Multi-frequency laser system for treating skin conditions

Abstract

A multi-frequency laser system and a method for treating skin conditions via a handpiece features an excitation laser module having a single laser beam at a first frequency. A dual laser module comprises dual free-running laser resonators for receiving the laser beam at the first frequency and generating a laser beam at a second frequency and a laser beam at a third frequency. A frequency conversion module is configured to accept the laser beam at the second frequency and the laser beam at the third frequency as inputs and selectively provide the laser beams to the handpiece, including a second harmonic generation at the second frequency, a second harmonic generation at the third frequency, a sum frequency generation of the second and third frequencies, the laser beam at the first frequency, the laser beam at the second frequency, and / or the laser beam at the first frequency combined with the laser beam at the second frequency. The handpiece receives the laser beams from the frequency module and emits the laser beams onto the skin for treatment.

Description

[Technical Field]

[0001] [Related applications] This application claims the benefit and priority of U.S. Patent Application No. 18 / 627533, filed on April 5, 2024, pursuant to Sections 119, 120, 363, and 365 of the U.S. Patent Act and Sections 1.55 and 1.78 of the U.S. Patent Act Enforcement Regulations, and the benefit and priority of U.S. Provisional Patent Application No. 63 / 495674, filed on April 12, 2023, pursuant to Sections 119, 120, 363, and 365 of the U.S. Patent Act and Sections 1.55 and 1.78 of the U.S. Patent Act Enforcement Regulations, which are incorporated herein by reference.

[0002] The invention of this subject relates to lasers used in dermatology. [Background technology]

[0003] Lasers are increasingly playing a significant role in treating a variety of skin conditions, including the removal of vascular lesions, unwanted hair, pigmented lesions, and skin rejuvenation. The rapid acceptance of laser applications in dermatology has been largely driven by the theory of selective photothermal decomposition. This theory correlates three laser parameters (wavelength, pulse duration, and fluence) with the size of the intended target in order to safely achieve the desired skin response. Specifically, the appropriate laser wavelength must be selected to selectively target the chromophore responsible for the particular skin condition. Some of the common chromophores in skin include hemoglobin (oxygenated and deoxygenated hemoglobin), melanosome melanin, tattoo ink, water, and adipose tissue. Each chromophore reveals itself through its characteristic absorption spectrum, as shown in Figure 1. To effectively treat vascular-related skin problems, including hemangiomas, port-wine stains, rosacea, and leg veins, it is preferable to selectively target deoxygenated hemoglobin using wavelengths in the 500-600 nm range. Clinically, several wavelengths (i.e., 532 nm, 585 nm, or 595 nm) are commonly used for vascular treatment: shorter wavelengths (i.e., 532 nm) for smaller, shallower vessels, and longer wavelengths (585 / 595 nm) for deeper, larger vessels. Near-infrared wavelengths may be necessary for even deeper vessels or patients with darker skin. For example, wavelengths of 755 nm or 1064 nm have proven effective for treating leg veins or patients with darker skin types. Therefore, multiple possible wavelengths, from green, yellow, and orange to near-infrared, are used for customized treatments that yield optimal clinical outcomes for different vascular lesions or different patient groups.

[0004] The removal of unwanted hair is another well-known application of two near-infrared wavelengths (i.e., 755 nm and 1064 nm). Furthermore, 755 nm can also be a good wavelength for pigmented lesions, thanks to its well-balanced wavelength that favors the absorption of melanosomes to hemoglobin. In addition to treating blood vessels, hair, and pigments, lasers are widely used for skin rejuvenation. For example, wrinkle reduction and skin tightening represent one of the fastest-growing areas. Long-pulsed lasers for skin tightening or wrinkle reduction primarily target water and are based on radiant heat bulk heating resulting from the substantial absorption of laser energy by water. The laser (laser beam) needs to penetrate deep enough to reach the dermis layer where collagen is located. Heating collagen to a temperature between 65°C and 80°C leads to collagen contraction because it breaks hydrogen bonds that reduce pigmentation in the triple-helix collagen fibers, resulting in rapid skin tightening or a secondary stimulus of collagen growth via an inflammatory healing response in the skin that occurs at lower temperatures. In this case, there are two requirements for the laser wavelength: sufficient water absorption and sufficient tissue penetration depth. Wavelengths ranging from 1.2 μm to 1.5 μm, as shown in Figure 1, may be suitable for this purpose. Therefore, a laser system with multi-wavelength capabilities covering a wide range from visible light to near-infrared light can provide optimal treatment for a variety of skin conditions, from vascular lesions, hair, and pigmentation to skin tightening.

[0005] Based on the theory of selective photothermal decomposition, the pulse duration must be shorter than the thermal relaxation time of the target chromophore present in the skin in order to selectively damage the target without causing undesirable thermal damage to adjacent tissues. Depending on the size of the target, such as blood vessels or hair follicles, the preferred pulse duration is estimated to be in the range of several hundred microseconds to several hundred milliseconds. To meet such clinical needs, medical aesthetic lasers must be designed so that the pulse duration is adjustable over a wide range from less than 1 millisecond to 100 milliseconds.

[0006] Other laser parameters include a sufficiently high output energy to support sufficient fluence for effective treatment with a sufficiently large spot, not only for deep targeting but also for rapid treatment. For example, up to 15 J / cm² to treat some vascular lesions. 2 This energy is typically required. This means that more than 4 J of emitted laser energy is supplied for a 6 mm spot size. 7 J / cm² for a 15 mm spot. 2 In that case, a laser energy of 12J is required to be emitted into the tissue, and if a pulse duration of 1ms is also required, a peak power of 12kW is needed, making it even more difficult.

[0007] However, no multi-joule level high-energy laser systems are known that can emit multiple wavelengths ranging from visible light to near-infrared wavelengths with adjustable pulse durations from hundreds of microseconds to hundreds of milliseconds. Several medical device companies are manufacturing lasers to meet some of these requirements. In some devices, the user can switch between handpieces connected to a control panel to generate two different laser wavelengths.

[0008] In terms of wavelength generation, some of the near-infrared wavelengths, such as 755 nm, 1064 nm, 1320 nm, 1440 nm, or 1550 nm, are produced by crystals doped with alexandrite and rare earth ions (i.e., Nd 3+ Yb 3+ , or Er 3+It can be produced by direct laser emission from several well-known laser crystals (nonlinear crystals, nonlinear optical crystals), including ). To obtain a green laser (i.e., 532 nm or 524 nm), a two-step process is typically involved: a first step to generate 1064 nm or 1047 nm with Nd:YAG or Nd:YLF, followed by a second harmonic frequency conversion by a nonlinear crystal (e.g., KTP or LBO). It should be mentioned that all methods for generating these wavelengths are based on solid-state lasers. However, yellow or orange wavelengths are commonly produced with dye lasers thanks to the broad wavelength tuning capability of the laser dyes. Clinically, dye lasers represent one of the most successful laser technologies in dermatological applications, primarily treating vascular lesions. In addition to emitting a clinically preferred wavelength of 595 nm, dye lasers can readily emit pulse energies exceeding 15 J in 1 ms, which is not possible with today's solid-state crystal lasers. However, dye lasers present challenges related to the necessary handling, refilling, and disposal of toxic liquid dye solutions, short and finite pulse counting, and low pulse-to-pulse consistency in implementation. To overcome these challenges, solid-state laser approaches combined with frequency conversion techniques may offer an alternative for generating substantial energy in short pulses at 595 nm.

[0009] Compared to dye lasers, solid-state lasers offer advantages such as smaller size, higher efficiency, greater robustness, and the absence of toxic dyes. To date, different solid-state laser techniques have been used to generate laser wavelengths in the yellow to orange range. The initial technique is direct emission from the laser medium. One example is praseodymium (Pr) excited with a blue diode, made possible by the recent development of this crystal in recent years. 3+ This is a YLF doped with ). The watt level of output at 607nm has been demonstrated with a slope efficiency of approximately 49%. However, further power scaling is limited by the availability of high-power blue diodes. Another classification is neodymium (Nd3+ Raman lasers using a gain medium doped with Nd are intended to shift the approximately 1 μm laser emission from an Nd-doped crystal to a yellow wavelength using some Raman medium. Nearly 5 W at 588 nm has been reported for Nd:YLF-based Raman lasers. However, the relatively low efficiency presents a technical challenge for further increasing the output, and it has not yet approached the required 12 kW.

[0010] Sum-frequency generation (SFG) lasers represent the most studied method for generating yellow and orange wavelengths. This method involves generating two wavelengths (i.e., approximately 1 μm and 1.3 μm) based on a laser material doped with rare earth ions, at least one of which is then converted to yellow-orange via an SFG using a nonlinear crystal such as KTP, LBO, or BIBO. Since the fundamental laser is coupled with the SFG when the laser is operated in quasi-CW or CW mode, SFGs in cavities are typically used to increase SFG efficiency at the expense of complex cavity configuration and high-precision alignment. Another configuration is a Q-switched laser with an electro-optical (EO) or acousto-optical (AO) modulator intended to increase peak power to achieve better SFG efficiency. However, the use of active Q-switching (EO or AO) results in increased cost and alignment complexity. Another drawback of this configuration is that the temporal overlap of the two Q-switched laser pulses requires highly precise temporal synchronization with nanosecond accuracy. Electronic jitter or environmental fluctuations can cause variations in the temporal overlap of the two fundamental laser pulses, potentially resulting in lower frequency conversion efficiency and pulse-by-pulse instability.

