JP2002094147A - Pulse wave co2 laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To vary the tilt angle of a mirror from the outside of a housing. SOLUTION: In a CO2 slab wavelength laser 10, an electrode is dimensioned to the form of guiding light inside a plane perpendicular to a reflection surface and the light parallel to the reflection surface is not constrained other than by resonator mirrors 30 and 32. A resonator structure is provided with a negative branch instable resonator in a non-waveguide dimension, a stable resonator is used in a waveguide dimension, and the mirror spacing from the end of the waveguide is based in part on the configuration of the unstable resonator. A unique support structure is disclosed for maintaining the electrodes in a spaced apart orientation without confining discharge. Further refinements are disclosed for cooling the laser and for accommodating the thermal expansion of parts. Improved adjustable mirror assemblies 26 and 28 for allowing the tilt angle of the mirror to be varied from the outside of the housing are supplied. The laser is capable of generating high energy short duration pulses usable for reducing trauma and treating tissues.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention provides an RF-excited C capable of generating short high-power pulses suitable for treating tissue.
O related to ₂ slab waveguide laser.

[0002] have been various forms considerable research on waveguide slab CO ₂ laser ( "waveguide laser review (The Waveguide Laser: A Review)" stress physical (Applied Physics) Vol. II, 1 Pp. 33 (1976)). Waveguide lasers differ from conventional lasers in that circulating light is guided over some part of the propagation path and does not obey the law of free space propagation. The term slab is used to mean a laser having a rectangular discharge area defined between two flat surfaces. In the context of the present invention, the term slab waveguide laser is used to mean a laser having a rectangular discharge area defined between two closely spaced electrodes, wherein light travels in a narrow dimension between the electrodes. It can be guided and propagate in a larger dimension of free space.

[0003] Slab waveguide CO₂Early research on lasers
Is a flowing gas system in which the gas is excited by a DC discharge.
(For example, “CW lateral discharge, lateral gas flow C
O₂: N ₂: Optical utility in He flat waveguide laser
Optical-gain Measurements in a CW Transver
se-discharge, Transverse-gas-flow CO₂: N₂: H
ePlanar-Waveguide Laser) "McMullen
Journal of Applied Physic
s) Volume 45, No. 11, November 1974, 5084
Page, see). Sealed CO₂Go to the laser with DC excitation
Efforts to expand it have not been very successful.

The first successful excitation strategy for sealed CO ₂ waveguide lasers is described in Laakmann, September 25, 1979, US Pat. No. 4,169,251. The laser disclosed in that patent is excited laterally by high frequency RF excitation. The discharge area is defined between a pair of spaced long electrodes. The Larkman patent
Teaches how to select the correct RF excitation frequency based on electrode spacing. Excitation with the correct RF frequency is required to maintain a stable discharge.

[0005] The electrodes of the laser disclosed in the Larkman patent are separated by a pair of long insulating members. A combination of electrodes and insulating members can be used to define both square and rectangular discharge areas. In the embodiment illustrated in the patent, the spacing between the insulating members is sufficiently small that
Light is guided in both dimensions, that is, between the electrodes and the insulating member.

In an effort to increase the power that can be generated per a given length of electrode, the teachings of the Larkman patent are applied to the development of a CO ₂ slab waveguide laser where light is narrow. It is guided only between the spaced electrodes and is allowed to propagate freely over a wider dimension. One of the earliest reports on this type of laser was at the Conference on Lasers and Electro-Optics.
Lasers and Electro-optics) summaries presented at June 1984, Gabai, Herzberg and Yatsuifu (Gabai, seen in "Radio Frequency excitation strip lines CO and CO ₂ lasers" of Hertzberg andYatsiv). In this laser, a pair of spaced, water-cooled X-band waveguide electrodes are operated at RF frequencies in the range of 25-50 MHz.
Excited by radiation. The electrode spacing was on the order of 4.5 mm, which was suitable for guiding light. The wider dimension of the electrode was 2.5 cm, which allowed light to propagate freely. Cavity experiments were performed using a plane mirror and a stable resonator. Supplemental information is presented in Yatsif's continuing paper, The Conference on Gas Flows and Chemical Lasers, 1986, The Sixth International Symposium Proceedings 1987, published by Springer, 1987, pp. 252-257, "Conductively Cooled It may be found bound to the RF excitation CO ₂ laser ".

