Compact laser head

Abstract

A laser head for a high power fiber laser system has a 5mm to 10mm tall housing provided with a bottom. The housing encloses an input collimator assembly that collimates single mode pump light at a fundamental frequency and a maximum power of 2kW. The housing also encloses a multi-stage cascaded nonlinear frequency converter that receives the collimated pump light to convert the fundamental frequency to its higher order harmonics, where the higher frequency converted light has a maximum power of 1kW. Enclosed in the housing are electronics and light guiding optical components mounted in the housing. The bottom of the housing is an electro-optical printed circuit board (EO PCB) that directly supports the input collimator assembly, multi-stage cascaded nonlinear frequency converter, electronics and optical components at respective designated locations.

Description

[0001] Public background Technical Field

[0002] This invention relates to high-power lasers operating in the visible spectrum. In particular, this invention relates to a miniature and cost-effective laser head for lasers of the aforementioned type. Background Technology

[0003] Visible light is generally defined as having wavelengths in the range between near-infrared (with longer wavelengths) and ultraviolet (with shorter wavelengths). Traditionally, industrial laser applications utilizing visible light include, but are not limited to, pharmaceuticals, materials processing, science, and consumer products. As the laser industry matures with the availability of new nonlinear crystals used in frequency conversion (i.e., frequency switching) schemes, lasers that generate visible light continue to find new applications, such as red-green-blue (RGB) light engines.

[0004] Several types of lasers exist to output visible emission. One type includes short-wavelength semiconductor laser diodes. Another type of known device is represented by various gas lasers. Another type of solid-state laser is based on nonlinear frequency conversion, which involves generating second-order and higher harmonics of the fundamental frequency, or using sum frequencies and parametric oscillations to obtain the desired frequency. Within the scope of this invention, particular interest is focused on solid-state lasers utilizing nonlinear frequency conversion schemes, such as fiber lasers. However, as those skilled in the art will understand, the main aspects of this invention are applicable to other solid-state lasers that require frequency conversion.

[0005] Figure 1 A group of fiber lasers 10 utilizing nonlinear conversion technology is shown. Each laser 10 includes a pulsed pump source 12 that outputs continuous wave (CW), quasi-continuous wave (QCW), or infrared (IR) pump light, for example, outputting infrared pump light in a 1 μm fundamental wavelength range between approximately 1030 nm and 1120 nm. The generated IR pump light also propagates through a transmission fiber 14 coupled to a laser head 16. The laser head is configured with a frequency converter to generate visible laser output.

[0006] U.S. Patent 10,008,819, which is incorporated herein by reference, discloses an exemplary QCW laser that generates red light at wavelengths of 615 nm, 635 nm, and longer by utilizing a combination of a Raman converter and a frequency conversion scheme. The Raman converter includes a Raman fiber configured with a cavity consisting of one or more pairs (cascaded) of fiber Bragg gratings. As known to those skilled in the art, the Raman converter provides a wavelength shift of the fundamental frequency of the pump light from within the Raman gain spectrum of the fiber. This Raman-shifted fundamental frequency pump light is then converted into red output light by a frequency converter (such as a second-order harmonic generator (SHG) mounted on the laser head).

[0007] The laser head 16 associated with a fiber laser operating in the visible spectrum is the subject of this disclosure. Compactness, automation, cost-effectiveness, cleanliness, optical efficiency, and stability relative to mechanical and thermal loads are all fundamental characteristics of a laser head. Each individual characteristic is defined by one or more specific components. Typically, improving one characteristic may adversely affect others. Therefore, improvements to the operation of the laser head require an integrated approach that necessitates modifications to multiple laser head components, as illustrated in the following development history of the laser head 16.

[0008] Figure 2 An exemplary laser head 16 configured to output red light is shown; however, those skilled in the art will readily recognize that the illustrated configuration will be relevant to any fiber laser operating in any region of the visible spectrum, with or without negligible variations. For example, a Raman converter can be omitted, as the frequency generator can utilize various nonlinear effects in addition to SHG. Nonlinear optical processes may include, for example, techniques for determining the frequency and the corresponding optical schematic, as are well known to those skilled in the art of lasers.

