Improved system and method for ultraviolet laser energy transfer for phototherapy

Abstract

A system and method for transmitting ultraviolet laser energy for phototherapy. A master laser is provided to generate laser light of wavelengths [lambda] 2 and [lambda] 3, where 1 / [lambda] 2 + 1 / [lambda] 3 is substantially equal to 1 / [lambda] 4, and where [lambda] 4 is in the UVB spectral band. The light is transmitted through a fiber optic cable to a separate housing having a UVB frequency conversion component within the housing for generating UVB light of wavelength [lambda] 4 from input light of wavelengths [lambda] 2 and [lambda] 3. The generated UVB light may be output from the handpiece and applied to the patient.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 488,272, filed on March 3, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to improved methods and systems for generating and delivering UVB laser energy for use in applications such as phototherapy. Background Art

[0004] Skin diseases (including atopic dermatitis, dyshidrosis, eczema, lichen planus, psoriasis, and vitiligo) are conditions that affect many people, often at some time in their lives. Psoriasis can range in severity from relatively mild, with some dryness and scaling of the skin, to very severe cases, with extensive, severe psoriasis. Even very mild psoriasis can be uncomfortable and unsightly. In severe cases, patients suffer significant physical and psychological damage, posing a serious threat to their overall health.

[0005] Although the underlying mechanisms of psoriasis are not fully understood, the disease involves abnormally rapid cell proliferation in the basal layer of the skin. This excessive proliferation can be reduced, thereby improving the disease, by a method commonly known as "phototherapy" (i.e., by exposing the affected skin surface to a light source, particularly ultraviolet light). One conventional treatment is targeted phototherapy, in which narrow-band ultraviolet light energy at a wavelength of 308 nm is applied in controlled doses to discrete areas of the patient's skin.

[0006] Current 308nm UV phototherapy systems use XeCl excimer lasers. These laser systems are FDA-approved medical devices for the optical treatment of psoriasis, atopic dermatitis (eczema), vitiligo, and other indications. The excimer laser and associated power supply and cooling system are housed in a housing (e.g., a movable cart). The laser directly generates 308nm laser radiation through an electrical discharge in a gas chamber. The laser radiation is then directed to a flexible light guide delivery system. The light guide delivers the 308nm laser radiation to a treatment handpiece that can be held by the system user, thereby applying the laser radiation to the patient. The handpiece has internal optical components that guide the 308nm laser light received through the light guide to an output aperture that can be placed directly on the patient's skin and used to deliver a certain dose of laser radiation, such as uniformly delivering the laser radiation over the area covered by the aperture (e.g., 4 cm 2 ).

[0007] The delivery system must be mobile so that the dose can be applied to all affected areas of the patient using the handpiece. In a typical treatment, the dose may need to be applied at a distance of 500 cm 2 The most common delivery system for delivering 308nm laser light from a light source to a handpiece is optical fiber. Conventional fiber optic assemblies have either a solid or liquid core and are used to transmit the 308nm beam from the laser source over lengths of up to 2m. In practice, liquid-core fiber can produce a 65% transmission rate over a 1.5m length and exhibits good fiber life over time. Solid-core fiber initially offers 80% transmission efficiency but degrades more rapidly over time.

[0008] To compensate for losses in the fiber, the source laser must be significantly more powerful than the desired dose power. For example, a 6-watt laser might be required to deliver 4 watts of laser energy to the patient. This need for higher power increases the cost of the laser. It also incurs operational costs, as the fiber connecting the handpiece to the laser source must be replaced when degradation becomes too severe.