Another CO ₂ slab waveguide laser is described in Tulip, Jan. 12, 1988, US Pat. No. 4,719,639. Similar to the device described in the Gavai article, the discharge area of the tulip device is rectangular and takes the form of directing light between the electrodes and propagating it to a larger dimension of free space. The Tulip patent also discloses that slab lasers may have used unstable resonator structures in the non-waveguide direction. The unstable resonator described in the Tulip patent includes one concave mirror and one convex mirror and is known to those skilled in the art as a positive branch unstable resonator.

[0008] Another slab waveguide laser is described in Applied Physics Letters, Vol.
No. 20,1950 pages, May 1989, described in Jackson (Jackson) Other "used unstable waveguide hybrid resonator CO ₂ large area discharge laser."
Like the laser described in the Tulip patent, the laser in this article is provided with a positive branch unstable resonator in the non-waveguide direction.

[0009] Yet another slab waveguide laser is disclosed in Opower, July 3, 1990, US Patent No. 4,939,738. This slab waveguide laser is also provided with a positive branch unstable resonator.

Many of the early designs of CO ₂ slab waveguide lasers reported in past literature, although promising, were not suitable for commercial development. In particular, many of the lasers described are for practical experimental purposes only, and little effort has been made to overcome the problems encountered when trying to operate the laser at high power levels for long periods of time. Was. For example, to provide a commercially acceptable laser, a variety of design issues must be addressed, including mirror assemblies, cooling systems, and electrode support assemblies.

Another problem with conventional slab lasers is that their resonator structures included mirrors located very close to the discharge and therefore subject to rapid degradation. The design of this resonator followed conventional wisdom of waveguide laser design, which defines the optimal placement and radius of the resonator mirror. More specifically, conventional theory has stipulated that mirrors should be placed very close to or large distance from the waveguide element. It was believed that placing the mirror near the end of the waveguide could force all of the light back into the waveguide channel. The cavity design where the mirror is located near the end of the waveguide has a type I resonator,
I was told. The mirrors used in Type I resonators were typically planar or had a very large radius of curvature. Type I resonators are good for experiments, but the degradation of the mirror due to exposure to nearby discharges makes this approach unsuitable for commercial use.

[0012] Conventional waveguide management theory has specified that there are two more locations far from the end of the waveguide, where mirrors could be placed and that losses could be reduced. These locations are a function of the distance between the electrodes and are conveniently designated as R and R / 2. If the mirror was placed at a distance R from the end of the waveguide, the resonator was called type II.
If the mirror is placed at a distance of R / 2, the resonator will be of type II
Called I. The radius of curvature of the mirrors of both type II and type III resonators is equal to R. The distance R in a typical waveguide configuration will be about 10 cm to 1 m. This separation of both mirrors from the end of the waveguide adds additional space to the laser package and will create potential alignment stability problems, and is not acceptable for commercial laser designs. hard.

Accordingly, it is an object of the present invention to provide a new and improved CO ₂ slab waveguide laser.

It is another object of the present invention to provide a CO ₂ slab waveguide laser that is stable and produces high power at a given length.

It is yet another object of the present invention to provide a CO ₂ slab waveguide laser having an improved resonator structure.

It is yet another object of the present invention to provide a CO ₂ slab waveguide laser having a negative branch unstable resonator in the non-waveguide direction.

It is another object of the present invention to provide a CO ₂ slab waveguide laser having a resonator mirror spaced from the end of the waveguide to reduce degradation.

It is yet another object of the present invention to provide a CO ₂ slab waveguide laser having resonator mirror spacing dependent on the geometry of the negative branch unstable resonator.

It is another object of the present invention to provide a CO ₂ slab waveguide laser having an improved electrode support structure.

It is yet another object of the present invention to provide a CO ₂ slab waveguide laser having an electrode support structure that allows for thermal expansion of the electrodes.

It is another object of the present invention to provide a CO ₂ slab waveguide laser having an electrode support structure that does not contain a discharge.

CO with improved electrode cooling system
It is a further object of the present invention to provide a _two slab waveguide laser.

CO with an improved mirror mount that allows adjustment from outside the sealed laser housing
It is another object of the present invention to provide a _two slab waveguide laser.

It is a further object of the present invention to provide an apparatus for initializing a discharge to facilitate operation.

It is another object of the present invention to provide a laser that produces short, high energy pulses suitable for treating tissue.

