses visible to the operator, preferably the light is'Blue'.

In a preferred embodiment the sets of optical block/laser are two, where the two optical block (2a, 2b) are in antithesis (see fig 4 and 5) in order to first burn the deeper follicles bulbs (14) and delmal papilla with the first optical (2a) block and secondly bum middle and upper sebaceous glands (16) in order to stop the hair regrowth with a second optical block (2b).

1 c and 1 d in Figure 4 illustrate the option of having a single plastic package with more than one emitter. Such emitters are integrated monlithically into one laser chip. In the same unbedded chip one or more emitters (1 c) can work at a shorter wavelength between 680-780nm in order to bum the deeper follicle bulbs and dermal papilla. Other

emitter/emitters (nid) will work at longer wavelengths between 800-980 nm in order to bum middle and upper sebaceus glands, within the same optical block.

This diode is created by continuous epitaxial growth of several laser zones, eventually of different material to gain the required wavelength on each other separated by tunnel junctions.

Because the several laser emitters are electrically connected in series an extra advantage is also gained in the output power, doubling with two emitters and tripling with three and so on, by applying the same current as for the standard laser chip. In contrast to the current the turn on voltage is doubled or tripled.

The laser apparatus has an internal sequence control device (15) (see fig 2) for controlling the laser to emit the series of pulses of coherent light energy sequentially. with a time delay preferably in the order of 20 Hz between the sequential pulses of the single laser of 100 ns.

All apparatus is included in two shells parts making a hand piece assembly (3) similar in size to a computer'mouse' (122-mm long by 60-mm width), the two parts are mechanically hooked on the front 3c, and at the extreme end with a cable holder"Mickey Mouse"shaped, (4a) (see figs 1 and 2).

The laser-pulse duration is preferably selected according to the general skin colour and hair thickness, hair-skin colour control is automatically done by pigment sensor (8) and emitter (9) (see fig 2 and 7), while over-dried skin is measured by the PH controller device (11), and its reference (12) which also functions as a switch security device to avoid beam eye staring (see fig 6). In addition two other sensors (8a) temperature and (8b) humidity are mounted close to the emitting window to monitor the external conditions before and during the treatments (see fig. 2).

The hair thickness analysis is done interpolating the hair-skin colour data with the PH data, because the hair strength is dependent on the melanin quantity on each hair.

Other than permanently to remove a plurality of hair follicles the system could be used to remove surface capillaries from the skin and skin marks.

In a review of how the various parameters affect performance, we designed a low cost pulsed laser diode (InGaAs/GaAs) hair remover device, our device features a pulse

duration of at least 100 ns and a flux of at least 2.5 J/cm2 every 1/20 of a second (20 Hz), through an linear emitting area ("'spot") size of 4 x 20 mm, emitting window (2).

Our wavelength choice was influenced by the test characteristics of the anticipated user population, where the majority of them were failing on certain different wavelength, our photoepilation device covers a range of wavelengths between 780 nm to 980 nm of the melanin absorption spectrum.

The shorter 780-nm wavelengths are better absorbed by a melanin than longer wavelengths are. For this reason, our device with a longer wavelength may be preferred for use in dark-skinned patients in whom it will be less likely to cause pigmentary changes.

In addition, the longer-wavelength 980-nm devices offer greater penetration, and this feature may offset their lower melanin absorption, since they may better reach the hair bulb and bulge that are the target structures for photoepilation.

In one of the embodiments there is two kind of laser emitting diodes working in parallel upon the encountered skin. One laser works on the shorter wavelength emission at a certain pulse for the 1-1.5 mm middle and upper air follicle; and the other longer laser wavelength will work on the deeper part at 3-7 mm. The laser diode is a low cost plastic package InGaAs/GaAs material with microstack laser technology including epitaxially stacked emitter.

With this approach no coolant is required as the lasers are controlled by a crosslink microprocessor analysis between a PH sensor and melanin/skin colour sensors.

The microprocessor also controls pulse duration, or the amount of time the light is t : l in contact with the skin, this influences hair destruction and also epidermal safety.