[0011] Furthermore, the overall light-to-light efficiency may be reduced due to the Q-switching process. It is worth noting that, in either configuration (i.e., CW or Q-switched), two separate excitation sources (i.e., flash lamps or diode lasers) are more commonly used to excite two laser cavities to generate the fundamental wavelength. The generation of maximized frequency conversion requires a temporal overlap between the two laser pulses of the two fundamental lasers, which is typically achieved by proper synchronization between the excitation sources for each laser cavity. Such synchronization of the two excitation lasers typically results in complex electronic timing control and potential instability of the output energy due to variations in circuit jitter. Configurations involving Q-switching mechanisms can become even more complex due to the synchronization of the Q-switch with the two excitation sources and the added nanosecond precision required. Regarding the output power of yellow / orange lasers, records of approximately 90W at 589nm have been reported in SFGs for two fundamental-wave lasers (i.e., 1064nm and 1319nm), but this is at least two orders of magnitude lower than the output power of flashlamp-excited dye lasers (i.e., over 10kW).

[0012] For the reasons mentioned above, high-power (over kW) / high-energy (Joule level) yellow-orange solid-state lasers with a simple and stable configuration (without complex synchronization) are preferred over liquid dye lasers to satisfy the clinical need to treat larger and deeper vascular lesions. Similarly, skin rejuvenation, as well as unwanted hair and pigmentation, will also benefit from high energy in the near-infrared wavelength for effective and rapid treatment. [Overview of the project] [Means for solving the problem]

[0013] Disclosed in one embodiment is a high-power (over kW) / high-energy (Joule level) long-pulse solid-state laser system capable of emitting multiple selectable wavelengths ranging from visible light wavelengths to near-infrared wavelengths through direct emission or nonlinear frequency conversion (i.e., second harmonic generation (SHG) and sum frequency generation (SFG)). A single long-pulse high-energy (up to 60 J) and high-power laser (over 20 kW) is used to excite two solid-state lasers to perform optical synchronization without introducing a control circuit. The design of unstable resonators with appropriate optical arrangement for each laser cavity enables the achievement of good beam quality (M2 ≥ 5) to ensure good focus matching capability, resulting in high efficiency of nonlinear frequency conversion at high power energies. The output of high-energy lasers with multiple switchable wavelengths provides customized treatments for a wide range of skin conditions, including vascular lesions, unwanted hair, pigmented lesions, and skin rejuvenation.

[0014] Disclosed is a novel apparatus for emitting high-energy long-pulse laser energy at multiple user-switchable wavelengths ranging from visible to near-infrared wavelengths for customized treatment of various skin problems, including vascular lesions, unwanted hair, pigmented lesions, and skin rejuvenation. The disclosed laser device can be excited with a high-energy (up to 60 J) laser in a single long pulse (from μs to ms) with an output exceeding 20 kW to generate two near-infrared laser wavelengths at approximately 1 μm (i.e., 1.03–1.08 μm) and approximately 1.3 μm (i.e., 1.3–1.35 μm) by performing optical synchronization of a laser medium doped with two rare-earth ions. An unstable cavity design is introduced to achieve both high energy and good beam quality (M2 greater than 5) without the use of any mode-selection elements. The high energy and good beam quality provide sufficient power intensity (10 MW / cm²) with good beam focus matching capability for efficient SHG or SFG. 2This makes it possible to achieve ultra-high wavelengths. Green wavelengths (i.e., 515–540 nm) and red wavelengths (e.g., 650–675 nm) are obtained with SHGs of fundamental wavelength lasers of approximately 1 μm or approximately 1.3 μm, respectively. Generation of yellow or orange lasers (i.e., 580–600 nm) can be carried out with SFGs of two fundamental wavelengths (i.e., approximately 1 μm and approximately 1.3 μm). In short, the device disclosed herein can emit six distinct wavelengths (i.e., 700–980 nm, 1.03–1.08 μm, 1.3–1.35 μm, 515–540 nm, 650–670 nm, and 580–600 nm). The device may also be configured to emit a laser beam with mixed wavelengths of two infrared lasers (i.e., approximately 1 μm and approximately 1.3 μm). The beam characteristics that can be emitted onto the skin include single beams, microbeam arrays, or two mixed beam profiles with adjustable spot sizes, depending on the needs of different treatments. All lasers of different wavelengths can generate laser pulses that vary from several hundred microseconds to several hundred milliseconds, determined by the pulse duration setting of the excitation laser.

[0015] It is characterized by a all-solid-state laser system that combines direct laser emission from two laser cavities, followed by non-linear frequency conversion and beam emission assembly. The system can emit laser beams with variable pulse durations that can be optically synchronized at switchable multi-wavelengths. The single high-energy / high-power pump laser has several unique capabilities, including those preferably used to excite two laser resonators to achieve optical synchronization without introducing a control circuit. The two laser resonators are preferably configured as unstable cavity arrangements to achieve high energy output with good beam quality (M2 of 5 or more), which ensures efficient non-linear frequency generation (i.e., SHG or SFG) with appropriate focusing alignment capabilities. The free-running operation of the two laser resonators without a Q-switch not only provides a compact and cost-effective design but also offers the possibility of optically implementing temporal synchronization without introducing expensive and complex control circuits. The free-running operation of the two laser resonators also makes it possible to generate truly long pulse outputs. The pulse duration can be easily adjustable by adjusting the pulse duration of the pump laser.

[0016] The configuration of non-linear frequency conversion (i.e., SHG or SFG) in an external cavity allows for a more compact arrangement and easier alignment. Two near-infrared wavelengths (i.e., approximately 1 μm and approximately 1.3 μm) can be generated from two laser resonators based on a laser medium doped with rare-earth ions through direct emission, while the other three visible wavelengths are generated through SHG and SFG of the two fundamental near-infrared wavelengths. The laser media of the two laser resonators can be crystals or ceramics doped with rare-earth ions (i.e., Nd 3+ or Yb 3+ ). The laser media for the two cavities can be of the same type or different types.

[0017] The device emits joule-level energy or kW-level peak power at all laser wavelengths, including green, yellow-orange, red, and near-infrared, enabling effective treatment of a wide range of skin conditions, from vascular lesions, pigmentation, hair, and skin rejuvenation. The ability to emit selectable wavelengths and variable pulse duration allows for customized treatments with various indications. The disclosed device can emit two laser pulses of different wavelengths with a predetermined time delay or simultaneously. The disclosed device can emit beam patterns that are mixed with different wavelengths (for example, a solid beam at one wavelength is superimposed with a segmented microbeam pattern at another wavelength).

[0018] Characterized is a multi-frequency laser system for treating skin conditions, comprising a handpiece for treating skin conditions and an excitation laser module having a single laser beam at a first frequency. The dual laser module comprises dual free-running laser resonators for receiving a laser beam at a first frequency and generating a laser beam at a second frequency and a laser beam at a third frequency. The frequency conversion module is configured to accept the laser beam at a second frequency and the laser beam at a third frequency as inputs and to selectively provide the laser beams to the handpiece, including a second harmonic generation at the second frequency, a second harmonic generation at the third frequency, a sum frequency generation of the second and third frequencies, a laser beam at the first frequency, a laser beam at the second frequency, and / or a laser beam at the first frequency combined with a laser beam at the second frequency. The handpiece receives a laser beam from the frequency module and emits the laser beam onto the skin for treatment in the form of a variable-size solid beam, a fractional microbeam pattern, or a hybrid beam pattern of solid beam and fractional microbeam.

[0019] A multi - frequency laser system may further include a first optical subsystem for directly providing laser output at a first frequency output by an excitation laser to a handpiece for emission to a patient's skin. The multi - frequency laser system may further include a second optical subsystem for directly providing laser output at a second frequency, laser output at a third frequency, and laser output at a mixed second and third frequency from a dual - laser module to the handpiece for emission to the patient's skin.

[0020] The excitation laser module is preferably a free - running long - pulse high - energy laser. The dual - laser resonator may include different types or the same type of laser medium. The laser resonator may be a free - running laser simultaneously excited by the excitation laser. The dual - laser resonator may be configured as an unstable cavity to achieve both high energy for efficient non - linear frequency conversion and good beam quality. The dual - laser resonator may include a crystal or ceramic doped with rare - earth ions as the laser gain medium.

[0021] Frequency conversion may be performed in an external cavity configuration. The frequency - conversion module may include at least one non - linear optical crystal.

[0022] In one example, the first frequency (or corresponding wavelength) is approximately 700 - 980 nm, the second frequency is approximately 1.03 - 1.08 μm, and the third frequency is approximately 1.3 - 1.35 μm. The laser output at the second harmonic frequency of the second frequency may be approximately 515 - 540 nm, and the laser output at the second harmonic frequency of the third frequency may be approximately 650 - 675 nm. The sum frequency of the second frequency and the third frequency can generate a laser beam at a frequency of approximately 580 - 600 nm.

[0023] The laser beams of the mixed second and third frequencies can be emitted to the skin with a predetermined delay or simultaneously. The laser system can emit a mixed beam pattern for the second and third frequencies. The laser system can emit a variable pulse duration ranging from several hundred microseconds to several hundred milliseconds that can be controlled by adjusting the pulse duration of the excitation laser.

[0024] Also characterized is a multi-frequency laser method for treating skin conditions, comprising the steps of providing a laser beam at a first frequency, using a dual free-running laser resonator to generate a laser beam at a second frequency and a laser beam at a third frequency from the laser beam at the first frequency, receiving the laser beam at the second frequency and the laser beam at the third frequency in a frequency conversion module, generating the second harmonic of the second frequency, generating the second harmonic of the third frequency, generating the sum frequency of the second frequency and the third frequency, and selectively providing the laser beam to a handpiece, including the laser beam at the first frequency, the laser beam at the second frequency, and / or the laser beam at the first frequency combined with the laser beam at the second frequency.

