WO1993021843A1

WO1993021843A1 - Device and method for variably blending multiple laser beams for medical purposes

Info

Publication number: WO1993021843A1
Application number: PCT/US1993/002966
Authority: WO
Inventors: Michael J. Yarborough; Gerald M. Mitchell; Kenneth J. Bossie
Original assignee: Coherent, Inc.
Priority date: 1992-05-05
Filing date: 1993-03-31
Publication date: 1993-11-11

Abstract

A device and method for providing a variable blend of laser beams, each having a different effect on biological tissue. Various techniques are used to produce and deliver a plurality of laser beams to biological tissue. The laser beams are variably blended by using a rotatable filter, or a rotatable mirror or a periodic emission cycle. The invention is particularly useful for variably blending a laser beam which is selected for its tissue cutting properties, with another laser beam which is selected for its tissue coagulating properties.

Description

DEVICE AND METHOD FOR VARIABLY BLENDING MULTIPLE LASER BEAMS FOR MEDICAL PURPOSES

This application is a continuation-in-part of prior copending application serial number 07/609,207, filed November 5, 1990.

Field of the Invention

The invention relates to medical lasers. In particular, the invention involves means for variably blending at least two laser beams from the same or separate lasers, each having different effects on biological tissue.

Background of the Invention

Medical practitioners frequently find it necessary to surgically remove or repair a patient's tissue. Many technological advances have evolved for this purpose. For example scalpels of various designs are used to cut tissue. An inherent problem which is encountered when cutting tissue is that blood vessels are severed causing blood loss. Thus surgeons have searched for effective ways of inhibiting blood loss during surgery.

One type of device which has been used both to cut and to coagulate tissue is the electrocautery machine which is based on the conductance of electricity through the patient's tissue. A problem with this device is that the commonly used monopolar electrocautery is difficult to control since it is dependent upon variable tissue conductances. Bipolar cautery is more controllable but of limited utility, being practically useless as a scalpel.

Monopolar cautery employs one waveform, the sinusoidal _jto cut, however provides no coagulation of the severed blood vessels, with ensuing bleeding. The other waveform of the cautery is a heavily dampened one. It works reasonably well for coagulating bleeding vessels, although with some charring and unwanted spread of damaging current. By blending these two waveforms, the surgeon can, within limits, achieve cutting with simultaneous coagulation of bleeding vessels. For larger bleeding vessels it is necessary to use a pure coagulating current or resort to other methods of hemostasis, usually ligature. Because of the vascularity of most tissues and the variable spread of current from the monopolar electrode, the use of cautery produces excessive charring and peripheral damage due to irregular current spread. For this reason it is seldom used for purposes which demand high precision, such as eye surgery.

Recently, lasers are becoming the surgical tool of choice, since they allow greater precision and control in.comparison to the traditional electrocautery machine or the metal scalpel. Lasers can be controlled with a precision measured in tens of microns, and have proven useful for both removing and repairing biological tissue. For example, lasers are used by surgeons to cauterize tissues including vascular beds and blood vessels (coagulation) ; incise tissues (scalpel like) ; ablate tissues and tumors (vaporization) ; anneal tissues, and combinations of the foregoing. Suitably designed laser beams can be used for cutting cartilage, drilling and cutting bone, and removal of atherosclerotic plague.

The type of laser beam which is used depends on what type of effect is desired. For example, it has been reported in the art that certain pulsed laser beams work well for cutting tissue when pulsed at sufficient energy. In contrast, certain continuous wave lasers at reduced power are useful for coagulation. r It is also known that laser beams of different 5 wavelengths produce different effects on biological tissue. The absorption spectra in Figure 1 shows how the absorption of laser beams in water, melanin and oxygenated blood varies as a function of wavelength. Other soft tissues such as muscle or liver exhibit

10 different light absorption characteristics. The degree to which a laser beam is absorbed in tissue will determine what type of overall effect is produced. More particularly, if the absorption in the tissue is relative low, the absorption depth will

15 increase such that the radiation will create more of a coagulation effect. In contrast, where the absorption is high, the radiation will be absorbed quickly and will cut tissue with little charring or coagulation. Based on this principle, a laser beam

20 of an appropriate wavelength may be selected for producing a desired effect on a particular type of biological tissue.