In order to destroy the hair, the pulse duration has to be shorter than the cooling time of the hair. In order to preserve the epidermis, however, the pulse duration needs to be longer than the cooling time of the epidermis, thus allowing the upper layer of the skin to cool while the device is pulsing. Hair cooling time increases with increasing hair diameter, while epidermal-cooling time is relatively constant. Selection of at least 100-ns pulse duration will optimise destruction of larger-diameter hair. Flux, or energy, influences the permanency of the hair removal, since with increasing energy there is more thermal damage to the target, increasing the longevity of the hair removal.

It is important to understand that the highest energy listed is usually for the smallest spot size because it takes a powerful laser to drive more energy through a larger spot size. In our optical system we succeed in delivering to the skin 85-90% of the emitted diode laser power through a larger emitting window, because of the optical engineering that is a completely sealed block with 10-15% losses in air-plastic. Other products have substantially more than 60-70% loss, than to reach the target needs more power an so on.

Embodiments of the present invention address the problem of the lack of a tailor made laser flux/energy set, with respect to each end user skin pigmentation, skin temperature, melanin and no PH control in the existing products.

Preferably, the controller comprises a Pulsed Laser Diode DriversLoad: attach appropriate laser diode or use dummy load by shorting A-K (see fig 9) with wire < 1" in length. Eye-safety procedures should be strictly enforced with exposed laser diodes. To improve eye-safety, set pulse rate as low as possible if a laser is used. If a dummy load is used, do not set pulse rate higher than maximum specification. Pulse should be positive, TTL compatible, width 20 ns-I u. s. when connecting a single supply to test the driver, parallel the supply input terminals 3 and 4. The power supply should be adjusted to nominally 320 Vdc (300-330Vdc). The driver current consumption will depend upon pulse rate but is typically 2mA-5mA.

The use of two power supplies allows for independent connection to terminals 3 and 4. In this way, the voltage present at terminal 4 can be varied from 0-400Vdc (up to 500Vdc for the DRIVER) to control the laser discharge voltage (and consequently, peak current through the laser diode). Terminal 3 should always remain biased at 320 Vdc.

The discharge voltage is easily monitored at the laser (or dummy load) cathode connection. A combination of wideband oscilloscope and probe with short (local) ground lead is recommended for this measurement. Alternatively, current through the load can be directly monitored with a wideband current probe attached to one lead of the laser diode or to the dummy load. This may, however, slow the measured risetime of the current through the load.

The peak discharge current is related primarily to three controllable factors: discharge voltage, discharge capacitance, and laser package inductance. Discharge

Voltage is the potential at terminal 4. It may be varied over the range of 0 to 400 Vdc (500Vdc for DRIVER). Discharge Capacitance is determined by Cl and C2. Laser Package Inductance is chosen to be a minimum and its value has an increasing impact on the risetime of the current pulse as larger package inductances are implemented. By integrating and linearizing the equation for current through a capacitor vs. time a simple expression to determine best case peak current can be illustrated as: Cdis Vdis = Iload tdis. For a DRIVER with 320V bias and discharge voltage with a measured discharge time of 20 nanoseconds (90%-10% discharge voltage at the cathode connection), the maximum estimated peak current through the load would be: Iload = (2nF) (320V)/ (20nS) = 32 Amps (pk). The actual value of peak current will be less due to voltage drop across the load, capacitors. and all components in the discharge loop including the MOSFET switch. Each has its own ESR and inductance which cause a dynamically changing voltage drop as the discharge progresses. This effectively reduces the amount of Vdis available to generate a high peak current. The peak voltage drop across a discharge loop component may be approximated as: Vdrop = (Lpkg) (Ipk)/ (tdis) + (Ipk) (RESR) The voltage discharge time is closely related to the current pulse width and are often referred to interchangeably. A DRIVER will typically produce a 20 nS pulse width at 320V discharge with a short dummy load. The discharge time is primarily dependent upon the discharge capacitance (Cl and C2), loop inductance and ESR, and the dynamic switching profile of the MOSFET Rds (on) during the discharge. It is also effected by the discharge voltage due to MOSFET switching characteristics. Higher voltages not only increase peak current, pulse width and risetime, they reduce the propagation delay from trigger to discharge. For this reason terminal 6 (discharge monitor output) is provided for temperature and voltage sensitive applications which demand nanosecond accurate measurements of laser pulse propagation such as OTDR's and laser rangefinders. The table below approximates expected pulse widths for an DRIVER with a short circuit load for different discharge capacitances (Cl + C2) with a 320V discharge potential ; The DRIVER is build with two 1000pF (500V or greater), low-ESR, lowinductance, multilayer X7R ceramic capacitors in a type 1206 SMD package.

