Patent Publication Number: US-2020281653-A1

Title: Laser beam control and delivery system

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to surgical lasers and more specifically to a laser beam control and delivery system that accurately and efficiently directs a laser beam into an optical fiber. The laser beam control and delivery system also provides additional functions, including a connection for a fiber tip temperature control system and a tissue temperature sensing system. The present invention also relates to a surgical laser system that has a high efficiency thermoelectric cooling system. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to surgical lasers of the type where the laser beam from a laser source is delivered to the surgical site through an optical fiber. The laser source may be a gas laser, a solid state laser or, advantageously, one or more laser diodes. Surgical laser systems that utilize laser diodes are described in U.S. Provisional Applications 61/068,165 filed on Mar. 4, 2008 and 61/137,157 filed on Jul. 28, 2008. These and all patents and patent applications referred to herein are incorporated by reference in their entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a plan view of a surgical laser system utilizing two laser diodes and an aiming laser that are directed into an optical fiber using the laser beam control and delivery system of the present invention. 
         FIG. 2  shows a side view of the surgical laser system of  FIG. 1 . 
         FIG. 3  shows an embodiment of the surgical laser system wherein the laser beam control and delivery system utilizes a camera for aligning the laser beam with the core of the optical fiber. 
         FIG. 4  illustrates the touch screen control panel of the surgical laser system. 
         FIG. 5  is an optical diagram of a surgical laser system with fiber tip temperature sensing. 
         FIG. 6  is an optical diagram of a surgical laser system with fiber tip temperature sensing and tissue temperature sensing. 
         FIG. 7  is a plan view of a surgical laser system with a cooling system according to the present invention. 
         FIG. 8  is a side view of the surgical laser system and the cooling system of  FIG. 7 . 
         FIG. 9  illustrates a surgical laser system utilizing the support stand as part of the cooling system. 
         FIG. 10  illustrates an optical fiber device for use with the surgical laser system of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a plan view of a surgical laser system  100  utilizing the laser beam control and delivery system of the present invention.  FIG. 2  shows a side view of the surgical laser system  100  of  FIG. 1 . 
     The surgical laser system  100  may utilize a laser source that comprises a gas laser, a solid state laser or, advantageously, one or more laser diodes  102 . In the example shown, the laser system utilizes two fiber-coupled laser diodes  102  and an aiming laser  104 . The output beams from the two laser diodes  102  and the aiming laser  104  are combined using a beam combiner  106 . The beam combiner  106  is formed by fusing the cores of the optical fibers  108  from the two laser diodes  102  and the aiming laser  104  together to create a single fiber that combines the output beams from the three laser sources. Alternate embodiments may utilize multiple laser diode modules or arrays of laser diodes and one or more aiming lasers. 
     The laser diodes  102  may comprise two laser diodes of the same wavelength, e.g. two 1470 nm laser diodes, or they may be different wavelengths, e.g. one 1470 nm laser diode and one 980 nm laser diode. In a currently preferred embodiment, the two laser diodes  102  have an output power of approximately 50 Watts each, for a combined power of approximately 100 Watts. Other wavelengths and combinations of wavelengths and power levels are also possible depending on the tissue effect that is desired from the surgical laser system  100 . The aiming laser  104  is a low power laser source with a visible output beam. The aiming laser  104  may produce a single color aiming beam, e.g. red, yellow, green or blue, or it may produce multicolored aiming beams that may be continuous or may be modulated to indicate the operating status of the laser system, as described in the above-referenced patent applications. 
     The central component of the laser beam control and delivery system is an optical block  110  that has an input end  112 , an output end  114 , a right side  116  with a first connection port  118  and a left side  120 , optionally having a second connection port  122 . The optical block  110  is roughly the shape of a hollow rectangular solid with feet or flanges  124  having mounting holes  126  for mounting the optical block to an optical deck  130  or other support surface within the laser system. Other shapes are also possible. Preferably, the optical block  110  is machined from a single piece of aluminum or other metal for strength and stability. 
