Tailored laser pulses for surgical applications

Abstract

To provide a laser system having a laser medium and a method for its controller.SOLUTION: A laser system includes a controller configured to generate a plurality of electrical pulses via a power supply. The plurality of electric pulses includes an electric pre-pulse and a plurality of excitation electric pulses. The electrical pre-pulse is configured to generate a first portion of optical energy with an optical pump, and the first portion of optical energy is configured to excite a laser medium to an energy level below a laser emission threshold of the laser medium. The plurality of excitation electric pulses is configured to generate a second portion of the optical energy by the optical pump, and the second portion of the optical energy is configured to excite the laser medium to energy level above the laser emission threshold of the laser medium to output a plurality of laser pulses.SELECTED DRAWING: Figure 4A

Description

[Technical field]

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 403,916, filed October 4, 2016, which is incorporated herein by reference in its entirety.

[0002] Various aspects of the present disclosure relate generally to laser systems and methods of using laser systems for medical applications. [Background technology]

[0003] In medical applications, laser energy is used for many procedures, non-limiting examples of which include incision, resection, dissection, vaporization, ablation, fragmentation, coagulation, hemostasis, modification, etc. of various body tissues. In some medical procedures, lasers having a wavelength of, for example, about 2100 nanometers (nm) (or 2.1 micrometers (μm)) can be used because energy at this wavelength is highly absorbed by water, which is a constituent of virtually all tissues.

[0004] Laser lithotripsy uses laser energy to break up stones within the urinary tract of a subject (e.g., a patient). In some applications, laser lithotripsy can be performed using a Holmium YAG (Ho:YAG) laser, which offers relatively high fragmentation efficiency for different types of stones. See Sandhu et al., Holmium:YAG Laser for Intracorporeal Lithotripsy, Medical Journal Armed Forces India, Vol. 63, No. 1, 2007. The Ho:YAG laser is a solid-state pulsed laser that emits light at 2100 nm. Although various commercially available models vary slightly, commercially available Ho:YAG lasers have pulse durations ranging from 200 to 1700 microseconds (μs), pulse energies of 0.2 to 8.0 Joules / pulse, frequencies between 3 and 100 Hz (single cavity resonators are typically 3-30 Hz), and average powers between 15 and 140 Watts (single cavity resonators are 15-50 W). Lithotripsy effect typically depends on the energy of the applied laser. Traditionally, laser energy is increased to increase efficiency (e.g., fragmentation efficiency). High energies may lead to rapid fragmentation, but they are believed to result in large stone fragments that may have to be extracted from the body using medical devices such as retrieval baskets. Lithotripsy using high energy lasers may also cause undesirable retropulsion effects of stone fragments. The disclosed systems and methods according to the present invention may remedy some of these and other deficiencies in known laser systems. However, the scope of the present disclosure is defined by the appended claims, and not by its ability to solve any particular problem. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Sandhu et al., "Holmium:YAG Laser for Intracellular Lithotripsy," Medical Journal Armed Forces India, Vol. 63, No. 1, 2007. Summary of the Invention

[0006] Disclosed examples according to the present invention relate, inter alia, to medical laser systems and methods of their use. Each of the examples disclosed herein may include one or more of the features described in connection with any of the other disclosed examples.

[0007] In one embodiment, a laser system is disclosed that includes a lasing medium and a controller configured to direct a plurality of time-spaced electrical pulses to a device that optically pumps the lasing medium, the lasing medium being configured to output quasi-continuous laser pulses in response to the optical pumping, the plurality of time-spaced electrical pulses including (a) a first electrical pulse and (b) a plurality of second electrical pulses following the first electrical pulse, the first pulse configured to excite the lasing medium to an energy level below a lasing threshold of the lasing medium, and the quasi-continuous laser pulses being output in response to the plurality of second electrical pulses.

[0008] Additionally or alternatively, embodiments of the system may include the following features: the lasing medium includes one of Ho:YAG, Tm:YAG, Tm:Ho:YAG, Er:YAG, Er:YLF, Nd:YAG, Tm-fiber laser, and CTH:YAG; each electrical pulse of the plurality of second electrical pulses has an electrical pulse duration of about 10-1000 μs; a spacing between adjacent electrical pulses of the plurality of second electrical pulses is between about 10-300 μs; and a laser pulse duration of the quasi-continuous laser pulse is about 10-300 μs. The duration may be between about 250 μs and 10 ms; the power of the quasi-continuous laser pulse may be between about 100 W and 1 KW; the quasi-continuous laser pulse has a continuous waveform; the quasi-continuous laser pulse includes a plurality of temporally spaced laser pulses having a frequency greater than or equal to about 1 kHz; and the first electrical pulse is configured to excite the lasing medium to an energy level greater than about 80% of a lasing threshold and less than the lasing threshold.

[0009] In another embodiment, a method of using a laser system having a lasing medium is disclosed. The method includes directing a plurality of temporally spaced electrical pulses to a device for optically pumping the lasing medium. The plurality of temporally spaced electrical pulses includes (a) a first electrical pulse and (b) a plurality of second electrical pulses following the first electrical pulse, the first electrical pulse configured to excite the lasing medium to an energy level below a lasing threshold of the lasing medium. The method further includes outputting quasi-continuous laser pulses from the lasing medium in response to the plurality of second electrical pulses.

