Laser generator using diffractive optical element

The present disclosure relates generally to devices, methods and systems for laser generators, and more specifically, to laser generators having an optical assembly, which allows fiber optic catheters to couple to laser generators while delivering laser beams.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to devices, methods and systems for laser generators, and more specifically, to laser generators having an optical assembly, which allows fiber optic catheters to couple to laser generators while delivering laser beams.

BACKGROUND

When performing a laser atherectomy procedure in a patient's vasculature and utilizing a disposable fiber optic catheter, the catheter is typically coupled to a laser generator, such as the CVX-300™ excimer laser system, which is manufactured by The Spectranetics Corporation, Colorado Springs, Colo., USA. Different laser generators generally produce different laser beams. The CVX-300™ excimer laser system produces a 308 nanometer laser beam with a pulse width of approximately 135 nano seconds (nsec). Other laser systems may produce a laser beam having a different wavelength and pulse width. For example, a Nd:YAG laser operating at its third harmonic produces a 355 nanometer laser beam with a pulse width of approximately 8 nsec. The 308 nanometer laser beam having pulse width of approximately 135 nsec may be capable of producing maximum energy output of 140 milli-joules (mJ), and the 355 nanometer laser beam having a pulse width of approximately 8 nsec may be capable of producing maximum energy output of 200 milli-joules (mJ). But the optical fibers in the laser catheter that are used to deliver the energy are potentially subject to failure if the amount of energy in a pulse exceeds a certain threshold. The likelihood of such failure is increased if the laser beam inherently has a greater peak power. For example, due to the relatively short duration (e.g., 8 nsec) of the puke width of the 355 nanometer laser beam in comparison to the 308 nanometer laser beam, which has a puke width of 135 nsec, the 355 nanometer laser beam must have a substantially higher peak power for a given puke because the puke width of the 355 nanometer beam k over sixteen times shorter than the length of the puke width of the 308 nanometer beam. Accordingly, there is a need to increase the pulse width of a laser beam in order to decrease the peak power of the energy traveling through the optical fibers in order to prevent the power level from exceeding the damage threshold of the fiber optic delivery device. Moreover, regardless of the wavelength of the laser beam, a need may exist to improve the symmetry and homogeneity of the intensity of the laser beam exiting the laser system and/or the disposable fiber optic catheter so as to further decrease the likely of damaging the optical fibers.

SUMMARY

The devices of the present disclosure increase the puke width of a laser beam and decrease the peak power of the energy traveling through the optical fibers, thereby minimizing and/or preventing the power level from exceeding the damage threshold of the fiber optic delivery device. Moreover, the devices of the present disclosure improve the symmetry and homogeneity of the intensity of the laser beam exiting the laser system and/or the disposable fiber optic catheter so as to further decrease the likely of damaging the optical fibers.

A device for performing intravascular ablation includes a laser generator comprising a laser source producing a beam of light and an optical assembly downstream of the laser source, wherein the optical assembly receives the beam of light, wherein the optical assembly comprises a waveplate receiving the beam of light, a thin film polarizer downstream of the waveplate and receiving the beam of light and reflecting a first portion of the beam and allowing a second portion of the beam to pass there through, a beam dump receiving the first portion of the beam, a beam expander downstream of the waveplate and receiving the second portion of the beam, a diffuser downstream of the beam expander and receiving the second portion of the beam of light, and a mixing fiber downstream of the diffuser and receiving the second portion of the beam of light, wherein the mixing fiber emits the second portion of the beam of light.

The laser generator of the preceding paragraph, wherein the laser source produces a beam of light comprising about 355 nanometers

The laser generator of any of the preceding paragraphs, wherein the laser source produces a beam of light between about 10 nanometers to about 5000 nanometers.

The laser generator of any of the preceding paragraphs, wherein the diffuser is a diffracting optical element.

Another device for performing intravascular ablation includes a laser generator comprising a laser source producing a beam of light having a plurality of pulses, wherein the pulses comprise a pulse width, and an optical assembly downstream of the laser source, wherein the optical assembly receives the beam of light, wherein the optical assembly comprises a waveplate receiving the beam of light, a thin film polarizer downstream of the waveplate and receiving the beam of light and reflecting a first portion of the beam and allowing a second portion of the beam to pass there through, wherein the second portion of the beam has the pulse width, a beam dump receiving the first portion of the beam, a means for stretching the pulse width of at least one of the plurality of pulses in the second portion of the beam, and a diffuser downstream of the means for stretching the pulse width and receiving and emitting the other portion of the second beam.