[0009] There is a need for higher efficiency in the transmission of laser radiation from the light source to the handpiece. This can be achieved by using lower power laser sources to reduce costs. Reducing the degradation of optical fibers is also desirable as it will provide a longer-lasting transmission means while also reducing system costs as the fiber does not need to be replaced as frequently. Summary of the Invention

[0010] The methods and systems disclosed herein provide these and other benefits for more efficiently delivering UVB laser radiation (e.g., 308 nm) to a treatment handpiece. In conventional UVB solid-state laser systems, there is a lower frequency primary laser and one or more frequency conversion stages to convert the initial lower frequency laser light to the desired UVB wavelength. The present methods and systems physically separate the intermediate frequency conversion stage from the final conversion stage. Advantageously, this allows a system to be constructed so that the high-frequency UVB light used for treatment does not need to be delivered to the handpiece through a light pipe. The laser produces an intermediate laser light, such as visible light or near-infrared (NIR) light. The intermediate light is transmitted to the handpiece via one or more fiber optic cables. The final conversion of the lower frequency laser radiation into high-frequency ultraviolet light is performed within the handpiece (e.g., by a frequency conversion crystal).

[0011] Compared to conventional systems that use optical fiber to deliver 308nm radiation to the handpiece, fiber-optic cables offer an efficient and flexible transmission system that facilitates the delivery of lower-frequency laser radiation to the handpiece with lower transmission losses and a higher threshold for laser-induced damage. Lower-frequency radiation can be transmitted very efficiently via optical fiber. This allows the use of lower-power lasers, reducing costs. Existing high-efficiency optical fibers can be used to optimize the transmission of visible and NIR light over long distances. Efficient transmission also significantly reduces, or can virtually eliminate, the need to replace optical fibers due to degradation caused by absorption of laser radiation. The longer lifespan of optical fiber components also reduces operating costs.

[0012] In one embodiment, a phototherapy treatment system includes a main laser that outputs laser light at wavelengths λ2 and λ3, where 1 / λ2 + 1 / λ3 substantially equals 1 / λ4, and where λ4 is in the UVB spectral band between 304 nm and 312 nm, more specifically, approximately 308 nm. A UVB frequency conversion assembly is provided within a housing separate from the main laser for generating UVB light at wavelength λ4 from input light at wavelengths λ2 and λ3. A first fiber optic cable optically connects the main laser to the housing.

[0013] In one embodiment, the master laser includes a primary-stage laser and an intermediate frequency conversion component, wherein the primary-stage laser generates light having a wavelength λ1, and the intermediate frequency conversion component generates light having wavelengths λ2 and λ3 from the light having the wavelength λ1.

[0014] The wavelength λ2 and wavelength λ3 laser light from the master laser can be delivered to the housing in a single optical fiber, or each wavelength laser light can be delivered in a separate optical fiber.

[0015] The housing with the UVB frequency conversion assembly can be a handpiece that can be used to apply the generated UVB light to the patient's skin. The housing can also be separate from the handpiece and connected to the handpiece using a second fiber optic cable that delivers the UVB light from the housing to the handpiece. The length of the second fiber optic cable can be significantly less than the length of the first fiber optic cable.

[0016] A method for generating UVB light (e.g., 308 nm light) for phototherapy treatment may include the following steps: connecting a master laser to a remote housing using a fiber optic cable. The master laser generates laser light at wavelengths λ2 and λ3, where 1 / λ2 + 1 / λ3 is substantially equal to 1 / λ4, and where λ4 is in the UVB spectral band between 304 nm and 312 nm. A UVB frequency conversion component in the housing is then used to convert the laser light at wavelengths λ2 and λ3 from the master laser to UVB light at wavelength λ4. The light at wavelengths λ2 and λ3 may be generated by using the master laser to generate light at wavelength λ1 and using an intermediate frequency conversion component to generate light at wavelengths λ2 and λ3 from the light at wavelength λ1.