[0009] The structure of the laser head 16 includes a combination of optical, fiber-related, and electrical / electronic components, all of which are mounted on the bottom 18 of the laser head housing. A transmission fiber 14 extends through a fiber optic connector 30 into the interior of the laser head 16, where the distal end of the fiber is received by an input collimator assembly or objective lens 32.

[0010] according to Figure 2 and turn Figure 3 The input collimator assembly 32 is provided with multiple elements, one of which is an end block 34 made of quartz and fused to the distal fiber end. The end block 34 minimizes damage to the distal fiber end and reduces the power density of the bundle to some extent. The extended pump bundle then propagates in free space and is collimated in the collimator 36.

[0011] The collimated pump beam and the frequency conversion scheme 40 include upstream and downstream nonlinear optical crystals (NLO) 38 (such as lithium triborate (LBO)). Figure 2The fundamental frequency of the Raman shift is doubled as the pump light propagates through the upstream NLO 38. The light generated at this frequency doubling and the unconverted portion of the pump light are first incident on a half-wave plate 41, which modulates the polarization of the incident red and IR light. The beam is further guided through the downstream NLO 38, where it interacts with the remaining pump light to generate additional converted light at double the frequency. A dichroic mirror (i.e., a dichroic mirror) 42 spectrally separates the converted and remaining IR pump beams, which are further separated from the head 16 via corresponding output ports 44, 46.

[0012] Based on the foregoing, input the collimator assembly or objective lens 32, such as... Figure 3 As shown, in addition to end block 34, it also includes a retainer 45 and a collimator 36. The collimator assembly 32 is large in size, and thus contributes to the large footprint of the laser head 16. Another major reason for the large overall footprint of the laser head 16 is the frequency conversion scheme that includes the nonlinear crystal 38, the corresponding crystal retainer assembly, and the guiding optics.

[0013] Miniaturization of the laser head 16 begins with replacing the input fiber 14 with an fiber having a smaller core diameter, which results in a reduction in the beam diameter of the single-mode (SM) pump light. This reduced beam diameter makes it possible to use miniaturized optical components. However, the reduced beam diameter also increases the IR pump light power density or intensity (I), which is the ratio of power (P) (in watts (W)) to the beam cross-sectional area (I = W / cm²). 2 The higher the power density of the light, the higher the optical efficiency of NLO 36. Therefore, the reduced beam diameter improves compactness and frequency conversion efficiency. However, the increased power density of the SM IR pump light at the desired wavelengths in the 1 μm wavelength range also presents problems when reaching the maximum high IR pump light power of about 2 kW or higher.

[0014] At relatively low IR powers, such as below 100W, the pump light has little or no environmental hazard when back-reflected from end block 34. However, all of this varies at high power densities as long as the SM pump operates within the aforementioned IR power range. In fact, high-density light causes a considerable number of unforeseen structural problems, as described below.

[0015] For example, when high-power IR pump light of a Raman-shifted wavelength is back-reflected from end block 34, it is coupled into the cladding of fiber 14. Guided within the silica cladding, the back-reflected light tends to detach from it and damage the polymer protective coating surrounding the cladding, making the fiber vulnerable to environmental hazards. As the laser source continues to operate, the elevated temperatures—high temperatures—can have a particularly dangerous effect on exposed fibers. Ultimately, the fiber can burn out and be completely destroyed. Typical mechanisms that handle cladding modes and are referred to as cladding mode strippers or mode filters are made of silicon, which has a refractive index higher than or similar to silica. However, when used alone, the effectiveness of mode filters at the desired high power densities is questionable.

[0016] Furthermore, as the temperature increases during laser operation, the refractive index of the cladding eventually equals that of the mode filter. As a result, the back-reflected light is not decoupled from the cladding to the mode filter, but instead propagates through the cladding towards the input port of the housing, through which the fiber optic connector 30 extends into the laser head 16. Typically, the gap in the input port surrounding the fiber optic connector 30 is sealed with epoxy resin, making the interior of the housing nearly sealed. When high-power back-reflected light is incident on the epoxy resin, it is susceptible to damage and may burn due to its low resistance to high temperatures. Consequently, the encapsulated fiber may be easily damaged, and the interior of the laser head is exposed to the surrounding environment, often leading to highly undesirable consequences. Moreover, the high optical power density and associated high temperatures in the experimental laser head cause the adhesive to gradually become contaminated with chemicals, eventually damaging the optical components. Clearly, all the problems discussed above are associated with existing collimator assemblies located at the input of known laser heads, and the need for calibration of the corresponding collimator assembly at the laser head's output.