The laser generator of the preceding paragraph, wherein the means for stretching the width of at least one of the plurality of pulses comprises a beam splitter and a plurality of mirrors creating a beam path.

The laser generator of any of the preceding paragraphs, wherein at least one of the mirrors is capable of translating.

The laser generator of any of the preceding paragraphs, wherein the means for stretching the width of at least one of the plurality of pulses comprises beam splitter.

The laser generator of any of the preceding paragraphs, wherein the beam splitter spots the second portion of the beam into a first beam and a second beam.

The laser generator of any of the preceding paragraphs, wherein the beam combines the second beam with the first beam after the second beam has passed through a time delay loop.

The laser generator of any of the preceding paragraphs, wherein the time delay loop comprises a plurality of mirrors.

The laser generator of any of the preceding paragraphs, wherein the time delay loop comprises a mixing fiber.

The laser generator of any of the preceding paragraphs, wherein the mixing fiber is a coherence mixing fiber.

The present disclosure also includes a method of using the laser generator of any of the preceding paragraphs, wherein the method comprises coupling the laser generator to a catheter having a plurality of optical fibers and inserting the catheter into a patient's vasculature and removing at least a portion an occlusion with the patient's vasculature.

The phrases “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. When each one of A, B, and C in the above expressions refers to an element, such as X, Y, and Z, or class of dements, such as X1-Xn, Y1-Ym, and Z1-Zo, the phrase is intended to refer to a single dement selected from X, Y, and Z, a combination of elements selected from the same class (e.g., X1 and X2) as well as a combination of dements selected from two or more classes (e.g., Y1 and Zo).

It should be understood that every maximum numerical limitation given throughout this disclosure is deemed to include each and every lower numerical limitation as an alternative, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this disclosure is deemed to include each and every higher numerical limitation as an alternative, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this disclosure is deemed to include each and every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the disclosure or that render other details difficult to perceive may have been omitted. It should be understood, of course, that the disclosure is not necessarily limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION

Referring toFIG. 1, there is depicted an exemplary ablation system100of the present disclosure. Ablation system100includes a laser apparatus130coupled to a laser controller135. Controller135includes one or more computing devices programmed to control laser130. Controller135may be internal or external to laser apparatus130, such as a laser generator. Laser apparatus130may include an excimer laser, a Nd:YAG laser or another suitable laser. In some embodiments, laser130produces light in the ultraviolet frequency range. In one embodiment, laser130produces optical energy in pulses.

Laser130is connected with the proximal end of a laser energy delivery system120, illustratively a laser catheter150via coupler140. Laser catheter150includes one or more transport members which receive laser energy from laser130and transports the received laser energy from a first, proximal end160of laser energy catheter150towards a second, distal end170of laser catheter150. The distal end170of catheter150may be inserted into a vessel or tissue of a human body110. In some embodiments, system100employs a plurality of light guides as the transport members, such as optical fibers, that guide laser light from laser130through catheter150toward a target area in human body110.

Exemplary laser catheter devices or assemblies may include laser catheters and/or laser sheaths. Examples of laser catheters or laser sheath are sold by The Spectranetics Corporation under the tradenames ELCA™ and Turbo Elite™ (each of which is used for coronary intervention or peripheral intervention, respectively, such as recanulizing occluded arteries, changing lesion morphology, and facilitating stent placement) and SLSII™ and GlideLight™ (which is used for surgically implanted lead removal). The working (distal) end of a laser catheter typically has a plurality of laser emitters that emit energy and ablate the targeted tissue. The opposite (proximal) end of a laser catheter typically has a fiber optic coupler140and an optional strain-relief member145. The fiber optic coupler140connects to a laser system or generator130. One such example of a laser system is the CVX-300 Excimer Laser System, which is also sold by the Spectranetics Corporation.

The laser controller135ofFIG. 1includes a non-transitory computer-readable medium (for example, memory), which includes instructions and/or logic that, when executed, cause one or more processors to control laser130and/or other components of the ablation system100. Controller135includes one or more input devices to receive input from an operator. Exemplary input devices include keys, buttons, touch screens, dials, switches, mouse, and trackballs which providing user control of laser130. Controller135further includes one or more output devices to provide feedback or information to an operator. Exemplary output devices include a display, lights, audio devices which provide user feedback or information.