[0025] However, in other embodiments, the invention of the present subject matter need not achieve all of the above objects, and the claims of the invention of the present subject matter should not be limited to structures or methods that can achieve these objects.

[0026] Other objects, features, and advantages can be envisioned by those skilled in the art from the following description of the preferred embodiments and the accompanying drawings.

Brief Description of the Drawings

[0027] [Figure 1] It is a graph of the absorption spectra of several major chromophores present in the skin. [Figure 2A]This is a schematic block diagram of a preferred system architecture for a solid-state laser system. [Figure 2B] This is a schematic block diagram of a preferred system architecture for a solid-state laser system. [Figure 3A] This is a schematic diagram of the excitation laser module. [Figure 3B] This is a schematic diagram of the excitation laser module. [Figure 3C] This is a schematic diagram of the excitation laser module. [Figure 4A] This is a schematic diagram of a dual laser module containing two cavities with separate cavity mirrors (the two laser media are made of anisotropic materials). [Figure 4B] This is a schematic diagram of a dual laser module containing two cavities with separate cavity mirrors (one of the laser media, i.e., LM1, is an isotropic material). [Figure 5A] This is a diagram illustrating an example of a Pump Beam Steering Assembly (PSA) for both unpolarized and polarized excitation lasers. [Figure 5B] This is a diagram illustrating an example of an excitation beam steering assembly (PSA) for both unpolarized and polarized excitation lasers. [Figure 5C] This is a diagram illustrating an example of an excitation beam steering assembly (PSA) for both unpolarized and polarized excitation lasers. [Figure 6] This is a diagram illustrating an example of an excitation beam steering assembly (PSA) for a linearly polarized excitation laser. [Figure 7] This is a schematic diagram of a dual laser module containing two cavities with a common output coupler. [Figure 8] This is a schematic diagram of a dual laser module containing two cavities with a common mirror HR. [Figure 9] This is a schematic diagram of a dual laser module containing two cavities with the same mirror HR and output coupler. [Figure 10]This is a schematic diagram of a dual laser module containing two monolithic cavities. [Figure 11] This is a diagram of a composite monolithic laser rod. [Figure 12] This is a schematic diagram of a dual laser module including a composite monolithic laser rod. [Figure 13] This is a diagram of a frequency conversion module with a single crystal for nonlinear frequency generation. [Figure 14A] This is a diagram of a frequency conversion module in wavelength-selective mode for outputting a single wavelength λ1. [Figure 14B] This is a diagram of a frequency conversion module, which is a wavelength-selective mode for outputting a single wavelength λ2, λ3 or a mixed wavelength of wavelengths λ2 and λ3. [Figure 14C] This is a diagram of a frequency conversion module, which is a wavelength-selective mode for outputting three visible light wavelengths (i.e., wavelengths λ4, λ5, and λ6) generated from a nonlinear frequency conversion. [Figure 15] This is a diagram of a frequency conversion module with three crystals for generating nonlinear frequencies. [Figure 16A] This is a schematic diagram of a frequency conversion module in emission wavelength mode with a single wavelength λ1. [Figure 16B] This is a schematic diagram of a frequency conversion module in emission wavelength modes of a single wavelength λ2, λ3, or a mixed wavelength of wavelengths λ2 and λ3. [Figure 16C] This is a schematic diagram of a frequency conversion module in the emission wavelength modes of wavelength λ4 or λ5, which are generated by a second harmonic frequency conversion of wavelength λ2 or wavelength λ3, respectively. [Figure 16D] This is a schematic diagram of a frequency conversion module in the emission wavelength mode of wavelength λ6, which is generated from sum frequency conversion with wavelength λ2 or wavelength λ3. [Figure 17A] This diagram illustrates the sequential emission of dual-pulse lasers with a specific time delay. [Figure 17B] This diagram illustrates the simultaneous emission of dual-pulse lasers. [Figure 18] This is a diagram of the emission of a mixed beam profile for a laser with mixed wavelengths. [Figure 19A] This is a diagram of a handpiece used to emit a blended beam profile onto the skin (a lens array is used). [Figure 19B] This is a diagram of a handpiece used to emit a blended beam profile onto the skin (a diffraction beam splitter is used). [Modes for carrying out the invention]

[0028] Apart from the preferred embodiments disclosed below, the present invention is capable of other embodiments and can be implemented or carried out in a variety of ways. Therefore, it should be understood that the present invention is not limited in its application to the structural and arrangement details of the components described below or shown in the drawings. Where only one embodiment is described herein, the claims are not limited to that embodiment. Furthermore, the claims should not be read restrictively unless there is clear and compelling evidence indicating a particular exclusion, limitation, or abandonment.

[0029] In one example shown in Figure 2A, a single excitation laser (excitation laser module) 10 has a laser output at a first frequency directed to a dual laser module 12, which generates a laser output at a second frequency and another laser output at a third frequency. A frequency conversion module 14 accepts the laser outputs at the second frequency and the laser output at the third frequency from the dual laser module 12 as input and is configured to selectively provide the handpiece 16 with laser outputs that are the second harmonic generation (SHG) of the laser output at the second frequency, the SHG of the laser output at the third frequency, the sum frequency generation wavelength of the second and third frequencies, the laser output at the first frequency, the laser output at the second frequency, and / or the laser output at the first frequency combined with the laser output at the second frequency.

[0030] In one example, for emission onto the patient's skin, a first optical subsystem 18 may be configured to directly provide a laser output at a first frequency to the handpiece 16, and a second optical subsystem 20 may be configured to directly provide laser outputs at a second frequency and a third frequency from the dual laser module 12 to the handpiece 16. In another embodiment, the laser outputs from the excitation laser 10 and the laser outputs from the dual laser module 12 are provided to a frequency conversion module 14, but no conversion is performed, and therefore the laser outputs at the first, second, and third frequencies are directed to the handpiece 16 without frequency conversion.

[0031] The excitation laser 10 is preferably a long-pulse high-energy laser. The dual laser module 12 may comprise two laser resonators, each configured as a laser medium. The frequency conversion module may include at least one nonlinear optical crystal. In one example, the first frequency (or corresponding wavelength) is 700–980 nm, the second frequency is 1.03–1.08 μm, and the third frequency is 1.3–1.35 μmde. In one example, the SHG of the laser output at the second frequency is 515–540 nm, the SHG of the laser output at the third frequency is 650–675 nm, and the SFG of the laser output at the second frequency and the SFG of the laser output at the third frequency. The SFG can generate a laser beam at frequencies of 580–600 nm. In some examples, the wavelengths output by the handpiece may be 593 nm, 755 nm, 1064 nm, and 1342 nm.

[0032] Figure 2A also shows an input / output area 24 (e.g., including a touchscreen) that allows the user to select one or more specific wavelengths, and a control device 26 that controls a frequency conversion module 14 and also controls optical subsystems 18,20 so that the handpiece accepts the selected wavelengths and emits them onto the patient's skin. The control device 26 may be a processor, microcontroller, or computer programmed with software instructions stored in a memory device.

[0033] One exemplary apparatus comprises four main modules, including an excitation laser module, a dual laser module, a frequency conversion module, and a treatment handpiece. Figure 2B is a block diagram of the exemplary system architecture. In short, the excitation laser 10 is a single laser source capable of emitting a peak power of 20 kW with over 60 J in long pulse mode (i.e., from several hundred microseconds to several hundred milliseconds) at a wavelength of λ1. The dual laser module 12 accepts the excitation laser and generates two near-infrared wavelengths λ2 and λ3 (i.e., approximately 1 μm and approximately 1.3 μm) via direct laser processing emission from two laser resonators. The frequency conversion module 14 takes the two wavelength lasers generated from the aforementioned module and the excitation laser as two inputs and selectively directs seven laser outputs of different wavelengths as outputs, namely λ1, λ2, λ3, mixed λ2 and λ3, λ2 / 2, λ3 / 2, and (λ2×λ3) / (λ2+λ3). The first four outputs are performed by appropriate beam steering optics, while the rest are generated through nonlinear frequency conversion (i.e., SHG or SFG) using at least one nonlinear crystal. As a final functional group, the handheld module (i.e., processing handpiece 16) can emit seven laser beams with different beam characteristics for different treatments (i.e., a single beam with an adjustable spot size or microbeam array).