     The distal end of the beam combiner  106  is attached to an input port  132  on the input end  112  of the optical block  110 . A collimating lens  134  is positioned to collimate the laser beam where it exits the distal end of the beam combiner  106  and enters the optical block  110 . The input port  132  is aligned with an output port  146  on the output end  114  of the optical block  110 . A refocusing lens  136  is positioned in front of the output port  146 . Fine adjustment screws  138  are provided for adjusting the position of the output port  146  with respect to the input port  132  along X and Y axes. A connector  144  is provided on the output end  114  of the optical block  110  for insertion of the proximal end of an optical fiber  204  for delivering the laser beam to the surgical site, which is shown in  FIG. 10 . Optionally, the optical fiber  204  includes a proximal connector  206  that contains a device  202  for identifying the optical fiber  204  and recording data about the use of the optical fiber  204  and the surgical laser system  100 . In one particularly preferred embodiment, the device  202  may be a 1-wire serial memory device. The proximal connector  206  may have electrical connections for communicating this information with the laser system or the proximal connector  206  may utilize radiofrequency identification (RFID) technology for one or two-way wireless communication with the laser system. In one preferred embodiment, an RFID tag placed on or near the proximal connector  206  of the optical fiber  204  communicates with a device on the surgical laser system using HF of near-field UHF transmission. No direct electrical connections are required. 
     A partially reflective mirror  140  or other type of beam splitter is positioned in the hollow space  128  of the optical block  110  between the input end  112  and the output end  114 . 
     Preferably, the partially reflective mirror  140  is positioned at an angle of approximately 45 degrees with respect to an optical axis that extends from the input port  132  to the output port  146 . Other mounting angles are also possible. The partially reflective mirror  140  is coated on both surfaces with an antireflective coating for the wavelength of the laser output beam(s) and coated on at least the distal, second surface with a reflective coating for infrared wavelengths. The combined output beams from the two laser diodes and the aiming laser are emitted from the distal end of the beam combiner  106  and pass through the collimating lens  134  and the partially reflective mirror  140  and are focused on the proximal end of the optical fiber  204  by the refocusing lens  136  so that as much of the laser energy as possible passes into the core of the optical fiber  204 . The optical fiber  204  is typically a 600 micron diameter fiber with a 550 micron diameter core. Other sizes of optical fibers can also be used. 
     Light returning to the output port  146  of the optical block  110  from distal portions of the optical fiber  204  strike the partially reflective mirror  140  and the infrared wavelengths and at least a portion of the visible wavelengths are reflected toward the first connection port  118  on the right side of the optical block  110 . The first connection port  118  is typically between 10 and 1000 microns in diameter, most typically approximately 100 microns in diameter. A combined infrared detector and visible light detector  150  positioned at or optically connected to the first connection port  118  intercepts the reflected light and produces a first signal indicative of the magnitude of the returning infrared light that is used for temperature monitoring and control of the optical fiber  204  by the fiber tip protection system and a second signal indicative of the magnitude of the returning visible light that is used by the scope protection system and the fiber breakage detector, as described in the above-referenced patent applications. In some embodiments, the first and second signals and the ratio between them may be used for each of these functions. 
     Additional connection ports may be provided for additional sensors or other functions. An optical fiber, a hollow waveguide or holey fiber can be inserted into one or more of the connection ports to transmit the light to one or more sensors or detectors. Hollow waveguides will be particularly useful for transmitting light at higher wavelengths that are not readily transmitted through an optical fiber. 
     In an alternate embodiment, a partially reflective mirror  140  coated with a reflective coating for infrared wavelengths may be used to separate the returning infrared light from the returning visible light and direct them to separate detectors, as described in the above-referenced patent applications. 
     Sampling of the infrared signal by the fiber tip protection system will take place while the laser source is switched off briefly, e.g. for a few microseconds, so that the high intensity output beam of the laser will not overwhelm the signal from infrared light returning through the optical fiber  204 . The signal-to-noise ratio of the infrared signal can be improved by using a phase-locked loop to eliminate other signals that are not in phase with the off periods of the laser source. 
       FIG. 5  is an optical diagram of a surgical laser system  100  that may utilize the laser beam control and delivery system of the present invention for fiber tip temperature sensing. This embodiment differs slightly from the embodiment illustrated in  FIGS. 1 and 2  in that two partially reflective mirrors M 1 , M 2  are used to combine the output of the laser diode  102  and the aiming beam laser  104  rather than the fiber optic beam combiner  106  described above. In this example, the laser diode  102  is a 1470 nm laser and the aiming beam laser  104  is a 635 nm, red laser. Mirror M 1  is coated to transmit 1470 nm light and to reflect other wavelengths. Mirror M 2  is coated to reflect 635 nm and “red” color and to transmit other wavelengths, including short IR wavelengths. In addition to the silicon IR and visible light detector  150  used for fiber tip temperature sensing, the surgical laser system  100  utilizes a second light detector  152  as an internal power meter. Most of the 1470 nm laser beam is transmitted directly through mirror M 1 , but a very small percentage of the beam is reflected toward the second light detector  152 . The second light detector  152  will produce a signal that is proportional to the total energy of the 1470 nm laser beam, which can be used to provide a display of the actual laser energy produced and/or to compare the actual laser energy produced with the set power level to determine laser efficiency. This measure of laser efficiency can be used to schedule maintenance of the laser system. 
