Abstract:
A dermatological treatment device is disclosed for generating a matrix of two dimensional treatment spots on the tissue. A handpiece carries a laser which generates a beam of laser pulses. The pulses are focused onto the tissue with a lens system. A diffractive element is positioned between the laser and the lens system for splitting the laser beam into a plurality of sub-beams. A scanner translates the beam over the diffractive element to generate the two dimensional spot pattern. The laser has a semi-monolithic resonator design with one integral end mirror defining the output coupler and a second, independent mirror for adjustment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 12/405,085, with a filing date of Mar. 16, 2009, which claims priority to U.S. Provisional Application Ser. No. 61/041,745 filed Apr. 2, 2008, the disclosures of which are herein incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of dermatological treatment, and more specifically to the field of dermatological treatment lasers. 
       BACKGROUND 
       [0003]    A dermatological treatment laser incorporating a laser resonator into a handpiece is disclosed in U.S. Publication No. US 2007/0265604, which is commonly owned with the present application and is incorporated herein by reference. The resonator includes an Er:YSGG or Cr,Er:YSGG gain medium, which has a primary output at 2.79 μm. The handpiece includes two stepper motors that scan the laser output in two axes. In one exemplary method, the handpiece is held in a fixed position while a pattern of 5 mm treatment spots is formed on the skin by stepping the treatment beam in X and Y directions. 
         [0004]    For certain applications such as treatment of deep wrinkles, it may be beneficial to treat the skin using a matrix of much smaller diameter (e.g. approximately 200-400 μ) non-overlapping spots. With the reduced spot size, a much larger number of spots is needed for a given treatment area. The present application discloses a laser handpiece suitable for generating the large number of spots more quickly than if each spot was generated individually. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of a handpiece housing a fractionalized laser scanner. 
           [0006]      FIG. 2A  is a top plan view schematically illustrating the components of the handpiece of  FIG. 1 . 
           [0007]      FIG. 2B  is a side elevation view schematically illustrating the components of the handpiece of  FIG. 1 . 
           [0008]      FIGS. 3A-3C  are side elevation views of the diffractive element and optics from the system of  FIGS. 2A and 2B , schematically illustrating splitting of the beam into sub-beam, and focusing of the sub-beams by the optics. 
           [0009]      FIGS. 4A through 4C  illustrate three examples of spot patterns that can be generated using the disclosed handpiece. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , a treatment apparatus  10  includes a handpiece  12  coupled to a treatment console  14  which includes a user interface  13 , a power supply  16  and a controller  19 . 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 laser product lines, and in particular the power supply used with the PEARL™ laser. 
         [0011]    The exterior of handpiece  12  includes a protective window  15  through which treatment energy exits the handpiece. A distance guide  17  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. 
         [0012]    Features housed within the handpiece  12  are shown in  FIGS. 2A and 2B . These features include a semi-monolithic laser resonator comprising a laser rod  18  and a planar mirror  20 . The laser rod  18  is preferably a Er:YSGG or a Cr,Er:YSGG rod. This gain medium has a primary output at 2.79 μm. In one embodiment, rod  18  has a length of 86 mm and a diameter of 3 mm, and the length of the resonator is 106 mm. 
         [0013]    As best shown in  FIG. 2B , laser rod  18  includes first and second planar ends. First end  22 , which serves as the output coupler, includes a polished surface coated with a partially transmissive coating. Second end  24 , which is positioned in alignment with the mirror  20 , has an anti-reflective coating. Mirror  20  is a planar mirror aligned with the second end  24  to permit light to circulate between the mirror  20  and the first end  22 . Mirror  20  is supported in a mount  21  which permits the tilt angle of the mirror to be adjusted during assembly to facilitate alignment with the resonator axis. 
         [0014]    This semi-monolithic resonator design, with the output coupler  22  formed on the gain rod  18  and the second mirror  20  being spaced from the end of the rod was developed to improve the M 2  output of the laser to increase the depth of focus of the beam. More specifically, in the laser resonator used in the assignee&#39;s Pearl laser system was fully monolithic wherein both ends of the gain rod were coated for reflection. In such a fully monolithic laser resonator, the ends of the rod were curved for stability purposes. Curved mirrors tend to produce a higher M 2  output with a short depth of focus. This short depth of focus was not a problem with the Pearl system because of its large spot size at the tissue. 
         [0015]    The semi-monolithic design reduces the M2 because it uses two flat mirrors and is longer than the prior art resonator. By mounting mirror  21  on a tiltable support, alignment is facilitated. The increased depth of focus is very useful for maintaining the desired spot size on the tissue for multiple small spots. 
         [0016]    The rod  18  is side-pumped flashlamp  26  to generate a pulsed output. A portion of the beam  100  exiting the laser resonator may be diverted to a photodetector (not shown) by a beam splitter  27  for use in monitoring output power. 
         [0017]    Mirrors  28 ,  29  and  31  are positioned to direct the output beam from the laser to a pair of scanning mirrors  30   a ,  30   b . Each of the scanning mirrors  30   a ,  30   b  is coupled to a corresponding stepper motor  32   a ,  32   b . Stepper motors  32   a ,  32   b  are simultaneously or independently operable to scan the output beam  100  in X- and/or Y-directions across a diffractive element  34 . 
         [0018]    Diffractive element  34  splits the scanned beams into a fixed number (e.g. 6, 8, or 10) of sub-beams  200  having fixed angles between them ( FIG. 3 ). The diffractive element may be manufactured in a number of ways to optimize uniformity of the sub-beams. For example, the diffractive element may be one that eliminates the effect of the zero order and/or that skips the even orders to maintain symmetry around the zero order. Off-axis diffractive elements may also be used. Suitable diffractive elements are manufactured by MEMS Optical of Huntsville, Ala. 