[0010] Additionally or alternatively, embodiments of the method include: each electrical pulse of the plurality of second electrical pulses has an electrical pulse duration of about 10-1000 μs; a spacing between adjacent electrical pulses of the plurality of second electrical pulses is about 10-300 μs; a laser pulse duration of the quasi-continuous laser pulse is about 250 μs-10 ms; a power of the quasi-continuous laser pulse is about 100 W-1 KW; and the quasi-continuous laser pulse is: (a) a single laser pulse having a continuous waveform; and (b) a frequency of about 1 kHz or higher. the first electrical pulse is one of a plurality of temporally spaced laser pulses having a frequency greater than or equal to a lasing threshold; the first electrical pulse is configured to excite the lasing medium to an energy level greater than about 80% of a lasing threshold and less than a lasing threshold; and the lasing medium includes one of Ho:YAG, Tm:YAG, Tm:Ho:YAG, Er:YAG, Er:YLF, Nd:YAG, Tm-fiber laser, and CTH:YAG.

[0011] In another embodiment, a method of using a laser system having a lasing medium is disclosed. The method can include directing a plurality of temporally spaced electrical pulses to a device that optically pumps the lasing medium. The plurality of temporally spaced electrical pulses can include (a) a first electrical pulse configured to excite the lasing medium to an energy level below a lasing threshold of the lasing medium, and (b) a plurality of second electrical pulses following the first electrical pulse. A first pulse of the plurality of second electrical pulses can increase the energy level of the lasing medium above the lasing threshold. The method can also include outputting quasi-continuous laser pulses from the lasing medium in response to the plurality of second electrical pulses. The quasi-continuous laser pulse can be one of (a) a single laser pulse having a continuous waveform, or (b) a plurality of temporally spaced laser pulses having a frequency greater than or equal to about 1 kHz.

[0012] Additionally or alternatively, embodiments of the system can include one or more of the following features: each electrical pulse of the plurality of second electrical pulses can have an electrical pulse duration between about 10-1000 μs; an interval between adjacent electrical pulses of the plurality of second electrical pulses can be between about 10-300 μs; the quasi-continuous laser pulse can be a single laser pulse having a continuous waveform and can have a laser pulse duration between about 250 μs and 10 ms and a power between about 100 W and 1 KW; the first electrical pulse can be configured to excite the lasing medium to an energy level greater than about 80% of the lasing threshold and less than the lasing threshold; and the lasing medium can include one of Ho:YAG, Tm:YAG, Tm:Ho:YAG, Er:YAG, Er:YLF, Nd:YAG, Tm-fiber laser, and CTH:YAG.

[0013] Both the general description above and the detailed description which follows are merely exemplary and explanatory, and are not limitations of the claimed features. As used herein, the terms "substantially," "approximately," and "about" refer to a ±10 percent variation from the recited value, and the term "exemplary" is used herein in the sense of "example" rather than "ideal."

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, show exemplary embodiments of the present disclosure. These drawings, together with the description, contribute to explaining the principles of the present disclosure. Some of these drawings show components / elements that will be recognized by those skilled in the art. If detailed descriptions of such known components and elements are not necessary for understanding the present disclosure, they are not presented herein. Similarly, some components / elements that are known to those skilled in the art as being part of the illustrated embodiments, but are not necessary for explaining the present disclosure, are not shown in the drawings for clarity. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of an example laser system. [Figure 2A] 2 illustrates an example discrete laser pulse generated by the laser system of FIG. 1. [Figure 2B] 2 illustrates an example discrete laser pulse generated by the laser system of FIG. 1. [Diagram 3] FIG. 2 illustrates the relationship between fluorescence lifetime and optical pumping energy in an exemplary laser system. [Figure 4A] FIG. 2 illustrates an example quasi-continuous laser pulse generated by the laser system of FIG. 1. [Figure 4B] FIG. 2 illustrates another exemplary quasi-continuous laser pulse generated by the laser system of FIG. 1. [Diagram 5] FIG. 2 illustrates another exemplary quasi-continuous laser pulse generated by the laser system of FIG. 1. [Figure 6]2 illustrates tailored laser pulses produced by the laser system of FIG. 1. [Figure 7] 2 illustrates an example method of using the laser system of FIG. 1 in an example medical procedure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The disclosed embodiments of the present invention relate to a laser system used for any medical application. That is, the disclosed laser system of the present invention can have any type of laser medium (e.g., Ho:YAG, Tm:YAG (thulium doped YAG), CTH:YAG (chromium, thulium, holmium doped YAG), Tm:Ho:YAG (thulium and holmium doped YAG), Er:YAG (erbium doped YAG), Nd:YAG (neodymium doped YAG), Er:YLF (erbium doped yttrium lithium fluoride), Tm-fiber laser, etc.) that is optically pumped in any way (flash lamp, arc lamp, diode, etc.) and can be used for any medical application. However, for convenience, only the optically pumped laser used for lithotripsy procedures will be described below to highlight the features of the disclosure of the present invention. Reference will now be made to the exemplary embodiments disclosed in the present invention as shown in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts.

[0017] FIG. 1 is a schematic diagram of an exemplary laser system 100 disclosed by the present invention. The laser system 100 is suitable for generating and delivering pulses of laser radiation directly or through a conventional laser delivery system (e.g., a flexible optical fiber 12) to a target site 10 within a subject's body (e.g., a stone in the subject's urinary tract). The laser system 100 includes an oscillator 20 configured to generate and deliver a laser beam in the form of laser pulses 60 to the target site 10 through the optical fiber 12. The oscillator 20 includes a solid-state lasing medium 22 including one or more lasing ions (e.g., Ho, Cr, Th, Er, etc.) doped at various concentrations in a host material (e.g., YAG, etc.). In some embodiments, the solid-state lasing medium 22 can have a relatively long emission and fluorescence lifetime. As known to those skilled in the art, the fluorescence lifetime is the time scale that electrons of the lasing medium 22 in an excited state spend before returning to a ground state by emitting a photon.