A laser source of laser130is operatively coupled to laser controller135. Laser source is operative to generate a laser signal or beam and provide the laser signal through a fiber optic bundle of catheter150to the human. Fiber optic bundle serves as delivery devices for delivering the laser signal to the target area of the human body110.

FIG. 1depicts the catheter150entering the leg, preferably through the femoral artery, of the human body. As discussed above, it may be desirable to treat either cardiac arterial disease (CAD) or peripheral arterial disease (PAD). After entering the femoral artery, if the catheter150is intended to treat CAD, the catheter150will be directed through the patient's vasculature system and to the coronary arteries. Alternatively, if the catheter150is intended to treat PAD, the catheter150will be directed through the patient's vasculature system and to the peripheral arteries, such as the vasculature below the knee, particularly the vasculature in the patient's legs and/or feet.

FIG. 2Adepicts a non-limiting example of a laser energy delivery system120, illustratively a laser catheter150via coupler140, which is suitable for coupling to laser generator130. For example, laser catheter150includes a proximal end160and a distal end170. The catheter coupler140is disposed at catheter proximal end160. Catheter coupler140includes a plurality of optical fibers205, which may be arranged in one or more sets of optical fibers205, wherein the optical fibers205are disposed throughout the length of the laser catheter150, including being housed within coupler140and exposed at the distal tip175of the distal end170. Laser catheter150may also include a T or Y connector180, wherein the connector180has an entry port185for a guidewire190to be inserted therein. The laser catheter150may further include a lumen extending from the connector180to the distal end170of catheter150at distal tip175, thereby allowing the guidewire190to be inserted through the catheter150.

Referring toFIG. 2B, there is shown is a cross sectional view of a bundle of a plurality optical fibers205of a rectangular fiber coupler140, particularly the proximal end of the coupler140. The cross section of the coupler140in this figure is depicted as being rectangular, wherein the rectangular shape has a width (W) and a height (H) to match the aspect ratio different of the beam entering the coupler140. The width (W) and a height (H) may be different than that shown in this figure, such as a smaller or larger width and/or a smaller or larger height to match the aspect ratio different of the beam entering the coupler140. Although the cross section of the bundle of fibers is depicted as being rectangular, the cross section of the bundle of fibers may be square, triangular, circular or some other shape.

Referring now toFIG. 3andFIG. 4, a distal end of a laser catheter150for an atherectomy procedure in accordance with the present disclosure is shown. The laser catheter150may (as depicted inFIGS. 3 and 4) or may not include a lumen210. If a lumen210is included in the laser catheter150, a clinician may slide the laser catheter over a guidewire (not shown) through lumen210. It may, however, be preferable for the laser catheter to have a separate guidewire lumen located between the inner band220and outer jacket215.

As shown, the catheter150comprises an outer jacket215or sleeve. The outer jacket215comprises a flexible assembly with the ability to resist user-applied forces such as torque, tension, and compression. The proximal end (not shown) of the laser catheter150is attached to a fiber optic coupler (not shown and discussed above). The distal end of the laser catheter150comprises a tapered outer band225, which is attached to the distal end of the outer jacket215, a plurality of optical fibers205acting as laser emitters, an inner band220creating an orifice that provides an entrance to an inner lumen210. The energy emitted by the optical fibers205cuts, separates, and/or ablates the scar tissue, plaque build-up, calcium deposits and other types of undesirable lesion or bodily material within the subject's vascular system in a pattern substantially similar to that of the cross sectional configuration of the laser emitters10.

In this particular example, the optical fibers205are provided in a generally concentric configuration. As the energy emitted by the optical fibers205contacts the undesirable bodily material within the subject's vascular system, it separates and cuts such material in a generally concentric configuration. AlthoughFIGS. 3 and 4illustrate the optical fibers205in a generally concentric configuration, those skilled in the art will appreciate that there are numerous other ways and configurations in which to arrange a plurality of laser emitters. Accordingly.FIGS. 3 and 4are not intended to represent the only way that the distal end of a laser catheter150may be configured.