[0034] [Excitation laser module] The excitation laser module preferably provides a long-pulse high-energy (over 60 J) laser capable of emitting a peak power of 20 kW with pulse durations that can vary from several hundred microseconds to several hundred milliseconds. In one example, the energy level is between 200 mJ and 20 J, and the pulse duration is between 0.5 ms and 100 ms. Its wavelength λ1 typically matches the absorption of a rare-earth ion-doped laser medium in the two laser resonators of the module. For example, this laser could be an alexandrite laser excited by a flash lamp emitting 60 J (or over 20 kW) at approximately 753 nm–3 nm to 753 nm+3 nm. In an alternative example, the excitation laser could be a high-power diode laser emitting laser in the range of 800–980 nm. The precise selection of the excitation wavelength is determined by the matching of the absorption of a particular laser medium. The excitation laser generates an excitation laser pulse at λ1, which can be emitted in a multimode fiber (i.e., Figure 3A) or in free space to a collimating lens L1 (i.e., Figure 3B). The parallelized excitation beam further propagates to a movable mirror MM1, the position of which can be configured to be either inside or outside the beampath. When mirror MM1 is positioned in the excitation beampath, it redirects the beam directly to a frequency conversion module, which, in combination with the mirror (i.e., M1), becomes one of the final laser output wavelengths (i.e., λ1). When the movable mirror is driven outside the beampath, the parallelized excitation laser is emitted as an excitation source to the next module's dual laser module. Thus, the excitation laser module can consist of two output ports: one for direct output at λ1 and the other for exciting the dual laser module. It is worth noting that such a movable mirror can be a mirror on a rotating or translational stage. In the case of a polarized-excited laser beam in free space (e.g., configuration B), mirror MM1 can be a polarization element for selectively directing the excitation beam to one of the ports based on the polarization characteristics of the incident beam.In one embodiment, the polarization element may be a combination of a rotating half-wave plate and a polarizer cube or thin-film polarizer, as shown in Figure 3C. The half-wave plate HWP is mounted on a rotating stage and can rotate the orientation of linear polarization. When the excitation laser is rotated to P polarization, it passes through the polarization element to excite the dual laser module without reflection loss. When an S-polarized excitation beam is obtained at the half-wave plate, all the excitation energy is reflected by the polarization element and mirror M1 as other outputs of this module.

[0035] [Dual Laser Module] A dual laser module is one functional module of the system. As shown in Figure 2, the dual laser module accepts a parallel-pumped laser at λ1 to activate two laser resonators to generate two laser beams at wavelengths λ2 and λ3. These two wavelengths are in the near-infrared range, with one at approximately 1 μm (i.e., 1.03–1.08 μm) and the other at approximately 1.3 μm (i.e., 1.3–1.35 μm). The laser medium for the two laser resonators, i.e., LM1 and LM2, can be a laser material doped with rare earth ions. In some embodiments, the dopant is neodymium (Nd 3+ ) or Ytterbium (Yb 3+The host material may include yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), yttrium vanadate (YVO4), yttrium lithium fluoride (YLF), yttrium scandium gallium garnet (YSGG), gadolinium scandium gallium garnet (GSGG), or gadolinium vanadate (GdVO4) in crystalline form. In other examples, the host material may be amorphous, i.e., a ceramic material. It should be noted that LM1 and LM2 may be two different laser materials or the same material. When the same laser material is used for two laser cavities, it can selectively emit light at two wavelength lines (i.e., about 1 μm and about 1.3 μm). Table 1 lists some typical examples of laser materials that may be used in the system. For example, a laser may include an Nd:YAG gain medium to generate a 1.064 μm laser, while a different laser crystal, Nd:YAP or Nd:YVO4, may be used to generate a 1.342 μm laser. As shown in Table 1, multiple laser media can produce wavelengths in these two regions, but the choice of laser medium depends on various factors, including material properties (i.e., thermal conductivity, thermal expandability, birefringence, temperature dependence of refractive index, mechanical adaptability, etc.), available size, and cost.

[0036] [Table 1]

[0037] Lasers of two wavelengths can be configured in several different ways, based on the different optical arrangements of the two laser resonators. Some examples of these configurations are described below.

[0038] [Configuration A: Two cavities with separate cavity mirrors] In this configuration, the dual laser module provides two laser resonators, each having a separate high reflector and output coupler. As shown in Figure 4A, the parallel-oriented excitation laser at λ1 is selectively directed to either resonator I or resonator II, or both. Different excitation modes produce different wavelengths. More specifically, excitation of resonator I can produce a laser beam at wavelength λ2, while excitation of resonator II can produce another laser beam at wavelength λ3. The two wavelengths, λ2 and λ3, can occur simultaneously when both resonators are excited to each other by divided excitation energies.

[0039] The excitation laser beam is directed towards one or both of the laser resonators through a focusing lens L2 or L3 to provide an appropriate spot size and achieve optimal laser efficiency. Each cavity has its own cavity mirror, i.e., high reflectors (mirrors) HR1 / HR2, and output couplers OC1 / OC2. High reflectors HR1 or HR2 each have a covering to highly transfer the excitation laser to the laser resonator and to highly reflect new laser wavelengths (i.e., λ2 or λ3) to facilitate laser oscillation. OC1 and OC2 are partial reflectors acting as output couplers for the laser at λ2 and λ3, respectively. LM1 and LM2 are the laser medium for resonator I and resonator II, respectively. If the laser medium is inherently anisotropic (e.g., YLF and YVO4 doped with rare earth ions), the generated laser is linearly polarized. Therefore, there is no need to introduce any polarization element into the cavity in order to select a preferred polarization as the output. This situation is shown in Figure 4A, where both laser media LM1 and LM2 are birefringent. However, when an isotropic laser medium (e.g., YAG doped with rare earth ions) is used in the resonator, a polarization element (i.e., PE) needs to be added to support only one preferred polarization that oscillates and becomes the output. This situation is illustrated in Figure 4B. To achieve good beam quality at high output energies, an unstable cavity design is applied to the arrangement of the two resonators. In this application, a simple scheme for implementing unstable cavity operation is proposed. Clearly, the unstable cavity is formed by a planar mirror HR (i.e., HR1 or HR2) and a convex output coupler (i.e., OC1 or OC2). The use of a convex output coupler is a simple way to improve the beam quality (i.e., M2) of the generated laser beam by eliminating higher-order modes without introducing an additional mode-selection element, without complicating cavity alignment, and without adding greater cost. Typically, a steeper curvature of the OC mirror results in better beam quality, albeit with a disadvantage in output energy.The optimal cavity design involves a good balance between appropriate beam quality and high energy (M2 of 5 or higher). To optimize the overall laser performance at two wavelengths, aiming for the best nonlinear frequency conversion (primarily SFG) in the next step, several parameter selections should be considered.

[0040] The parameters mentioned above include the excitation beam splitting ratio, the focal lengths of the focusing lenses L2 and L3, the reflectivity and curvature of the output coupler, and the specifications of the laser crystal (i.e., doping concentration, length, and location). The output laser beams from the two resonators typically diverge. The output laser beams are parallelized by collimating lens L4 or L5 for each resonator. Each newly parallelized laser beam passes through half a wavelength (i.e., HWP1 or HWP2) before being combined with a dichroic mirror. The use of one half-wave plate for each laser beam (λ2 or λ3) is intended to adjust the polarization of the two beams to achieve phase matching for nonlinear frequency conversion. The two laser beams at wavelengths λ2 and λ3 propagate collinearly after the beam combiner DM1 and are emitted into the frequency conversion module.

[0041] The selection of different excitation modes is performed by an excitation beam steering assembly (PSA). Figure 5 shows an example of the optical configuration of the PSA. The PSA may include a translation stage equipped with two mirrors. One mirror HR has a highly reflective coating at wavelength λ1, and the other optical system BS is a beam splitter that can split the excitation beam into a portion directed to resonator I via transmission and the remaining portion of the excitation energy directed to resonator II via reflection. The splitting ratio of the excitation laser energy to resonator I to the excitation laser energy to resonator II is determined by optimizing the output energy from the two resonators to achieve the maximum frequency conversion, which is mainly sum-frequency generation. The PSA assembly has three positioning stops. When the translation stage is positioned so that neither mirror is in the excitation beam path (Figure 5A), all the excitation laser energy is directed to resonator I, producing a single wavelength λ2. When mirror HR is positioned in the excitation beam path (Figure 5B), the incident beam is completely reflected by mirror HR and further directed by mirror M2 to excite resonator II and generate a laser at wavelength λ3. In the final position (Figure 5C), the beam splitter BS is positioned in the excitation beam path, allowing both resonators to be excited simultaneously. In this case, two laser wavelengths can be generated. This excitation beam steering configuration can be used for both polarized and unpolarized incident excitation lasers.

[0042] In other words, this excitation beam steering configuration can work for both configurations of the excitation beam module (i.e., fiber-coupled excitation laser (Figure 3A) and excitation laser emitted in free space (Figure 3B)). In another example, excitation beam steering can be performed by a combination of a half-wave plate, HWP, and polarizing element when the excitation laser is linearly polarized (see Figure 6). The half-wave plate is mounted on a rotating stage and can rotate the orientation of the linear polarization. When the excitation laser is rotated to P polarization, it passes through the polarizing element without reflection loss. Thus, only cavity I is selectively excited, and only λ2 is produced. If an S-polarized excitation beam is obtained with a half-wave plate, all the excitation energy is reflected by the polarizing element to excite cavity II and produce wavelength λ3. If the polarization of the excitation laser is adjusted to be at any position between P-polarization and S-polarization, the incident excitation beam will be split into P-polarization and S-polarization to excite both cavities. If equal excitation energies are required to excite two cavities, the polarization of the excitation beam should be rotated by 45° with respect to the polarization direction of the S-polarized or P-polarized beam.

[0043] With an excitation beam steering selector (PSA), the aforementioned module can emit near-infrared lasers in three modes: a single wavelength λ2, a single wavelength λ3, and two mixed wavelengths. In some examples, a 60 J and 20 kW alexandrite laser is used as a single excitation source. Modules with Nd:YAG and Nd:YAP materials emit an output of approximately 30 J at 1.064 μm from the Nd:YAG resonator, an output of approximately 25 J at 1.342 μm from the Nd:YAP resonator, or simultaneously emit two wavelengths (i.e., approximately 15 J at 1.064 μm and approximately 13.5 J at 1.342 μm).

