Irradiating device

Abstract: An irradiating system comprising an irradiating device is disclosed. An input of the irradiating device is connected to a capacitive energy storage device via a switching means, and a control unit is connected to the switching means and is operable to actuate the switching means. Means for inputting to the control unit a variable demand value of output energy (E D ) representative of a user requirement of energy to be discharged as a pulse of radiant energy from the irradiating device is also disclosed, as is means for inputting to the control unit a variable demand value of output pulse length (t D ) corresponding to a user requirement of pulse length of the pulse of radiant energy. The control unit is operable and having an estimated voltage value (V E ) representative of a voltage to which the energy storage device is required to be charged to enable the irradiating device to receive sufficient electrical current for the pulse of radiant energy to have actual values of output energy and output pulse length (E O , t O ) corresponding substantially to the demand value of output energy (E D ) and the demand value of output pulse length (t D ) respectively. A charging circuit is provided to charge the storage device to a supply voltage V S corresponding to the estimated voltage value as is trigger means, to close the switching means to initiate a supply of current (i) to the input of the irradiating device. The control unit is operable to open the switching means to terminate the resulting pulse of radiant energy such that the supply of current to the input of the irradiating device is terminated before complete discharge of the energy storage device.

Description: This invention relates to an irradiating device and in particular but not exclusively to a method of operating a medical irradiating device producing a pulse of radiant energy of variably controllable energy and pulse length for use in skin treatments such as vein removal or depilation. It is known to provide light pulses for skin treatment by means of an irradiating device comprising a flash lamp or comprising a laser optically pumped by a flash lamp, the light pulse being delivered to a localised area of skin to effect treatment. It is important to control the output energy and output pulse length associated with the light pulse at the localised area of skin in order to optimise treatment and avoid tissue damage and to adapt the output energy and output pulse length to suit particular skin types which may for example vary according to pigmentation. US-A-5059192 discloses a method of depilation in which the output energy is controlled in order to determine the depth of penetration of laser light and the output pulse length is controlled to be shorter than the thermal relaxation time of melanin associated with a hair follicle. It is also known from US-A-5405368 to provide a treatment device in which the irradiating device consists of a flash lamp delivering a pulse of incoherent light and a delivery device for collecting and delivering the light to a treatment area of skin, energy supplied to the light source being provided by a pulse forming circuit to enable the output pulse length of the light source to be variable. Such irradiating devices, whether a flash lamp or laser pumped by a flash lamp, require a relatively high current of the order of 1000 amps to be delivered to the flash lamp during an input pulse length typically in the range 100 µsec to 100 milsec from a capacitive storage device. Variation in the input energy delivered to the input of the irradiating device and shaping of the input pulse of current to effectively vary the input pulse length have hitherto been achieved by switching circuits in which successive passive networks of inductors and capacitors are connected to the input of the light source via a switch which, when triggered, allows total discharge of the energy stored in the capacitors to be discharged as input energy with the input pulse of current decaying to zero according to the time constant of the selected network. DE3439005 discloses an irradiating system comprising an irradiating device having an input connected to a capacitive energy storage device via a switching means and a control unit connected to the switching means and operable to actuate the switching means. The present invention seeks to provide an improved method of operating such an irradiating device, particularly with a view to improving the control of input energy and input pulse length to thereby achieve better control of output energy and output pulse length. According to the present invention, there is disclosed a method of operating an irradiating device to provide a discharge therefrom in the form of a pulse (E D , t D ) of radiant energy, the irradiating device having an input selectively coupled to a capacitive energy storage device via a controllable switching means, the method characterised by: charging the capacitive energy storage device to a voltage V S , wherein a total stored energy in the capacitive energy storage device is between three and four times a maximum energy required to be delivered at each pulse; closing the