For these and many other purposes, the present invention provides a CO with many features intended to enhance performance.
Give a _two slab waveguide laser. Slab laser is
Consists of a pair of spaced, planar electrodes having opposing light reflecting surfaces. The spacing of the electrodes is arranged such that light is guided in a plane perpendicular to the reflecting surface. In contrast, light in a plane parallel to the light reflecting surface is allowed to propagate in free space and is confined only by the resonator.

In one aspect of the invention, the stability is increased,
A new type of resonator structure is used to improve the mode quality. More specifically, a negative branch unstable resonator is selected to reflect light in a non-waveguide dimension. Negative branch unstable resonators have also been used for other lasers, but there is no way that this structure was used for CO ₂ slab waveguide lasers. Previous researchers have made the wrong assumption that a negative branch unstable resonator would greatly reduce the power of such a laser. It has been found that negative branch unstable resonators can be used without significant power reduction.

Another feature of the new resonator design is that the mirror is spaced a sufficient distance from the end of the waveguide to reduce degradation problems. This mirror spacing does not follow the prior art teachings on waveguide structures. More specifically, the mirror is spaced from the end of the waveguide by a significantly greater distance than the type I resonator. In addition, the mirror is also a type II
Or much closer to the end of the waveguide than any of the Type III resonators.

According to the invention, the mirror isolation and curvature are first selected based on the required optical output coupling of the negative branch unstable part of the resonator. For cost savings, a spherical mirror is preferably used. Thus, the radius of curvature of the mirror in both the waveguide dimension and the non-waveguide dimension is equal.

After the mirror isolation and curvature are selected in the non-waveguide dimension, the length of the waveguide is such that the spacing between the waveguide end and the mirror optimizes the reflection of light returning into the tube. Is selected. According to the invention, this optimization is obtained by setting the length of the waveguide such that the radius of curvature of the wavefront of the laser beam at the mirror coincides with the selected radius of curvature of the mirror. This approach has been found to maximize output, despite previous theory pointing out that roughly 15% loss would occur.

Another important feature of the present laser lies in the support structure used to maintain electrode isolation.
More specifically, in the prior art, electrodes were isolated by mounting a pair of long insulating blocks between the electrodes. This approach provided the necessary electrical insulation between the electrodes. However, insulating blocks tend to sharply define the edges of the discharge.

In contrast, according to the present invention, the device for supporting and insulating the electrodes is isolated from the discharge. In this way, the discharge has no sharp limits and presents a mild edge. This configuration is believed to contribute to the excellent mode performance of the laser. Another advantage of this configuration is that it allows hot dissociated laser gas to flow freely out of the space between the electrodes, while allowing cooler gas to enter and supplement the discharge. .

In another aspect of the electrode support structure,
Considerations are taken to address thermal expansion of the electrodes during operation. Therefore, one end of the electrode is fixedly attached to one end of the housing. The other end of the electrode is slidably mounted on the other end of the housing to allow movement by thermal expansion.

The present invention also includes an improved cooling system. Of course, the more power the laser operates, the more important cooling becomes. In the past, cooling pipes were only attached to the electrode surface. In this design, the cooling pipe is in a passage formed in the electrode. In addition, specific locations of the passages are designed to reduce stresses caused by differences in the coefficient of thermal expansion between the pipe material and the electrodes. The cooling pipe is also designed to reduce short circuits between the high voltage electrodes and the grounded laser housing.

Another feature of the present laser is an improved mirror assembly. This mirror assembly adjusts the angle of the resonator mirror from outside the housing without having to slide the vacuum seal.

Another feature of the present laser is that it includes a low-pressure mercury-argon lamp used to pre-ionize the discharge. The lamp allows the laser to start reliably, even at low operating currents.

The laser is particularly suitable for treating tissue,
Able to generate short high energy pulses.

Further objects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

Referring to FIGS. 1 to 5, the C of the present invention is shown.
O ₂ slab waveguide laser 10 is illustrated. The main portion of the laser 10 includes a cylindrical aluminum housing 20 vacuum sealed by a pair of end plates 22,24. The end plate is an adjustable mirror mounting assembly 26,2 of the present invention.
8 inclusive. The mirror mounting assembly supports the resonator mirrors 30,32. As shown in FIG. 3, mirror 30 is shorter than mirror 32 to couple light out of the cavity. The mirror mounting assembly 26 also supports a window 34 that allows light exiting the housing across the end of the mirror 30 to pass through.