Medical lasers are essentially "optical scalpels" of great precision and controllability. In

25 addition to cutting tissue, when appropriate wavelengths are selected, they are also useful for coagulating blood vessels as well as performing other useful functions. Many prior art devices are designed primarily for one purpose. Other devices

30 allow the doctor to switch between different types of laser beams so that the same device can be used for

A different purposes. However, these latter devices do not allow the doctor to variably blend multiple laser beams, achieving simultaneously the effect of

35 multiple beams used alone, for example, precise. clean incision of tissue with concomitant coagulation of the cut edges. Rather, they only allow the user to select one type of beam at any one time.

Outside the medical field, lasers have been designed in which a plurality of light beams are mixed. For example. United States Patent No. 4,114,112 to Epstein et al. discloses a device in which a plurality of laser beams are synthesized to produce white light. However, none of these devices allow variable blending of multiple laser beams.

Therefore, it is an object of the invention to provide a means for variably blending multiple laser beams for producing different effects on biological tissue simultaneously. A more specific object of the invention is to variably blend two or more laser beams of differing wavelengths and differing ef ects upon (a) given tissue(s) to produce a desired mix. of cutting, coagulating, vaporizing, or other desired effects on biological tissue(s) .

Summary of the Invention

The above objects are accomplished with the medical laser apparatus of the present invention. The apparatus is capable of generating multiple laser beams, each having a different effect on biological tissue. Various techniques are disclosed to allow the operator to vary the relative proportions of the blended laser beams delivered to the tissue.

In one embodiment, laser beams of different wavelengths are polarized into different orientations so that a rotatable polarizing filter can be used to vary the relative blend of the emitted laser beams. In another embodiment, the laser beams are split by a prism and then rotatable mirrors are used to vary the relative reflection efficiency for each laser beam. Another embodiment allows variable blending of two or more laser beams by adjusting relative emission periods over a repeating duty cycle. In a further embodiment, the pulses from a plurality of lasers are combined and the number of pulses from each laser is varied to achieve variable blending.

The invention is particularly useful for medical applications in which, for example, a surgeon desires to simultaneously produce variable degrees of cutting and coagulating effects on the patient's biological tissue, such as bone, cartilage, liver or skin. Therapeutic applications, such as photo-dynamic therapy (PDT) , may also benefit from using more than one wavelength simultaneously.

Brief Description of the Drawings

Figure 1 is a graph of absorption spectra as a function of laser beam wavelength in water, melanin and blood.

Figure 2 is schematic diagram of a first embodiment of the present invention.

Figure 3 is a graph showing the relative power output of the two laser beams produced by the first embodiment.

Figure 4A is a schematic diagram of a second embodiment of the present invention.

Figure 4B shows a variation of the second embodiment.

Figure 5 is a schematic diagram of a third embodiment of the present invention. Figure 6 is a timing diagram showing the relative power output of two laser beams produced by the third embodiment. Figure 7 is a timing diagram showing the relative power output for two laser beams produced by the third embodiment.

Figure 8 is a schematic diagram of a fourth embodiment of the present invention.

Figure 9 is a schematic view of a fifth embodiment of the present invention.

Figure 10 is a schematic view of a sixth embodiment of the subject invention. Figure 11 is a timing diagram illustrating the output which can be generated from the laser system shown in Figure 10.

Detailed Description of the Preferred Embodiments

The invention involves variably blending laser beams each of which produce different effects on biological tissue. Each of the embodiments described below include a means for generating and combining at least two laser beams, and a structural means for allowing the user to vary the relative proportion of each laser beam transmitted to the tissue.

A first embodiment of the present invention, shown in Figure 2, is a medical laser for variably blending two laser beams. One of the laser beams is selected, for example for its cutting effects on the tissue. The other beam is selected, for example for its coagulating effect on biological tissue. As shown, a lasing medium, for example a single Neodymium YAG crystal 2, is pumped by flashlamp 4 to generate at least two laser transitions in the gain medium. In this illustrated embodiment, one wavelength is 1.06 microns and the other is 1.44 microns. The 1.06 micron wavelength is appropriate for coagulating tissue, while the 1.44 micron wavelength is appropriate for cutting tissue. A polarizing beam splitter 8 is used in conjunction with effectively coated mirrors 14 and 16 to polarize the two wavelengths into different orientations. The 1.06 laser beam 10 is reflected off of coated mirror 14, while the 1.44 micron laser beam 12 is reflected off of coated mirror 16.