switching means to initiate a supply of current (i), associated with discharge of energy from the capacitive energy storage device, to the input of the irradiating device to cause generation of the pulse of radiant energy (E D , t D ); and opening the switching means to terminate the pulse of radiant energy (E D , t D ) such that the supply of current to the input of the irradiating device is terminated before complete discharge of the capacitive energy storage device. There is also provided an irradiating system having an irradating device comprising an input selectively coupled, via a controllable switch, to a capacitive energy storage device connectable, in use, to a voltage source V S , the controllable switch operationally closeable to initiate a supply of current (i), associated with discharge of energy from the capacitive energy storage device,to the input of the irradiating device to cause generation of a pulse (E D , t D ) of radiant energy having an energy up to a maximum energy; the irradiating system characterised in that: the controllable switch is operable to terminate the pulse of radiant energy by terminating the supply of current to the input of the irradiating device at a point before complete discharge of the capacitive energy storage device and a total stored energy in the capacitive energy storage device is between three and four times the maximum energy required to be delivered at each pulse. An advantage of such a method is that energy storage is achieved using a capacitive energy storage device of fixed capacitance, without the need for switching circuits to vary the capacitance to meet varying energy requirements. A further advantage is that it obviates the need for inductors in the energy supply circuitry, thereby avoiding the discharge of relatively large currents through inductors so that the resulting apparatus is relatively free of mechanical shock and therefore quieter, and also creates less electromagnetic interference to surrounding equipment. A further advantage is to provide greater flexibility in determining the energy and pulse length The irradiating device will generally comprise a flash lamp connected to the input such that the current i is discharged through the flash lamp. The estimated voltage value V E is preferably determined by the control unit processing the demand values of output energy E D and output pulse length t D according to a pre-determined algorithm defined below. The radiant energy from the flash lamp may be delivered to an output aperture of the irradiating device for presentation to a treatment site in use. A pulse of incoherent radiation in the form of visible light or infrared radiation may thereby be produced. The estimated value of input energy E E required to be input to the flash lamp is preferably proportional to the demand value of output energy E D , the estimated value of input pulse length t E being taken to be substantially equal to the demand value of output pulse length t D . Optionally, the estimated value of input pulse length t E may additionally include a dwell period corresponding to the rise time of current through the flash lamp. Alternatively, the irradiating device may comprise a flash lamp connected to the input and further comprising a laser, the method including the step of optically pumping the laser with light from the flash lamp. Laser light from the laser may then be delivered to an output aperture for presentation to a treatment site in use. Preferably the laser comprises a ruby laser, the flash lamp being placed in close proximity with the ruby material. The estimated value of input energy E E may then be determined by the control unit according to a predetermined algorithm to comprise an estimated pumping energy Ep required to be input to the flash lamp during an estimated pumping period t P before lasing commences and an estimated input energy E L required to be input to the flash lamp so as to sustain operation of the laser during a subsequent output pulse length t O . The control unit may also determine the estimated value of input pulse length t E to be the sum of the estimated pumping period t P and the demand value of output pulse length t D , the estimated pumping period t P being determined by means of a predetermined algorithm. The method may include the step of measuring the current i, inputting to the control unit a measured current signal i M corresponding to the instantaneous amplitude of the current, integrating the measured current signal i M over a period commencing with the closing of the switching means to obtain a cumulative value, the control unit opening the switching means when the cumulative value is equal to a threshold value corresponding to the input energy E I received by the flash lamp being equal to the estimated value of input energy E E . An advantage of such a method is that the energy input to the flash lamp can be closely controlled relative to the calculated estimate value of input energy E E . The use of the measured current to provide feed back improves the accuracy with which the energy delivered to the flash lamp can be controlled, and thereby improves the accuracy with which the output energy