[0018] The oscillator 20 may include an optical pump 24 for optically exciting the lasing medium 22 to generate a laser beam. The optical pump 24 may include any known type of device used to optically excite the lasing medium 22 (e.g., a flash lamp, an arc lamp, an electrically pumped LED, a laser diode, a diode-pumped laser, a solid-state crystal or fiber laser, etc.). The optical pump 24 may be powered by a power supply 30 that includes components for operating the optical pump 24. These components may include, among others, a capacitor for energy storage and release, an inductor for pulse shaping, and a trigger circuit for ionizing the optical pump 24.

[0019] The power supply 30 can be configured to deliver electrical pulses from the capacitor to activate the optical pump 24. The pump chamber 26 contains both the lasing medium 22 and the optical pump 24 and allows optical radiation to travel from the optical pump 24 to the lasing medium 22. The pump chamber 26 can also allow for efficient cooling of both the lasing medium 22 and the optical pump 24. The laser oscillator 20 can include a housing to which the pump chamber 26, the total internal reflection optics 28, and the partial internal reflection optics 32 are attached. Both the total internal reflection optics 28 and the partial internal reflection optics 32 can include one or more optical components (lenses, mirrors, etc.) of various physical shapes and can be coated for reflection and / or transmission of various wavelengths of radiation. In some embodiments, these optics 28, 32 can be positioned on adjustable mounts that allow these components to be centered on the path of the laser beam traveling through the solid-state lasing medium 22.

[0020] The cooling system 40 can provide a coolant for cooling the heat generating components of the laser system 100. A liquid or gas coolant can be recirculated through the pump chamber 26 in a closed loop to cool the heat generating components of the oscillator 20. In some embodiments, the cooling system 40 can be air cooled. In some embodiments, other components of the laser system 100 (e.g., the power supply 30) can also be cooled by the coolant of the cooling system 40. It is also contemplated that in some embodiments, the cooling system 40 can be used to heat components of the oscillator 20.

[0021] The operation of the laser system 100 may be controlled by a controller 50. As is known in the art, the controller 50 may include a central processing unit (CPU) and other components that facilitate control of the laser system 100 (e.g., power supply 30, cooling system 40, oscillator 20, etc.) based on user input and / or feedback from sensors / detectors monitoring the performance of the laser system 100. For example, based on user input, the controller 50 may control the power supply 30 to generate electrical pulses of desired characteristics (amplitude, frequency, pulse duration, etc.) to operate the optical pump 24. Similarly, based on the measured temperature of the oscillator 20, the controller 50 may control the operation of the cooling system 40. The functionality of the controller 50 of a laser system is known in the art and will not be further described herein.

[0022] During operation of the laser system 100, the controller 50 controls the power supply 30 to direct a current / voltage waveform or electrical pulse having desired characteristics (amplitude, duration, magnitude, etc.) to the optical pump 24. The resulting optical energy generated by the optical pump 24 is coupled into the lasing medium 22. For optimal coupling, the optical pump 24 may be positioned around and in close contact with the lasing medium 22. In some embodiments, the coupling of the optical energy into the lasing medium 22 may be improved by reflection from the inner surface of the pump chamber 26. The optical energy from the optical pump 24 raises the energy level of the electrons in the lasing medium 22 to achieve population inversion. Population inversion occurs when more of the electrons of the lasing medium 22 are in their excited state (i.e., a higher energy state) than their ground state (i.e., a normal or lower energy state). With population inversion achieved, optical radiation of one or more wavelengths passes through the lasing medium 22 multiple times and is reflected from both the total reflection optics 28 and the partial reflection optics 32. When the electron excitation level reaches a threshold (called the lasing threshold or laser threshold in laser physics), a laser pulse 60 is generated and emitted along axis 34 of oscillator 20 .

[0023] A portion of the emitted laser pulse 60 may be sampled by the photodetector 36 to facilitate monitoring and control of the laser system 100. For example, the controller 50 may use the signal from the photodetector 36 (representing the emitted laser beam) to monitor and control the operation of the oscillator 20, the power supply 30, the cooling system 40, and other components of the laser system 100. The emitted laser pulse 60 may then be guided through one or more optical coupling elements 38 to condition a subsequent ejection pulse for injection into the proximal end of the optical fiber 12. The laser pulse 60 may then be transmitted through the optical fiber 12 to its distal end, which is positioned in contact with (or in close proximity to) a stone (not shown) at the target site 10. At the target site 10, the impacting laser pulse 60 may fragment the stone.

[0024] The laser system 100 of FIG. 1 may also include additional components (e.g., controllers, mirrors, focusing elements, beam blocking devices, Q-switching elements, or mode-locking elements, etc.) that are known to those skilled in the art and are not shown in FIG. 1 or described herein. For example, in some embodiments, the laser system 100 may further be controlled using reflected radiation from the stone (or re-scattered, re-emitted, wavelength-shifted radiation, etc., from the stone material) transmitted back through the optical fiber 12 to its proximal end. Additionally, in some embodiments, a visible aiming beam (e.g., a low power semiconductor diode laser, a Helium Neon (HeNe) laser, etc.) may be provided to aid in focusing the emitted laser pulses 60 at the target site 10.

