referring to fig1 a , in an exemplary embodiment of a treatment apparatus 10 includes a handpiece 12 coupled to a treatment console 14 housing a power supply 16 . power supply 16 may be a high voltage power supply of the type provided by cutera , inc . ( brisbane calif .) in consoles for use with its nd : yag laser product line , and in particular any of the power supplies used with the coolglide family of lasers ( coolglide cv , coolglide excel , and coolglide vantage ), or with the coolglide xeo , xeo sa and solera opus consoles . laser source 18 is provided with an er : ysgg or a cr , er : ysgg gain medium . this gain medium has a primary output at 2 . 79 μm which has a depth of coagulation in skin that falls between the depths associated with co 2 lasers ( wavelength = 10 . 6 μm ) and er : yag lasers ( wavelength = 2 . 94 μm .). the characteristic depth of coagulation in skin after laser ablation is 40 μm for 2 . 94 μm light , 75 μm for 2 . 79 μm light and 125 μm for 10 . 60 μm light ( kaufmann et al j dermatol surg oncol 1994 ; 20 : 112 - 118 ). as discussed in greater detail below , use of a primary wavelength of 2 . 79 μm ablates to remove a precise amount of tissue , while also coagulating to create a natural dressing and to promote new collagen formation . a laser based on an er : ysgg or cr , er : ysgg gain medium offers two other advantages . first , it is more efficient than er : yag . second , the upper level lifetime is ten times longer , allowing low threshold operation allowing longer pulse durations relative to er : yag lasers at similar energy levels . longer pulse durations may be exploited to produce different post - ablation thermal damage profiles in treated skin . in exemplary modes of operation , pulse durations on the order of 0 . 2 to 25 ms and preferably 0 . 5 to 10 ms are contemplated , with spot sizes on the order of between 1 and 10 mm , repetition rates ranging from single shots to 20 hz , and preferred fluences within the range of 0 . 25 and 20 j / cm 2 . as shown in fig1 a , in the exemplary embodiment , laser source 18 is integrated into the handpiece 12 . integrating the laser components ( e . g . monolithic laser rod resonator , excitation flash lamp , cooling features ) and associated power detectors , optical components etc . into the handpiece avoids the problems of delivering the light from the console to the tissue . thus , light can be delivered directly to the target tissue directly from the handpiece without having to pass through an articulated arm or fiber optic element . as discussed in greater detail below , the handpiece preferably includes a two - axis scanner 20 operable to uniformly scan the beam of light across the tissue surface to produce a two - dimensional treatment pattern on the skin . the handpiece 12 is illustrated in fig1 b . handpiece includes includes an umbilical cable 13 that houses electrical cables to provide power from the power supply to drive the flash lamp and scanner motors , to provide a signal path for detector signals , encoders , serial communication , a memory device that identifies the handpiece , and a supply and return water line ( to remove heat generated by the flash lamp ). the proximal end of the umbilical cable is semi - permanently attached to the laser system console and the distal end is permanently attached to the body of the delivery hand piece . an activation switch ( not shown ) such as a foot pedal is provided for use in initiating and terminating treatment . fig2 schematically illustrates the optical components within the handpiece . as shown , the handpiece includes a laser resonator cavity 22 containing the excitation flash lamp , laser crystal and associated mirrors . a portion of the beam 100 exiting the laser cavity 100 is diverted to a pair of photodetectors 24 a , 24 b by a pair of independent beam splitters 26 a , 26 b for use in monitoring output power . an aiming diode 28 generates an aiming beam of light 102 . beam combining mirror 30 combines the beam 100 from the laser 18 with the aiming beam 102 so that the aiming beam is parallel and coincident with the treatment beam . during use , the aiming beam shows the user where the energy from the laser is impinging on the skin . a safety shutter 32 is positioned between the laser cavity 22 and the combining mirror 30 . the shutter has open and closed positions . when the shutter is in the open position the beam 100 passes to the next optical component , which in fig2 is the combining mirror 30 . in the closed position , the beam 100 is deflected into a beam dump ( not shown ). when not directed to the beam dump , the beam 100 impinges onto x - y scanning mirror 34 which is driven by stepper motors to provide x - y movement of the beam 100 on skin s . a protective window 36 on the handpiece ( see also fig1 b ) protects the internal optical components . a distance guide 38 , which may be stainless steel , sets the distance between the handpiece 12 and the target treatment site . during use , the distance guide is placed in direct contact with the