[0017] The housing may include a treatment handpiece, or the treatment handpiece may be optically connected to the housing using a second fiber optic cable. UVB light generated by UVB frequency conversion is emitted from the handpiece through the aperture and applied to the patient. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are disclosed in detail below with reference to the accompanying drawings:

[0019] Figure 1 is a schematic diagram of a system for delivering ultraviolet laser radiation to a patient;

[0020] Figure 2 Shows Figure 1 An exemplary embodiment of a handpiece having a single fiber transmission configuration;

[0021] Figure 3 Shows Figure 1 An exemplary embodiment of a handpiece having a dual fiber transmission configuration; and

[0022] Figure 4 An alternative embodiment is shown in which the UVB frequency conversion stage is not housed in the handpiece. DETAILED DESCRIPTION

[0023] Figure 1 FIG2 is a schematic diagram of a system 100 for delivering UVB laser radiation to a patient during phototherapy treatment. In one embodiment, the UVB laser radiation is light in the UVB spectral band substantially at 308 nm. The UVB radiation can be applied to a patient via a suitable handpiece to treat a variety of skin conditions.

[0024] refer to Figure 1, system 100 includes a primary laser system 105 and a handpiece 110. The primary laser system 105 includes a primary laser 115, which generally provides the highest laser power level. For example, the laser 115 can be a high-power, electrically efficient diode laser that outputs light at a wavelength λ1. In one embodiment, the laser 115 is a solid-state laser. However, other laser sources, such as gas lasers, can also be used. The initial λ1 wavelength radiation from the primary laser 115 is passed to an intermediate frequency conversion component 120. The intermediate frequency conversion component 120 is used to convert the input laser radiation from the initial λ1 wavelength to output radiation at one or more intermediate wavelengths (e.g., λ2 and λ3).

[0025] Frequency conversion within the intermediate frequency conversion component 120 can be performed using a variety of techniques and can include one or more intermediate frequency conversion stages. In one embodiment, the primary laser 115 is used to pump a secondary laser within the intermediate frequency conversion component 120. The secondary laser can include a laser crystal (e.g., Nd:YAG), one or more tunable lasers (e.g., Ti:Sapphire), a high-power fiber amplifier (e.g., Yb-doped, Er-doped silicate) with a low-power seed laser input, or other configurations known to those skilled in the art. The output of the secondary laser can be directed to one or more additional conversion stages as needed to generate the intermediate wavelengths λ2, λ3. In one embodiment, the intermediate wavelengths are generated using a nonlinear optical crystal (e.g., LBO) by harmonic generation or sum frequency generation of intermediate wavelength radiation.

[0026] The intermediate wavelength radiation generated by the intermediate frequency conversion assembly 120 is then guided to the UVB frequency conversion assembly 130 via a light guide. In one embodiment, the light guide comprises a flexible fiber optic cable 130, which can be connected to the intermediate frequency conversion assembly 120 and the UVB frequency conversion assembly 125 using fiber optic couplers 135a and 135b, respectively. The UVB frequency conversion assembly 120 is configured to generate high-frequency light having a wavelength λ4 from the intermediate wavelengths λ2 and λ3 radiation. In one embodiment, λ4 is in the UVB spectral band between 304 nm and 312 nm, and in a further embodiment, λ4 is substantially equal to 308 nm. In one embodiment, the UVB frequency conversion assembly can be integrated into the handpiece 110. The fiber optic couplers 135a and 135b connected to the laser system can be permanent or include quick disconnects to facilitate easy removal / reassembly and replacement of, for example, the fiber optic cable 130 or the handpiece 110 when needed.

[0027] The UVB frequency conversion assembly can include a nonlinear crystal to generate the desired therapeutic wavelength λ4 through harmonic generation or sum-frequency generation. Any residual intermediate wavelengths in the final beam can be substantially removed using a dichroic mirror (DM) 140 to redirect this residual light, for example, to an absorptive heat sink (HS) 145 or equivalent device. The dichroic mirror 140 can be integrated into the handpiece 110. The therapeutic radiation at wavelength λ4 (e.g., 308 nm) can then be directed to the output aperture via an optical structure as needed. The intermediate wavelengths generated by the primary laser 105 and transmitted by the optical fiber 130 can be in the visible to near-infrared (NIR) wavelength range. This allows the use of conventional optical fibers, which are designed to transmit light in this wavelength range over long distances with minimal loss (e.g., those used for data transmission). Visible and NIR wavelengths have excellent transmission efficiencies of up to 99.5% over a range of 1.5 m through solid-core optical fibers (e.g., fused silica). Compared to fibers transmitting ultraviolet radiation, there is less potential for laser-induced damage within the fiber because there is less absorption of energy at intermediate wavelengths within the fiber.