In the first embodiment, the gain of the 1.06 micron laser beam is much greater than that of the 1.44 micron laser beam. Therefore, the coating for mirror 16 must be chosen to discriminate against the 1.06 micron wavelength so that the mirror 16 has high transmission at 1.06 microns. Mirror 16 could be replaced by a turning mirror, followed by the high reflector to give further discrimination against 1.06 microns.

The first embodiment is also provided with a rotatable polarizing filter 18 disposed in the laser beams' path, so that the relative amounts of each laser beam transmitted may be varied by rotating the filter. A controller 19 is connected to the filter

18 allowing the operator to manipulate the controller

19 to achieve the desired blend of the two wavelengths.

The transmission of a given wavelength is maximized when the polarization direction of filter 18 coincides with the orientation of the polarized laser beam. Conversely, the transmission of a particular laser beam is minimized when the polarization direction of the filter 18 is perpendicular to the orientation of the laser beam. Figure 3 shows the relative power output for each laser beam as the angle of rotation of the polarizing filter is varied. The Figure 3 graph shows that either of the laser beams can be completely blocked or transmitted, or various mixtures of each may be selected.

Those skilled in the art will appreciate the usefulness of such a variable blending means. Often a surgeon desires to vary the effect of the laser while operating. For example, the surgeon may initially want to use the laser to cut through super icial tissue in order to get to a deeper structure which requires repair. In this case it would be desireable to set the laser primarily in a cutting mode at first with sufficient coagulation to control bleeding at the cut edges of the incised tissues. Once the superficial tissue is cut, the surgeon may desire to gradually switch to more of a coagulating mode in order to repair the deeper structure or tissue which has a more extensive vascular bed. The present invention satisfies these objectives by allowing the surgeon to infinitely vary the blend of laser wavelengths between a pure "cutting" mode and a pure "coagulating" mode.

In several respects, surgery often involves working on a highly variable target. Biological tissues are usually quite heterogeneous and are constantly in a dynamic state. For example, tissues vary significantly in their degree of vascular development. The present invention allows the surgeon to coagulate blood vessels which will be severed when the tissue is cut. If the surgeon is cutting through tissue which has substantial vasculature, then more of a simultaneous coagulating effect is appropriate. Whereas, a primary cutting mode may be appropriate for cutting tissue which has minimal vasculature, such as cartilage. Ideally, the surgeon will want to be able to vary the blend of cutting and coagulating laser wavelengths according to vascular variations encountered during the operation.

If the right blend of laser wavelengths and/or modes is used, the surgeon can substantially coagulate vessels prior to cutting them, thus minimizing blood loss from the incision. This can be accomplished by blending a relatively low power continuous wave beam with a higher power pulsed beam. The continuous beam tends to penetrate deeper into the tissue than the pulsed beam. Therefore, if the proper blend is used, the coagulation function can be maintained ideally just ahead of the cutting function.

As previously mentioned with reference to Figure 1, different tissues exhibit different light absorption characteristics. This fact accounts for the differing colors of various tissues. Since a surgeon frequently encounters a plurality of tissues in the course of a single operation, it is very helpful to be able to adjust the wavelength blend to suit the particular tissue or combination of tissues which the surgeon is working on.

Additionally, the light absorption characteristics of a given tissue tends to change during exposure to laser radiation. As water is vaporized and proteins are denatured, it is desireable to be able to vary the blend of laser wavelengths to correspond to the changing tissue. For all of the foregoing reasons it is desireable to be able to adjust the laser wavelength blend "on the fly". For example, the first embodiment described above could be operated by having separate buttons, one for cutting alone, another for coagulating alone, and (a) dial(s) for relatively blending the two wavelengths. Figure 4A shows a second embodiment of the present invention in which two laser beams of different wavelengths are produced from a single Neodymium YAG crystal 20, which is pumped by a flashlamp 21; A prism 24 is used to split laser beam 22 into two wavelengths, 1.44 microns 26, and 1.06 microns 28. Both wavelengths are directed onto different portions of rotatable mirror 30. By rotating the mirror 30 the relative proportions of the two wavelengths which reflect back through crystal 20 may be varied. As the mirror 30 rotates the reflection efficiency for each laser beam changes. It is necessary to select a mirror having an appropriate size and curvature so that rotation of the mirror will yield a dynamic blend of the laser beams similar to that obtained with the first embodiment.