[0025] The characteristics of the emitted laser pulse 60 (energy, pulse width, power, frequency, etc.) may depend on the characteristics of the optical pulse generated by the optical pump 24. These optical pulse characteristics may depend on the electrical pulses directed to the optical pump 24 from the power supply 30. Figures 2A and 2B are simplified diagrams showing an example relationship between the electrical pulses to the optical pump 24 and the resulting laser pulse 60 from the oscillator 20 in a standard operating mode. In these figures, the upper part shows the electrical pulses directed to the optical pump 24 and the lower part shows the resulting laser pulse 60. Figure 2A shows the case where a relatively short electrical pulse is directed to the optical pump 24, and Figure 2B shows the case where a relatively long electrical pulse is directed to the optical pump 24.

[0026] Although the electrical pulses in Figures 2A and 2B are shown as rectangular pulses, this is merely a simplification. In reality, these pulses may be more rounded due to losses in the components. In contrast to such typical electrical pulses, the corresponding laser pulses 60 (Figures 2A and 2B) have a characteristic shark fin shape. That is, these laser pulses 60 have a high initial peak followed by a rapid drop. The area under the curve in Figures 2A and 2B indicates the energy of the laser pulse 60. As can be seen in both Figures 2A and 2B, there is a finite time delay (t delay ) is a time delay related to the time it takes for the lasing medium 22 to reach the lasing threshold. delay The energy of the electrical pulse in is used to raise the excitation level of electrons in the lasing medium 22 to a lasing threshold. When this threshold is reached or exceeded, a laser pulse 60 is generated. The time delay can be a function of the energy of the electrical pulse and the laser pulse 60.

[0027] Moreover, as can be seen in both Figures 2A and 2B, the emitted laser pulse 60 is shorter (in time scale) than the electrical pulse that generates it. For example, in Figure 2A, the electrical pulse has a duration of about 500 μs, and the laser pulse 60 generated from this electrical pulse is only about 370 μs, and in Figure 2B, the electrical pulse has a duration of about 1300 μs, but the resulting laser pulse 60 has a duration of only about 900 μs. This difference in duration is the result of energy losses occurring in the oscillator 20, as well as due to optical pumping and reduced fluorescence lifetime due to thermal effects. Moreover, as can be seen by comparing Figures 2A and 2B, the increase in energy (area under the laser pulse curve) generated from the longer electrical pulse is not significant due to the rapidly decaying shape of the laser pulse curve.

[0028] Conventionally, to increase the energy of a laser pulse, the power (or magnitude) of the electrical pulse (or pumping energy) is increased. Increasing the power of the electrical pulse (and thus the optical pumping energy) increases the magnitude of the initial peak of the corresponding laser pulse. However, since the higher magnitude initial peak only exists for a short period of time, the total energy of the pulse 60 may not be substantially increased. Furthermore, it is known that the fluorescence lifetime of a lasing medium may be strongly dependent on the optical pumping energy. FIG. 3 shows the fluorescence lifetime of a CTH:YAG lasing medium as a function of optical pumping energy density. As can be seen from FIG. 3, when the lasing medium 22 is pumped at a low energy level, the fluorescence lifetime of the lasing medium 22 is substantially longer than when it is pumped at a high energy level. For example, when the optical pumping energy density is about 30 J / cm 3 to about 300 J / cm 3 When the laser power is increased to 100 J / cm, the fluorescence lifetime of the laser medium decreases from about 6 milliseconds (ms) to about 2 ms. Conventional laser systems provide about 100-300 J / cm for lithotripsy applications. 3 An optical pumping energy of 1000 .mu.m is used.

[0029] Additionally, due to the higher magnitude initial peak resulting from the high power electrical pulse, the energy of the laser pulse 60 may, at least momentarily, exceed the desired value. This momentary increase in laser energy may damage the optical components of the laser system 100 and may result in undesirable effects such as retropulsion and large stone fragments (which may have to be removed using additional medical devices such as retrieval baskets).

[0030] For some lithotripsy applications (e.g., "stone dusting" where small fragments of a stone are chipped off and removed by suction), it may be desirable to increase the energy of the laser pulse 60 without producing a sharp energy spike at the initial peak region of the pulse. Contrary to conventional wisdom, in some embodiments of the present disclosure, the energy of the laser pulse is increased by increasing the duration of the laser pulse and lowering the pumping energy (i.e., the power of the electrical pulse) that generates the laser pulse. For example, in some embodiments, the controller 50 may increase the energy of the laser pulse 60 by approximately 50 J / cm (to reduce the power of the emitted laser pulse 60). 3 4. Controlling the energy of the electrical pulse to be lower than 1000 Hz increases the duration (and therefore the amount of energy) of the emitted laser pulse 60 without a concomitant increase in the magnitude of the initial peak.

[0031] FIG. 4A is a simplified diagram illustrating the relationship between electrical pulses and the resulting laser pulse in one embodiment of the present disclosure. In this embodiment, multiple time-spaced electrical pulses (labeled A, B, C, D) are directed from the power supply 30 to the optical pump 24 such that the laser pulse generated from these time-spaced electrical pulses is a quasi-continuous waveform (quasi-continuous laser pulse 60'). With reference to FIG. 4A, in some embodiments, the initial electrical pulse to the optical pump 24 can be a pre-pulse (A) configured to raise the energy level of the lasing medium 22 to a value close to but just below the lasing threshold (e.g., to about 80-99% of the lasing threshold). Because the excitation caused by pre-pulse A does not reach the lasing threshold, pre-pulse A does not result in the emission of a laser pulse 60. However, at time t 1 At the end of pre-pulse A, the electrons in the lasing medium 22 are ready to emit radiation in the form of a laser pulse 60 upon the further application of a small amount of energy. Three successive electrical pulses (B, C, D) are then applied to the optical pump 24 with a short interval between them to initiate a quasi-continuous laser pulse 60' from the oscillator 20. In general, the pulses A, B, C, D can be spaced such that an electrical pulse is within the fluorescence lifetime of the immediately preceding pulse (i.e., pulse B is within the fluorescence lifetime of pulse A, pulse C is within the fluorescence lifetime of pulse B, etc.).