[0028] The intermediate frequency conversion component 120 can be configured to generate any two wavelengths λ2 and λ3 such that 1 / λ2 + 1 / λ3 is substantially equal to 1 / λ4, where λ4 is the target wavelength, for example, 308 nm (±0.5 nm). A configuration where λ2 = λ3 is also possible, known as frequency doubling.

[0029] Various specific exemplary embodiments of the intermediate frequency conversion assembly 120 that may be used in the primary laser system 105, and the functions implemented in the UVB frequency conversion assembly 125, are detailed below:

[0030] (A) Intracavity upconversion optical parametric oscillator (OPO): A 1064 nm Nd:YAG laser is frequency doubled to produce 532 nm (λ2) light, which is used to pump the OPO tuned to oscillate at 731.5 nm (λ3). The residual 532 nm light and the 731.5 nm light are transmitted by optical fiber 130 and sum-frequency mixed in the second conversion component 125 to produce 308 nm light.

[0031] (B) A frequency-doubled Nd:YAG laser pumps a tunable Ti:Sapphire laser. This laser is tuned to oscillate at 924 nm (λ2) and then frequency-doubled to 462 nm (λ3). The remaining 924 nm and 462 nm light are transmitted through optical fiber 130 and sum-frequency mixed in second conversion component 125 to produce 308 nm light.

[0032] (C) A 1232 nm pulsed fiber laser source based on Raman conversion of Yb-doped fiber is frequency doubled to 616 nm (λ2 and λ3). The 616 nm light is transmitted by fiber 130 and then frequency doubled in the second conversion component to produce 308 nm light.

[0033] (D) 1030nm and 1535nm MOPA (master oscillator, power amplifier) ​​lasers based on Yb-doped fiber and Er-doped fiber amplifiers are frequency doubled to 515nm (λ2) and 768nm (λ3). These wavelengths are transmitted by optical fiber 130 and sum-frequency mixed in the second conversion component 125 to produce 308nm light.

[0034] The transmission of the multiple different wavelengths (e.g., wavelengths λ2 and λ3) generated by the intermediate frequency conversion component 120 to the second component 125 can be performed via a single or multiple optical fibers. In a single-fiber embodiment, the intermediate wavelengths are combined (e.g., by a dichroic mirror) and then focused onto a single optical fiber. After exiting the optical fiber, the combined beam is focused into a nonlinear crystal in the UVB frequency conversion component 125. In a multi-fiber embodiment, each intermediate wavelength (e.g., wavelengths λ2 and λ3) is focused into its own optical fiber. After entering the second conversion component 125, the beams are combined (e.g., by a dichroic mirror) and then focused into the nonlinear crystal.

[0035] The choice of a single-fiber or dual-fiber system in a given embodiment can be based on various factors. Using a single fiber optic cable to transmit both wavelengths allows the combination optics to be placed within the primary laser 105, rather than as part of the UVB frequency conversion assembly 125. In a configuration where the UVB frequency conversion assembly 125 is integrated within the handpiece 110, the use of a single cable can result in a smaller handpiece size, which is preferable for ease of operation for the user. Using separate fiber optic cables allows each used optical fiber to be optimized for the respective wavelength it transmits (e.g., by selecting an appropriate fiber core substrate). Using separate cables also reduces heat absorption by each cable. However, the cost of a dual-fiber system can be higher than that of a single-fiber system. Furthermore, combination optics are required at the UVB frequency conversion assembly 125 to combine the light from each optical fiber. In a configuration where the UVB frequency conversion assembly 125 is integrated within the handpiece 110, this additional equipment can increase the size and cost of the handpiece 125.