Inside the housing 20, a pair of flat aluminum upper and lower electrodes 36, 38 are mounted.
The spacing D between the electrodes (FIG. 5) is chosen such that light is guided between the opposing inner surfaces of the electrodes. In the preferred embodiment, the spacing D is equal to 2 mm. In this design, there are no containment elements in a plane perpendicular to the light reflecting surface,
The laser light simply propagates freely in free space controlled by the resonator mirrors 30,32.

In order to reduce losses, the inner light reflecting surface of the electrode is. It is cut to a flatness within 002 in (50.8 μ). In addition, the surface finish is 32 rms microinches (0.813 rms μ) roughness. In the illustrated embodiment, each electrode is 44 mm wide, 12 mm thick and 61.5 mm long.
2 cm.

In a preferred embodiment, the laser emitting medium is a standard CO 2 emitting radiation with a dominant wavelength of 10.6 μm.
_{2 is a} laser-emitting mixed gas. The gas mixture contains helium, nitrogen and carbon dioxide in a ratio of 3: 1: 1 with the addition of 5% zenone. Gas is 50-110 to
rr, preferably at a pressure of about 80 torr. The gas is electrically excited by coupling a radio frequency oscillator between the electrodes. 81.36MHZ with power higher than 4kW
A standard solid state RF oscillator producing an output of z was used. The oscillator output is coupled to the laser using a suitable impedance matching network (not shown) that matches the oscillator to the luminescent discharge. In this embodiment, the standard insulated feed through wire 4 arranged as close as possible to the mounting point
2, the RF current is connected to the hot electrode 36 at one point.

The other electrode 38 and the housing 20 are connected to ground. A plurality of inductance coils 44 are electrically connected between the electrodes to eliminate capacitance effects and control voltage distribution along the electrodes. Preferably, the resonance frequency of the electrode to which the induction coil is added is several MH of the RF excitation frequency.
within z.

As mentioned above, the present laser includes an improved support system for the electrodes. More specifically, lower electrode 38 is coupled to end plate 24 via support bracket 50. The other end of the lower electrode 38 is connected to the second support bracket 5.
2 supported. The second support bracket is securely coupled to the electrode. The free end of the bracket 52 is a pin 5
4 and the pins are in mating mating holes 56 in the end plate 22.
Stick out inside. The length that the pin is received in the hole changes as the length of the electrode 38 changes during operation of the laser.
Thus, the electrodes are not constrained in a manner to distort the required isolation between the electrodes.

In the embodiment shown, a spring 58 is mounted on the pin 54 of the second support member in a manner abutting the end plate 22. The spring has the function of providing an electrical connection to enhance the earth connection of the electrode 38.

As described above, in conventional slab lasers, a pair of electrodes are typically separated by a long insulating block, which also contained the discharge and provided a sharp edge to the electric field. In contrast, in the present laser, the device supporting the upper electrode from the lower electrode is spaced from the discharge, so that the sides of the discharge are blurred.

As best seen in FIGS. 6 and 7, the support device includes a plurality of insulating brackets 60. In the preferred embodiment, there are only three narrow brackets 60 on each side.
The discharge is virtually uninterrupted. Furthermore, the brackets are generally U-shaped so that the center of each bracket is spaced from the discharge. With this mechanism,
The discharge is confined by the electric field alone, resulting in a much smoother density reduction near the edges. This design is believed to contribute to improved modal performance. Another advantage of this configuration is that the hot dissociated laser flows freely out of the space between the electrodes, while allowing a cooler gas to enter and supplement the discharge. A further advantage of this design is that the discharge can be observed if the housing is provided with a window.

In order for a laser to operate effectively at high power, a cooling system must be provided to carry heat away from the electrodes. In the present invention, the cooling system comprises a pair of upper and lower fluid transport copper pipes 70,72.
including. The ends of the pipes 70, 72 extend through the end plate 24 of the housing 20 and are grounded thereto. The end portion of each pipe runs near the inner surface of the housing along the length of the electrode. Each pipe includes a central portion that turns and runs along the electrodes.

According to the invention, the outer surfaces of the electrodes are provided with passages 76, 78 for receiving pipes. Desirably, the bottom of each passage is nickel plated and the pipe center portions 74, 75 are brazed into the passage to improve heat transfer. The depth of the passage is designed to approach the geometric center of the electrode. In this manner, electrode distortion that may be caused by stresses caused by differences in the coefficient of thermal expansion between the pipe and the electrode is reduced.

As best seen in FIG. 2, U-bends 82 are provided at the ends of both pipes, which are also twisted out of plane. These sections provide some flexibility for the pipe to expand and move.