[0032] In general, the shape of the quasi-continuous laser pulse 60' depends on the characteristics of the laser system 100 (e.g., power, spacing, duration of the electrical pulses, material of the laser medium, etc.). In some embodiments, as shown in FIG. 4A, the quasi-continuous laser pulse 60' generated from the spaced apart electrical pulses A, B, C, D can be a continuous waveform with an extended duration Eμs. As used herein, a laser pulse with a continuous waveform is a laser pulse whose magnitude can vary from any maximum value to any non-zero minimum value during the duration of the pulse. That is, the continuous waveform has a magnitude of zero only at its ends. In the embodiment of FIG. 4A, the quasi-continuous laser pulse 60' is generated by integrating (or combining) the individual laser pulses 60 generated by the individual electrical pulses B, C, and D. In some embodiments, each electrical pulse of a set of spaced apart electrical pulses may not be integrated to generate the quasi-continuous laser pulse 60'. For example, in some embodiments, the quasi-continuous laser pulse 60' can be generated by integrating only the laser pulses generated by the electrical pulses B and C. If the pulse duration of the laser pulses generated by the individual electrical pulses (e.g., B and C) is 250 μs, the duration of the quasi-continuous laser pulse 60' can be greater than 250 μs and less than 500 μs (e.g., if generated by combining the laser pulses from two electrical pulses).

[0033] As shown in FIG. 4A, after the pre-pulse A, a small amount of energy is further applied to the already prepared laser medium 22, and at time t 2The beginning of the quasi-continuous laser pulse 60' is seen at . The durations of the electrical pulses (a, b, c, d) and the intervals between them (ab, bc, cd) may depend on the characteristics of the laser system 100 and the power of the electrical pulses. In general, the duration a of pre-pulse A should be such that the lasing medium 22 reaches an excitation level of about 80-99% (but less than 100%) of the laser emission threshold at the end of pre-pulse A. And the intervals ab between pulses A and B, and between B and C should be such that the energy dissipation from the prepared lasing medium 22 is minimized. As is known in the art, in the absence of population inversion, a significant amount of energy remains stored in the lasing medium 22 at the end of each laser pulse (e.g., laser pulse 60 resulting from electrical pulse B). If the interval bc between electrical pulses B and C is too large (but still within the fluorescence lifetime), this stored energy will be wasted in sub-threshold radiative and non-radiative decay before being pumped by electrical pulse C. However, if pulse C begins immediately after electrical pulse B, most of the stored energy is available for generating the next laser pulse 60, thereby reducing the pumping energy required to achieve population inversion.

[0034] In different embodiments of the present disclosure, the durations a, b, c, d and the intervals ab, bc, cd between the electrical pulses A, B, C, D can vary between about 10-1000 μs, and the resulting quasi-continuous laser pulse 60′ can be between about 250 μs and 10 milliseconds (ms). In some embodiments, one or more of the durations a, b, c, d can be between about 10-200 μs (or between 10-300 μs), and one or more of the intervals ab, bc, cd can be between about 10-100 μs (or between 10-200 μs). 4, the duration a of pre-pulse A can be about 30-300 μs, the interval ab between pulses A and B can be about 10-100 μs, the duration of pulses B, C, and D can be about 10-500 μs, the intervals bc and cd between pulses B, C, and D can be about 10-100 μs, and the resulting duration E of the resulting quasi-continuous laser pulse 60' can be about 600-1500 μs. In some embodiments, the power of the resulting quasi-continuous laser pulse 60' can be about 100 W to 1 KW.

[0035] It should be noted that the shape shown in FIG. 4A, a quasi-continuous laser pulse 60' with a smooth continuous waveform, is merely exemplary. FIG. 4B shows another exemplary quasi-continuous laser pulse 60' with a continuous waveform that originates from multiple electrical pulses spaced apart in time. As shown in FIG. 4B, the magnitude of the quasi-continuous laser pulse 60' may vary from an average maximum of about 5 arbitrary units (au) (e.g., Joules) to a minimum average value of about 1.25 au (i.e., 25% of the maximum) within a duration of Eμs. However, the waveform has zero magnitude only at its two ends and has non-zero magnitudes throughout its duration. It should be noted that while the magnitude of the continuous waveform between the two ends is always non-zero, the maximum and minimum values ​​shown in FIG. 4B are merely exemplary. In general, the minimum value is any percentage (e.g., 10%) of the maximum value.