[0036] As previously mentioned, conventional solid-core optical fibers have very high efficiency for visible and NIR light. In embodiments where it is desirable to maximize the efficiency of the nonlinear crystal in the UVB frequency conversion assembly 125 in generating the UVB spectral band, a single-mode beam profile at intermediate wavelengths should be maintained within the optical fiber as much as possible. A single-mode Gaussian profile provides optimal focusing, resulting in higher peak power and conversion efficiency within the nonlinear crystal. Since profile degradation may be limited due to short propagation lengths (e.g., approximately 2 m or less), standard step-index optical fibers may be used.

[0037] However, in some embodiments, single-mode fiber or graded-index fiber may be preferred. Single-mode fiber has good profile retention, but also has a smaller diameter, on the order of + / - 10 μm. This limits the power carrying capacity and can result in significant heating, which may require the use of a thermal management system. Graded-index fibers can also maintain a near-Gaussian profile. They typically have a larger diameter than single-mode fibers. This allows for higher power handling. Relative to single-mode fibers, the input and output surface areas are larger, the tolerance to laser-induced damage is also higher, and anti-reflection coatings can be used. Due to the large powers transmitted (potentially up to 18 watts), thermal management may still be required to prevent damage to the fiber. Thermal management can include the use of flexible solid, liquid, or paste materials with high thermal conductivity and / or high heat capacity surrounding and in contact with the fiber.

[0038] Examples of specific embodiments of the system 100 are set forth below.

[0039] The master laser 115 is a 976 nm (λ1) diode laser. The first conversion assembly 120 includes two low-power seed lasers, outputting at 1535 nm and 1030 nm, respectively. The output of the 1535 nm seed laser is amplified by a multi-stage Er-doped fiber amplifier, and the output of the 1030 nm seed laser is amplified by a multi-stage Yb-doped fiber amplifier. Both fiber amplifiers are pumped by the master laser 115. The amplified outputs are converted to 768 nm (λ2) and 515 nm (λ3), respectively, via second harmonic generation (SHG), and the seed laser wavelength is removed by a dichroic mirror. These intermediate wavelengths of 768 nm (λ2) and 515 nm (λ3) can be combined in the master laser system 105 and then directed to the second conversion assembly 125 in the handpiece 110 using a single optical fiber, or they can be transmitted to the second conversion assembly 125 in two separate optical fibers and combined within the second conversion assembly 125 in the handpiece.

[0040] Figure 2 An exemplary embodiment of a handpiece 200 is shown having a single fiber transmission configuration.

[0041] Intermediate wavelengths λ2 and λ3 are delivered to handpiece 200 by a single optical fiber 205. Fiber 205 can be connected to handpiece 200 via a fiber coupler 210. Fiber 205 is rigidly attached to an optical platform 215 within handpiece 200. Input beam 220 is captured by lens L1 and refocused into nonlinear crystal (NLC) 225, which generates UVB (e.g., at 308n) and a frequency-generated output beam 230, which may contain residual intermediate wavelengths λ2 and λ3. Beam 230 is collected and collimated by lens L2. Intermediate wavelengths λ2 and λ3 are stripped from beam 230 by dichroic mirror DM1 235. The residual intermediate wavelengths are reflected by DM1 toward an absorptive heat sink 240, such as a thick aluminum wall coated with black light-absorbing paint. The generated heat is absorbed by the aluminum block and dissipated into the environment. UVB beam 245 is transmitted through DM1 235 to diverging lens L3. Light beam 245 enters conduit 250, which has a wall 255 with an appropriate UVB reflective surface on its inner surface and has an aperture 260 at the opposite end. Conduit 250 can be a square cross-section conduit with UVB reflectors on all four inner walls. The central beam and the reflected edges form a relatively uniform profile in the plane of the aperture.

[0042] Figure 3 An exemplary embodiment of a handpiece 300 is shown having a dual fiber optic transmission configuration.