[0017] Another issue with IR input and output (cleared) collimator assemblies compared to Raman converter-based red lasers is more relevant to lasers producing other wavelengths in the visible spectrum. The desired output is red light over a wide wavelength range. For example, Figure 1 Pump 12 can output light with a pump wavelength of 1060 ± 5 nm. SM fiber Raman converters can induce first, second, third, and fourth order frequency Stokes shifts in pump light, covering, for example, a very wide wavelength range. Typically, "good" anti-reflective (AR) coatings reflect less than 3% of the incident light, and even then, their optical effectiveness is questionable. Therefore, an improved AR structure capable of effectively covering a spectral range of several hundred nanometers is needed.

[0018] Figures 4A to 4CAn exemplary laser head 16, at one of the advanced development stages, is shown, highlighting a range of issues related to the frequency conversion assembly (more specifically, the crystal holder assembly 50). The crystal holder assembly 50 includes a thermoelectric cooler (TEC) 52 and a resistance temperature detector (RDT), such as a thermistor (not shown) supported by an optical experimental stage or optical bench 20, a C-shaped bracket 54, and an L-shaped sheath 56. The sheath 56 and bracket 54 are configured to hold the crystal 38 in place by a spring 60. Screw 58 ( Figure 4B The sheath 56 is rigidly connected to the bracket 54. The entire assembly is mounted on the bottom 18 of the laser head housing. Figure 4A The specific shape and configuration of the support 54 and sheath 56 can vary, but the combination of these components with the relatively thick base 18 and optical experimental stage 20 makes the assembly 50 too large, too tall, and too heavy. The dimensions (W×L×H) mm of the fully assembled laser head 16 in Figure 4 correspond to the corresponding (105 to 115) × (215 to 220) × (60 to 75) mm. Although these dimensions can vary from one type of conversion scheme to another and depending on the IR source parameters, despite Figure 4C The laser head operates with a reduced IR beam diameter, but the footprint of the laser head 16 disclosed above is very typical. It is reiterated that one of the problems this disclosure attempts to address is the need to reduce the footprint and weight of the frequency conversion components.

[0019] The housing bottom 18, optical experimental stage 20, and crystal sheath 54 are all made of copper (Cu). The material homogeneity, characterized by a uniform coefficient of thermal expansion (CTE), helps minimize the inevitable displacement of multiple components relative to each other during operation. However, other laser head components, such as the TEC 52 and LBO crystal 38 (…),… Figure 2 The LBO crystal 38 and other components have a corresponding CTE different from Cu. TEC 52 continuously adjusts the temperature of the crystal 38. Cooling the LBO crystal 38 during red light generation or heating the LBO crystal 38 during green light generation is necessary because a uniform (constant) temperature is a prerequisite for effective frequency conversion. The LBO crystal has a special response to high temperatures—it not only expands differently along its two axes but also tends to contract along its third axis.

[0020] The expansion and contraction of LBO 38 causes displacement of it relative to the other components of the crystal holder assembly 50, because its CTE differs from that of all Cu components and TEC 52. This displacement of the assembly components results in increased thermal loads that can deform the crystal 38, reducing its conversion efficiency and typically requiring replacement of the crystal 38.

[0021] To minimize the CTE mismatch between TEC 52 and crystal 18 to some extent, crystal retainer assembly 50 ( Figure 4A A C-shaped bracket 54 is used, which is configured to prevent direct contact between the TEC 52 and the crystal 38, such as... Figure 4A and Figure 4B As shown in the diagram. The support 54, together with the base 18 and the optical experimental stage 20, elevates the assembly 50, and therefore makes it mechanically unstable when in use. To minimize undesirable instability, the crystal holder assembly 50 utilizes screws 58 and springs 60 (…). Figure 4B The screws and springs reliably secure the C-shaped sheath 56 relative to the crystal 38. A plate 62 (which is clearly another element contributing to the overall height of the assembly) is placed between the crystal and the fasteners to minimize deformation of the crystal 38 caused by the bending moment generated by the screw 58 on the crystal. This relatively rigid connection between the crystal 38 and the sheath 56 is undesirable, as the crystal should "breathe" during temperature fluctuations. Rigidly restricting its expansion could be a cause of crystal failure. Based on the foregoing, it is clear that CTE mismatch should be minimized, which can be achieved by carefully selecting materials for the component parts with substantially closed corresponding CTEs. Based on the foregoing, the configuration of all assembly components should be modified to reduce the footprint of the laser head, with particular emphasis on the height of the head 16.