E O is controlled. In practice, the estimated value of input energy E E will be subject to systematic and statistical error and, particularly in medical applications, accurate control of the pulse energy is to be preferred to accurate control of pulse length. Alternatively, where accurate control of pulse length is preferred, the method may include the step of measuring the elapsed time t, from the closure of the switching means, the control unit opening the switching means when the elapsed time t, is greater than or equal to the estimate value of input pulse length t E . The control unit is preferably an analogue computer. This is particularly advantageous in some medical environments where digital processing equipment may introduce unwanted interference or may be considered to be unduly susceptible to external interference. Preferably the control unit is operable to receive continuously variable values of the demand value of output energy E D and the demand value of output pulse length t D . The user may thereby be able to continuously and accurately adjust pulse energy and pulse length, and to control each of these parameters independently of each other. The method may optionally include the step of measuring the radiant energy directed to the output aperture, comparing the measurement of radiant energy with the demand value of output energy E D , and actuating a safety cut out to prevent further operation of the irradiating device if the measured value exceeds the demand value by a predetermined safety margin. Preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings of which; Figure 1 is a schematic diagram illustrating the supply of current to an irradiating device in accordance with the present invention; Figure 2 is a schematic diagram of an irradiating device comprising a flash lamp; Figure 3 is a schematic diagram illustrating an alternative arrangement for the supply of current to an irradiating device; Figure 4 is a schematic circuit diagram showing the discharge of current through a flash lamp; Figure 5 is a graphical illustration of the approximation of drive voltage to a rectangular pulse shape; Figure 6 is a schematic representation of an alternative irradiating device comprising a flash lamp and a laser; Figure 7 is a graphical representation of pulse shapes for an irradiating device comprising a flash lamp; Figure 8 is a graphical representation of pulse shapes for an irradiating device comprising a flash lamp and laser; and Figure 9 is an energy level diagram for a ruby laser. In Figure 1, an irradiating device 1 is required to deliver to a treatment site a pulse of light characterised by output energy E O and an output pulse length t O . The irradiating device 1 has an input 2 which receives current i from a capacitive storage device 3 via a switching device 4. The capacitance storage device 3 comprises a bank of capacitors having a combined capacitance C. A current sensor 5 comprising a transformer is arranged to sense the current i and output a measured current signal i M to a control unit 6. The switching device 4 is actuated by the control unit 6, an actuating signal S determining the opening and closing of the switching device 4. The capacitive storage device 3 is charged to a supply voltage V S by means of a charging circuit 7 which is controlled by the control unit 6 such that the supply voltage V S is determined variably in accordance with an estimated voltage value V E produced by the control unit, the value of V S being proportional to V E . A user interface 8 in the form of a control panel allows a user to input a demand value of output energy E D and a demand value of output pulse length t D to the control unit 6, the demand values E D and t D corresponding to the values of radiant energy and pulse length required by the user to be delivered to the treatment site. The user interface 8 is provided with potentiometer controls 13 and 14 allowing the user to continuously vary the demand values E D and t D . A trigger 15 is also connected to the control unit 6, enabling the user to input an initiating signal to commence the actuation of the irradiating device 1. According to a first embodiment of the present invention, the irradiating device 1 as shown in Figure 2 consists of a flash lamp 9 in combination with a delivery device 10 arranged to collect and concentrate light emitted by the flash lamp and deliver the collected light to an output aperture 11. The output aperture 11 is comprises a window placed in contact with a localised area of skin at the treatment site 12. The irradiating device 1 also includes a simmer circuit 19 which provides a relatively low level of continuous current through the flash lamp such that the flash lamp is maintained in a standby mode allowing the rapid onset of discharge in response to a voltage being applied via the switching device 4. Maintaining this low level of discharge avoids the need for a high voltage to initiate conduction by breakdown of the flash lamp gaseous medium. As illustrated in Figure 7 the demand value of energy E D translates to a demand value of power P D over the pulse length t D , the pulse shape being ideally rectangular. The actual