patient &# 39 ; s skin . control electronics are schematically illustrated in fig3 . independent signals from photodetectors 24 a , 24 b are received by microcontroller 40 , which uses the input to monitor and regulate laser power . the photodetectors utilize detector circuits that are independent from each other and that use no shared components . this ensures that no single component failure lead to generation of inaccurate readings by both detectors . this avoids delivery of improper levels laser treatment energy to the patient . microcontroller 40 additionally provides drive signals to the stepper motors of the x , y scanner 20 . encoders associated with x and y direction stepper motors provide feedback for use by the microcontroller in identifying the rotational positions of the stepper motor shafts . as discussed , safety shutter 32 is positioned to terminate delivery of the treatment beam to the patient s . an encoder attached to the shaft of the shutter motor detects the position of the safety shutter . the microcontroller 40 monitors the position of the safety shutter 32 and in the event of a discrepancy can terminate laser exposure by closing the safety shutter . others ways of terminating exposure include disabling the high voltage power supply to prevent charging of the main charging capacitor or disabling the discharge of the main charging capacitor ( thus preventing the firing of the flash lamp ). details of the x , y scanner assembly 20 will next be discussed in connection with fig4 - 7b . in general , the x , y scanner 20 is operable to move the scanning mirror 34 ( fig2 ) in two orthogonal directions to produce a pattern of treated regions on the skin . referring to fig4 , the scanner 20 includes an x - motion scanning unit 60 for scanning the light across the tissue surface in a first direction ( arbitrarily labeled the “ x ” direction ), and a y - motion scanning unit 58 for moving the light in a second direction that is preferably orthogonal to the x - direction . although various scanner configurations may be used for this purpose , one suitable scanner uses a pair of stepper motors operable to move a single mirror relative to two axes . this scanner is differentiated from prior scanners in part for its single moving mirror design , use of stepper motors for precise movement and miniature size . fig5 shows a side view of scanning mirror 34 mounted on a rectangular mirror mount 46 . mount 46 is attached to the face of mirror 34 that is opposite to the reflective surface 48 used by the mirror to reflect laser light onto tissue . this figure schematically illustrates general movement of the mirror and mount during scanning . one direction of movement , referred to here as y - direction movement , involves using a first stepper motor to pivot the mount in a forward and backward direction as indicated by arrows “ y ”. the second form of movement , referred to here as the x - direction movement , involves using a second stepper motor to pivot the mount laterally as indicated by arrows “ x ”. components of the scanner 20 are shown in fig6 a and 6b . scanner includes a base 50 fixed within the handpiece . base 50 is a u - shaped piece defining an opening 52 . a yoke 54 is mounted within the opening 52 . yoke 54 is mounted to the base by pins 56 and is pivotable about the pins to produce y - direction movement of the mirror . mirror mount 46 , which carries mirror 34 , is coupled to the yoke 54 . y - movement scanning unit 58 is mounted to the base 50 . x - movement scanning unit 60 is mounted to the yoke 54 . in general , the y - movement scanning unit 58 has components that abut the yoke 54 to produce forward / backward pivoting of yoke 54 about pins 56 , causing corresponding movement of mount 46 and mirror 34 . see the arrows marked “ y ”. the x - movement scanning unit pivots the mount 46 back and forth as indicated by arrows “ x ” to produce side to side movement of the mirror 34 . details of the y - movement scanning unit 58 will be described with reference to fig7 a through 7b . the unit 58 includes a stepper motor 62 that produces rotation of shaft 64 . a cam 66 having a central mount 68 is coupled to the shaft 64 . cam 66 includes a cam bearing 70 and a spring saddle 72 . cam bearing 70 is positioned in contact with a cam follower bearing 74 ( fig6 a and 7b ) on the yoke 54 . the cam 66 and shaft 64 are coupled such that the mount 68 is laterally offset from the shaft 64 . thus , activation of the motor to rotate the shaft 64 produces eccentric rotation of the cam . a useful way to visualize the movement of the cam is to picture an automobile wheel being rotated about an axel that is laterally offset from the center of the wheel . the eccentric movement of the cam 66 results in cyclic movement of the cam bearing 70 towards and away from the cam follower bearing 74 with which the cam bearing 70 is in contact . as a result , the yoke 54 ( as well as all components carried by the yoke ) pivots back and forth about the pins 56 , moving the mirror 34 as indicated by arrows “ y ” in