Referring toFIG. 5, there is shown an ablation system400of the present disclosure that includes a means for coherence mixing. Coherence mixing is a method for reducing spatial coherence damage in optical fibers used in transmitting relatively short pulsed width light, such as 355 nanometers. An example of a laser405that produces relatively short pulsed width light includes a Quantel DRL laser (Quantel Inc. Bozeman, Mont.), having a wavelength of 355 nanometers (nm), a pulse width of 8 nano seconds (nsec), a repetition rate of 1 to 30 Hertz (Hz) and a maximum energy output of 140 milli-joules (mJ). An alternate example of a laser405includes the Spectranetics Corporation's CVX-300 Excimer Laser System having a wavelength of 308 nanometers (nm), a pulse width of 135 nano seconds (nsec), a repetition rate of 1 to 80 Hertz (Hz) and a maximum energy output of about 200 milli-joules (mJ).

As discussed above, the optical fibers205in the laser catheter150that are used to deliver the energy are potentially subject to failure if the amount of energy in a pulse exceeds a certain threshold. The likelihood of such failure is increased if the laser beam inherently has a greater peak power. For example, due to the relatively short duration (e.g., 8 nsec) of the pulse width of the 355 nanometer laser beam in comparison to the 308 nanometer laser beam, which has a pulse width of 135 nsec, the 355 nanometer laser beam must have a substantially higher peak power for a given pulse because the pulse width of the 355 nanometer beam is over sixteen times shorter than the length of the pulse width of the 308 nanometer beam. Accordingly, there is a need to increase the pulse width of a laser beam in order to decrease the peak power of the energy traveling through the optical fibers in order to prevent the power level from exceeding the damage threshold of the fiber optic delivery device.

Continuing to refer toFIG. 5, laser light energy is emitted from laser405and into a single optical fiber520(or fiber optic bundle). For example, the laser light may include a wavelength of 355 nm as discussed above. After exiting the laser405, the laser light may be deflected by a mirror410, which directs the laser light to an energy control system415. The energy control system415controls the amount of or intensity of energy entering the ablation system400after the laser light departs the laser405. For example, the energy control system415may decrease the level of energy. The energy control system415may include a waveplate420and a thin film polarizer425. The waveplate420is an optical device that alters the polarization state of a light travelling through it. One type of waveplate is a half-wave plate, which shifts the polarization direction of linearly polarized light. The half-wave plate may be mounted in a manual or motorized rotational mount, and may be disposed prior to the thin film polarizer425relative to the laser light's travel path. The energy control system415, such as the waveplate420and thin film polarizer425, therefore, reduces the energy level(s) of the light during component and fiber input alignment, as well as the output of the delivery fiber and/or catheter150. The light that passes through the waveplate420and subsequently reflected by the thin film polarizer425is directed into a beam dump430, which is an optical element used to absorb a beam of light.

As shown inFIG. 5, thin film polarizer425reflects a portion of the light to the beam dump430and the remaining portion of the light to the mirror435. As such, after the light passes through the energy control system415, the beam of light may be deflected by a mirror435and subsequently expanded by a beam expander440. The beam expander440may aid in reducing the energy density of the laser light that is incident on the optics further downstream in system's optical path. Reducing the energy density of the laser light assists in preventing the light from exceeding the optical components' threshold damage levels, thereby increasing the useful life of the optical components. For example, the beam expander440may expand the size of the beam of light by 2.5 times or other increment, such as 1.5, 2.0, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 times, etc. or any sub-increment there between. One type of beam expander440may include a Keplerian telescope, which includes two optical lenses445,450.

After exiting the beam expander440, the light beam then passes through a shutter455followed by a diffuser-lens assembly460. The shutter455is used to switch (on/off) the light entering or not entering into the downstream optical system. The diffuser-lens assembly460may include an engineered diffuser465, such as a diffractive optical element (DOE), and a lens470downstream of the diffuser465. The engineered diffuser465will preferably be designed and/or selected such that the shape of the beam exiting the engineered diffuser465will resemble the shape of the mixing fiber475and/or the delivery fiber510. For example, if it is desirable for the shape of the beam exiting the engineered diffuser465to be round, then it may desirable to use P.N.: RH-217-U-Y-A manufactured by Holo/Or Ltd. 13B Einstein Street, Science Park, Ness Ziona, 7403617 Israel because this engineered diffuser outputs a round beam. The specifications for this diffuser are as follows:

As an alternative example, if it is desirable for the shape of the beam exiting the engineered diffuser465to be square, then it may desirable to use P.N.: HM-271-U-Y-A manufactured by Holo/Or Ltd. 136 Einstein Street, Science Park, Ness Ziona, 7403617 Israel because this engineered diffuser outputs a square beam. The specifications for this diffuser are as follows:

As mentioned above, the diffuser-lens assembly460may include an engineered diffuser465, such as a diffractive optical element (DOE), and a lens470downstream of the diffuser465. The lens470may be a 100 mm focal length lens producing a 1.17 mm spot, which is focused incident on the input face of the coherence mixing fiber475. The coherence mixing fiber475allows the typically coherent laser light entering the fiber to become out of phase due to the mixing fiber's relatively long length and large diameter, thereby emitting light portions of which are time delayed with respect to other portions. A photon of light that enters the fiber and follows the shortest path possible down the center of the fiber has a much shorter path length than a photon that enters the fiber at a steeper angle and continuously bounces off of the interior walls of this fiber. Due to the different angles of the photons entering the fiber and the length of the fiber, the coherence of the laser light is mixed and/or scrambled at the output end, thereby creating a resulting beam of light that is less coherent than that entering the mixing fiber. When this less coherent light is launched into the smaller delivery fibers the ability of the light to achieve constructive interference is greatly reduced. The coherence mixing fiber475may be a 1.5 mm core diameter by 1.5 meter long, fused silica rnultimode fiber. The light exiting the mixing fiber475is collimated using collimator480, which may include two focal length lenses485,490. For example, lens485may be a 75 mm focal length lens, and lens490may be a 25 mm focal length lens.

The pulse widths of the beam entering and/or exiting the diffuser-lens assembly460were measured using a pulse detector465, such as Thoriabs DET10A photo diode (Thorlabs, Newton, N.J.). The pulse detector465also triggered an oscilloscope for counting pulses during tissue ablation experiments. The beam exiting the diffuser-lens assembly460enters the delivery fiber510, and is measured by an energy detector495. An example of an energy detector495is a Genter Maestro energy meter (Gentec-EO, Lake Oswego, Oreg.). An example of a deliver fiber510includes a UV grade fused silica core and cladding with a polyimide buffer coating, wherein the fiber has a 1.1 to 1 core cladding ratio and a 0.22 numerical aperture (Polymicro Technologies, Phoenix, Ariz.). Although the delivery fiber510inFIG. 5is described as a single fiber, the delivery fiber510may alternatively be a bundle of fibers205in a laser catheter150as described in relationship toFIGS. 1, 2A, 2B, 3 and 4above.

Coherence Mixing Example

Using the ablation system400inFIG. 5, including the use of the coherence mixing method created by the incorporation of the coherence mixing fiber475into such system, energy output of up to 42 mJ corresponding to fluencies of 150 mJ/mm2at 20 Hz were consistently achieved through the 600 μm core diameter fiber. Coupling efficiencies from the laser output to the 600 μm optical fiber were approximately 30%. The 150 mJ/mm2out of the fiber reported in these results were limited by the 140 mJ laser output. This transmission testing was repeated 5 times with a duration of 5 minutes each run and resulted in 0 fiber failures. That is, the fiber did not break or become damaged due to light exceeding the damage threshold of the fused silica material with which fibers are constructed.

Referring toFIG. 6, there is shown an ablation system500of the present disclosure that includes a means for stretching the pulse width of the beam. By stretching the width of a pulse of the original laser beam and creating a resulting laser beam, the peak power of the resulting light pulse(s) can be reduced relative to the peak power of the original light pulse, while maintaining the overall energy contained in the original pulse. Also, by lowering the peak power of the original pulse, higher energy levels can be transmitted through the optical fibers. The means for stretching the pulse width of the beam includes the use of optical components to split one beam into two beams, transmit one of the split beams through an optical delay loop, and re-combine the split beams into a resulting beam.

Continuing to refer toFIG. 6, the ablation system500is similar to the ablation system400inFIG. 5in that the optical components upstream of the waveplate520inFIG. 6are the same as the optical components upstream of the diffuser-lens assembly460inFIG. 5. For the purpose of brevity, those optical components will not be discussed again with respect toFIG. 6. The ablation system500inFIG. 6includes a waveplate520between the shutter455and the beam sputter525. By rotating this waveplate455, the transmission and/or reflective characteristics of the split beams exiting the beam splitter525can be adjusted, such as the energy intensity of the split beams and the ratios of the split beams, thereby allowing modification of the height or amplitude of the pulses705and710inFIGS. 7A and 7Bsuch that the amplitudes of the pulses are the same or similar. Accordingly, the resulting pulse715has an effective width with a more relatively consistent and similar amplitude.