output power P O for an irradiating device 1 comprising a simple flash lamp 9 will vary proportionally to the current i passing through the flash lamp, the output pulse length t o corresponding to the input pulse length t i of current i input to the irradiating device. The level of current i passing through the flash lamp 9 will be determined by the supply voltage V S , taking into account the impedance k O of the flash lamp, the impedance R of the switching device 4 and associated conductors. Referring to Figure 1, the control unit 6 comprises an analogue computer configured to determine the estimated voltage value V E which must be delivered to the charging circuit 7 in order to achieve the supply voltage V S appropriate to a user requirement defined by E D , t D . The charging circuit 7 is then operable to charge the capacitive storage device 3 until the required supply voltage V S is achieved, the "ready" status of the charging unit then being indicated to the user by means of an indicator panel 16. The user is then able to initiate irradiation by means of the trigger 15 in response to which the control unit 6 generates the actuating signal S to close the switching device 4. Current i then commences to flow through the flash lamp 9 as the capacitive storage device 3 progressively discharges. A measured current signal i M is input to the control unit 6 from current sensor 5 and the control unit performs an integration to determine a measure of input energy E M delivered to the flash lamp. The control unit 6 also determines from the demand value of output energy E D an estimated value of input energy E E required to be supplied to the input 2 in order to produce a value of output energy E O equal to the demand value of output energy E D . The measured value of input energy E M is compared with the estimated value of input energy E E and the actuating signal S is terminated to open the switching device 4 when E M = E E . The relationship between E E and E D is established by calibration measurements of E O and the control unit 6 configured accordingly. The resulting output pulse length t O of the light pulse delivered to the treatment site 12 will in general correspond closely to the demand value of output pulse length t D . Some variation is however expected since for example the rise time of the current i will vary from pulse to pulse following closure of the switching device 4, this phenomenon being referred to typically as jitter of the flash lamp 9. The measured current signal i M thereby enables the control unit 6 to provide feed-back to accurately control the output energy E O . As illustrated in Figure 3, the shape of the pulse of current i is not exactly rectangular since the supply voltage V S and hence current i will decay as the capacitive storage device 3 progressively discharges. As a further safety feature, a light detector 17 is connected to the irradiating device 1 so as to input to the control unit 6 an intensity measurement signal I M which the control unit integrates to determine a measure of the output energy E O by means of a predetermined calibration constant. The control unit 6 compares the measurement of output energy E O with the demand value of output energy E D and indicates a fault condition if the difference exceeds a safety margin of 20%. In response to the fault condition being flagged, the control unit 6 ceases to respond to further actuation of the trigger 15. The switching device 4 is an insulated gate bipolar transistor which is suited to the switching of high currents and enables the current i to be interrupted before the capacitive storage device 3 has been fully discharged, unlike current switching devices such as thyristors which require the current to fall to zero before the device turns off. In practice, the total energy stored in the capacitive storage device is between three and four times the maximum amount of energy required to be delivered at each pulse. The control unit 6 calculates the estimated voltage value V E from the following algorithm. V E = V T + E E R t E V L + V L + E E 2CV L where: V T = constant voltage across the switching device when conducting; k O = input impedance of the flash lamp; R = resistance between the capacitive storage device and the input of the irradiating device. The manner in which this algorithm is derived is explained below at Appendix A. The calculation according to the algorithm is performed by means of an analogue computer in the preferred embodiment but alternatively may be performed using an electronic digital processor such as a microcomputer running appropriate software. A second embodiment shown in Figure 3 will now be described using corresponding reference numerals to those used above where appropriate for corresponding elements. In the embodiment of Figure 3, the control unit 6 utilises a timing circuit 18 to generate the actuating signal S so as to precisely determine the timing of the closing and opening of the switching device 4 to correspond to the estimated value of input pulse length t E . In this embodiment it is not necessary to measure the current i and so the transformer 5 has been omitted. The control unit 6 continues to