       FIG. 3  shows an embodiment of the surgical laser system wherein the laser beam control and delivery system utilizes a camera  160  for aligning the laser beam with the core of the optical fiber  204 . A small camera  160  such as a CMOS chip camera or CCD camera is mounted to intercept the reflected light from the partially reflective mirror  140  in the optical block  110 . As shown in  FIG. 3 , a second partially reflective mirror  142  or other type of beam splitter coated with a reflective coating for infrared wavelengths may be used to separate the returning infrared light from the visible light. The second partially reflective mirror  142  directs the returning infrared light to an infrared detector  150 , while the visible light is allowed to pass through to the camera  160 . Alternatively, the second partially reflective mirror  142  may have a reflective coating for visible wavelengths to direct the visible light to the camera  160 , while the infrared light is allowed to pass through to the infrared detector  150 . The camera  160  provides an image of the proximal end of the optical fiber  204  allowing precise adjustment of the X and Y axes on the input port  132  so that the laser spot from the beam combiner  106  is positioned precisely on the core of the optical fiber  204  and not on the cladding or the jacket of the optical fiber. The camera  160  can also be used to image and identify any hotspots that develop when the laser is on. This will allow quick diagnosis and troubleshooting of problems with the optical fiber or alignment of the laser beam control and delivery system. 
     Alternatively, the camera  160  can be mounted directly to or optically connected to the first connection port  118  on the right side of the optical block  110 . This can be done temporarily, for example to align the X and Y axes on the input port  132  during assembly of the laser system. A camera  160  can be permanently mounted directly to or optically connected to the first connection port  118  without the second partially reflective mirror  142  and without the infrared detector or visible light detector if the camera  160  is able to provide a quantitative measure of the returning infrared light and the returning visible light for use by the fiber tip protection system, the scope protection system and the fiber breakage detector. 
     In another embodiment of the surgical laser system, a second camera  162  can be mounted at or optically connected to the second connection port  122  on the left side of the optical block  110 . The second camera  162  will produce an image of the input port  132  and surrounding structures. Information from the second camera  162  and/or an infrared detector may be used to determine the temperature and therefore the operating condition of the beam combiner  106 , collimating lens  134 , etc., which can be used to diagnose and troubleshoot problems with these parts of the laser beam control and delivery system. Since the partially reflective mirror has an antireflective coating for the laser wavelength, the camera will be safe from damage from the laser beam. In another embodiment of the surgical laser system, the fiber tip protection system can be configured to provide a quantitative measure of the actual temperature of the fiber tip or other portions of the optical fiber. One means of accomplishing this is with two infrared detectors configured to sense infrared light in two different ranges of infrared wavelengths (or a single infrared detector capable of providing separate measures of infrared light in two different wavelength ranges). The total magnitude of the infrared signal will correlate with the location where the optical fiber is overheating (i.e. proximal end or distal end), whereas the ratio of the magnitudes of the signals in the two different ranges of infrared will correlate with the temperature of the hotspot detected. This infrared temperature sensor can be calibrated using a black body radiator (with emissivity of approximately 1) to create a look-up table to determine the temperature. 
     The thermal constant of the hotspot detected will also correlate with the location where the optical fiber is overheating and can be used for diagnosis and troubleshooting of problems with the optical fiber or alignment of the laser beam control and delivery system. For example, the infrared signal from carbonized tissue on the fiber tip will have a rapid decay, whereas the infrared signal from an overheated fiber tip will have a longer decay, and the infrared signal from an overheated optical block  110  will have a much longer decay time because of the higher thermal mass. 