Regarding the laser diode pulse width and duty cycle, these are limited to lOOns and 0. 1% respectively due to laser chip heating. The minimum pulse width depends on

the deployed diode driver. , A physical limit is given by the delay and relaxation time of the stimulated laser emission. The pulse width is actually determined by the capacitors of the integrated driver circuit. A fine tuning can be done by the width of the trigger signal for the MOSFET gate leading to a range from 10 to 40 ns. The maximum duty cycle is limited to 0. 1%.

The optical semiconductor high power laser diode show excellent reliability. The laser structure consists of an InGaAlAs double quantum well as active layer embedded in a large optical cavity waveguide structure. The layers were grown in a low pressure MOVPE reactor.

In a qualification procedure laser diodes of each series have been exposed to accelerated ageing test that means operation at an ambient temperature of 85 C. During these tests no sudden failures occurred and low degradation in optical power was measurable.

A summary of various features of embodiments of the present invention are set out below.

Embodiments of the present invention comprise a portable coherent light hair removal device comprising: a device having a skin-contacting optical end ; a laser radiation source carried internally by a miniaturised optical system block and having a recessed optical linear window through which hair follicles damaging radiation passes to the user skin in a perpendicular manner. They may further comprise a PH sensor pulse actuator button carried by the device body. in order to switch the laser on and work only in contact with the skin. The PH sensor senses if the skin is over-dried or within the correct melanin values.

The device may further comprise an optical sensor for determining the user hair and skin pigmentation, and modulate the laser flux/pulse and to work only in contact with the skin within the correct melanin values. The optical sensor is preferably a 3-colour based detector, blue. red and yellow preferably on a single chip.

The optical chamber of the device may comprise an entry surface facing one impulse laser diode, one internal negative aspherical lens, a reflecting parabolic optical lens element and an emitting window, wherein the reflecting parabolic surface has the

function of shaping a non-collimated light into collimated light and spreading the photon beam in a rectangular coherent and perpendicular shape to the skin.

In some embodiments, the exit aperture is elongate and rectangular and in others it is square, or has other possible geometrical forms.

Furthermore, the emitting window has good irradiance and laser distribution and avoidance of a spot-circular beam where coolant is required.

The optical chamber comprises light-reflecting walls, which help to equalise the flux of radiation passing through the exit aperture. Furthermore, the optical elements are manufactured in a single rectangular fused polymer block, by means of sophisticate moulding process. The optical chamber may also comprise a beam size-defining lens system by which the lateral size of the radiation beam passing through the recessed window can be controlled.

The device may further comprise a moisture wicking stick reference element extending over the device surface and embedded within it, with the function of closing electrically the circuit PH measures. This may be a user removable stick.

The body of the device is a hand-grippable body, with miniaturised dimension and shape similar to a computer'mouse'.

The emitting optical block are at least two; where one block is emitting a certain pulsed laser light at the shorter wavelength in order to target 1-1.5 mm middle and upper air follicle; a second optical block emitting a longer wavelength that will work on the deeper part at 3-7 mm of the follicle.

The two laser pulsing emissions are working alternatively one at the shorter wavelength and the other at longer wavelength, to maintain the flux at different state of energy for different depths and to time natural skin cooling without switching off the laser pulses.

The two optical block are in antithesis in order to first bum the deeper follicles bulbs and dermal papilla with the first optical block and secondly bum middle and upper sebaceous glands in order to stop the hair regrowth with a second optical block. Chemical coolants may not be required, due to the alternating power sources and automatic electronic monitoring.

Embodiments of the invention comprise a method that electronically sets a hairremoval device for use comprising: determining the typical diameter of the hair to be removed from a user through a skin pigmentation algorithm ; and selecting laser-pulse duration for the hair removal device according to PH value. The hair diameter algorithm is determined upon comparison of initial PH data and skin colour pigmentation.