[0022] Traditionally, the laser head packaging process involves assembling the optical and electrical components associated with the fiber optics separately. Packaging of the laser head 16 only begins after these component groups have been assembled. For example, the wires connecting the TEC 52 to the external power supply penetrate the interior of the laser head and are manually connected to the TEC. This disassembly assembly method is too time-consuming and not cost-effective for mass production.

[0023] In addition, such as Figures 4A to 4C As illustrated in the diagram, the Cu base 18 and the optical stage 20 together define a height slightly less than half that of the laser head 16. Considering the mass production of the laser head 16, it would be highly advantageous to use a thinner base component instead of the base 18 and the optical stage 20. Furthermore, the thinner base / stage component should be configured to eliminate the need for manual packaging of the laser head 16.

[0024] Therefore, a high-power visible light laser with a lightweight, compact laser head is required, in which:

[0025] The electro-optical printed circuit board (EO PCB) functionally and structurally replaces the housing bottom and optical experimental stage of known laser heads, and facilitates the automated assembly of the laser head of this invention.

[0026] The input collimator assembly has a simple configuration, thus preventing back-reflected light from damaging the near-sealed internal structure of the laser head; and

[0027] The crystal retainer assembly is configured with a lightweight and compact structure that accommodates various components with different CTEs in order to minimize thermal stress on the LBO crystal. Summary of the Invention

[0028] These requirements are met by a modular visible fiber laser equipped with an IR light source and a laser head, which is configured with a frequency converter. Several structural aspects related to the corresponding laser head components and solutions to the problems listed above are disclosed. Each aspect individually includes one or more features, which, individually or in arbitrary combinations with other features of the same and other aspects, contribute to a miniaturized, lightweight, automation-friendly, and cost-effective laser head.

[0029] According to one aspect, the laser head of the present invention is configured with an electro-optic printed circuit board (EO PCB), which is made of ceramic, covered with a metallization layer, and has electrical paths and precisely designated positions for corresponding optical and electrical components. Therefore, the EO PCB can be used both as a support base or bottom for the laser head and as an optical experimental stage. It serves as an alternative to the bottom of large, stacked Cu housings and Cu optical experimental stages. The thin, lightweight EO PCB reduces the footprint and weight of the disclosed laser head and is important for automating the laser head assembly process.

[0030] The EO PCB support is a frame made of Kovar iron-nickel-cobalt alloy (Kovar) or aluminum (Al) and typically extends along the edge of the EO PCB. One side of the frame has an inwardly recessed portion that provides a pocket-like structure on the EO PCB. The shape and size of the pocket-like structure are designed to receive a USB cable plug. The latter provides electrical coupling between the electrical components of the laser head and external devices such as power supplies and controllers. The recessed portion of the frame isolates the USB plug from the rest of the head's interior and eliminates the need for additional partitions and expansion materials typically installed in known laser heads to isolate the plug from the interior of the laser head housing. The cover and frame can be manufactured as separate components or as a single piece.

[0031] On the other hand, the input and output IR collimator assemblies are mounted in a housing. Each collimator assembly includes a one-piece retainer supporting the distal end of an optical fiber, which is coupled to an end block made of quartz, the collimator, and additional components, as discussed below.

[0032] According to one feature of this aspect, instead of glue connecting the fiber distal end and end block in known collimator assemblies, these components are laser-welded to each other. In contrast to glue, the weld or weld joint offers high resistance to the substantial thermal loads generated by high-power light within the housing.

[0033] Inevitably, as high-power IR light propagates within the housing, it will be partially deflected and back-reflected from the end block toward the input port. The input port receives a fiber optic connector sealed to the housing. This back-reflected light can compromise the integrity of the seal, and damage to the seal can expose the interior of the housing to environmental hazards and sometimes cause the fiber to burn.