     In another embodiment, the surgical laser system can be configured to provide a quantitative measure of the temperature of the target tissue. This capability would be useful in applications such as laser liposuction, wound healing, tissue welding and cancer detection. An infrared detector or camera for detecting short wavelength infrared (around 1.7 microns), such as an In/GaAs sensor, can be mounted in a manner similar to the visible light camera described above. Other types of infrared detectors that can be utilized include silicon, germanium and pyroelectric detectors. During periods that the laser source is switched off, the infrared detector or camera can detect the temperature of the target tissue. The infrared tissue temperature sensor can be calibrated using a black body radiator (with emissivity of approximately 1) to create a look-up table to determine the temperature. 
     For greater accuracy, a visible light camera can be used to produce a color image of the tissue being measured to estimate the emissivity of tissue. Charred tissue will have an emissivity of approximately 1, whereas normal tissue will have an emissivity of less than 1. A correction factor based on the estimated emissivity of the tissue can be applied to the infrared signal or a look-up table that takes both measures into account can be created. 
       FIG. 6  is an optical diagram of a surgical laser system  100  that may utilize the laser beam control and delivery system of the present invention for fiber tip temperature sensing and tissue temperature sensing. This embodiment is similar to the embodiment illustrated in  FIG. 5  except that it utilizes a third mirror M 3  for separating the signals for fiber tip temperature sensing and tissue temperature sensing. Again, in this example, the laser diode  102  is a 1470 nm laser and the aiming beam laser  104  is a 635 nm, red laser. Mirror M 1  is coated to transmit 1470 nm light and to reflect other wavelengths. Mirror M 2  is coated to reflect 635 nm and “red” color and to transmit other wavelengths, including IR wavelengths. Mirror M 3  is coated to reflect all wavelengths below 1000 nm, and to transmit light in the range of 1400 nm to 2100 nm wavelengths. Mirror M 3  separates the light returning from the optical fiber  204  by reflecting the light below 1000 nm toward a silicon IR and visible light detector  150  for fiber tip temperature sensing and transmitting light in the range of 1400 nm to 2100 nm to an InGaAs infrared detector  162  for tissue temperature sensing. Most of the 1470 nm laser beam is transmitted directly through mirror M 1 , but a very small percentage of the beam is reflected toward the second light detector  152 . The second light detector  152  will produce a signal that is proportional to the total energy of the 1470 nm laser beam, which can be used to provide a display of the actual laser energy produced and/or to compare the actual laser energy produced with the set power level to determine laser efficiency. This measure of laser efficiency can be used to schedule maintenance of the laser system. Alternatively, this embodiment laser system  100  may utilize a fiber optic beam combiner  106 , as described above in connection with  FIGS. 1 and 2 , to combine the output beams of the laser diode  102  and the aiming beam laser  104 . 
     The tissue temperature sensing may be calibrated using a black body radiator, as described above. Variations in the optical fiber  204  may affect the calibration of the tissue temperature sensing. To account for this, the transmission of each optical fiber  204  may be measure to determine a correction factor to be utilized by the laser system  100  for determining the tissue temperature. This correction factor may be entered manually by the operator, or the correction factor may be programmed into the memory device  202  in the proximal connector  206  of optical fiber  204  so that the laser system  100  will automatically recalibrate to the optical fiber  204  when it is plugged into the laser system  100 . 
       FIG. 4  illustrates the touch screen control panel  170  of the surgical laser system. The touch screen control panel  170  includes a real-time bar graph  172  of the operating power of the laser diodes. The display may be in units of Watts of laser power, a percentage of the maximum power of the laser system or a percentage of the current laser power setting. This bar graph moves back and forth in real time to show the actual laser power being applied through the optical fiber by the laser control system. A reduction in the power level below the set power level is an indication that the fiber tip protection system has cut back on the laser power because the temperature of the fiber tip has reached its temperature threshold. In addition to the moving bar graph  172 , the color of the bar graph can change to indicate the current operating condition of the optical fiber. For example, the bar graph can be green when the optical fiber is in good operating condition, it can turn yellow when the optical fiber is approaching the end of its usable life and it can turn red when the optical fiber has reached the end of its usable life and should be changed before continuing the surgical procedure. Other color schemes are, of course, possible. Alternatively or in addition, an optical fiber status indicator that changes color and/or size can be provided on the display panel separate from the power bar graph. Any one of these features will allow the operator to ascertain the current operating condition of the optical fiber with a quick glance at the display panel. 