Adjustment of the angle of rotation of the mirror 30 allows variable blending of the two wavelengths, which are emitted through mirror 36 located at the other side of the crystal 20. Since all wavelengths have a common output mirror 36, alignment of the various beams is automatic. A controller 31 is connected to the mirror 30, which allows the operator to adjust the mirror's angle of rotation.

Figure 4B shows a variation of the second embodiment, in which each wavelength is directed onto different mirrors 32 and 34, each being independently rotatable. The principle is the same as described above, except that the reflection efficiency of either laser beam may be altered independently by rotating the respective mirror.

The embodiments described above involve the blending of laser beams which are simultaneously emitted ("simultaneous emission embodiments") . Another way to accomplish the same variable blending effect is to allow the operator to change the relative time periods over which the laser beams are emitted ("periodic emission embodiments") . This can be accomplished by making the laser beams transmit during alternating periods of variable length, or during overlapping emission periods. By making the emission periods for the two laser beams sufficiently short and close together, the overall effect on the tissue is the same as that produced by the simultaneous emission embodiments.

Figure 5 shows a third embodiment of the present invention in which two laser beams 40 and 42 are produced by separate gain mediums 44 and 46 respectively. The laser beams are produced inside a housing 48 which has two shutters 50 and 52 in the paths of the laser beams, so that each laser beam can be blocked by closing or opening its respective shutter.

Outside of the housing a combining means such as a prism 54 is used to combine the laser beams into the same light beam which is directed onto mirror 56. The third embodiment also includes a controller 58 which controls and coordinates the opening and closing of the shutters 50 and 52 over defined emission periods which correspond to a particular blend which the operator has selected.

The laser beams employed in the third embodiment are preferably selected so that one is useful for cutting and the other is useful for coagulating biological tissue. For example laser beam 40 could be 1.44 microns produced from a Nd.YAG crystal for cutting tissue. Laser beam 42 could be 1.06 microns also produced from a Nd.YAG crystal which is effective for coagulating tissue. Alternatively, laser beam 42 could be a low power continuous wave beam which also is effective or coagulating biological tissue. One way to coordinate the laser beams to produce such a blend is illustrated in Figure 6 which shows the power output for two wavelengths 74 and 76. Laser beams 74 and 76 are emitted during selected periods within a duty cycle. The lengths of the selected periods for each wavelength are variable, and the duty cycle is sufficiently short so that the laser beams affect the tissue as a single blend. The limit of how long the duty cycle can be while still producing a blending effect on the biological tissue, depends on what type of tissue is being operated on and what purpose the laser is being used for.

For example, if the purpose is to cut through tissue with substantial vasculature, the surgeon will want to coagulate the vessels prior to cutting them. However, it would be undesirable to coagulate vessels which are substantially below the cutting target. This objective can be accomplished by blending a low power continuous wave laser beam with a higher power pulsed beam. The continuous wave beam tends to penetrate deeper then the pulsed beam. By making the "on" period of the continuous wave beam sufficiently long relative to the "on" period for the pulsed beam, the coagulating function can be maintained just ahead of the cutting function, thus minimizing blood loss due to the incision.

As shown in Figure 6, the selected periods for each wavelength alternate. The 1.06 micron laser beam is emitted over 25% of the duty cycle, whereas the 1.44 micron laser beam is emitted over 75% of the duty cycle. Assuming each laser beam operates at the same power during its "on" period, the relative blend of lasers delivered to the tissue will substantially correspond to the relative emission periods. The relative blend of the two laser beams can be varied by varying the ratio of the selected period for a given wavelength in relation to the duty cycle, or by varying the power of a given wavelength during its "on" period. The power output shown in Figure 6 could be produced by a laser beam operating at a single wavelength which is switched from a continuous wave mode to a pulsed mode. Alternately, short high power pulses could be super imposed on a low power continuous output. The requirements of the subject invention would be satisfied if the relative powers or duty cycles of the two modes could be varied with respect to each other.

