# Patent

## Title
Fractional scanner for dermatological treatments

## Abstract

A dermatological treatment device is disclosed for generating a matrix of two dimensional treatment spots on the tissue. A handpiece carrier 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.

## Background
PRIORITY
This application claims priority to U.S. Provisional Application Ser. No. 61/041,745 filed Apr. 2, 2008, the disclosure of which is incorporated herein by reference.


TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to the field of dermatological treatment, and more specifically to the field of dermatological treatment lasers.
BACKGROUND
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.
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 200-400μ) 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
FIG. 1 is a perspective view of a handpiece housing a fractionalized laser scanner.
FIG. 2A is a top plan view schematically illustrating the components of the handpiece of FIG. 1.
FIG. 2B is a side elevation view schematically illustrating the components of the handpiece of FIG. 1.
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.
FIGS. 4A through 4C illustrate three examples of spot patterns that can be generated using the disclosed handpiece.



DETAILED DESCRIPTION
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 PEARLTM laser.
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's skin.
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.
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.
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 M2 output of the laser to increase the depth of focus of the beam. More specifically, in the laser resonator used in the assignee'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 M2 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.
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.
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.
Mirrors 28, 29 and 31 are positioned to direct the output beam from the laser to a pair of scanning mirrors 30a, 30b. Each of the scanning mirrors 30a, 30b is coupled to a corresponding stepper motor 32a, 32b. Stepper motors 32a, 32b are simultaneously or independently operable to scan the output beam 100 in X- and/or Y-directions across a diffractive element 34.
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.
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 36a and a double convex lens 36b, each of which is made of sapphire. See also FIGS. 3A-3C.
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).
For example, in one embodiment illustrated in FIG. 3B, the lenses 36a, 36b are designed to impinge 300 μl 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.
In contrast, FIG. 3C illustrates another design of lenses 36a, 36b which create 300μ diameter spots with a 41 mm working distance, a 3 mm depth of focus, and a 0.84 mm spot offset/degree beam angle.
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.
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 200-400μ) treatment spots on a treatment area of the skin. Treatment spots may have a depth of approximately 200μ 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 cm2/sec.
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.
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 32a, 32b are energized between laser pulses to step the mirrors 30a, 30b, 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.
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.
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 FIGS. 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.
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 30a and 30b. Some additional details of control circuitry suitable for implementing the design is set forth in U.S. Publication 2007/0265604 with particular reference to FIG. 3.
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.

## Claims

1. A laser handpiece for generating radiation for treating tissue comprising:
a housing;
an elongated laser rod located within the housing;
a laser resonator surrounding the rod;
a flashlamp for pumping the rod to generate a beam of laser radiation;
optics for focusing the beam onto the tissue wherein the optics include a diffractive optical element for splitting the beam into at least three spaced apart sub-beams and a lens assembly adjacent and closely spaced to the diffractive optical element without any beam steering elements therebetween, said lens system for directing the beams along separate paths and for focusing the sub-beams onto tissue in a linear array of spots; and
a reflective scanner positioned between the resonator and the diffractive optical element for varying the entry angle of the beam and for translating the beam to different positions on the diffractive optical element to cause the sub-beams to be directed to different locations on the tissue.