[0044] [Configuration B: Two laser cavities sharing one common output coupler] This configuration is a variation of configuration A. As shown in Figure 7, the two cavities share one common output coupler OC but are accompanied by separate high reflectors HR1 or HR2. The use of a single convex output coupler OC aims to implement unstable cavity operation for both resonators in order to achieve good beam quality at both laser wavelengths (i.e., wavelengths λ2, λ3). The reflectivity of this output coupler is designed to obtain optimally high energy at wavelengths λ2, λ3. Mirror M3 and dichroic mirror DM1 are used within the coupled cavity to direct the oscillating beam at wavelength λ2 and combine it with the second oscillating beam at wavelength λ3. Dichroic mirror DM1 is configured to highly reflect light at wavelength λ2 and highly transmit light at wavelength λ3. The combined output lasers are parallelized by lens L6 before entering the frequency conversion module. In the example shown in Figure 7, it should be noted that the two laser media (i.e., LM1 and LM2) are inherently birefringent so that the laser output is inherently polarized. Adjusting the polarization of each beam generated from each resonator can be achieved by rotating either laser medium LM1 or laser medium LM2. If an isotropic laser medium is used, a polarization element should be inserted into the resonator to generate a linearly modified beam.

[0045] [Configuration C: Two laser cavities sharing one common high-reflectivity material to form a cavity] In another embodiment, two laser cavities share a single common high reflector HR. Figure 8 shows this configuration in which two resonators have a birefringent laser medium. Similar to configuration A, each new laser beam emerging from the corresponding resonator has its own collimating lens (i.e., L4 or L5) to keep the laser beam parallel, and a half-wave plate (i.e., HWP1 or HWP2) to rotate its polarization to optimize the nonlinear frequency conversion in the next module. With regard to using a single common high reflector HR, two additional dichroic mirrors (i.e., DM2 and DM3) are required not only to form two laser resonators but also to introduce the excitation beam into the corresponding resonators. Dichroic mirror DM2 is used to highly reflect the laser beam at wavelength λ2 and highly transmit the excitation laser. Dichroic mirror DM3 has a coating that is highly reflective at wavelength λ3 and highly transparent at the excitation wavelength. The two beams at wavelengths λ2 and λ3 follow the same beam path after the dichroic mirror DM1.

[0046] [Configuration D: Two laser cavities sharing the same cavity mirror] This configuration is a combination of configurations B and C. The same mirror HR and output coupler OC are used to form two coupled laser resonators to achieve a more compact design and easier alignment. The mirror HR has a highly reflective coating for two laser wavelengths (wavelengths) λ2 and λ3. The functionality of this configuration is almost identical to that of configuration B, except that the same HR is used. Figure 9 shows an example of this configuration in which the two laser rods are anisotropic.

[0047] [Configuration E: Two laser cavities formed by two separate monolithic rods] In some examples, the two laser resonators are configured as a monolithic arrangement, as shown in Figure 10, where each laser cavity is formed by the laser rod itself. In this case, the coverings at the front and exit ends of each rod act as high reflectors and output couplers to form the laser resonator. For the laser rod (laser medium) LM1, its incident surface S1 has a covering that is highly reflective at the laser wavelength λ2 and highly transparent at the excitation wavelength (wavelength) λ1 to perform the function of a mirror HR. The exit end of LM1, i.e., S2, has a concave curve intended to achieve unstable cavity operation and obtain good beam quality at high energies. This concave curve also has a partially reflective covering for coupling the laser emanating from the cavity. Similarly, the laser rod LM2 forms a monolithic resonator II with coverings at the incident end S1 and exit end S2, which act as high reflectors and output couplers for the cavity, respectively. The parallelism between the two surfaces of each rod (i.e., the input end S1 and the output end S2) should be within 5 arc seconds to ensure proper laser oscillation. Such a monolithic approach offers several advantages, including a compact design and the elimination of the need for resonator alignment. It should be noted that, since there is no way to add a polarization element within the cavity, such a configuration is only applicable to laser media that can provide the linearly polarized output required for frequency conversion.

[0048] [Configuration F: Two laser cavities formed by one composite monolithic rod] In one embodiment, the cavity can be further simplified by fabricating a composite monolithic rod. As shown in Figure 11, such an integrated rod consists of two regions, each of which is a monolithic laser for generating one laser wavelength (i.e., λ2 or λ3). The interface between the two regions is provided with a coating that is highly reflective for two wavelengths, λ2 and λ3, to act as a common mirror HR for each monolithic resonator. The two surfaces of the composite rod have a concave curvature with specific coatings to act as an output coupler forming two monolithic resonators, with their common HR coating sandwiched between the two regions. Specifically, one surface end (i.e., the incident end S1) has a coating that can partially reflect the laser at wavelength λ2 and transmit the excitation laser highly, while the other surface exit end S2 is covered with a coating that is partially reflective at wavelength λ3 and transmits the excitation laser wavelength (i.e., λ1) highly. The parallelism between the HR interface and the incident end S1, or between the HR interface and the exit end S2, must be within 5 arc seconds to ensure proper laser operation. The fabrication of such a composite monolithic rod may be through optical bonding or diffusion bonding. The materials in each region may be of the same or different types. When different types of laser host media are used, optical contact is a preferred method for forming the monolithic composite rod. Similar to configuration E, the laser medium used to form this composite rod must, in essence, have the anisotropy necessary to produce a linearly polarized laser.

[0049] The use of such a composite monolithic rod (i.e., LM) involves introducing excitation lasers from each end of the rod, as shown in Figure 12. One arm of the excitation beam passes through a focusing lens (i.e., L2) and a dichroic mirror DM2 and is focused to a first region of the composite rod to generate a laser at wavelength λ2. The output of this laser beam is reflected by dichroic mirrors DM2 and mirrors M5, M3 and then combined with a second generated laser at wavelength λ3 via dichroic mirror DM1. As in the previous configuration, lens L4 is positioned to parallelize the first laser. A half-wave plate HWP1 is used to adjust the polarization of the output beam (i.e., λ2) for later frequency conversion. Excitation of the second region (or resonator II) is carried out by two mirrors (i.e., mirrors M2, M4), focusing lens L3, and dichroic mirror DM4. The dichroic mirror DM4 is highly capable of reflecting the excitation beam and transmitting the laser beam generated from resonator II (i.e., the second region of the monolithic composite rod) highly effectively. Lens L5 and half-wave plate HWP2 are used to parallelize and tune the polarization of the newly generated laser at wavelength λ3.

[0050] [Frequency conversion module] The frequency conversion module can receive laser beams from the dual laser module in three modes (i.e., a single wavelength λ2 or λ3, or two combined wavelengths) (see Figure 2). The frequency conversion module can also receive a laser beam at the excitation wavelength λ1, which is one of the outputs of the excitation laser module. Figures 13 and 15 show two typical examples of this module. The frequency conversion module has at least two functions. The first function is to selectively emit four near-infrared lasers to the handpiece module. These four near-infrared lasers include one laser beam at λ1 (i.e., 700–980 nm) and three laser beams generated from the dual laser module at λ2 (i.e., approximately 1 μm), λ3 (i.e., approximately 1.3 μm), or mixed wavelengths λ2, λ3. As another function, the frequency conversion module can perform nonlinear frequency conversion through at least one nonlinear optical crystal to generate three new wavelengths in the visible light range. These are a green laser at λ4 (i.e., 515-540 nm), corresponding to a frequency twice that of λ2 (i.e., approximately 1.03-1.08 μm); a red laser at λ5 (i.e., 650-675 nm), corresponding to a frequency twice that of λ3 (i.e., approximately 1.3-1.35 μm); and a yellow / orange laser at λ6 (i.e., approximately 580-600 nm), which is the sum frequency of wavelengths λ2 and λ3. In short, this module can emit six distinct wavelengths λ1-λ6 (i.e., 700-980 nm, 1.03-1.08 μm, 1.3-1.35 μm, 515-540 nm, 650-670 nm, and 580-600 nm). The device can also be configured to emit a laser beam with a mixed wavelength (i.e., wavelengths λ2, λ3) of two infrared lasers.

[0051] The implementation of nonlinear frequency conversion can be achieved by using at least one crystal. In one embodiment, a single crystal may be used to create all three visible light wavelengths via second generation (λ4 = λ2 / 2 and λ5 = λ3 / 2) and sum frequency generation (λ6 = λ2 × λ3 / (λ2 + λ3)). In other embodiments, two or more nonlinear crystals are used for frequency conversion.

[0052] [A single nonlinear crystal for generating all three visible light wavelengths via frequency conversion] In this case, the phase matching condition can be satisfied by either critical or noncritical phase matching. Different nonlinear frequency generation is preferred by introducing a noncritical phase matching method that can be achieved by adjusting the crystal temperature without adjusting the crystal orientation. Figure 13 shows a typical example of this method. In this configuration, a direct excitation beam from the excitation laser module is directed to the handpiece as a final output wavelength of λ1 (i.e., 700-980 nm) with an energy of up to 60 J and a peak output of approximately 20 kW. The second input to this module is one of three laser beams of two wavelengths (λ2, λ3, or λ2 mixed with λ3). A removable mirror MM2 selectively directs one of these three incident beams to the handpiece as the other output (i.e., λ2, λ3, or λ2 mixed with λ3) or to an arm made of a nonlinear crystal for frequency conversion. The removable mirror MM2 may be a reversible mirror or a mirror mounted on a translation / rotation stage. The mirror MM2 is provided with a coating that can be highly reflective at two near-infrared laser wavelengths (i.e., λ2 and λ3). Based on the different laser configurations generated from the excitation laser module and the dual laser module, the module here can selectively emit seven laser beams with six different wavelengths as described below.