[0034] Therefore, another feature of this aspect helps to minimize the propagation of back-reflected stray light toward the seal. Specifically, a light blocker is mounted on the retainer between the end block and the input port. The position of the light blocker prevents back-reflected stray light from propagating further toward the seal.

[0035] One possible configuration of the light blocker has a clamshell structure comprising a bottom plate or base plate and a top plate or top plate. The bottom plate is mounted on the retainer and has a top surface that contacts the bottom surface of the top plate. One or both of the top and bottom surfaces are machined with corresponding generally U-shaped recesses that form channels for the optical fiber to be stretched through when the top plate is mounted on top of the bottom plate. The channels are sized such that stray light back-reflected is incident on the distal surface of the respective plate, which thus acts as a protective barrier, minimizing the propagation of back-reflected light.

[0036] In another configuration of the light blocker, both plates are mounted on the retainer such that their respective inner sides are abutted against each other. Similar to the thicker plate, one or both adjacent sides have their own recesses, which are aligned to form a channel. The optical fiber extends through this channel, the inner diameter of which is slightly larger than the outer diameter of the optical fiber. These sides of the corresponding plates facing the end block prevent most of the back-reflected stray light from propagating further toward the seal.

[0037] Back-reflected IR light is also coupled into the cladding of the optical fiber, posing the same danger to the seal as stray light. To minimize the impact of cladding-guided back-reflected light, the optical fiber can be configured with a cladding mode filter formed along a fiber stretcher stripped from the polymer protective layer and located between a light blocker and the input port. The mode filter is made of silicon, which, due to its higher refractive index than silicon dioxide, is decoupled from the back-reflected light from the cladding. The light blocker and the cladding mode filter, individually or in combination, significantly reduce the amount of high-power back-reflected light incident on the seal.

[0038] Another feature of this aspect includes a ferrule, which is mounted on the retainer and through which the optical fiber stripped from its protective layer passes. The center hole of the ferrule is almost no larger than the outer diameter of the cladding and substantially smaller than the channel formed in the light blocker. The ferrule can be paired with any light blocker and modulated filter, or any of these elements individually, or even used alone.

[0039] Another feature of the collimator assembly of this invention is more relevant to red lasers, but can certainly be used with all types of visible light lasers. To output a wide wavelength range of red light, the IR input light should preferably cover the wavelength range of 1000 nm to 1400 nm, as needed. Therefore, according to the features of this invention, the surface of the end block laser-welded to the end of the fiber is provided with randomly arranged subwavelength nanospikes. The structured surface of the end block has proven effective in the desired absorption spectrum.

[0040] If the optical fiber used in this invention is Teflon TM Fluoropolymer buffers further enhance all of the aforementioned characteristics for their intended purpose. The latter provides optical fibers with beneficial resistance to high temperatures, chemical reactions, corrosion, and stress cracking.

[0041] Another aspect of the invention relates to a frequency conversion assembly, and more particularly to a crystal holder subassembly. The main difficulties associated with the crystal holder subassembly stem from the unique response of the LBO to temperature gradients and the multiple components having different CTEs (Constant Temperature Responses).

[0042] According to one feature of this aspect, the crystal holder subassembly includes a TEC coupled to the EO PCB. The TEC is typically made of semiconductor n-type and p-type materials having a CTE matching the CTE of the EO PCB. The subassembly also includes a thermal sheath and an RDT, the thermal sheath being mounted on top of the TEC and being sized to receive an LBO crystal.

[0043] The configuration of the thermal jacket takes into account the different CTEs between each LBO crystal and the thermal jacket. Since CTE mismatch between these components is practically unavoidable, the disclosed thermal jacket has various variations, each of which allows the LBO crystal to expand substantially without restriction.

[0044] According to a variation of the thermal jacket, two identical metal sheets or sheet metals are constructed as corresponding halves of the thermal jacket. Each metal sheet or sheet metal is first laser-treated to have a series of spaced-apart slits extending from one longitudinal edge of the metal sheet or sheet metal toward the opposite longitudinal edge. However, the slits terminate at a distance from the opposite edge. Subsequently, each sheet is shaped to have a generally C-shaped or Z-shaped cross-section. The shaped sheets are then mounted on the TEC or sub-mount or any other base structure such that the corresponding slotted edges face each other. The assembled sheets form an internal channel extending along the longitudinal axis and are sized to receive the crystal.