The means for stretching the pulse width of the beam may include a beam splitter525and a series of mirrors530,535,540,545. The series of mirrors is designed to create an optical path that forces the beam in the optical delay loop to travel a certain distance in order to create a predetermined time delay. For example, a 120 inch optical path length may create a predetermined time delay of about 10 nsec. A longer optical path length will create a longer time delay, and a shorter optical path length will create a shorter time delay. The present disclosure contemplates using other optical path lengths to produce time delays other than 10 nsec. One way of adjusting the optical path length and the time delay includes moving one or all of the mirrors530,535,540,545. Although all of the mirrors530,535,540,545may be fixed or moveable,FIG. 6illustrates an example of mirror535, which is capable of translating axially, thereby allowing for adjustment(s) of the length of the optical delay path and corresponding distance between the peaks of the pulses.

The optical delay loop begins with a beam splitter525, which divides the original beam entering the beam splitter525into two beams: one of the two beams travels through the optical delay loop; and the other of the two beams does not enter the delay loop and is directed to mirror550and collimator480. After the beam that travels through the delay loop travels there through, the beam sputter525reunites the beam that travels through the delay loop with the beam that did not enter the delay loop, thereby creating a resulting beam. And when the beam spatter525reunites these two spat beams, the resulting beam will comprise the same amount of energy as the original beam entering the beam splitter525, but the peak power of the resulting beam will be substantially reduced (e.g., less than half the peak power of the original beam). The peak power of the resulting beam is substantially reduced in comparison to the original beam entering the beam splitter525because the optical delay loop causes the beam that traveled through the delay loop to overlaps with the portion of the beam that originally did not enter the optical delay loop at a predetermined time, such that the peak energy levels of the two portions are offset by such predetermined time, thereby creating a resulting beam that appears to have a longer pulse width because the peak energy levels of the two split beams are adjacent one another and appear, in combination, to be a single peak for a longer duration of time.

Referring toFIG. 7A, there is depicted an energy signal emanating from the beam splitter525toward the mirror550in the ablation system depicted inFIG. 6. Assuming the beam splitter525is a 40/60 beam splitter, the beam splitter525receives the original beam from the waveplate520and splits the original beam into two beams, wherein one beam having about 40 percent of the energy originally entering the beam splitter525, does not travel through the optical delay loop and is directed to the mirror550, and the other split beam has about 60 percent of the energy originally entering the beam splitter525and travels through the optical delay loop. This energy signal705inFIG. 7Ais representative of the split beam that does not travel through the optical delay loop, and this beam has a pulse width of about 7.5 nanoseconds (nsec). Accordingly, the original beam entering the beam splitter525would have a peak power of about 2.5 times greater than that shown inFIG. 7A, but the pulse width of the original energy signal would still be about 7.5 nsec. As such the amount of energy produced by the signal inFIG. 7Ais about 40 percent of the amount of energy of the original signal entering the beam splitter525. Accordingly, 60 percent of the amount of energy entering the beam splitter525is in the split beam entering the time delay loop. Although a 40/60 beam splitter is discussed, the scope of the present disclosure includes other beam splitters having other ratios, such as 5/95, 10/90, 15/85, 20/80, 25/75, 30/70, 35/65, 45/55, 50/50, 55/45, 60/40, 65/35, 70/30, 75/25, 80/20, 85/15, 90/10, 95/5 and any other ratio(s). Also, the beam spatter receiving the original beam can spat the original beam into two beams, and one beam that travels through the optical delay loop can have any percentage of the energy originally entering the beam splitter, and the other split beam can have the remaining percentage of energy and not travel through the optical delay loop. Using other ratios of beam splitters will adjust the peak energy of the resulting signal.

Referring toFIG. 7B, there is shown a resulting energy signal emitted from the ablation system depicted inFIG. 6, wherein the resulting energy signal is a combination of the split beam that did not enter the time delay loop and has about 40 percent of the energy originally entering the beam splitter525and the split beam that entered the time delay loop which contains the remaining energy that traveled through the time delay loop. As shown inFIG. 7B, the first peak705correlates to the beam or pulse that did not travel through the optical delay loop, and the second peak710correlates to the beam or pulse that travels through the optical delay loop. As one of skill in the art can see, the two peaks have substantially the same height, which means that each pulse has substantially the same amount of energy, and when the two pulses are combined, the resulting signal has substantially the same amount of energy that enters the beam splitter525, but the peak energy of the resulting signal is reduced and spread over a longer duration715having an stretched puke width (15 ns) that is effectively twice as long as the pulse width (7.5 ns) entering the beam splitter, thereby minimizing potential damage to the delivery fiber(s)510. Although this example illustrates stretching the width of the original pulse to a pulse width in the resulting beam to twice as long, the present disclosure encompasses stretching the width of the original pulse to other lengths, such as any increment between 1 and 10.