[0053] [The excitation laser beam as the final output (i.e., λ1)] A unique configuration of this application allows the system to directly emit an excitation laser (excitation laser beam) as the final output to the handpiece. The ability to emit long-pulses (i.e., from μs to ms) lasers at wavelengths of 700–980 nm enables not only the treatment of unwanted hair but also the treatment of vascular lesions and pigmentation in dark skin. This output mode can be operated when a moving mirror (mirror) MM1 in the excitation laser module is positioned in the excitation beam path, as shown in Figure 3. Emission of the excitation laser to the handpiece is carried out by mirror M8 and a moving mirror MM3, which may be a reversible mirror or a mirror mounted on a translation / rotation stage (see Figure 14A). Both mirrors M8 and MM3 are provided with a coating that can be highly reflective at the excitation laser wavelength (i.e., λ1).

[0054] [One of the near-infrared wavelength laser beams (λ2, λ3, or λ2 mixed with λ3) generated from the dual laser module as output.] This configuration is achievable when the movable mirror MM1 in the excitation laser module is moved out of the excitation beam path (see Figure 3). As previously mentioned, when the excitation laser is emitted to the dual laser module, three laser beams of two wavelengths (i.e., λ2 and λ3) can be selectively generated from the dual laser module. As shown in Figure 14B, when these three near-infrared laser beams (wavelengths λ2, λ3, or λ2 mixed with λ3) are emitted to the frequency conversion module, they are selectively directed to one of two arms with a movable mirror MM2 that highly reflects the laser at both wavelengths λ2 and λ3. When mirror MM2 is positioned in the input beam path, the input beams of wavelengths λ2, λ3, or mixed λ2, λ3 are directed to the handpiece as the output laser beam via mirrors M6, M7 and the dichroic mirror DM5. Mirrors M6 and M7 have coatings that highly reflect the laser at both wavelengths λ2 and λ3. In one example, the dichroic mirror DM5 may be a dichroic mirror with a coating that is highly reflective at two near-infrared wavelengths (i.e., λ2 and λ3) and highly transparent at three visible light wavelengths (i.e., 515–540 μm, 650–670 nm, and 580–600 nm). In an alternative example, the dichroic mirror DM5 may be a movable mirror coated with a coating that is highly reflective at both wavelengths (i.e., λ2 and λ3). In this case, the emission of one of the three near-infrared laser beams is performed by the dichroic mirror DM5 positioned in the beam path. After being reflected by the dichroic mirror DM5, this fundamental near-infrared laser beam is simultaneously propagated to the handpiece by three visible light laser beams obtained from a nonlinear frequency conversion process described later.

[0055] [A visible light laser beam generated as an output via nonlinear frequency conversion] As the mirror MM2 moves out of the input beam path, the focus of the input laser beam at wavelengths λ2, λ3, or mixed λ2, λ3 is aligned with the nonlinear crystal NLC with a focusing lens L7 for frequency conversion, in order to generate new wavelengths (i.e., λ4 (=λ2 / 2), λ5 (=λ3 / 2), or λ6 (=λ2×λ3 / (λ2+λ3))), as shown in Figure 14C. Specifically, wavelengths λ4 and λ5 can be generated by second harmonic frequency conversions of the fundamental wavelengths of λ2 and λ3, respectively. Wavelengths λ4 and λ5 fall in the green wavelength range (i.e., λ4 = 515-540 μm) and the red wavelength range (i.e., λ5 = 650-670 nm), respectively. Wavelength λ6 is in the yellow / orange wavelength band (i.e., 580-600 nm) and is obtained by sum frequency conversion of the two fundamental wavelengths of λ2 and λ3. All three of these nonlinear frequency conversion processes can be carried out in a common nonlinear crystal NLC. Lens L8 is positioned immediately after the nonlinear crystal NLC to parallelize the laser beam at any of the wavelengths λ4, λ5, and λ6. The dichroic mirror DM6 reflects the remaining unconverted laser at wavelengths λ2, λ3, or mixed wavelengths λ2, λ3, sending them to the beam dump, while the newly converted laser beam passes through the dichroic mirror DM6 and then propagates further through the dichroic mirror DM5. As previously mentioned, the dichroic mirror DM5 is designed to function for multiple wavelengths. In other embodiments, the dichroic mirror DM5 may be a removable mirror. The generated visible light wavelength propagates forward and follows the same beam path as one of the near-infrared fundamental lasers (i.e., wavelengths λ1, λ2, λ3, or mixed wavelengths λ2, λ3), accompanied by a mirror MM3 outside the beam path.

[0056] In other words, with two inputs, three selectable operating modes emitted by the dual laser module, and a selectable excitation laser power, the module disclosed herein is capable of creating seven laser beams: six single wavelengths (i.e., λ1-λ6) and one mixed wavelength (i.e., λ2,λ3). The optical layout is designed so that all seven of these laser beams propagate simultaneously to the handpiece for final beam emission. In one example, the excitation laser is a 60J alexandrite laser with a peak power of over 20kW at 753nm. 3+ In the case of two laser cavities containing laser crystals doped with (i.e., Nd:YAG for 1.064 μm and Nd:YAP for 1.342 μm), the disclosed device can emit joule-level power for all wavelengths (e.g., 60 J at 753 nm, about 30 J at 1.064 μm, about 24 J at 1.342 μm, more than 5 J at 532 nm, more than 5 J at 671 nm, more than 5 J at 593 nm, and more than 25 J at the mixed wavelength of 1.064 μm and 1.342 μm).

[0057] The disclosed apparatus may comprise a single nonlinear laser crystal (NLC). This crystal is used for both second harmonic generation (SHG) of each laser wavelength (λ2 or λ3) generated from a dual laser module, and sum frequency generation (SFG) of these two wavelengths (i.e., λ2, λ3). In one embodiment, such nonlinear frequency conversion is performed with noncritical phase matching, which can be achieved by adjusting the crystal temperature. In a preferred example, the crystal is lithium triborate (LBO). For the 1.064 nm SHG from Nd:YAG laser emission, the 1.342 nm SHG from Nd:YAP emission, and the two SFGs, the LBO temperature can be adjusted to 275 K, 422 K, and 307 K to achieve type I noncritical phase matching (i.e., O+O→E). The crystal is housed in a temperature oven for temperature stabilization and adjustment.

[0058] In terms of sum-frequency generation, several laser materials can be used to generate lasers of approximately 1 μm and 1.3 μm as fundamental input beams. Table 2 lists several examples to illustrate the generation of yellow / orange wavelengths via the SFG process.

[0059] [Table 2]

[0060] [Two or more crystals for generating three visible light wavelengths via frequency conversion] In an alternative embodiment, two or more nonlinear crystals may be used for a frequency conversion process involving the generation of second harmonics at two fundamental wavelengths λ2, λ3 and their sum frequency. Figure 15 illustrates an example of an optical layout for a frequency conversion module with three crystals (i.e., NLC1, NLC2, and NLC3), each dedicated to one specific nonlinear frequency conversion. Selective beam emission of the excitation wavelength and direction of the three input laser beams for the corresponding frequency conversion are carried out by three moving mirrors, including mirrors MM3, MM4, and MM5. Both mirrors MM3 and MM4 are provided with coatings that may have high reflectivity at the two fundamental wavelengths (i.e., λ2, λ3) generated from the dual laser module, while mirror MM5 has a coating for high reflectivity of the excitation laser beam at wavelength λ1. In this configuration, there are four optical arms for four different functionalities, which may be described as follows:

[0061] [The excitation laser beam as the final output (i.e., wavelength λ1)] This output mode is achievable when the moving mirror MM1 in the excitation laser module is positioned in the excitation beam path, as shown in Figure 3. As the excitation beam enters the frequency conversion module, it is further directed towards the handpiece via mirror M8, dichroic mirror DM7, and moving mirror MM5 (see Figure 16A). The dichroic mirror DM7 is a dichroic mirror that is highly transparent at all three near-infrared wavelengths (i.e., λ1–λ3) and highly reflective at the sum frequency of wavelengths λ2 and λ3 (i.e., wavelength λ6). There are several clinical benefits to the availability of excitation wavelengths (i.e., 700–980 nm) with pulse durations ranging from several hundred microseconds to several hundred milliseconds, including various treatments of pigment in vascular lesions and dark skin, as well as unwanted hair.

[0062] [One of the near-infrared wavelength laser beams (wavelength λ2, λ3, or λ2 mixed with λ3) generated from the dual laser module as output.] This configuration is made possible when the movable mirror MM1 in the excitation laser module is moved outside the excitation beam path (see Figure 3). As previously mentioned, three laser beams of two wavelengths can be selectively generated from the dual laser module.

[0063] As shown in Figure 16B, when one of three near-infrared laser beams (wavelengths λ2, λ3, or λ2 mixed with λ3) is emitted to the frequency conversion module, it is selectively directed to one of four laser beam arms accompanied by a set of movable mirrors MM3, MM4 that highly reflect the laser at both wavelengths λ2 and λ3. This beam emission mode can be activated when both mirrors MM3, MM4 are moved out of the beam path. In this case, one of the three fundamental laser beams at wavelengths λ2, λ3, or mixed λ2, λ3 passes through the dichroic mirror DM10 as the output (or input to the handpiece) of this frequency conversion module. The dichroic mirror DM10 has a multifunctional coating that can highly transmit the laser at the two fundamental wavelengths λ2 and λ3 and highly reflect the two visible light wavelengths (i.e., λ4 and λ5) arising from the second harmonic conversion of wavelengths λ2, λ3. The use of the dichroic mirror DM10 ensures that two visible light laser beams can propagate to the handpiece simultaneously at wavelengths λ2, λ3, and a combined λ2, λ3 fundamental wave laser beam.