calculate V E according to the above algorithm. This simplified arrangement amounts to an open loop system in which no feed-back of input energy E I is utilised. Greater statistical fluctuation in the output energy E O is therefore anticipated in this embodiment but this embodiment may be preferred where it is considered more appropriate to have closer control over the output pulse length t O . A third embodiment will now be described using corresponding reference numerals to those of previous embodiments where appropriate for corresponding elements. An alternative irradiating device 20 as shown in Figure 6 has an input 2 connected to a flash lamp 9 which is used to optically pump a ruby laser 21. The ruby laser 21 has a delivery device 10 in the form of an articulated arm arranged to deliver the coherent light output of the laser to an output aperture 11 which in use is deployed at a treatment site 12. The schematic diagram of Figure 1 is also applicable to the embodiment of Figure 3 although the manner of operation of the control unit is different in an important respect. For each pulsed operation of the irradiating device 20, the flash lamp 9 is required not only to continue operation during the period during which the laser provides coherent light output, i.e. during the output pulse length t O , but also during a pumping period t p during which the light output of the flash lamp excites the active material of the laser to a point where population inversion allows lasing to commence. The control unit 6 will therefore determine an estimated value of input pulse length t E which exceeds the demand value of output pulse length t D by the pumping period t P . Similarly, the control unit 6 will determine an estimated value of input energy E E which takes account of the additional energy required to be input to the flash lamp during the pumping period t P . Having determined the estimated value of input energy E E and the estimated value of input pulse length t E , the above algorithm referred to with reference to the first and second embodiments is then implemented. As shown schematically in Figure 9, the energy levels in a ruby laser may be visualised as comprising a ground state having population N1, a pumping level having a population N3, and a laser level having a population N2, the populations N1, N2 and N3 referring to electron energy populations in the active material. The pumping mechanism relies on the flash lamp providing excitation from the ground state to the pumping level from which population of the laser level is effected by decay from the pumping level with a relatively short time constant. Lasing at the frequency corresponding to the N2-N1 transition occurs when population inversion is achieved i.e. N2 > N1. The pumping period t P during which the flash lamp will need to irradiate the active material of the laser before lasing commences will depend upon the time constant τ of the N2-N1 transition, the rate at which the flash lamp supplies energy to the active material and the ratio of N2 -N1 at which lasing occurs. Given the demand values of energy and pulse length E D , t D , the control unit 6 is required to operate the flash lamp 9 for a sufficient period and with sufficient energy to achieve pumping of the laser and subsequently maintain laser action by re-populating the laser level N2. As illustrated in Figure 8, the control unit must determine an estimated value of input pulse length t E given by t E = t P + t D where: t p is the pumping period and t D is the demand value of output pulse length which will be substantially equal to t o , the actual output pulse length for which the laser output power P O is achieved. The control unit may determine t P according to an algorithm of the following form; where n = E L m + x 1-x and m = t D τ where x = population inversion ratio = N 2 N 1 + N 2 τ = lifetime of laser state and E L is a dimensionless parameter proportional to E D and representative of the energy supply by the flash lamp during lasing. In order to determine the estimated voltage value V E the control unit 6 also requires the estimated value of input energy E E which may be computed according to the following algorithm; E E = B n τ (t P + t D ) where B = a constant In the above expressions the constants A and B may be determined empirically. The control unit may therefore determine the required values of t E and E E from the user demand values of t D and E D and then control the flash lamp operation as indicated above with reference to the first embodiment. The present invention has been described above primarily with reference to medical irradiating devices. The present invention may alternatively be utilised in the operation of irradiating devices for other purposes such as drilling and welding where both radiation pulse length and energy need to be accurately controlled. An irradiating device for drilling or welding may for example comprise a YAG laser pumped by a flash lamp, the flash lamp being connected to the input of the irradiating device so as to receive current from a capacitive energy storage device via a switching means as described above. Appendix A For a given pulse length and