Referring again toFIG. 6, the ablation system500is similar to the ablation system400inFIG. 5except the coherence mixing fiber475inFIG. 5is replaced with the means for stretching the puke width of the beam, and the ablation system500inFIG. 6also includes a waveplate520between the shutter455and the beam splitter525. The means for stretching the pulse width of the beam may include a beam splitter525and a series of mirrors530,535,540,545. The series of mirrors is designed to create a predetermined time delay of about 10 nsec over about a 120 inch optical path length. It may also be desirable for one or more of the mirrors, such as mirror535, to translate axially, thereby allowing for adjustment(s) of the length of the optical delay path and corresponding distance between the peaks of the pulses.

As discussed above, the engineered diffuser465assists in focusing the beam into the desired shape, such as round or square shape. The engineered diffuser465is also incorporated in the ablation system500ofFIG. 6such that the engineered diffuser465is located downstream of the means for stretching the pulse width of the beam. The combination of such means and the engineered diffuser465allows the ablation system500to output a resulting beam having increased symmetry and homogeneity in comparison to a resulting beam exiting the ablation system500without the engineered diffuser. As depicted inFIG. 8A, the energy density of a beam produced by an engineered diffuser465outputting a round beam is symmetrical and relatively homogeneous, and as depicted inFIG. 8B, the energy density of a beam produced by an engineered diffuser465outputting a square beam is symmetrical and relatively homogeneous, Although the delivery fiber510inFIG. 6may be a single fiber, the delivery fiber510may alternatively be a bundle of fibers205in a laser catheter150as described in relationship toFIGS. 1, 2A, 2B, 3 and 4above.

Pulse Width Stretching Example 1

Using the pulse stretching launch method described above with a 355 nm laser, energy outputs of up to 56 mJ at 20 Hz were achieved through single 600 μm fibers. This output energy corresponds to a fluence of 200 mJ/mm2. Coupling efficiencies from the laser output to the 600 μm optical fiber were in the 40% range. The fiber output energy achieved was limited by the 140 mJ laser output energy. This transmission testing was repeated 5 times with a duration of 6 minutes each run, and resulted in 0 fiber failures.

Pulse Width Stretching Example 2

Using the pulse stretching launch method described above with a 355 nm laser, 2.0 mm (97×100 μm core diameter fiber) multi-fiber catheters were tested in air at energies of 43.5 mJ corresponding to a fluence of 55 mJ/mm2. Coupling efficiencies from the laser output to the multi-fiber catheter were approximately 31%. The fiber output energy achieved was limited by the total energy available using this launch method. No fiber damage at the coupler, tip, or mid-shaft of the catheter was observed. This transmission testing was repeated 5 times with a duration of 5 minutes each run and resulted in 0 fiber failures. The lack of fiber damage that was observed in section 3.2 and absent using this launch method is thought to be due to the homogenized input beam profile that is achieved with the placement of the DOE previous to the fiber coupling lens.

Tissue Ablation Example

To perform tissue ablation comparisons of 355 nm laser light to 308 nm light, fresh porcine aorta tissue was used. The tissue was sent via overnight delivery the day of harvest. It was placed in a bag with saline and stored at 15° C. until use. All tissue was tested within 5 days of harvest to limit tissue degradation prior to testing. When comparative results are presented, samples were derived from the same tissue and the testing was performed on the same day.

The porcine aorta was trimmed to produce a flat tissue sample that was consistent in thickness. This sample was then pinned to a piece of cork sheet intimal surface up. The cork sheet had a through hole that the tissue spans. The cork and tissue sample were then placed in a petri dish and submerged in saline. The petri dish was then placed on a digital scale to set and monitor the downward force of the fiber. The fiber optic was held in a teeter-totter type balance that allowed fine adjustment of the downward force applied.