[0043] Intermediate wavelengths λ2 and λ3 are delivered to the handpiece in separate optical fibers 305a and 305b. The two optical fibers 305a and 305b can be connected to the handpiece 300 via fiber couplers 310a and 310b, respectively. Optical fibers 305a and 305b are rigidly attached to an optical platform 315 within the handpiece 300. Input beams carrying wavelengths λ2 and λ3 are captured and collimated by lenses L4 and L5, respectively. The λ3 beam is reflected by mirror 320 and directed to a dichroic mirror 325, which reflects the λ3 wavelength and transmits the λ2 wavelength to combine the λ3 beam with the λ2 beam. Lens L6 focuses the combined beam into the NLC 225. Figure 3 The NLC 225 and the rest of the optical process in the handpiece 300 are Figure 2 The single fiber approach in the handpiece 200 is the same.

[0044] In a representative implementation of a single-fiber or multi-fiber configuration, the diameter of the lens and reflector is typically about 12.5 mm. The NLC is typically about 3 mm x 3 mm x 35 mm and can be housed in a small oven (not shown) to maintain a constant temperature. The output conduit through which the UVB output beam (e.g., 308 nm wavelength) passes is about 7.5 cm long and has an aperture of about 2 cm x 2 cm. While representative dimensions are disclosed herein, the components of any particular embodiment may be larger or smaller in size.

[0045] This output conduit can be specifically configured to produce a beam output that closely resembles the beam output produced by the existing handpiece design used in Strata Skin Sciences' Xtrac phototherapy system, where a XeCl excimer-generated beam exits the light guide. Various aspects of this handpiece design are disclosed in U.S. Patent No. 11,471,695, the entire contents of which are incorporated herein by reference.

[0046] In the embodiments described above, the components of the UVB frequency conversion assembly are shown as being within the handpiece housing. In the alternative embodiment 400, and with reference to Figure 4 A UVB frequency conversion assembly 125 for generating UVB therapeutic radiation from λ2 and λ3 wavelength light input is located in a housing 405 separate from a handpiece 410. The output λ2 and λ3 wavelength light generated by the primary laser system 105 is supplied to the UVB frequency conversion assembly via a fiber optic cable 130. A second fiber optic cable 415 delivers the UVB radiation generated by the UVB frequency conversion assembly from the housing 400 to the handpiece 410.

[0047] This alternative embodiment allows the use of conventional handpieces that require an external source of UVB therapeutic radiation, while still retaining most of the advantages provided by embodiments having a UVB frequency conversion assembly 125 within the handpiece. The secondary fiber optic cable 410 can be significantly shorter than the primary fiber optic cable 130. For example, the main fiber optic cable 130 can be 1.5 m or 2 m in length, while the secondary fiber optic cable 410 can be between 10 cm and 30 cm or between 5 cm and 50 cm. Due to its short length, energy absorption within the secondary cable 410 is relatively low, so overall UVB power loss may not be significant. Although the secondary cable 410 may degrade over time, if it needs to be replaced, its cost will be lower than replacing the much longer main cable 130. The UVB frequency conversion assembly housing 400 can be configured to be worn by the handpiece operator (e.g., around the waist or arm) so as to not interfere with operation of the handpiece.

[0048] While the present system is presented in the context of generating light in the UVB spectral band (e.g., substantially 308 nm) to provide ultraviolet phototherapy treatment, the improved system and method may also be used to improve the efficiency of other systems that currently transmit high-frequency laser energy through optical fibers and where the length and composition of the optical fibers result in significant energy losses.

[0049] While various aspects, embodiments and examples of the present invention have been disclosed and described herein, modifications, additions and substitutions may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the accompanying claims.

Claims

1. A phototherapy treatment system comprising: a master laser that outputs laser light at wavelengths λ2 and λ3, wherein 1 / λ2 + 1 / λ3 is substantially equal to 1 / λ4, and wherein λ4 is in the UVB spectral band between 304 nm and 312 nm; a housing having a UVB frequency conversion assembly therein for generating UVB light having a wavelength of λ4 from input light having wavelengths of λ2 and λ3; and A first fiber optic cable optically connects the master laser and the housing and is configured to transmit the laser light from the master laser to the housing.