The upper cooling pipe 70 is further provided with a pair of insulating portions 84. The insulating portion 84 functions to electrically insulate the electrically hot pipe center section 74 from the electrically grounded pipe end section. In a preferred embodiment, the pipe end is located very close to the grounded housing. An electrically hot section of the pipe is spaced from the grounded housing and hot electrode 36
, The insulating portion 84 is directed obliquely.

As will be explained in more detail below, the choice of mirror spacing in the present laser is important in maximizing power and improving mode control. It is desirable to keep the mirrors 30, 32 far enough away from the ends of the electrodes to reduce degradation due to discharge. On the other hand, the mirror must not be far enough to make the whole container bulky. In order to meet this requirement from the standpoint of consolidation, it is necessary to place the mirror in the housing 20. To maximize performance, it is also necessary to provide a device for adjusting the angle of the mirror from outside the sealed housing.

The latter is intended for improved mirror assemblies 26,2.
8 is achieved. Obviously, these two assemblies are functionally equivalent. The only difference is that the mirror assembly 26 includes a window 34 for passing laser light.

The mirror assembly is better shown in FIGS. Each mirror assembly is formed in an end plate 22, 24 and has a circular groove 9
Contains 0. The grooves extend radially toward the inner surface of the endplate by an amount sufficient to define a planar flexure area 92. Groove 90 also defines a tilting member 94 radially inward of the groove.

The mirror mounting base 96 is connected to the tilting member 94 on the inner surface of the end plate. Obviously, as the angle of the tilting member changes, so does the angle of the mirror mount 96.

The mirror assembly includes a device for adjusting the angle of the tilting member. More specifically, as best seen in FIGS. 10 and 13, four pins 98
Is slidably mounted on the end plate so as to contact the end plate. A threaded member 102 threadedly engaging a mating hole 104 is associated with each pin 98. By turning the screw member 102, the associated pin is pressed against the tilting member 94. As can be seen in FIGS. 8 and 11, when the pin is pushed into the tilting member 94, the tilting member tends to rotate about the radial flexure region. By adjusting the positions of the screw member and the pin, the mirror can be adjusted in angle from outside the housing.

The mirrors 30 and 32 are fixedly mounted on a mirror mounting base 96. Each mirror includes a silicon substrate, which is coated with a gold or silver metal coating, and overcoated with an insulating stack of thorium fluoride and zinc sulfide to enhance the mirror's reflectivity at the laser wavelength. About 2 to further protect the mirror from deterioration
An extremely thin topcoat of μ thickness can be added.
Suitable overcoating materials include a thorium fluoride or germanium supplemental layer. Germanium is better able to withstand types of scratches arising from handling, but is more susceptible to absorption problems at high powers. The supplemental coating layer causes some loss increase, which must be balanced with extended life.

As described above, the stability, output and mode control are enhanced by the resonator structure of the present laser. The resonator structure is better seen in FIGS. More specifically,
As shown in FIG. 3, mirrors 30, 32 define a slab, a negative branch unstable resonator in the non-waveguide dimension. A confocal unstable resonator is the required resonator configuration to generate a collimated light output beam and obtain maximum laser efficiency. As mentioned above, since mirror 30 is shorter than mirror 32, light is coupled out of the resonator through the end of mirror 30, through hole 110 and window 34. This resonator is regarded as a negative branch unstable resonator. That is, the beam travels the optical axis an odd number of times, in this case 1
Because it crosses times. As mentioned above, prior art CO 2
_{In the two-} slab waveguide laser, only the positive branch unstable resonator was used. Despite conventional wisdom, it is believed that negative branch unstable resonators provide higher performance.

In a preferred method of designing a resonator,
The desired length of the gain medium was first determined. Next, the required output coupling was selected. In this case, the output coupling is desirably about 16%. Using these two numbers, the radii of curvature of the two mirrors were selected based on the following standard formula: (1) (R ₁ + R ₂ ) / 2 = one pass of the parallel light beam in the confocal state (2) (M-1) / M = 21% (required output coupling) where M is a magnification and given by: (3) R ₂ / R ₁ = magnification In the embodiment where the electrode length is 60 cm, the radius of curvature of the full-size mirror 32 is 730 mm and that of the shorter mirror 30 is 580
mm, and the mirror spacing is one half of the average radius of curvature. Since both mirrors are spherical, they have the same radius of curvature in both dimensions.