[0036] In FIG. 4A and FIG. 4B, the laser pulses 60 generated from each electric pulse merge with each other to generate a quasi-continuous laser pulse 60' in the form of a continuous waveform. However, generating a power laser pulse in the form of a continuous waveform is not limited. In some embodiments, for example, when a laser medium 22 (e.g., Er:YAG, Nd:YAG, Er:YLF, etc.) having a faster energy transfer process compared to CTH:YAG is used, the laser pulses 60 generated from the successive input electric pulses may be separated in time. For example, referring to FIG. 4A, when the intervals bc and cd between the electric pulses B, C, and D are less than or equal to about 100 μs, the oscillator 20 can output a quasi-continuous laser pulse 60' in the form of a continuous waveform. However, when the electric pulses B, C, and D are separated by more than 100 μs, the oscillator 20 may output a quasi-continuous laser pulse 60' including separate laser pulses 60 separated in time (i.e., not forming a continuous waveform as a whole). However, because the frequency (and thus the repetition rate) of these spaced apart laser pulses 60 exceeds about 1 kHz (at room temperature), the resulting spaced apart laser pulses 60 resemble, and may in fact be, a substantially continuous laser pulse. Thus, in this disclosure, the term quasi-continuous laser pulse is used to collectively refer to both (a) multiple laser pulses 60 that are combined to form a laser pulse having a continuous waveform (e.g., similar to that shown in Figures 4A and 4B), and (b) multiple laser pulses 60 that are spaced apart in time from one another and have a frequency that exceeds about 1 kHz.

[0037] 5 is a simplified diagram showing another exemplary quasi-continuous laser pulse 60' in continuous waveform form generated from multiple electrical pulses spaced apart in time. In the embodiment of FIG. 5 (as in the embodiment of FIGS. 4A and 4B), an initial pre-pulse A excites the lasing medium 22 to just below its lasing threshold. That is, at the end of pre-pulse A, a laser pulse 60 has not yet been generated from the oscillator 20, but application of a small amount of additional energy will cause a laser pulse to be emitted. Following pre-pulse A, the optical pump 24 is pumped using a relatively long sequence (e.g., about 50 pulses) of temporally spaced electrical pulses B, C, D, etc., each of which produces about 50 J / cm. 3 The pulses have an energy density of less than 100 ms and a duration of about 50 μs, with adjacent pulses spaced apart by only about 50 μs. This sequence of temporally spaced electrical pulses used to drive the optical pump 24 may be referred to herein as digitized electrical pulses or digital pumping. As a result of such optical pumping, a quasi-continuous laser pulse 60' (comprising successive laser pulses 60 integrated to form a continuous waveform) having a relatively long duration (e.g., about 4300 μs) is generated from the oscillator 20. It should be noted that this laser pulse duration is merely exemplary. It is believed possible to vary the power laser pulse duration to any value between about 250 μs and 10 ms using digitized electrical pulses with different characteristics (number, duration, spacing, etc.).

[0038] In general, the magnitude of the electrical pulse can be configured to generate a laser pulse 60 having any magnitude. However, as discussed above, there are several advantages to reducing the pump energy and the resulting laser power (increased fluorescence lifetime, reduced backpulsation, etc.). Thus, as shown in FIG. 5, in some embodiments, the energy density of the electrical pulse can be set to 50 J / cm2. 35A , and can generate a quasi-continuous laser pulse 60′ having a smaller magnitude (e.g., varying from about 0.5 to 0.25 au) and a longer duration (e.g., about 4.3 milliseconds (ms)) compared to laser pulse 60 of FIG. 2A. Although the magnitude of quasi-continuous laser pulse 60′ (of FIG. 5A ) is lower than laser pulse 60 (of FIG. 2A ), its substantially longer duration generates a total energy amount of quasi-continuous laser pulse 60 that is greater than or equal to the total energy amount of laser pulse 60.

[0039] For example, to generate a laser beam with an energy of 500 mJ, a conventional CTH:YAG laser pumps the laser medium at approximately 100-500 J / cm per pulse. 3 to generate laser pulses having peak powers of about 2.5-1.0 kW and durations of about 200-500 μs. In contrast, to generate a laser beam having the same energy (i.e., 500 mJ), the exemplary laser system disclosed herein pumps the lasing medium to about 2-50 J / cm 3 The laser pulse 60' may be pumped multiple times (e.g., 30-100 times) as described above with an energy of about 100 Hz to generate a quasi-continuous laser pulse 60' having a duration of about 4.5 ms and a peak power of about 70-150 W (e.g., 100-130 W). This smaller magnitude and longer duration laser pulse 60' may increase the efficiency of the laser system 100 by minimizing undesirable effects such as retropulsion. The smaller magnitude and longer duration quasi-continuous laser pulse 60' may be used for medical applications such as stone dust removal, where it is desirable to remove dust-sized particles of a stone without breaking the stone into multiple larger sized pieces.

[0040] To compare the performance of the quasi-continuous laser pulse 60' (generated by the exemplary laser system 100 of the present disclosure) with the conventional laser pulse 60 (generated by a conventional laser system) in the context of a lithoablation application, the cavitation dynamics of the two pulses in water were studied with a high-speed camera. Both laser systems were set so that the energy of the laser pulse generated by each laser system was substantially the same (about 1000-1300 mJ). Although both laser pulses have the same energy, the quasi-continuous laser pulse 60' has a duration (generated from successive spaced electrical pulses) of about 4100 μs and the conventional laser pulse 60 has a duration of about 310 μs. Significant differences were observed in these studies. The cavitation bubbles generated by the conventional laser pulse 60 grew in size rapidly, reaching their maximum size near the end of the pulse, while the bubbles of the quasi-continuous laser pulse 60' grew more slowly, only reaching about 40% of the size of the bubbles of the conventional pulse. As a result, the collapse of the quasi-continuous laser pulsed bubbles did not emit as strong acoustic shock waves as the collapse of the conventionally pulsed bubbles, and therefore the backward thrust effect on the stone (to which each laser pulse is applied) is expected to be significantly reduced for the quasi-continuous laser pulse 60' compared to the conventional laser pulse 60.