pulse energy into a flash lamp there is a unique drive voltage. However the ideal case is not easily achieved in reality as effects such as capacitor bank voltage droop during the pulse (due to the finite capacitor size), resistive cable voltage drop and constant drop due to bipolar switching devices reduce the actual voltage appearing across the lamp terminals. Compensation factors have to be added in to adjust the capacitor bank voltage to allow for these drops. The proposed schematic is shown in Figure 4. Ideally, the current through a flash lamp, at currents above the voltage minimum on the I-V curve, is related to the voltage and lamp impedance by: V L = k O i where: V L = Lamp Voltage; k O = Lamp impedance; i = Lamp current; For a constant voltage the energy in to the lamp is given by: E E = V L .i.t E where: E E = Estimated value of lamp energy required; t E = Estimated pulse length required; The energy stored in the capacitor is given by: E C = 1 2 CV 2 C where: E C = Energy stored in storage capacitor; C = Storage capacitor; V C = Capacitor voltage. To account for voltages across the wiring to the lamp and the voltage across the switching device, the estimated voltage value for charging the capacitor is given by: V E = V T + i R + V L where: V T = Constant voltage across the switching device; R = Resistance of connections from capacitor to lamp. If we combine and rearrange (1) and (2) we get: Also from (1): i = V 2 L k 2 O Substituting (1) and (2) in (6) and using (5), (4) becomes: A final compensation must be made to adjust for the finite size of the capacitor storage element. For practical reasons the total energy stored is optimum at 3 to 4 times the maximum required pulse energy. The above calculations are based upon a fixed drive voltage but in the practical situation this is not the case. From (3), for a given change in capacitor voltage the change in stored energy is given by: δE c δV c = 1 2 C.2.V c For simplicity we now make two approximations. Firstly that for small changes in drive voltage the lamp current varies linearly as shown in Figure 5. We can then say that if we increase the storage capacitor voltage by half the predicted voltage droop, then the total energy delivered to the lamp will be correct. Secondly for true compensation we need to use the adjusted capacitor voltage V C in our calculation for voltage droop, this would however lead to an iterative calculation. Therefore V C is approximated to V L . The final compensation function is: V E = V T + E E R t E V L + V L + E E 2C VL where:

Claims: A method of operating an irradiating device (1, 9, 20) to provide a discharge therefrom in the form of a pulse (E D , t D ) of radiant energy, the irradiating device (9) having an input (2) selectively coupled to a capacitive energy storage device (3) via a controllable switching means (4), the method characterised by : charging the capacitive energy storage device (3) to a voltage V S , wherein a total stored energy in the capacitive energy storage device is between three and four times a maximum energy required to be delivered at each pulse; closing the switching means (4) to initiate a supply of current (i), associated with discharge of energy from the capacitive energy storage device, to the input (2) of the irradiating device (1, 9, 20) to cause generation of the pulse of radiant energy (E D , t D ); and opening the switching means (4) to terminate the pulse of radiant energy (E D , t D ) such that the supply of current to the input of the irradiating device (1, 9, 20) is terminated before complete discharge of the capacitive energy storage device (3). The method of operating an irradiating device according to claim 1, wherein charging of the capacitive energy storage device further includes setting the voltage applied to the capacitive energy storage device to a value that represents a desired rate of energy into the irradiating device (1, 9, 20). The method of operating an irradiating device according to claim 1 or 2, wherein the total stored energy in the capacitive energy storage device proportionally reflects a power to be delivered during a pulse of radiant energy from the irradiating device. The method of operating an irradiating device according to claim 1, 2 or 3, wherein a pulse of radiant energy reduces an initial total stored energy of the capacitive energy storage device by no more than one third. The method of operating an irradiating device according to any preceding claim, wherein a control unit is coupled to the switching means for operational control thereof, and the method further includes: inputting to the control unit a variable demand value of output energy (E D ) representative of a user requirement of energy to be discharged as a pulse of radiant energy from the irradiating device; inputting to the control unit a variable demand value of output pulse length (t D ) corresponding to a user requirement of pulse length of the pulse of radiant energy; and determining by operation of the control unit an estimated voltage value (V E ) representative of a voltage to which the energy storage device is required to be charged to enable the irradiating device to receive sufficient electrical