Figure 7 shows a graph illustrating another way to vary the blend of two laser beams. In this example one of the laser beams is emitted constantly, while the other laser beam is emitted only during selected periods. The relative blend of the two laser beams can be varied by altering either the duration or the frequency for the periodic laser beam.

The device shown in Figure 4A and 4B, previously described as a simultaneous emission embodiment, may also be configured to operate as a periodic emission embodiment of the present invention. As shown in

Figure 4A, the controller 31 may be programed to move the rotatable mirror 30 between first and second positions. By selecting an appropriate mirror curvature, prism angle and prism to mirror distance, the device can be designed so that when the mirror is in the first position, laser wavelength 28 is efficiently reflected back through the gain medium, while laser wavelength 26 is dissipated. Conversely, when the mirror 30 is in the second position, wavelength 26 is efficiently reflected back through the gain medium, while wavelength 28 is dissipated.

By defining and programming a duty cycle similar to that described with reference to the third embodiment, the device shown in Figure 4A can be used to produce the power output illustrated in Figure 6. In this approach, generally only one of the beams will be aligned and lasing at once. The mirror can be rapidly tilted, i.e. rotated, back and forth between the two (or more) beams. The duty cycle of each wavelength can be adjusted continuously by adjusting the time period during which a particular wavelength is aligned. By using a small light mirror 30, the mirror can be moved to provide "on" times for each wavelength variable over a large range. Due to the thermal response times of biological tissue, switching rapidly between dif erent wavelengths is equivalent to having them present simultaneously.

The modified device shown in Figure 4B, which employs separate rotating mirrors for each wavelength, may be similarly configured to operate as a periodic emission embodiment. In such a configuration, each of mirrors 32 and 34 are switchable between two positions, i.e., "on" and "off" positions. When one of the mirrors is in its "on" position, its respective wavelength is efficiently reflected back through the gain medium. When the mirror is in the "off" position, its respective wavelength is dissipated. Greater versatility is achieved by employing multiple rotating mirrors, because the programmer or operator has the option of having all wavelengths lase at the same time, i.e. each mirror in the "on" position. Or for example, one laser could lase continuously while the other laser operates in a periodic mode, yielding a power output as illustrated in Figure 7.

Figure 8 shows a fourth embodiment which is also a periodic emission device. This device can be used to produce the timing power output patterns of Figures 6 and 7, similar to the third embodiment. The fourth embodiment includes a multi-wavelength lasing medium 60 optically pumped by a flashlamp 62 to produce a coherent laser beam 64. On one side of the lasing medium 60 is a mirror 66 which is highly reflective at the operating wavelengths of the laser. On the other side of the lasing medium 60 is a mirror 68 which is partially transmissive so that a portion of the laser beam is directed out of the device.

Disposed between lasing medium 60 and mirror 66 in optical alignment with laser beam 64 are an optically active birefringent component 70 and an electrooptically active element 72 such as a Pockels' cell. Component 70 consists of an anisotropic material such as calcite or sodium nitrate having the property of spatially separating the emission from lasing medium 60 into linearly polarized wavelengths 74 and 76. In this example the laser beams are polarized into different planes as indicated by the dots on beam 74 and the lines on beam 76.

Component 72 comprises a transparent crystal such as lithium niobate having a first set of electrodes 78 engaging the sides of component 72 in alignment with laser beam 74. Component 72 has a second set of electrodes 80 similarly mounted on the side of component 72 aligned with laser beam 76. Electrodes 78 are energized by an electronic driver 82 such as a triggered thyratron. Similarly, electrodes 80 are energized by an electronic driver 84.

Drivers 82 and 84 are connected to a controller 86 which operates to switch the drivers on and off.

When a proper voltage is applied to either electrodes 78 or 80, an electrically induced birefringence occurs in the component causing a 45 degree rotation of polarization of the respective beam. Upon reflection of the beam from mirror 66 and back through component 72, the polarization of the beam is rotated an additional 45 degrees for a total of 90 degrees from the original polarization. Consequently the beam is refracted away from its original path through element 70 and laser oscillation at the wavelength of that beam is inhibited.

The switching mechanism in the fourth embodiment is similar to one disclosed in United States Patent No. 4,441,186 to Erickson. However, the Erickson device merely provides a way to switch between different wavelengths. Whereas, the controller 86 in the fourth embodiment of the present invention is designed to control and coordinate emission periods for each wavelength in response to the operator's adjustment to provide a variable blending effect on biological tissue.