[0045] Based on the foregoing, the thermal sheath is configured with multiple clamps, each clamp having a pair of flexible arms that press against the corresponding sides and top of the crystal. This contact between the sheath and the crystal prevents displacement of the crystal relative to the sheath. However, the flexible arms do not substantially impede the expansion of the LBO. It is well known that the maximum CTE is observed along the longitudinal axis of the LBO crystal, but the sheath has relatively axially spaced open ends, which allows the crystal to expand freely in the axial direction.

[0046] Another feature of the crystal holder involves a sheath support structure that may include a ceramic sub-mount located on top of the EO PCB. A heating layer is mounted on top of the sub-mount and covers a dielectric insulator. A dielectric layer is then placed on top of the heating layer and the crystal sheath, which is soldered to the dielectric layer via inserted pads. The dielectric layer between the heating layer and the crystal sheath provides electrical insulation between these components.

[0047] According to another aspect of the invention, most large optical components (such as lenses and mirrors) are supported by corresponding brackets, which are in turn directly mounted on the EO PCB. One problem during laser head assembly includes optically aligning the optical components after they have been mounted to the head. Alignment is necessary to minimize light loss within the laser head. Alignment may include tilting, rotating, or yawing the brackets about an axis substantially orthogonal to the plane of the EO PCB.

[0048] The bracket is configured with a base supporting the optical components and a pair of sides that resiliently press against corresponding surfaces of the optical elements. To provide tilting for the bracket, a pair of resilient blades are welded to the EO PCB; these blades are cut from the bottom of the bracket and bent outwards. Applying an external force to the EO PCB causes one of these blades to yield. Yaw movement of the bracket is achieved by bosses formed like leaves on the outer surface of the bracket's bottom and coupled to the EO PCB.

[0049] The above and other aspects will be more easily understood if considered in conjunction with the following attached diagram, in which: Attached Figure Description

[0050] Figure 1 Several known fiber laser assemblies, including their respective laser heads, are shown.

[0051] Figure 2 It is a top view of a laser head, without a cover, configured according to known prior art;

[0052] Figure 3 This is an axial cross-sectional view of one of the known collimator components;

[0053] Figure 4A This is a front perspective view of a crystal holder sub-assembly of known prior art;

[0054] Figure 4B yes Figure 4A A cross-sectional view of the crystal holder subassembly;

[0055] Figure 4C It includes Figure 4A and Figure 4B A perspective view of a known laser head for a crystal holder subassembly;

[0056] Figure 5 The laser head of the present invention is shown;

[0057] Figure 6 yes Figure 5 A top view of the bottom of the laser head of the present invention;

[0058] Figure 7A and Figure 7B The configurations of the input collimator assembly of the laser head of the present invention are shown respectively;

[0059] Figure 8 This is a frontal perspective view of another configuration of the disclosed input collimator assembly;

[0060] Figure 9A and Figure 9B Each shows yet another configuration of the disclosed input collimator assembly;

[0061] Figure 10 It has Figure 5 An exemplary electro-optical schematic diagram of the laser head of the present invention. Figure 6 Top view of the EO PCB;

[0062] Figure 11A yes Figure 5 An exemplary cross-sectional side view of the laser head of the present invention;

[0063] Figure 11B yes Figure 5 Another exemplary cross-sectional side view of the laser head of the present invention;

[0064] Figure 12A This is a front view of the crystal retainer assembly;

[0065] Figure 12B and Figure 12C These are characterized by configurations of crystal clamps or thermal sleeves, respectively. Figure 12A Front view of the crystal holder;

[0066] Figure 12D Show Figure 12B and Figure 12D Half of the heat-shrink jacket;

[0067] Figure 12E and Figure 12F They are Figures 12B to 12D Assembly drawings and exploded views of variant examples of the thermal jacket;

[0068] Figures 13A to 13C They are support Figure 12A Exploded view, top view, and bottom view of the base of the crystal holder subassembly;

[0069] Figure 14A and Figure 14B These are examples of mounting optical components to... Figure 6 Schematic diagrams of different technologies for EO PCBs; and

[0070] Figures 15A to 15C These are front views of the large component retainer. Detailed Implementation

[0071] Reference will now be made in detail to the disclosed subject matter. Where possible, the same or similar reference numerals are used in the drawings and description to refer to the same or similar parts or steps. The drawings are simplified and are far from precise scale. For convenience and clarity only, the terms “connection,” “coupling,” “combination,” and similar terms and their inflectional morphemes do not necessarily indicate direct and indirect connections, but also include connections via intervening elements or devices.