current for the pulse of radiant energy to have actual values of output energy and output pulse length (Eo, to) corresponding substantially to the demand value of output energy (E D ) and the demand value of output pulse length (t D ) respectively; . and wherein the voltage is a supply voltage corresponding to the estimated voltage value. The method of operating an irradiating device according to claim 5, wherein the estimated voltage value V E is determined by the control unit processing the demand values of output energy E D and output pulse length t D according to a pre-determined algorithm. The method of operating an irradiating device according to claim 6, wherein the algorithm comprises: V E = V T + E E R t E V L + V L + E E 2C VL where: V L = the voltage at the input to the flash lamp; V T = a constant voltage across the switching device; K O = the input impedance of the flash lamp; R = the resistance between the capacitive storage device and the input of the flash lamp; C = capacitance of the capacitive energy storage device; E E is an estimated value of input energy required to be input to the flash lamp in order to provide output energy E O equal to the demand value of output energy E D; and t E is an estimated value of input pulse length required to produce an output pulse length to corresponding to the demand value of output pulse length t D . The method of operating an irradiating device according to claim 7, wherein the estimated value of input energy E E to be input to the flash lamp is determined by the control unit as being proportional to the demand value of output energy E D and wherein the estimated value of input pulse length t E is determined by the control unit to be substantially equal to the demand value of output pulse length t D . The method of operating an irradiating device according to claim 7 or 8, wherein the estimated value of input energy E E is determined according to a predetermined algorithm by the control unit to comprise an estimated pumping energy E P required to be input to the flash lamp during a pumping period before lasing commences and an estimated laser input energy E L required to be input to the flash lamp during a subsequent output pulse length t o during which lasing occurs. The method of operating an irradiating device according to claim 9. wherein the estimated value of input pulse length t E is determined by the control unit to be the sum of the estimated pumping period t P and the demand value of output pulse length t D and wherein the estimated pumping period t P is determined by means of a predetermined algorithm. The method of operating an irradiating device according to any of claims 7 to 10, including: measuring the current i; inputting to the control unit a measured current signal i M corresponding to an instantaneous amplitude of the current; integrating the measured current signal i M over a period commencing with the closing of the switching means to obtain a cumulative value, and wherein the control unit opens the switching means when the cumulative value is equal to a threshold value corresponding to the input energy E I received by a flash lamp being equal to the estimated value of input energy E E . The method of operating an irradiating device according to any of claims 7 to 11, including measuring the elapsed time t I from the closure of the switching means, and wherein the control unit opens the switching means when the elapsed time t I is greater than or equal to the estimate value of input pulse length t E . The method of operating an irradiating device according to any of claims 7 to 12, including: measuring radiant energy directed to an output aperture; comparing the measurement of radiant energy with the demand value of output energy E D ; and actuating a safety cut out to prevent further operation of the irradiating device if the measured value exceeds the demand value by a predetermined safety margin. The method of operating an irradiating device according to any of claims 5 to 13, wherein the control unit is operable to receive continuously variable values of the demand value of output energy E D and the demand value of output pulse length t D . The method of operating an irradiating device according to any of claims 1 to 4, further comprising: determining an amount of energy applied to the irradiating device; setting a desired energy requirement for the pulse (E D , t D ) of radiant energy; and controlling the switching means to deliver the desired energy requirement in response to the determined amount of energy applied to the irradiating device. The method of operating an irradiating device according to claim 15, further comprising: measuring both current applied to the irradiating device (1, 9, 20) and a voltage across the irradiating device (1, 9, 20) to determine an amount of power applied to the irradiating device; and determining an energy applied to the irradiating device by integrating the amount of power over time. The method of operating an irradiating device according to any preceding claim, further including: delivering radiant energy from a flash lamp to an output aperture of the irradiating device for presentation, in use, to