Figure 9 shows a fifth embodiment of the present invention, in which two separate gain mediums 90 and 92 are pumped by separate flashlamps 94 and 96 respectively. Gain medium 92 produces laser beam 98, and gain medium 90 produces laser beam 100. Laser beams 98 and 100 are selected to have different effects on biological tissue. In this embodiment the relative blend of the two laser beams 98 and 100 may be varied by altering the relative amount of flashlamp pumping impinging on each gain medium. Controller 102 is connected to the flashlamps and provides appropriate flash signals depending on the blend setting adjusted by the operator. Figure 10 illustrates a sixth and preferred embodiment of the laser system 120 of subject invention which includes three separate laser heads. More particularly, laser system 120 includes a first laser 122 having a Nd.YAG rod 124 located between the mirrors 126, 128 of a resonant cavity. The mirrors are provided with suitable dielectric coatings to favor an output of about 1.32 microns through coupler 128. The second laser 132 includes a Ho:YAG rod 134 located between mirrors 126 and 128. The Ho:YAG laser is configured to generate an output of about

2.1 microns. The third laser 142 includes an Er:YAG rod 144 which is located between mirrors 146 and 148. The Er:YAG laser is configured to generate an output of about 2.9 microns. The various output wavelengths described above have been selected based on their different effects on tissue. As can be seen from Figure 1, the absorption coefficient in tissue is the lowest for the Nd:YAG laser at 1.32 microns such that its coagulation effects will be the greatest of the three lasers. The level of absorption of the Er:YAG laser at 2.9 microns is the highest and therefore would be best suited for cutting, or at higher powers, ablating tissue. The absorption coefficient of the Ho:YAG laser at 2.1 microns is between the other two output wavelengths and has an intermediate effect. Each of the rods is excited by an associated flashlamp assembly 150, 152 and 154. In the . preferred embodiment, each of the flashlamps are independently energized by the same power supply 160. The output of the power supply is controlled by a microprocessor based, programmable controller 162.

The subject system further includes a means for optically combining the beams so that they may be delivered to the tissue along a single path. There are a variety of approaches which can be used to achieve this goal. In the illustrated embodiment, the beams are combined using appropriate dichroic filters. More specifically, the output beam from the Er:YAG laser 142 is aligned with the main output path and passes through dichroic mirror 170. The beam from the Ho:YAG 132 laser is reflected upwardly by dichroic mirror 172 and redirected along the output path by mirror 170. The beam from the Nd:YAG laser 122 is reflected upwardly by mirror 174 and passes through mirror 172 to be reflected along the common path by mirror 170.

In this embodiment, the output from each of the lasers is pulsed. The controller 162 will typically be programmed with a desired repetition rate, for example, 30 Hz. In this example, the power supply will generate 30 sequential energy pulses per second so that thirty laser pulses will be generated in that time frame. In accordance with the subject invention, the controller 162 can be used to select the number of pulses which will be generated from each laser in a given time frame. The range of selection can vary from having all the pulses emanate from one laser, to an equal number of pulses from all lasers. Various intermediate combinations can also be selected. The mix of pulses will be chosen based on the desired tissue effect to be achieved.

Figure 11 illustrates one type of pattern that might be selected. More specifically, the operator could determine that the relative energies of the three lasers should be in the ratio of 1:2:1 for the Nd:YAG, Ho:YAG and Er:YAG lasers respectively. The operator can then be allowed to select the number of pulses, and sequence of pulses which would achieve this result. In the preferred embodiment, the processor in the controller can make this selection automatically based on ratio information provided by the operator. Given a ratio of 1:2:1, the processor might create a pattern of two pulses from the Nd:YAG laser, followed by four pulses from the Ho:YAG laser, followed by two pulses from the Er:YAG laser. This pattern would be repeated for as long as the treatment energy is being delivered. It should be noted that the time period which would elapse during the delivery of eight pulses at 30Hz is about 250 milliseconds. This time period is relatively short compared to the time it takes for the laser energy to interact with the tissue. Therefore, even though the pulses are being delivered sequentially and in groups, the effect will be as if a single beam having the desired blend of characteristics is being delivered.