2. The system according to claim 1, wherein: The housing includes a handpiece configured to emit UVB light generated by the UVB frequency conversion assembly through an aperture in the handpiece, wherein the emitted UVB light can be applied to the skin of a patient.

3. The system of claim 2, wherein the first fiber optic cable has a first end and a second end, The master laser includes a first fiber optic coupler to which the first end of the fiber optic cable is connected; and The handpiece includes a second fiber optic coupler to which the second end of the fiber optic cable is connected.

4. The system of claim 1 , further comprising a handpiece separate from the housing, the handpiece being connected to the housing via a second fiber optic cable, wherein The second fiber optic cable is used to transmit UVB light generated by the UVB frequency conversion assembly from the housing to the handpiece, and the handpiece is configured to emit UVB light through an aperture therein, wherein the emitted UVB light can be applied to the patient's skin.

5. The system according to claim 4, wherein: The length of the second fiber optic cable is significantly less than the length of the first fiber optic cable.

6. The system according to claim 4, wherein: The housing is wearable.

7. The system of claim 1 , wherein the master laser comprises: a primary laser generating light having a wavelength λ1; as well as An intermediate frequency conversion component is used to generate light with wavelengths λ2 and λ3 from light with wavelength λ1.

8. The system according to claim 1, wherein: The master laser outputs a laser beam having a wavelength of λ2 and a laser beam having a wavelength of λ3 in separate beams. The first fiber optic cable includes a first optical fiber and a second optical fiber, the first optical fiber is optically connected to the master laser to transmit laser light of wavelength λ2, and the second optical fiber is optically connected to the master laser to transmit laser light of wavelength λ3; The UVB frequency conversion assembly includes a combining optical component for combining the laser light of wavelength λ2 received through the first optical fiber and the laser light of wavelength λ3 received through the second optical fiber.

9. The system according to claim 1, wherein: The wavelength λ4 is substantially 308 nm.

10. The system of claim 1, wherein the first fiber optic cable has a length of at least 1 m.

11. A method for generating UVB light for phototherapy treatment, the method comprising the steps of: Connect the master laser to the remote housing using a fiber optic cable; generating laser light of wavelengths λ2 and λ3 using the master laser, wherein 1 / λ2 + 1 / λ3 is substantially equal to 1 / λ4, and wherein λ4 is in the UVB spectral band between 304 nm and 312 nm; and Laser light at wavelengths λ2 and λ3 from the master laser is converted to UVB light at wavelength λ4 using a UVB frequency conversion assembly in the housing.

12. The method according to claim 11, wherein The housing includes a handpiece having an aperture, the method further comprising the step of emitting UVB light generated by the UVB frequency conversion through the aperture.

13. The method according to claim 11, further comprising the steps of: A handpiece having an aperture is optically connected to the housing using a second fiber optic cable, wherein UVB light generated in the housing is transmitted by the second fiber optic cable to the handpiece and emitted from the aperture of the handpiece.

14. The method according to any one of claims 12 to 13, further comprising the following steps: UVB light emitted from the aperture of the handpiece is applied to the patient.

15. The method according to claim 11, wherein the step of using the master laser to generate laser light of wavelengths λ2 and λ3 comprises the following steps: generating light having a wavelength λ1 using a primary laser; as well as Light having wavelengths λ2 and λ3 is generated from the light having wavelength λ1 using an intermediate frequency conversion component.

16. The method according to claim 11, wherein The generated laser light at wavelength λ2 and the generated laser light at wavelength λ3 are each transmitted from the master laser through separate optical fibers in the first optical fiber cable, the method further comprising combining the light at wavelength λ2 and the light at wavelength λ3 in the housing.

17. The method according to claim 11, wherein The wavelength λ4 is substantially 308 nm.

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