a treatment site. The method of operating an irradiating device according to any of claims 1 to 16, wherein the irradiating device comprises a flash lamp connected to the input and further comprising a laser, the method further comprising: optically pumping the laser with light from the flash lamp and delivering laser light from the laser to an output aperture of the irradiating device for presentation, in use, to a treatment site. The method of operating an irradiating device according to claim 18, wherein the laser is a ruby laser. The method of operating an irradiating device according to any preceding claim, wherein the switching device comprises a gated semi-conductor device. A method of operating an irradiating device as claimed in any preceding claim, including operating a flash lamp in a standby mode in which a relatively low level of continuous discharge is established through the flash lamp. An irradiating system having an irradating device (1, 9, 20) comprising an input (2) selectively coupled, via a controllable switch (4), to a capacitive energy storage device (3) connectable, in use, to a voltage source V S , the controllable switch (4) operationally closeable to initiate a supply of current (i), associated with discharge of energy from the capacitive energy storage device (3), to the input (2) of the irradiating device (1, 9, 20) to cause generation of a pulse (E D , t D ) of radiant energy having an energy up to a maximum energy; the irradiating system characterised in that : the controllable switch (4) is operable to terminate the pulse of radiant energy by terminating the supply of current to the input (2) of the irradiating device (1, 9, 20) at a point before complete discharge of the capacitive energy storage device (3) and a total stored energy in the capacitive energy storage device is between three and four times the maximum energy required to be delivered at each pulse. The irradiating system according to claim 22, wherein the irradiating device comprises a flash lamp (9) connected to the input (2) such that the current i is discharged through the flash lamp. The irradiating system according to claim 22 or 23, further comprising: means for selecting a voltage to be applied to the capacitive energy storage device, the voltage representative of a desired rate of energy transfer into the irradiating device (1, 9, 20). The irradiating system according to claim 22, 23 or 24, wherein the total stored energy in the capacitive energy storage device reflects a power to be delivered during a pulse of radiant energy from the irradiating device. The irradiating system according to any of claims 22 to 25, wherein a pulse of radiant energy is arranged to reduce an initial total stored energy of the capacitive energy storage device by no more than one third. The irradiating system according to any of claims 22 to 26, further comprising: means (5, 6) for determining an amount of energy applied to the irradiating device; means (8) for setting a desired energy requirement for the pulse (E D , t D ) of radiant energy; and means (6) for controlling the switching means to deliver the desired energy requirement in response to the determined amount of energy applied to the irradiating device. The irradiating system according to claim 22, wherein the controllable switch is coupled to a control unit arranged to actuate the controllable switch, the irradiating system further comprising: means (13, 14) for inputting to the control unit (6) a variable demand value of output energy (E D ) representative of a user requirement of energy to be discharged as a pulse of radiant energy from the irradiating device; means (13, 14) for inputting to the control unit a variable demand value of output pulse length (t D ) corresponding to a user requirement of pulse length of the pulse of radiant energy; the control unit (6) being operable to control an estimated voltage value (V E ) representative of a voltage to which the capacitive energy storage device (3) is required to be charged to enable the irradiating device (1, 9, 20) to receive sufficient electrical current for the pulse of radiant energy to have actual values of output energy and output pulse length (E O , t D ) corresponding substantially to the demand value of output energy (E D ) and the demand value of output pulse length (t D ) respectively; a charging circuit (7) operable to charge the capacitive energy storage device (3) to a supply voltage Vs corresponding to the estimated voltage value; a trigger (15) operable to close the controllable switch (4) to initiate a supply of current (i) to the input of the irradiating device (1, 9, 20); and wherein the control unit (6) is operable to open the controllable switch to terminate the resulting pulse of radiant energy such that the supply of current to the input (2) of the irradiating device (1, 9, 20) is terminated before complete discharge of the energy storage device.

Inventors: GREENWOOD MARK, MILLER DONALD W, SARKIES PAUL H, GREENWOOD, MARK, MILLER, DONALD W., SARKIES, PAUL H.
Applicants: SPECTRON LASER SYSTEMS LTD, SPECTRON LASER SYSTEMS LIMITED
Application year: 1997
Main classification: H05B41
IPC codes: A61B18, H05B41