       FIG. 7  illustrates a surgical laser system  100  that utilizes a cooling system  180  according to the present invention.  FIG. 8  is a side view of the surgical laser system  100  and the cooling system  180  of  FIG. 7 . The surgical laser system  100  is preferably configured with a laser source that comprises one or more laser diodes  102 . In the example shown, the surgical laser system utilizes two fiber-coupled laser diodes  102  and an aiming laser  104 . The output beams from the two laser diodes  102  and the aiming laser  104  are combined using a beam combiner  106 . The laser diodes  102  may comprise two laser diodes of the same wavelength, e.g. two 1470 nm laser diodes, or they may be different wavelengths, e.g. one 1470 nm laser diode and one 980 nm laser diode. In a currently preferred embodiment, the two laser diodes have an output power of approximately 50 Watts each, for a combined power of approximately 100 Watts. Other wavelengths and combinations of wavelengths and power levels are also possible depending on the tissue effect that is desired from the surgical laser system. The aiming laser  104  is a low power laser source with a visible output beam. The aiming laser may produce a single color aiming beam, e.g. red, yellow, green or blue, or it may produce multicolored aiming beams that may be continuous or may be modulated to indicate the operating status of the laser system, as described in the above-referenced patent applications. 
     The laser diodes  102  are highly efficient as compared to previous surgical laser systems that utilized gas lasers or solid state lasers, therefore the bulky, complicated and heavy fluid-circulating or refrigeration-cycle cooling systems that these other laser systems required are not needed. However, for stable operation of the laser diodes  102  some cooling system is still needed to maintain the laser diodes within their operating temperature range, particularly if the laser diodes are operated at high power for extended periods, as may be required in some surgical applications. The challenge is to create a cooling system that is compact, efficient and streamlined as befits the more compact and efficient laser diodes. Another challenge is to create a cooling system that is as quiet and free of vibration as possible. This attribute by itself would be a notable improvement over previous surgical laser systems. 
     Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the temperature gradient (from cold to hot), with consumption of electrical energy. 
     Thermoelectric coolers are available with cooling capacity sufficient for dissipating the waste heat produced by the laser diodes. However, the cooling ability of the thermoelectric cooler for this application is limited by the small surface area of the laser diode modules that is available for transferring heat to the cool side of the thermoelectric cooler. Directly coupling a thermoelectric cooler to the laser diode modules will not result in sufficient cooling to maintain the laser diodes within their operating temperature range because of the thermal resistance presented by the small thermal contact area of the laser diode modules. What is needed is a way to increase the effective thermal contact area of the laser diode modules for thermal coupling to a thermoelectric cooler in order to decrease the thermal resistance in the cooling system. The cooling ability of the thermoelectric cooler is also limited by the surface area on the hot side of the thermoelectric cooler that is available for dissipating heat. For this reason, it would also be advantageous to increase the effective surface area on the hot side of the thermoelectric cooler to further decrease the thermal resistance in the cooling system. It would be preferable to accomplish these objectives as efficiently as possible and without unduly increasing the bulk and complexity of the surgical laser system. 
     The cooling system of the present invention  180  utilizes a first heat spreader  182  to thermally couple the laser diodes  102  to the cool side of a thermoelectric cooler  184 . The thermoelectric cooler  184  used in the currently preferred embodiment is capable of approximately 600 Watts of continuous cooling with a temperature difference from the hot side to the cool side of approximately 15 degrees Celsius, with a reserve power of approximately 900 Watts of cooling. Other sizes and power ratings of thermoelectric coolers may be appropriate for other laser systems. The first heat spreader  182  has an approximately planar configuration and simultaneously spreads the heat away from the laser diodes in two dimensions. This effectively increases the thermal contact area between the laser diode modules  102  and the cool side of the thermoelectric cooler  184 . The materials and the structure of the first heat spreader are chosen to minimize the thermal resistance between the laser diode modules  102  and the cool side of the thermoelectric cooler  184 . Preferably, the surface area of the first heat spreader  182  is approximately equal to the surface area of the cool side of the thermoelectric cooler  184 , as additional surface area would be ineffective for heat transfer and therefore wasteful. In the example shown, the first heat spreader  182  has dimensions of approximately 156 by 120 mm, with a thickness of approximately 1-3 mm, and the thermoelectric cooler  184  has dimensions