         [0019]    Optics  36  focus the sub-beams  200  to a predetermined spot size onto the tissue to be treated. In the illustrated embodiment, optics  36  includes a meniscus lens  36   a  and a double convex lens  36   b , each of which is made of sapphire. See also  FIGS. 3A-3C . 
         [0020]    The separation distance between the spots impinged onto the target tissue is determined by the focal length of the optics  36  and the angles of the sub-beams  200  formed by the diffractive element. The arrangement of the optics  36  also determines the working distance (defined as the distance between the tissue surface and the output of the optics  36 ). 
         [0021]    For example, in one embodiment illustrated in  FIG. 3B , the lenses  36   a,    36   b  are designed to impinge 300 μ diameter spots onto the tissue surface, with a 20 mm working distance, and a 1.3 mm depth of focus. This arrangement gives a 0.44 mm spot offset/degree beam angle, meaning that if the diffractive element gives angles of 1 degree between each beam, the center-to-center separation distance between the spots will be 0.44 mm. 
         [0022]    In contrast,  FIG. 3C  illustrates another design of lenses  36   a,    36   b  which create 300 μ diameter spots with a 41 mm working distance, a 3 mm depth of focus, and a 0.84 mm spot offset/degree beam angle. 
         [0023]    Referring again to  FIGS. 2A and 2B , the handpiece additionally includes an aiming diode  38  positioned to generate a visible aiming beam of light that is combined with the laser output beam  100 . The aiming beam is likewise diffracted into sub-beam so that the aiming sub-beams are parallel and coincident with the treatment sub-beams. 
         [0024]    In a preferred mode of operation, the scanning mirrors scan the pulsed output beam across the diffractive element. As a result, the sub-beams  200  generated by the diffractive element form a matrix of small diameter (e.g. approximately 200-400 μ) treatment spots on a treatment area of the skin. Treatment spots may have a depth of approximately 200 μ to 1 mm, and the energy per pulse of each treatment sub-beam is approximately 30-150 mJ. An optimal treatment speed is approximately 1 cm 2 /sec. 
         [0025]    The stepper motors may be operated in a number of treatment modes to produce spot matrices having a variety of spot densities. Three exemplary modes will be described with reference to  FIGS. 4A-4C , which illustrate three examples of treatment patterns that can be produced using the disclosed laser. Each of the illustrated treatment patterns represents a pattern generated in a 14 mm by 18 mm treatment area using a diffractive element that yields eight treatment sub-beams. 
         [0026]    In  FIG. 4A , treatment begins with the formation of column  102  of treatment spots when the eight sub-beams are in their initial position. Scanning motors  32   a,    32   b  are energized between laser pulses to step the mirrors  30   a,    30   b,  causing a shift in the sub-beam orientations. Activation of the scanning motors causes one of the scanning mirrors to shift the orientation of the sub-beams along the X-axis, and causes the other one of the scanning mirrors to shift the orientation of the sub-beams downwardly along the Y-axis, forming column  104  of treatment spots. The mirrors are again scanned, this time to move the sub-beams to the right along the X-axis and upwardly along the Y-axis, so that the next pulse of energy from the laser  18  generates column  106  of treatment spots. The process is repeated (toggling the array of spots up and down) to produce multiple columns of treatment spots.  FIG. 4A  shows a matrix of 80 treatment spots with a spot density of approximately 4%. The system is capable of forming the matrix in less than 1 second, and preferably approximately 0.5 sec. 
         [0027]    The  FIG. 4B  treatment pattern may be formed using a mode similar to that described with respect to  FIG. 4A , but by shortening the X-direction scanning distance by half to form a denser spot array. Here, a matrix of 160 treatment spots with a spot density of approximately 8% is shown. In one embodiment, the treatment time to form this matrix of spots may be approximately one second. 
         [0028]    In the treatment pattern shown in  FIG. 4C , the spot density is further increased to 16%. As shown, although the diffractive element produces eight sub-beams, each column includes sixteen treatment spots. In column  110 , boxes are drawn around alternate spots to identify the initial eight treatment spots. The Y-axis stepper motor is then activated between treatment pulses to reorient the eight treatment sub-beams to form additional spots between the initial eight treatment spots. The X-axis stepper motor is then used to orient the sub-beams to form additional treatment columns. As with the  FIG. 4A and 4B  patterns, the pattern is created by repeatedly stepping the X-axis and Y-axis motors to re-orient the eight treatment sub-beams. The sequence of the X-axis and Y-axis shifts needed to complete the pattern is not critical, but is generally optimized to minimize the treatment time, which in this mode is ideally about 2 sec or less for the entire matrix. 
         [0029]    In use, the operator would select the desired spot density through the user interface  13  on the console  14 . Based on this input, the controller  19  sends signals to the flashlamp to generate the laser pulses and coordinates the pulsed operation with the movement of the scanning mirrors  30   a  and  30   b . Some additional details of control circuitry suitable for implementing the design is set forth in U.S. Publication 2007/026504 with particular reference to  FIG. 3 . 
         [0030]    It should be recognized that a number of variations of the above-identified embodiments will be obvious to one of ordinary skill in the art in view of the foregoing description. Accordingly, the invention is not to be limited by those specific embodiments and methods of the present invention shown and described herein. Rather, the scope of the invention is to be defined by the following claims and their equivalents.