The short mirror 30, the output mirror, must be cut off so that the distance between the mirror edge and the discharge edge causes the proper part of the beam to exit the resonator. The dimensions of this mirror are
It is determined by the width of the electrode minus a small correction for edge effects and mechanical tolerances. A small mirror must be cut off so that the width of the output beam is the partial output coupling times the effective width of the electrode. In the above example, the width of the electrode was 44 mm, including 1 mm for edges and mechanical tolerances. Therefore, the width of the output beam is: (4) 0.21 × (44-1) mm = 8.8 mm The experiment was performed using an electrode of 40 cm. The following negative branch unstable resonator design was found to be acceptable.

Case I Case II Radius of mirror 30 384 mm 377 mm Radius of mirror 32 420 mm 430 mm Spacing L 402 mm 403 mm

FIG. 4 illustrates the waveguide dimensions on which a stable resonator is defined. As mentioned above, in prior art waveguide lasers, the mirror was placed very close to the end of the waveguide, close to the type I resonator configuration, typically less than 4 mm.

In contrast, in the present invention, the end of the waveguide is spaced at least 10 mm, preferably 20 mm, from the mirror. Instead of using conventional theories for the shape and arrangement of the mirrors, it has been found desirable to first optimize the resonator design in the unstable resonance dimension. Once the position and radius of curvature of the mirror are determined, the actual length of the waveguide electrode is determined in order to optimize the spacing taking into account the curvature of the mirror. More specifically, the spacing between the end of the electrode and the mirror is chosen such that the radius of curvature of the wavefront as the beam approaches the mirror matches the radius of curvature of the mirror.

The relationship between the radius of curvature of the wavefront and the distance from the end of the waveguide is illustrated in FIG. In this figure, the light wavelength is 10.6 μm, has a planar wavefront as it exits the 1.9 mm square waveguide, and the light mode structure is substantially TEM.
Assume that it is equivalent to ₀₀ mode. If the radius of curvature of the mirror is known, the required spacing can be easily matched. This approach will return substantially all of the light into the waveguide except for the effects of diffraction.

It should be understood that this approach to resonator design is significantly different from the teachings of the prior art. For example, according to conventional theory, in a type II resonator, the radius of curvature of the mirror used is 850 mm, and the distance from the end of the waveguide is 8 mm.
Will be 50mm. For a type III resonator, the radius of curvature of the mirror at a distance of 130 mm from the end of the waveguide is 260
mm. Using conventional theory to analyze the structure of the present invention, the loss would be about 15%. results of the experiment,
It has been found that the resonator structure is as efficient as that used in the prior art, more stable and less degraded. Moreover, mode operation has been enhanced.

FIG. 15 shows the operation in pulse mode 6.
5 is a curve of average power versus operating time of a 0 cm slab laser. Peak RF input is 1200W, pulse length 500μ
S, and 50% duty cycle. The RF input is sent to the laser at a frequency of 81.4 MHz, and the gas mixture has a helium, CO ₂ , nitrogen ratio of 3: 1: 1 and 5% zenone added. The RF and gas mixture parameters are the same in the experiments shown in FIGS. FIG. 15 also plots the waveguide pressure,
It shows no significant change from 56 torr over the duration of this test.

FIG. 16 shows a graph of 60 as a function of average RF input.
The average power of cm slab laser is shown. Tube operating pressure is 8
0 torr, pulse length of 300 μS and 10-50%
Operating in pulse mode with a duty cycle of
The peak RF input was set at 3 kW and 4 kW peak.

FIG. 17 shows the effect on average power when operating tubes with different pulse lengths. This is 10
It was operated in pulse mode with a duty cycle in the range of ５０50% and pulse lengths of 30 μS and 300 μS.

FIG. 18 shows the change in average output when the average RF input is increased at various gas pressures. At 4 kW peak input and 300 μS pulse length, significant changes in performance at various gas pressures occur only at the highest average input of about 1800 W.

FIG. 19 shows the change in beam diameter as the beam propagates away from the laser. The modal diameter was determined by measuring the mode burn of a 3/8 inch (9.53 mm) thick plexiglass made at an output of about 100 W. The beam diameter versus distance curve shows that both the waveguide axis and the unstable resonator axis coincide at M ² 1.2.