The method further comprising preferably the automatic step of selecting hair removal laser intensity based on skin pigmentation, and wherein the laser wavelength range is preferred to be 780 nm to 980 nm, more preferably using laser energy having a wavelength of about 1.06 microns.

The selecting step is carried out so that hair diameters from about 25 to 150 micrometers result in laser-pulse durations of about 100 ns.

Claims

CLAIMS 1. A skin treatment device comprising: a laser radiation source for delivering coherent radiation to skin to be treated; a sensor for sensing at least one property of said skin; and a controller operable to control laser radiation emitted by said laser radiation source in response to said at least one property sensed by said sensor.
2. A skin treatment device according to claim 1, wherein said laser radiation source comprises a pulsed laser diode.

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3. A skin treatment device according to claim 2, wherein and said controller is operable to control at least one of, energy, pulse width, and pulse interval of said pulsed laser diode.
4. A skin treatment device according to claim 2 or claim 3, wherein a pulse width of said pulsed laser diode is between 0.5 ns and 100ns.
5. A skin treatment device according to any preceding claim, wherein said controller is operable to control flux emitted by said laser radiation source.
6. A skin treatment device according to any preceding claim, wherein said controller is operable to control beam size of said laser radiation source.
7. A skin treatment device according to any preceding claim, wherein said sensor comprises a pigment sensor operable to sense the pigmentation of epidermis and/or hair under treatment.
8. A skin treatment device according to claim 7, wherein said pigment sensor Z-1 comprises a single chip blue, red and yellow detector.

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9. A skin treatment device according to any preceding claim, wherein said sensor comprises a PH sensor.
10. A skin treatment device according to any preceding claim, wherein said sensor comprises a temperature sensor operable to sense the temperature of said skin.
11. A skin treatment device according to any preceding claim, wherein said pulsed laser radiation source comprises a MICROSTACK-Multiple Epitaxially Stacked Emitters InGaAs/GaAs.
12. A skin treatment device according to any preceding claim, wherein said pulsed laser radiation source is encased in a plastic package.
13. A skin treatment device according to any preceding claim, wherein said pulsed laser radiation source comprises an emitting surface of between 150llm and 250pu, preferably 200nom.
14. A skin treatment device according to any preceding claim, wherein said laser radiation source comprises a further laser radiation source, said two laser radiation sources having different wavelengths and working in parallel upon said skin under treatment.
15. A skin treatment device according to claim 14 wherein said controller is operable to control laser radiation emitted by said two laser radiation sources in response to at least one property sensed by said sensor.
16. A skin treatment device according to any preceding claim, wherein said controller

.. comprises a microprocessor.

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17. A skin treatment device according to any preceding claim, wherein said device further comprises an optical block, said optical block comprising an entry surface arranged to receive radiation emitted by said laser radiation source and an emitting window arranged to emit said radiation.
18. A skin treatment device according to claim 17 wherein said device further comprises a housing arranged to receive said optical block and said laser radiation source, said optical block being arranged within said housing such that in use said emitting window faces said skin to be treated.
19. A skin treatment device according to any one of claims 17 and 18, when dependent on claim 6, wherein said optical block comprises a lens for controlling the size of a beam of said emitted laser radiation.
20. A skin treatment device according to any one of claims 17 to 19, wherein said optical block comprises a reflecting parabolic surface operable to focus a beam emitted by said laser radiation source into a collimated beam perpendicular to said emitting window.
21. A skin treatment device according to any preceding claim, wherein said pulsed

2 energy flux emitted by said laser radiation source is between 1 and 60 J/cm2.
22. A skin treatment device according to any preceding claim, wherein said wavelength of said laser radiation source is between 780nm and 980nm.
23. A skin treatment device according to any preceding claim, wherein said pulsed laser radiation source comprises a plurality of laser emitters.
24. A skin treatment device according to claim 23, wherein said plurality of laser emitters comprises a plurality of diode emitters monolithically integrated within a single chip and electrically connected in series.

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25. A method of treating skin with laser radiation comprising the steps of : (i) sensing at least one property of said skin; (ii) delivering laser radiation to said skin, wherein said delivered radiation is controlled in response to said at least one property sensed.