[0041] Furthermore, a unique observed feature of the cavitation dynamics of the quasi-continuous laser pulse 60' was a long-lived (~2.6 ms) permanent cavitation channel that formed after the initial turbulence associated with bubble formation, collapse, and recoil subsidence. In this channel, the water (water vapor) density and corresponding absorption of the laser pulse energy is significantly reduced. As a result, the controlled layer-by-layer ablation of the stone material (or the "solid dusting" effect) is expected to be significantly improved.

[0042] 4A and 5 show pre-pulse A consisting of a single electrical pulse, but this is not limiting. In some embodiments, pre-pulse A may also include multiple shorter duration pre-pulses (e.g., similar to electrical pulses B, C, etc.), each of which increases the excitation level of the lasing medium 22 in a stepwise manner to a value just below the lasing threshold. Furthermore, the magnitudes of electrical pulses A, B, C, D are shown to be the same in FIG. 4A and FIG. 5, but this is also merely exemplary. In general, these input electrical pulses may have the same magnitude or different magnitudes. As mentioned above, the power of pre-pulse A may be adapted to increase the energy of the lasing medium 22 to a value just below the lasing threshold of the lasing medium 22. In some embodiments, the magnitude of the immediately following electrical pulse (i.e., B) may be smaller than pre-pulse A (e.g., to increase the energy of the lasing medium 22 to a value just above the lasing threshold to initiate laser emission).

[0043] In the embodiment of FIG. 5, the duration of the electrical pulses (B, C, D, etc.) and their spacing are all constant. Such an electrical pulse profile can produce a quasi-continuous laser pulse 60′ having a profile including a uniform repeating pattern as shown in FIG. 5. However, the constant duration and spacing of the electrical pulses is not a requirement. In some embodiments, one or all of the duration of the electrical pulses, the spacing between the electrical pulses, and the magnitude of the electrical pulses can be modified to tailor the profile of the resulting laser pulse 60′ as desired. That is, the pattern of optical pumping of the lasing medium 22 can be configured to adjust (increase, decrease, etc.) the pulse width and shape of the resulting laser beam.

[0044] FIG. 6 is a simplified diagram illustrating an example tailored laser pulse 60' profile resulting from a preselected pattern of electrical pulses. As in the previous embodiment, pre-pulse A can raise the excitation level of the lasing medium 22 to a value just below the lasing threshold (i.e., to about 80-99% of the lasing threshold). Pre-pulse A can be followed by multiple electrical pulses spaced in time to raise the excitation level of the lasing medium 22 slightly above the lasing threshold to initiate emission of the laser pulse 60. The spacing between electrical pulses in the different regions, and the duration of the electrical pulses, can be selected to produce a laser pulse 60' contour having any desired shape. For example, a sequence of seemingly digital electrical pulses directed to the optical pump 24 can be such that the spacing between pulses (and / or the duration of the pulses) in one region of the sequence is different from that in another region, generating differences in the shapes of the resulting waveforms corresponding to the two regions. Thus, by adjusting the pattern of electrical pulses used to pump the lasing medium 22, power laser pulses can be controlled to have any desired shape and contour.

[0045] In some embodiments, the control system (e.g., controller 50) of the laser system 100 can determine an appropriate pattern of electrical pulses based on a user's desired laser pulse profile and direct these electrical pulses to the optical pump 24. The oscillator 20 of the laser system 100 can then output quasi-continuous laser pulses 60' having a profile similar to the user's desired pulse profile. For example, the user can input (using a keypad, screen, or other input device) a desired laser pulse profile (that the user knows to be particularly suitable for a medical procedure based on prior knowledge, experience, etc.) into the control system. Furthermore, based on known characteristics of the laser system 100, the control system can determine a pattern of electrical pulses that will generate the user's desired power. Alternatively or additionally, in some embodiments, the user can determine the pattern of electrical pulses to generate a desired laser pulse profile. In general, any characteristic of the electrical pulses (duty cycle, frequency, pulse duration, power, etc.) can be varied in different regions to generate any tailored laser pulse profile.

[0046] FIG. 7 is a flow diagram illustrating an exemplary method of using the laser system 100 of FIG. 1 in a laser lithotripsy procedure. A subject is prepared for a medical procedure and an appropriate catheter (endoscope, ureteroscope, etc.) is inserted into the subject's body through an orifice with the optical fiber 12 extending therethrough (step 110). The catheter is then manipulated within the body to position the distal end of the optical fiber 12 proximate to the stone (step 120). A user then inputs electrical pulse characteristics (duration, magnitude, spacing, pattern, etc.) into the controller 50, which generates quasi-continuous laser pulses 60' having a desired profile, duration, and magnitude (step 130). These characteristics can be selected by the user based on prior experience and knowledge of the laser system 100. The generated quasi-continuous laser pulses 60' are then used to separate small pieces from the stone (step 140).

[0047] While the principles of the present disclosure have been described herein with reference to illustrative examples for specific applications, it should be understood that the present disclosure is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize that additional modifications, applications, embodiments, and equivalent substitutions are all within the scope of the features described herein. Accordingly, the claimed features are not to be construed as limited by the foregoing description.