of approximately 156 by 120 mm, with a thickness of approximately 3-6 mm. Other dimensions for the first heat spreader  182  and the thermoelectric cooler  184  are also possible. The cooling system utilizes a second heat spreader  186  to thermally couple the hot side of the thermoelectric cooler  184  to a heat sink  188  with cooling fins. The second heat spreader  186  has an approximately planar configuration and simultaneously spreads the heat away from the laser diodes in two dimensions. Configurations other than planar are also possible, particularly for the edges of the second heat spreader  186  that are beyond the edges of the thermoelectric cooler  184 . The second heat spreader  186  increases the effective surface area on the hot side of the thermoelectric cooler  184  for decreased thermal resistance and improved heat dissipation. The materials and the structure of the second heat spreader  186  are chosen to minimize the thermal resistance between the hot side of the thermoelectric cooler  184  and the heat sink  188 . Preferably, the second heat spreader  186  has a surface area that is significantly larger than the surface area of the hot side of the thermoelectric cooler  184 . In the example shown, the second heat spreader  186  has dimensions of approximately 558 by 355 mm, with a thickness of approximately 1-3 mm, and the heat sink  188  has dimensions of approximately 558 by 355 mm, with cooling fins having a height of approximately 50 mm across the entire surface of the heat sink  188 . Other dimensions for the second heat spreader  186  and the heat sink  188  are also possible. In this example, the thermoelectric cooler  184  has a surface area of approximately 19,800 mm squared and the second heat spreader  186  has a surface area of approximately 198,000 mm squared, or approximately ten times the surface area of the thermoelectric cooler  184 . Other sizes and surface area ratios may be appropriate for use with other laser systems. Preferably, the cooling system will also include one or more fans or blowers  190  for circulating cooling air across the cooling fins of the heat sink  188 . For example, a high-performance variable speed electric fan, such as the Squall  50 , available from Xcelaero Corp. of San Luis Obispo, Calif., may be used. The high efficiency of such a fan will reduce the overall power demands of the cooling system. Optionally, baffles or ducting may be used to direct and distribute the airflow from the fan  190  over the cooling fins of the heat sink  188 . 
     In one embodiment of the cooling system of the present invention, the first and second heat spreader  182 ,  186  are configured as two-phase evaporative heat spreaders. One such heat spreader suitable for use in the present invention is the NanoSpreader™, which is commercially available from Celsia Technologies, Miami, Fla. The NanoSpreader™ is a copper encased two-phase vapor chamber into which pure water is vacuum sealed. The liquid is absorbed by a copper-mesh wick and passed as vapor through a micro-perforated copper sheet where it cools and returns as liquid to the wick. Nano Spreaders™ are half the weight of solid copper, yet can transfer heat at roughly ten times the rate (thermal conductivity). The NanoSpreader™ is a completely passive heat transfer device and requires no external power input. Multiple standard size or custom size NanoSpreader™ modules may be used together to achieve the dimensions of the heat spreaders noted in the example above. Other heat spreaders with different heat transfer fluids can also be used. 
     In one preferred embodiment, the second heat spreader  186  may be configured with cooling fins integrated directly into the two-phase evaporative heat spreader to act as an integral heat sink  188  and to reduce the number of material interfaces and therefore reduce the total thermal resistance of the cooling system. 
     In another embodiment of the cooling system of the present invention, the first and second heat spreader  182 ,  186  are constructed of a material with significantly higher thermal diffusivity and thermal conductivity than either aluminum or copper. One material suitable for use as heat spreaders in the present invention is CarbAl™, which is a carbon-based metal nanocomposite (CA1) comprised of 80% carbonaceous matrix and a dispersed metal component of 20% aluminum commercially available from Applied Nanotech Holdings, Inc., Austin, Tex. The nanocomposite heat spreader is a completely passive heat transfer device and requires no external power input. Another potential advantage of the nanocomposite heat spreader is that the heat transfer can be made directional. The nanocomposite heat spreader can be made to spread the heat in the X and Y directions and/or the Z direction to move the heat away from the diode laser modules as effectively as possible. 
     In one preferred embodiment, the second heat spreader  186  may be configured with the cooling fins integrated directly into the nanocomposite heat spreader to act as an integral heat sink  188  and to reduce the number of material interfaces and therefore reduce the total thermal resistance of the cooling system. 
     In other embodiments, the cooling system of the present invention may utilize a two-phase evaporative heat spreader for either the first or the second heat spreader  182 ,  186  and a nanocomposite heat spreader for the other heat spreader. 