fig6 a and 7a . spring saddle 72 aids in maintaining contact between the cam follower bearing 74 and the cam bearing 70 throughout scanning . x - axis scanning unit 60 includes a stepper motor 76 carried by the yoke 54 . stepper motor 76 includes a shaft 78 coupled to the mirror mount 46 . activation of the motor 76 pivots the mirror 34 side to side relative to the axis of the shaft 78 . each of the stepper motors 62 , 76 is preferably provided with an anti - backlash spring 86 a , 86 b coupled to its shaft , to prevent backlash of the shaft when the polarity of the input to the motor is reversed . referring to fig8 , the console may include a user interface 80 allowing a user to select one or more treatment parameters . for example , a user might have the option to scroll through and select from a menu of available treatment patterns using pattern select keys 82 . similarly , the degree by which spots in the treatment pattern overlap or are spaced apart may be selected using overlap / spacing keys 84 . a selected pattern / spacing may produce distinct spaced - apart treatment spots , or overlapped spots , or a continuous “ painting ” of the skin surface . other input keys may be used to select pulse width , fluence , pulse duration etc . in an exemplary embodiment , operational and treatment parameters might , but are not limited to , the following : wavelength : 2790 nm output power : up to 20 w pulse energy : up to 1 j per pulse pulse duration : 100 - 600 μsec repetition rate : up to 20 hz spot size : approx 5 mm maximum pattern size : 3 cm × 3 cm treatment fluence range approx 2 - 5 j / cm 2 ablation depth : 20 - 50 μm subsequent damage ( e . g . coagulation depth ): additional 30 - 50 μm beyond the ablation depth . during use of the disclosed treatment apparatus , the user selects the appropriate treatment parameters . next , the handpiece 12 ( fig2 ) is positioned such that the distance guide 38 is in contact with the skin of a patient . with the distance guide in contact with the skin , the laser is activated such as by depressing a footswitch . the user maintains the handpiece position while the scanner steps the treatment beam in the x and y directions as discussed to create the desired treatment pattern . as illustrated in fig9 , skin treatment using the disclosed laser operating at a wavelength of 2 . 79 μm allows three effects to be achieved . first , application of the treatment beam ablates approximately 20 - 50 μm , and preferably approximatlely 30 - 50 μm , of the epidermis ( region a in fig9 ) at a temperature in the range of approximately greater than 90 ° c ., and more preferably greater than approximately 100 ° c . residual heat ( in the range of approximately 70 - 90 ° c . and preferably approximately 80 ° c .) coagulates an additional 30 - 50μ of the epidermis ( region b ), creating a natural dressing for the skin . this natural dressing peels from the skin in approximately 3 - 5 days . the residual heat raises the temperature of a portion of the dermis ( region c ) to a temperature in the range of approximately 45 - 65 ° c . ( and preferably approximately 55 ° c . ), which promotes generation of new collagen within the dermis . the disclosed apparatus and associated methods have been described in connection with resurfacing and / or rejuvenating skin for treatment of dermatological conditions such as improvement of facial texture by eliminating fine lines , wrinkles , and / or scars , or for eliminating discoloration caused by photo damage . however , the method and apparatus may also be used to treat for other applications and / or to treat other biological tissue . while various embodiments have been described above , it should be understood that they have been presented by way of example , and not limitation . it will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention . this is especially true in light of technology and terms within the relevant art ( s ) that may be later developed . additionally , it is contemplated that the features of the various disclosed embodiments may be combined in various ways to produce numerous additional embodiments . thus , the present invention should not be limited by any of the above - described exemplary embodiments , but should be defined only in accordance with the following claims and their equivalents . any and all patents , patent applications and printed publications referred to above , including those relied upon for purposes of priority , are incorporated by reference .
a dermatological treatment method includes directing laser energy having a wavelength of 2 . 79 μm onto skin . according to disclosed methods , the energy can function to ablate a first portion of epidermal tissue , coagulate an underlying second portion of epidermal tissue , and promote collagen formation in tissue of the underlying dermis . tn an exemplary treatment apparatus , a laser using a ysgg gain medium is mounted in a handpiece . the handpiece may include a two - axis scanner to allow for uniform scanning of the energy over the tissue surface .