Claims

1. 1. A laser system comprising: a power source configured to generate a plurality of electrical pulses; an optical pump configured to generate optical energy in response to the plurality of electrical pulses; a lasing medium optically coupled to the optical pump and configured to output a laser pulse in response to the optical energy; a controller connected to the power source and configured to cause the power source to generate the plurality of electrical pulses; 11. A laser system comprising: a laser device including: a laser medium having a laser beam splitter and a laser output stage; a laser output stage configured to split a laser beam splitter into a laser beam splitter and a laser output stage configured to output ...

2. 10. The laser system of claim 1, wherein the multiple laser pulses overlap to form a quasi-continuous laser pulse.

3. 3. The laser system of claim 2, wherein the quasi-continuous laser pulse has a pulse width of 250 μs to 10 ms.

4. 3. The laser system of claim 2, wherein the quasi-continuous laser pulse power is between 100W and 1KW.

5. 2. The laser system of claim 1, wherein each of the plurality of electrical pulses has a pulse width of 10 to 1000 μs.

6. 6. The laser system of claim 5, wherein each electrical pulse of the plurality of electrical pulses has an equal pulse width.

7. 10. The laser system of claim 1, wherein a pulse delay between adjacent ones of said plurality of electrical pulses is between 10 and 1000 μs.

8. 8. The laser system of claim 7, wherein the pulse delays between adjacent electrical pulses are equal.

9. 10. The laser system of claim 1 , wherein the plurality of laser pulses have a frequency of 1 kHz or greater.

10. 10. The laser system of claim 1, wherein the lasing medium comprises one of Ho:YAG, Tm:YAG, Tm:Ho:YAG, Er:YAG, Er:YLF, Nd:YAG, Tm-fiber laser, and CTH:YAG.

11. 1. A laser system comprising: a power source configured to generate a plurality of electrical pulses; An oscillator; a cooling subsystem configured to cool the oscillator; a controller connected to the power source and configured to cause the power source to generate the plurality of electrical pulses; the oscillator includes an optical pump configured to generate optical energy in response to the plurality of electrical pulses and a lasing medium configured to receive the optical energy; 11. A laser system comprising: a laser device including: a laser medium having a laser beam splitter and a laser output stage; a laser output stage configured to split a laser beam splitter into a laser beam splitter and a laser output stage configured to output ...

12. 12. The laser system of claim 11, wherein the multiple laser pulses overlap to form a quasi-continuous laser pulse, and the pulse width of the quasi-continuous laser pulse is between 250 μs and 10 ms.

13. 12. The laser system of claim 11, wherein the multiple laser pulses overlap to form a quasi-continuous laser pulse, and the power of the quasi-continuous laser pulse is between 100W and 1KW.

14. The pulse width of each of the plurality of electrical pulses is 10 to 1000 μs; or a pulse delay between adjacent electrical pulses of the plurality of electrical pulses is between 10 and 1000 μs; or 12. The laser system of claim 11, wherein a pulse width of each electrical pulse of the plurality of electrical pulses is between 10 and 1000 μs and a pulse delay between adjacent electrical pulses of the plurality of electrical pulses is between 10 and 1000 μs.

15. The pulse width of each of the plurality of electrical pulses is equal; or the pulse delays between adjacent electrical pulses of the plurality of electrical pulses are equal; or 12. The laser system of claim 11, wherein the pulse width of each electrical pulse of the plurality of electrical pulses is equal and the pulse delay between adjacent electrical pulses of the plurality of electrical pulses is equal.

16. 12. The laser system of claim 11, wherein the lasing medium comprises one of Ho:YAG, Tm:YAG, Tm:Ho:YAG, Er:YAG, Er:YLF, Nd:YAG, Tm-fiber laser, and CTH:YAG.

17. 12. The laser system of claim 11 , wherein the plurality of electrical pulses includes a first set of electrical pulses and a second set of electrical pulses, and at least one of (i) a pulse width, (ii) a pulse delay, and (iii) a pulse amplitude of the first set of electrical pulses is different from a pulse width, a pulse delay, and a pulse amplitude of the second set of electrical pulses.

18. 1. A method for a controller of a laser system including a power supply configured to generate a plurality of electrical pulses, an optical pump configured to generate optical energy in response to the plurality of electrical pulses, and a lasing medium configured to receive the optical energy, comprising: transmitting a control signal to the power source configured to cause the power source to generate a plurality of electrical pulses; 13. The method of claim 12, wherein the plurality of electrical pulses includes one or more electrical pre-pulses and a plurality of excitation electrical pulses, the electrical pre-pulses configured to cause the optical pump to generate a first portion of the optical energy, the first portion of the optical energy configured to excite the lasing medium to an energy level below a lasing threshold of the lasing medium, and the excitation electrical pulses configured to cause the optical pump to generate a second portion of the optical energy, the second portion of the optical energy configured to excite the lasing medium above a lasing threshold of the lasing medium, and outputting a plurality of laser pulses.

19. The pulse width of each of the plurality of electrical pulses is 10 to 1000 μs; or a pulse delay between adjacent electrical pulses of the plurality of electrical pulses is between 10 and 1000 μs; or 20. The method of claim 18, wherein a pulse width of each electrical pulse of the plurality of electrical pulses is between 10 and 1000 μs and a pulse delay between adjacent electrical pulses of the plurality of electrical pulses is between 10 and 1000 μs.

20. The pulse width of each of the plurality of electrical pulses is equal; or the pulse delays between adjacent electrical pulses of the plurality of electrical pulses are equal; or 20. The method of claim 18, wherein the pulse width of each electrical pulse of the plurality of electrical pulses is equal and the pulse delay between adjacent electrical pulses of the plurality of electrical pulses is equal.

Images