One advantage of the present laser design is that it can quickly generate and maintain high pulse energy. This can be important when using lasers for medical procedures. More specifically, in medical procedures, it is desirable to evaporate a relatively large area surface of tissue without damaging the surrounding tissue by heat flow. This can be achieved using short high power pulses from the present laser. Most prior art medical lasers could deliver as much as 50 millijoules of energy per pulse. In contrast, the present laser has a repetition rate of 500 Hz, up to 50 milliseconds up to 1 millisecond.
It produces a peak power of 0 W (joules / second), which is an order of magnitude higher than in the past. 500 millijoules per pulse can be delivered.

Experiments on tissue have shown that when the energy per pulse exceeds 100 millijoules, the nature of the beam-tissue interaction changes. The tissue remaining after ablation was found to be much cleaner, with a more pronounced lack of scorch, coupled with a thinner damaged tissue layer. The required pulse width should be less than 1 millisecond,
Desirably close to 0.5 millisecond. It can be used with repetition rates up to several hundred pulses per second. In addition to more common surgical procedures, such short, high energy pulses could be used for burn wound removal.

When operating at relatively high power levels and fast repetition rates, there is typically sufficient input to fire the discharge and start the laser. However, at low powers (i.e., less than 10 W average power) and at low repetition rates (i.e., more than 50 milliseconds between pulse occurrences), a mismatch between the RF oscillator and the non-emissive discharge will result in a supply of that energy. And there can be a significant delay in exciting the discharge.
One way to overcome this problem is to place the power supply in simmer mode (si
mmer mode) to maintain the discharge light emission and the minimum power generated by the laser.

In another approach, a device can be provided to initially ionize the discharge to promote dissociation of the laser gas. In the preferred embodiment, the device is mounted in a housing and is provided by a lamp, shown in FIG. Lamp 110 is a low pressure mercury argon quartz lamp available from Jelight of Laguna Hills, California, USA under part number 81-3306-2.
Ultraviolet light (185 and 254 nm) from this lamp acts to dissociate molecules in the gas and promote discharge. The use of a lamp also keeps the gas at a higher pressure and increases power.

In the fabricated laser, the lamp is mounted above the hot electrode, beyond the immediate discharge area.
Higher efficiency would have been obtained if it had been mounted where UV radiation could reach the discharge more directly. It would also be possible to mount the lamp on the outside of the housing, opposite the window that sends the UV light into the housing.

As shown in FIG. 4, RF energy can be coupled to one end of the hot electrode. This way was found to be suitable for short, about 40 cm electrodes. 60
It has been found that when cm electrodes are used, performance is better if RF energy is coupled to the center of the length of the electrodes.
In testing longer lasers, the electrode length is R
It has been found that supplying RF energy at only one location results in a non-uniform discharge since it begins to coincide with the length of the F-wave.

Thus, when the electrode length is 80 cm or more, it is desirable to couple RF energy to the electrode at two or more locations. However, R coupled to the laser at two points
The F energies must be in phase. FIG. 20 illustrates one way to achieve this result.

The laser shown in FIG. 20 has a pair of electrodes 120, 1
22. The RF energy is coupled to the hot electrode 120 at two locations. Energy is generated by a pair of amplifiers 124, 126 driven by a common oscillator 128 that keeps the amplifiers in phase. The output from the amplifier is passed through separate impedance matching networks 132, 134 to the hot electrodes. To limit the interaction between the amplifier and the load provided by the laser tube, the amplifier 1
A combiner 136 may be interposed between 24, 126 and respective matching networks 132, 134 so that each amplifier can provide equal power to the laser. All electrical leads should be the same length to ensure that the energy delivered to the electrode 120 at the two locations is in phase. By using this method, a more stable and homogeneous discharge can be maintained.

[0079] Although not shown, an auxiliary mechanism to reduce mirror degradation would be to add a ceramic spacer at the end of the waveguide electrode. Although the ceramic spacer still has the ability to direct light, the discharge will end at the end of the aluminum electrode. This ceramic material will interact with the neutral and ionized molecular debris and reduce diffusion towards the mirror surface. It is believed that if these molecular fragments are left diffused toward the mirror surface, it will lead to degradation of the mirror surface.

In summary, a CO ₂ slab waveguide laser has been disclosed. The laser includes a pair of spaced electrodes having opposing light reflecting surfaces. The electrodes are dimensioned to direct light in a plane perpendicular to the reflective surface. Light parallel to the reflecting surface is not constrained except by the resonator mirror. The resonator structure includes a negative branch unstable resonator in a non-waveguide dimension. Although a stable resonator is used in the waveguide dimension, the spacing of the mirror from the waveguide end is based in part on the configuration of the unstable resonator.