     Another way to describe the configuration of the cooling system of the present invention is that the thermoelectric cooler  184 , positioned with the cool side up and the hot side down, is “sandwiched” in between the first heat spreader  182  on the top and the second heat spreader  186  on the bottom. The laser diode modules  102  are mounted directly on top of the first heat spreader  182  for good thermal contact. The heat sink  188  with cooling fins is mounted directly below the second heat spreader  186  or, more preferably, integrated directly into the second heat spreader  186 . Other orientations of the cooling system are also possible to accommodate different configurations of laser systems. Optionally, each interface of this “sandwich” can be configured to enhance thermal coupling between the various components. For example, contacting surfaces can be lapped together to improve surface-to-surface contact. Alternatively or in addition, thermal coupling can be enhanced by applying thermal grease or another heat transfer compound between contacting surfaces, by bonding with a thermally conductive adhesive or by soldering. Preferably, the cooling system will include at least one temperature sensor for measuring the operating temperature of the laser diode modules. Optionally, additional temperature sensors may be used for measuring the temperature of the cool and/or hot side of the thermoelectric cooler  184  and/or the temperature of the heat sink  188 . The signal(s) from the temperature sensor(s) will be used by a microcontroller for dynamic control of the cooling system. The microcontroller controls the current to the thermoelectric cooler  184  and, optionally, the current to the cooling fan(s) to maintain the operating temperature of the laser diode modules within an acceptable range. The microcontroller may use PID (proportional-integral-derivative) control, PWM (pulse width modulation) control or other known control scheme to optimize the power usage of the cooling system while maintaining the operating temperature of the laser diode modules within an acceptable range. One objective of the microcontroller is to optimize the heat exchange for the lowest possible power use. This helps to make the surgical laser system and cooling system capable of operating using a standard 120 volt AC outlet, without requiring more costly high amperage or 240 volt wiring in the operating room. 
     Optionally, the cooling system may be sealed into a thermally insulated box with a dry gas, such as dry nitrogen, inside to prevent condensation from forming on any of the cool side components. Only the heat sink  188  and the cooling fins would be exposed on the outside of the insulated box to allow the cooling air from the cooling fan(s)  190  to flow over the fins to dissipate heat. Alternatively, the cooling system may include a humidity sensor to avoid forming condensation on any of the cool side components. Moisture from condensation is not only potentially damaging to the components of the laser system and the cooling system, but it also indicates that the cooling system may be working too hard and wasting energy by condensing moisture from the air. Optimizing the power usage of the cooling system should include avoiding forming condensation. 
     If desired, the cooling system may be configured to transfer the waste heat farther away from the laser diode modules. For example, waste heat may be absorbed at the heat sink  188  and transferred to a heat exchanger located outside of the laser system enclosure. One technology for accomplishing this is a bubble pump closed loop liquid cooling system, such as the SILENTFLUX® bubble pump available from Noise Limit Inc., Cupertino, Calif. Another technology for accomplishing this is a loop heat pipe or a thermosyphon heat pipe, such as those available from Thermacore, Inc., Lancaster, Pa. These technologies are capable of transferring heat to a location from 1 to 23 meters from the heat source. They are passive devices that can operate silently. The only source of noise and vibration is the optional cooling fan that would be located at the heat exchanger. 
     Another option would be to utilize the support stand  192  for the laser system  100  as part of the cooling system.  FIG. 9  illustrates a surgical laser system  100  utilizing the support stand  192  as part of the cooling system. Various components of the cooling system could be housed in the support stand, such as the cooling fan  190  and/or an external heat exchanger. Locating an external heat exchanger in the support stand  192  connected to the cooling system  180  would move waste heat farther from the source of heat at the diode laser modules. This arrangement could also reduce the total noise level of the laser system  100 . In one option, the pedestal leg  194  of the support stand  192  could be used as an air duct  196  to bring cool air up underneath the laser system enclosure. As shown in  FIG. 9 , a cooling fan  190  could bring cool air in through side holes  198  located on the pedestal leg  194  of the support stand above the floor level. A screen and/or filter  200  can be used to prevent the cooling fan from bringing in dust or debris. Although the cooling system of the present invention has been described in connection with a diode laser system, the cooling system may also be used for temperature management in other laser systems, such as gas lasers or solid state lasers, or in other electronics or industrial applications requiring a cooling system. 
     While the present invention has been described herein with respect to the exemplary embodiments and the best mode for practicing the invention, it will be apparent to one of ordinary skill in the art that many modifications, improvements, combinations and subcombinations of the various embodiments, adaptations and variations can be made to the invention without departing from the spirit and scope thereof.