As can be appreciated, a number of different sequencing patterns could be used to achieve the result achieved by the pattern of Figure 11. The important factor is that the pulses are multiplexed or interleaved through a time division approach.

As noted above, the selected pattern of pulses would typically be repeated. However, it may be desirable to slowly vary the blend of the beams during the procedure. Therefore, the controller could .be programmed to start with a pure cutting blend of 0:0:1, move to an intermediate blend of 1:1:1 and finish with a coagulating blend of 2:2:0. In addition to changing the number of pulses, the ratio of energies from the lasers can also be a varied by varying the energy per pulse. The energy per pulse can be varied by varying the height or width of the pulse. The variation of pulse width is similar to the approach described with respect to Figure 6. In the preferred embodiment, the controller can vary both the number of pulses and the pulse height and width to obtain the desired tissue effects. In this manner, the output for each laser can be independently controlled.

While the present invention has been described with reference to six particular embodiments illustrated by the drawings, it will be readily apparent to those of ordinary skill in the art that modifications can be made to the described embodiments which are still within the scope of the claimed invention.

Claims

CLAIMS What is claimed is:

1. A medical laser apparatus for treating tissue comprising: means for generating a pulsed laser beam having a first wavelength; means for generating a pulsed laser beam having a second, different wavelength and wherein said first and second wavelengths have different effects on tissue; means for optically combining the beams along the same path so that both beams can be delivered to the tissue to be treated; and means for controlling the relative number of pulses delivered from each beam during a given period such that the effects on the tissue can be varied.

2. An apparatus as recited in claim 1 wherein said pulses are delivered sequentially.

3. An apparatus as recited in claim 2 wherein said period is sufficiently short so that effect on the tissue is substantially equivalent to delivering the two beams simultaneously over that period.

4. An apparatus as recited in claim 3 wherein said control means further functions to vary the length of the pulses to further vary the effects on the tissue.

5. An apparatus as recited in claim 3 wherein said control means further functions to deliver a pattern of pulses from said beams during said period and thereafter repeats that pattern during successive periods, with the pattern of pulses determining the relative energy delivered by the two beams.

6. A method of treating tissue comprising the steps of: generating a pulsed laser beam having a first wavelength; generating a pulsed laser beam having a second, different wavelength and wherein said first and second wavelengths have different effects on tissue; optically combining the beams along the same path so that both beams can be delivered to the tissue to be treated; and controlling the relative number of pulses delivered from each beam during a given period such that the effects on the tissue can be varied.

7. A method as recited in claim 6 wherein said pulses are delivered sequentially.

8. A method as recited in claim 7 said wherein period is sufficiently short so that effect on the tissue is substantially equivalent to delivering the two beams simultaneously over that period.

9. A method as recited in claim 8 further including the step of varying the length of the pulses to further vary the effects on the tissue.

10. A method as recited in claim 3 further including the step of delivering a pattern of pulses from said beams during said period and thereafter repeating that pattern during successive periods, with the pattern of pulses determining the relative energy delivered by the two beams.

11. A medical laser apparatus for treating tissue comprising: a first laser for generating a pulsed laser beam having a first wavelength; a second laser for generating a pulsed laser beam having a second wavelength; a third laser for generating a pulsed laser beam having a third wavelength with each of said wavelengths having a different effect on the tissue; means for optically combining the beams along the same path so that the beams can be delivered to the tissue to be treated; a common power supply connected to each of said lasers; and means connected to the power supply for controlling the output of the lasers in a manner such that a sequential pattern of pulses can be generated in a given period with the number of pulses from each laser generated in each period being variable to vary the effects on the tissue.

12. A medical laser apparatus for treating tissue comprising: a Nd:YAG laser for generating a pulsed laser beam having a wavelength of about 1.32 microns; a Ho:YAG laser for generating a pulsed laser beam having a wavelength of about 2.1 microns; an Er:YAG laser for generating a pulsed laser beam having a wavelength of about 2.9 microns with each of said wavelengths having a different effect on the tissue; means for optically combining the beams along the same path so that the beams can be delivered to the tissue to be treated; a common power supply connected to each of said lasers; and means connected to the power supply for controlling the output of the lasers in a manner such that a sequential pattern of pulses can be generated in a given period with the number of pulses from each laser generated in each period being variable to vary the effects on the tissue.