[0064] [Green / red laser beam as output] This beam emission mode is achievable when the moving mirror MM3 is positioned outside the incident beam path (Figure 16C), and another moving mirror immediately following it (i.e., MM4) is in the beam path. When a fundamental laser beam at wavelength λ2 is selected, the fundamental laser beam is directed via reflections from mirror MM4 and dichroic mirror DM8 to an optical arm consisting of a nonlinear optical crystal NLC1 for frequency doubling of the fundamental laser wavelength λ2. The dichroic mirror DM8 has a covering that can highly reflect the laser at wavelength λ2 and highly transmit the laser at other fundamental wavelengths (i.e., λ3). This optical arm further consists of a pair of lenses: lens L11 for focusing the fundamental laser beam at wavelength λ2 and lens L12 for aligning the newly generated green laser (i.e., wavelength λ4) via the SHG. In one embodiment, the wavelength λ4 is in the range of 515 nm to 540 nm. This green laser beam at wavelength λ4 can be further emitted to the handpiece and, through reflection by dichroic mirrors DM9 and DM10, follows the same beam path as the fundamental laser beam (i.e., wavelengths λ2, λ3, or mixed λ2, λ3). Dichroic mirror DM9 is highly capable of reflecting the green laser beam at wavelength λ4 and highly capable of transmitting lasers at the infrared wavelength λ2 and the red wavelength λ5. The unconverted fundamental laser at wavelength λ2 passes through dichroic mirror DM9 and is regenerated by beam dumping.

[0065] If another fundamental wavelength (i.e., λ3) is selected, that fundamental wavelength passes through the dichroic mirror DM8 and is directed by mirror M9, which is highly reflective at wavelength λ3, to another optical arm consisting of a second nonlinear optical crystal (i.e., NLC2). The nonlinear optical crystal NLC2 is used for second harmonic frequency conversion of wavelength λ3 to generate a red laser wavelength λ5, which is in the range of 650 nm to 670 nm. The combination of the three mirrors (i.e., DM11, DM9, DM10) directs the newly generated red laser at wavelength λ5 to the next module (i.e., the handpiece), so that the red laser is collinear with the green laser beam (i.e., λ4) and all near-infrared laser beams (i.e., wavelengths λ1-λ3, and the mixed λ2 and λ3). The dichroic mirror DM11 is covered with a coating that is highly reflective of the red laser beam at wavelength λ5 and highly responsive to the unconverted fundamental laser at wavelength λ3. Lenses L13 and L14 are used to focus the fundamental wave laser beam at wavelength λ3 onto the nonlinear optical crystal NLC2, and to parallelize the converted red beam, respectively.

[0066] [Yellow / orange laser beam as output] This mode is activated when a laser with two blended fundamental wavelengths is selected from the dual laser module. As shown in Figure 16D, the blended laser beam is sent to an optical arm equipped with a third nonlinear optical crystal NLC3 for sum frequency conversion to generate a yellow / orange laser by reflection from moving mirrors MM3, M6. As with the other two arms for nonlinear frequency conversion, sets of lenses (i.e., lenses L9, L10) are positioned before and after the nonlinear optical crystal NLC3 to focus the blended wavelengths λ2 and λ3 incident on the crystal, and to parallelize the converted yellow / orange laser at λ6 (i.e., 580-600 nm), respectively. The parallelized yellow / orange laser is further emitted to the next module (i.e., the handpiece) by a dichroic mirror DM7 and a moving mirror MM5. The functionality of the dichroic mirror DM7 and mirror MM5 is described separately. Two unconverted, mixed wavelength laser beams (i.e., λ2 and λ3) can be stopped by beam dumping. It should be noted that all of the laser beam emitted by this module propagates simultaneously to the next module.

[0067] In selecting a nonlinear crystal, at least three factors should be considered: high second-order nonlinearity, sufficient transparency at the wavelength of interest, ease of phase matching, and reasonable cost. In some examples, these crystals may be LBO, KTP, KDP, BBO, etc. Both noncritical and critical phase matching can be used for frequency conversion, depending on the properties of the crystal as well as design preferences.

[0068] [Handpiece] The handpiece module accepts output from a frequency conversion module, which may include six laser wavelengths and seven laser beam modes. In one example, the handpiece comprises at least one lens system capable of emitting at least one laser beam onto the treatment site (i.e., skin) with full beams of different spot sizes. This is therefore called a zoom handpiece. More than one handpiece may be involved. If one common handpiece is used for all wavelengths, that handpiece must be operational for all emitted laser beams. More specifically, the optical coating in the optics within the handpiece should function for all wavelengths. In some alternative embodiments, two or more handpieces may be used. In this case, some of the laser beam emissions will share the same handpiece. Typically, laser beams for treating vascular lesions, pigments, and unwanted hair may involve using a zoom handpiece to generate laser beams of specific spot sizes at visible light wavelengths (i.e., λ4–λ6) or two infrared wavelengths (i.e., λ1 and λ2).

[0069] In some other examples, a laser beam from a frequency conversion module can be emitted onto the skin in an array of many microbeams. This is therefore called fractional treatment. This treatment is intended to create micro-injuries in the skin while leaving untreated areas. Fractional treatments have proven safer than full-beam treatments in terms of shorter rest times and less complexity. For fractional skin treatments, at least one of the near-infrared wavelengths generated by the device (i.e., around 1.3 μm) is useful. At this wavelength, the laser can penetrate the dermis thanks to minimal melanin absorption and, due to sufficient water absorption, can create micro-injuries in that skin layer. Heating collagen can stimulate collagen contraction, resulting in skin tightening, or stimulate collagen growth by bringing about a healing response in the skin that can be caused by induced non-ablational microthermal damage. At least one beam splitting element is required to generate the microbeam pattern. In one example, the beam splitting element may be a refractive lens array. In other examples, the beam splitting element may be a combination of a diffraction beam splitter and a lens.

[0070] In alternative embodiments, two or more laser pulses of different wavelengths may be emitted sequentially or simultaneously. This feature may be useful for skin rejuvenation treatments using two near-infrared lasers (i.e., approximately 1 μm (λ2) and approximately 1.3 μm (λ3)). Emission of two laser beams at approximately 1 μm and approximately 1.3 μm in different modes may be enabled by an excitation beam steering assembly (PSA), as shown in Figures 4 to 5, as described in the section on dual laser modules. When two laser pulses of different wavelengths (i.e., λ2 and λ3) are selected to be emitted sequentially, the time delay between the two pulses is determined by the switching time between two positions of the PSA (i.e., positions A, B) in the configuration shown in Figure 5, or by the switching time between two orientations of the half-wave plates for S-polarization and P-polarization in other configurations of the PSA shown in Figure 6. Figure 17A shows the sequential emission of two laser pulses of two wavelengths. The emission of two laser pulses at two different wavelengths, λ2 and λ3, can be achieved by positioning the PSA in step (C) shown in Figure 5, or by positioning a half-wave plate to generate polarization at 45° for S-polarization or P-polarization, as shown in Figure 6. Figure 17B shows two pulses at wavelengths λ2 and λ3 emitted simultaneously. It should be noted that the energies for the two laser pulses may be the same or different depending on the specific treatment requirements. Output energy control can be achieved by varying the pulse energy emitted to each laser resonator, as shown in Figures 4, 7 through 10, and 12. In other examples, the energy variation of each laser pulse can be achieved by introducing a laser energy attenuator provided in the handpiece for each laser.

[0071] In terms of beam profile characteristics for emitted laser beams with mixed wavelengths, the mixed wavelength laser beam can be configured as two overlapping solid beams or as a mixed beam profile. In the case of a mixed beam profile, in one embodiment, the laser at λ2 (i.e., about 1 μm) is emitted to the treatment site (i.e., skin) in the form of a solid beam, while the other laser at λ3 (i.e., about 1.3 μm) may be split into multiple microbeams, which can be used to generate a microbeam array in the skin for fractional treatment, as shown in Figure 18. The introduction of a mixed beam profile for two wavelengths can offer several clinical benefits. A single solid beam at about 1 μm can penetrate beyond the epidermis to heat the dermis, while a fractional microbeam at the other longer wavelength (i.e., about 1.3 μm) can perform non-ablation fractional treatment to create micro-damage within the dermis. The combination of localized bulk heating caused by a laser of approximately 1 μm and micro-damage created by a laser of approximately 1.3 μm can result in more effective collagen regeneration compared to individual treatments for each beam mode and wavelength. Implementing such a blended beam profile emitted into the skin can be accompanied by further beam separation of the two wavelengths, followed by beam conditioning and beam recombination.

[0072] In one preferred embodiment, a dedicated handpiece may be designed to achieve this function. Figure 19 shows two examples of handpieces capable of emitting the mixed beam profile mentioned earlier. These two handpieces accept two mixed laser beams of wavelengths (i.e., approximately 1 μm and approximately 1.3 μm). The collinear laser beams may be separated by a dichroic mirror DM8, which is coated to be highly reflective of the shorter wavelength (i.e., approximately 1 μm) and highly reflective of the other wavelength (i.e., approximately 1.3 μm). The reflected approximately 1 μm laser beam is then directed to a dichroic mirror DM9 by mirrors M12, M13. The dichroic mirror DM9 can combine the reflected approximately 1 μm laser beam with the transmitted approximately 1.3 μm laser beam, and the combined beam can be directed to the treatment site. An energy attenuator A1 is used to limit the emitted energy at approximately 1 μm. The transmitted laser beam at approximately 1.3 μm passing through the dichroic mirror DM8 can be split into multiple microbeams by the lens array LA (see Figure 18(a)) or the diffraction beam splitter DBS (Figure 18(b)). Another energy attenuator A2 is used to control the energy for this wavelength (i.e., approximately 1.3 μm). The dichroic mirror DM9 functions similarly to the dichroic mirror DM8. In configurations with a diffraction beam splitter, lens L15 is used to generate the desired microbeam spot size in the skin. As a result, the final output of these handpieces is a single solid beam at approximately 1 μm superimposed with an array of many microbeams at approximately 1.3 μm.