A unique support structure is disclosed to keep the electrodes in a spaced orientation without confining the discharge.
Further improvements are disclosed to cool the laser and accommodate thermal expansion of the part. Finally, an improved adjustable mirror assembly is provided which allows the mirror to be tilted from outside the housing.

The laser is suitable for treating tissue,
Has the ability to generate high energy pulses.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that various changes and modifications can be made without departing from the scope and spirit of the invention as defined in the appended claims. Will.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view of a CO ₂ slab waveguide laser of the present invention.

FIG. 2 is an exploded perspective view of a CO ₂ slab waveguide laser of the present invention.

FIG. 3 is a cross-sectional view of the CO ₂ slab waveguide laser of the present invention, taken along line 3-3 in FIG.

4 is a cross-sectional view of the CO ₂ slab waveguide laser of the present invention, taken along line 4-4 in FIG.

FIG. 5 is a sectional view of the CO ₂ slab waveguide laser of the present invention, taken along line 5-5 in FIG. 1;

6 is a cross-sectional view of the CO ₂ slab waveguide laser of the present invention, taken along line 6-6 of FIG.

FIG. 7 is an exploded view of a portion of a CO ₂ slab waveguide laser electrode support system of the present invention.

FIG. 8 is a sectional view of the mirror mount and the output window of the laser of the present invention, taken along line 8-8 in FIG. 1;

9 is a cross-sectional view of the laser mirror mount of the present invention, taken along line 9-9 of FIG.

FIG. 10 is a sectional view of the mirror mount and output window of the laser of the present invention, taken along line 10-10 in FIG. 8;

FIG. 11 is a cross-sectional view of the other mirror mount of the laser of the present invention, taken along line 11-11 of FIG. 1;

FIG. 12 is a cross-sectional view of the laser mirror mount of the present invention, taken along line 12-12 of FIG. 11;

FIG. 13 is a sectional view of the laser mirror mount of the present invention, taken along line 13-13 of FIG. 11;

FIG. 14 is a plot of the radius of the wavefront as a function of distance from the end of the waveguide.

FIG. 15 is a plot of average power versus operating time of a laser constructed in accordance with the present invention.

FIG. 16 is a plot of the average power as a function of the RF input of the laser.

FIG. 17 is a plot similar to FIG. 16, showing the effect of different pulse lengths.

FIG. 18 is a plot similar to FIG. 16, showing the effect of different gas pressures in the laser.

FIG. 19 is a plot illustrating the beam diameter as it propagates from the end of a laser constructed in accordance with the present invention.

FIG. 20 is an explanatory diagram showing coupling of RF excitation energy to multiple points on a hot electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Laser 20 Housing 26, 28 Mirror mounting assembly 30, 32 Mirror 36 Upper (thermal) electrode 38 Lower (ground) electrode 70, 72 Cooling pipe

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Joseph Dallarosa United States, 94062 Redwood City, CA, Bayview 711 (72) Inventor Philip Gardner, United States, 95615 Cupertino, CA, Drake Drive 19690 (72) Inventor Who Wayne S. Mephard United States, 94022 Miranda Road, Los Altos Hills, California 14500 (72) Inventor Jay Michael Yarborough United States, 85718 Tascon, Arizona, North Plasita Pequena 6437 F-term ( Reference) 5F071 AA05 CC07 DD05 DD07 EE01 FF08 GG02 GG07 HH07 JJ03 JJ06

Claims (2)

[Claims] 1. An adjustable mirror assembly for mounting to an end of a laser housing, the endplate being mounted to the housing end of the laser to provide a vacuum seal between the assembly and the housing. Wherein the outer surface of the end plate comprises a peripheral groove having a depth sufficient to form a flexure region between the peripheral groove and an inner surface of the end plate, A part of the end plate radially inside the peripheral groove is an end plate forming an inclined member; and a mirror mount supporting the mirror coupled to the inner surface of the end plate radially inside the peripheral groove and on the inclined member. An assembly comprising: said end plate; and means mounted on the outside of said housing for torque to said tilt member to adjust an angle of said mirror mount. 2. The means for applying torque comprises a plurality of pins mounted on the end plate radially outside the tilting member and extending through the peripheral groove, wherein the radial position of the pin is the tilting position. The assembly of claim 1, wherein the assembly is adjustable to provide varying torque to the member.