A shutter in the laser beam path previous to fiber coupling was opened to allow light into the delivery fiber. The tissue was monitored as the fiber penetrated through it. When the fiber exited through the back side of the tissue, the shutter was closed and the number of pulses used for penetration was recorded. The tissue was removed after testing and the thickness was measured in the location of the ablated holes using a dial thickness gauge. The penetration per pulse was then calculated and compared.

The tissue testing was performed using a 600 μm single fiber transmitting a fluence of 60 mJ/mm2and a pulse repetition rate of 20 Hz for 355 nm and 308 nm. Typically, 60 mJ/mm2fluence output represents the energy fluence setting used by physicians that are currently using the Spectranetics CV X excimer laser. The 20 Hz pulse repetition rate was chosen to fall within the specification of the 355 nm laser being tested. Testing was conducted with 4 different downward forces applied to the fiber optic. Ten full penetration samples were collected at each downward force setting for 355 nm and 308 nm. After testing the tissue samples were photographed at 50× magnification and fixed in a 10% formalin solution.

Tissue samples were sent out to an outside lab and processed for histopathology. Slide sections for each sample were stained with hematoxylin and eosin (H&E) for light microscopy evaluation and imaging.FIG. 9shows the comparative tissue penetration rates between 355 nm and 308 nm at different applied fiber forces using the method(s) described in the Tissue Ablation Example. The penetration of the 308 nm light was approximately 3 times faster with 1 gr of downward force and approximately 8 times faster penetration with 10 gr of downward force on the fiber. The appearance of the ablated holes is similar at 1 gr of force but smaller for 308 nm holes produced with 10 gr of downward force on the fiber. These results of testing were analyzed for penetration rates only.

During the testing, distal end fiber failures were observed 4 times out of the 40 samples during the 355 nm sample testing and 0 times out of the 40 samples during the 308 nm testing. It is believed that this fiber damage was a result of the higher peak powers of the short pulse width 355 nm laser light.

FIG. 10Ais an image of holes ablated in a porcine aorta with a single 600 micron optical fiber applying a downward force of about 5 grams and using 355 nm laser system similar to or the same as that illustrated inFIG. 6, wherein the fiber outputs about 60 mJ/mm2at 20 Hz.FIG. 10Bis an image of holes ablated in a porcine aorta with a single 600 micron optical fiber applying a downward force of about 5 grams and using 308 nm laser system, wherein the fiber outputs about 60 mJ/mm2at 20 Hz. The ablated holes inFIGS. 10A and 10Bhave similar appearance and show no visible charring when viewed at 50× magnification.

FIG. 11Ais an image of a histological cross section of the holes ablated in a porcine aorta with a single 600 micron optical fiber applying a downward force of about 5 grams and using 355 nm laser system similar to or the same as that illustrated inFIG. 6, wherein the fiber outputs about 60 mJ/mm2at 20 Hz.FIG. 11Bis an image of a histological cross section of the holes ablated in a porcine aorta with a single 600 micron optical fiber applying a downward force of about 5 grams and using 308 nm laser system, wherein the fiber outputs about 60 mJ/mm2at 20 Hz. A number of variations and modifications of the disclosure may be used. It would be possible to provide for some features of the disclosure without providing others.FIGS. 11A and 11Bshow that laser-produced holes were full thickness through the vessel wall with resulting localized tissue disruption and heat-generated tissue denaturation lining the defects. The fiber penetration was initiated from the intimal surface of the aorta sample.

Referring toFIG. 12, there is shown a further alternative ablation system600of the present disclosure. The ablation system600of is similar to the ablation system500inFIG. 6except that the means for stretching the pulse width of the beam inFIG. 12may include a beam splitter525and an optical coherence mixing fiber610of sufficient length to cause the split beam to travel there through and create the desired predetermined time delay in lieu of using a beam splitter525and a series of mirrors530,535,540,545as shown inFIG. 6. Continuing to refer toFIG. 12, it may be desirable to include a coupling lens605between the beam splitter525and the optical coherence mixing fiber610, and it may be desirable to include a collimator615that includes two optical lenses620,625to collimate the light as it re-enters the optical path, including the beam splitter. Incorporating the optical coherence mixing fiber610into the means for stretching the pulse width of the beam provides the ablation system with the advantages of reducing the peak energy of the original beam by spreading the energy over a longer duration and creating a more homogenized signal, thereby minimizing potential damage to the delivery fiber(s)510.