[0073] In terms of laser wavelength generation capability, the device disclosed herein can emit six distinct wavelengths (i.e., 700–980 nm, 1.03–1.08 μm, 1.3–1.35 μm, 515–540 nm, 650–670 nm, and 580–600 nm). The device may also be configured to emit a laser beam with mixed wavelengths of two infrared lasers (i.e., approximately 1 μm and approximately 1.3 μm).

[0074] The illustrated and previously described disclosure is merely an example. While many characteristics and advantages of the technology are described in the foregoing, along with details of the structure and function of the disclosure, the disclosure is merely illustrative and may be modified in detail, particularly in terms of the shape, size, and arrangement of components within the principles of the disclosure, to the extent indicated by the broad general meaning of the terms used in the appended claims. It is therefore understood that the previously described examples may be modified within the scope of the appended claims.

[0075] One preferred device is a long-pulse, joule-level solid-state laser system capable of selectively emitting lasers of wavelengths from green, orange, red, and near-infrared for customized treatment of vascular lesions, unwanted hair removal, pigmented lesions, and skin rejuvenation. This device can replace liquid dye lasers excited by flash lamps, but is expected to emit similar energy or peak power with much better reliability and consistency. Furthermore, the ability to generate green wavelengths (e.g., 524nm or 532nm), orange wavelengths (e.g., 593nm), and near-infrared wavelengths (e.g., 1064nm) allows for customized treatment of blood vessels of different sizes and depths. A 755nm laser may be used for hair removal or pigmented lesions. Additionally, the addition of two near-infrared wavelengths (i.e., approximately 1μm and 1.3μm) can extend the treatment range to include skin tightening. Thus, such high-energy laser devices with switchable multi-wavelength capabilities and multiple beam profiles could have more clinical applications than current systems, leading to better market penetration.

[0076] Furthermore, the disclosed device could also gain a better position and help compete with some solid-state vascular lasers on the market by offering multiple wavelengths and higher energies for more versatile and effective treatments.

[0077] Certain features of the present invention are shown in some drawings, and not in others, for convenience only, as each feature can be combined with any or all of the other features of the present invention. The terms “including,” “equipped with,” “having,” and “accompanying,” as used herein, are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Furthermore, no embodiment disclosed herein should be understood as the only possible embodiment. Other embodiments may be conceivable to those skilled in the art and fall within the scope of the following claims.

[0078] Furthermore, any amendments made during the examination of the patent application relating to this patent are not a waiver of any claim elements presented in the application as it was filed, and a person skilled in the art cannot reasonably expect that the claims will be drafted to verbatim cover all possible equivalents, for many equivalents are unpredictable at the time of amendment and (if any) beyond a fair interpretation of what is being waived, the logical basis for the amendment may have only a minor relation to many equivalents, and / or there are many other reasons for which it cannot be expected that the applicant will describe any particular non-substantial substitute for any claim element that is amended.

Claims

1. A multi-frequency laser system for treating skin conditions, A handpiece for treating skin conditions, An excitation laser module having a laser beam at a first frequency, A dual laser module comprising a plurality of dual free-running laser resonators for receiving the laser beam at the first frequency and generating a laser beam at a second frequency and a laser beam at a third frequency, A frequency conversion module configured to accept the laser beam at the second frequency and the laser beam at the third frequency as inputs, and to selectively provide the laser beam to the handpiece, including generating a second harmonic at the second frequency, generating a second harmonic at the third frequency, generating a sum frequency of the second and third frequencies, the laser beam at the first frequency, the laser beam at the second frequency, and / or the laser beam at the first frequency combined with the laser beam at the second frequency. Equipped with, The handpiece is a multi-frequency laser system that receives the laser beam from the frequency conversion module and emits the laser beam onto the skin for treatment as a variable-size solid beam, a fractional microbeam pattern, or a hybrid beam pattern of a solid beam and a fractional microbeam.

2. The multi-frequency laser system according to claim 1, further comprising a first optical subsystem for directly providing the handpiece with the laser output at the first frequency output by the excitation laser module for emission onto the patient's skin.

3. The multi-frequency laser system according to claim 1, further comprising a laser output at the second frequency, a laser output at the third frequency, and a second optical subsystem for directly providing the mixed laser outputs at the second and third frequencies from the dual laser module to the handpiece for emission onto the patient's skin.

4. The multi-frequency laser system according to claim 1, wherein the excitation laser module includes a free-running long-pulse high-energy laser.

5. The multi-frequency laser system according to claim 1, wherein the dual laser module includes different or the same type of laser medium.

6. The multi-frequency laser system according to claim 1, wherein each of the dual free-running laser resonators is a free-running laser that is simultaneously excited by the excitation laser module.

7. The multi-frequency laser system according to claim 1, wherein each of the dual free-running laser resonators is configured as an unstable cavity to achieve both high energy and good beam quality for efficient nonlinear frequency conversion.

8. The multi-frequency laser system according to claim 1, wherein each of the dual free-running laser resonators includes a crystal or ceramic doped with rare earth ions as a laser gain medium.

9. The multi-frequency laser system according to claim 1, wherein the frequency conversion module is implemented in an external cavity configuration.

10. The multi-frequency laser system according to claim 1, wherein the frequency conversion module includes at least one nonlinear optical crystal.

11. The multi-frequency laser system according to claim 1, wherein the first frequency is 700 to 980 nm, the second frequency is 1.03 to 1.08 μm, and the third frequency is 1.3 to 1.35 μm.

12. The multi-frequency laser system according to claim 1, wherein the laser output at the second harmonic frequency of the second frequency is 515 to 540 nm, and the laser output at the second harmonic frequency of the third frequency is 650 to 675 nm.

13. The multi-frequency laser system according to claim 1, wherein the sum frequency of the second frequency and the third frequency generates a laser beam with a frequency of 580 to 600 nm.

14. The multi-frequency laser system according to claim 1, wherein the laser beams of the mixed second and third frequencies can be emitted to the skin with a predetermined delay or simultaneously.

15. The multi-frequency laser system according to claim 1, which emits a beam pattern that is a mixture of the second frequency and the third frequency.

16. The multi-frequency laser system according to claim 1, which emits a controllable pulse duration ranging from several hundred microseconds to several hundred milliseconds by adjusting the pulse duration of the excitation laser.

17. A method for treating a skin condition, The steps of providing a laser beam at a first frequency, The steps of generating a laser beam at a second frequency and a laser beam at a third frequency from the laser beam at the first frequency, The steps of receiving the laser beam at the second frequency and the laser beam at the third frequency, and selectively providing the laser beam to the handpiece, including generating a second harmonic at the second frequency, generating a second harmonic at the third frequency, generating a sum frequency of the second frequency and the third frequency, the laser beam at the first frequency, the laser beam at the second frequency, and / or the laser beam at the first frequency combined with the laser beam at the second frequency, A multi-frequency laser method having [a specific characteristic].

18. The method according to claim 17, further comprising the step of directly providing the handpiece with the laser beam at the first frequency for emission onto the patient's skin.

19. The method according to claim 17, further comprising the step of directly providing the handpiece with the laser beam at the second frequency, the laser beam at the third frequency, and a mixture of the laser beams at the second and third frequencies for emission onto the patient's skin.

20. The method according to claim 17, wherein the laser beam at the first frequency is generated by a free-running long-pulse high-energy laser.

21. The method according to claim 17, wherein a dual laser resonator is used to generate the laser beam at the first frequency, the laser beam at the second frequency, and the laser beam at the third frequency.

22. The method according to claim 21, wherein each of the dual laser resonators is a free-running laser that is simultaneously excited by an excitation laser.

23. The method according to claim 21, wherein each of the dual laser resonators is configured as an unstable cavity to achieve both high energy and good beam quality for efficient nonlinear frequency conversion.

24. The method according to claim 21, wherein each of the dual laser resonators includes a crystal or ceramic doped with rare earth ions as a laser gain medium.

25. The method according to claim 17, wherein frequency conversion is performed in an external cavity configuration.

26. The method according to claim 17, wherein the first frequency is 700 to 980 nm, the second frequency is 1.03 to 1.08 μm, and the third frequency is approximately 1.3 to 1.35 μm.

27. The method according to claim 17, wherein the laser output at the second harmonic frequency of the second frequency is 515 to 540 nm, and the laser output at the second harmonic frequency of the third frequency is approximately 650 to 675 nm.

28. The method according to claim 17, wherein the sum frequency of the second frequency and the third frequency generates a laser beam with a frequency of approximately 580 to 600 nm.

29. The method according to claim 17, wherein the laser beams of the mixed second and third frequencies are emitted to the skin with a predetermined delay or simultaneously.

30. The method according to claim 17, comprising the step of creating a beam pattern that is a mixture of the second frequency and the third frequency.

31. The method according to claim 17, comprising the step of emitting a variable pulse duration in the range of several hundred microseconds to several hundred milliseconds.

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