[0072] Figure 5 The present invention illustrates a miniature laser head 100 with a footprint comparable to a typical iPhone 70. While the size of the laser head 100 may vary, the smallest known laser head—laser head 16 (e.g.)—is... Figures 4A to 4CThe dimensions shown are 75 mm wide (W), 120 mm long (L), and 22 mm high / thickness (H). In contrast, the disclosed laboratory-tested laser head 100 is 75 mm (W) × 112 mm (L) × 8 mm (H). According to the structure of the invention, the height / thickness of the laser head housing can vary between 5 mm and 10 mm. The compactness of the laser head 100 of the invention is a result of the reconfiguration of several main head components, which in particular include the housing 78, the input collimator assembly 80, the output collimator assembly, and the crystal holder assembly 82.

[0073] To combine Figure 5 See the method Figure 6 The housing 78 is equipped with a bottom 75 ( Figure 6 ), frame 84 and cover 86 ( Figure 5 Based on the dimensions of the laser head 100 disclosed in the previous paragraph, its height / thickness is similar to... Figures 4A to 4C The size has been significantly reduced compared to known laser heads. Two main components need to be redesigned to provide a laser head 100 with a miniaturized structure: the bottom 75 of the housing 78 and the crystal holder assembly 82. Figure 5 ).

[0074] Compared to known laser heads with a large Cu base combined with an optical stage, the base 75 is made of ceramic (such as aluminum nitride (AlN) or beryllium oxide (BeO)) and also serves as an optical stage. Conceptually and functionally, the base 75 is an electro-optical printed circuit board (EO PCB), with precisely defined locations 76 for the corresponding optical components and traces 74 for the electrical components. The latter is one of the significant features of the invention, taking into account the maximum power of the pump and the converted light, which will be explained below. Optical components may include a folding mirror 235, a dichroic mirror 241, and a focusing lens 237. The improved configuration of the base 75 is crucial for the fully automated assembly of the laser head 100.

[0075] Frame 84 ( Figure 5 The frame 84 can be made of Kovar or preferably aluminum (Al) or any other lightweight and durable material having desired thermal and electrical properties that substantially match the desired thermal and electrical properties of the bottom / EO PCB 75. It can be glued, sintered, soldered, or laser-welded to the EO PCB and covered by a cover 86, preferably made of the same material as the frame 84. The frame 84 and cover 86 can be two separate components coupled to each other during head assembly, or they can be a one-piece integral component.

[0076] One of these sides of frame 84 has an inwardly recessed portion to provide a pouch-like portion 88. Figure 5The latter is shaped and sized to receive a USB cable plug (which is typically indicated as 92). The plug 92 is connected via a corresponding trace 74 (…). Figure 6 It provides electrical coupling between the TEC and RDT and external devices such as power supplies and controllers. The recessed portion of the frame isolates the USB plug 92 from the rest of the head.

[0077] The miniaturization of the disclosed laser head depends on the beam diameter. For example, currently, the transmission fiber has a 14 μm core, which outputs a beam with a beam diameter of 14 μm (four times the beam diameter of known laser head designs). The core diameter is generally inversely proportional to the light intensity, meaning that in the disclosed laser head 100, the light intensity is four times that in known designs. Considering that single-mode pump IR light can have a maximum power in the range of 1 kW to 2 kW at a selected wavelength within the 1 μm spectral range, the light intensity at the far end of the transmission fiber poses safety concerns. Furthermore, such high-intensity light can damage the adhesive degassed at high temperatures, thus affecting the connections between components, optical parts, and (of course) the fiber ends. To mitigate the risks associated with high-intensity light, the far end of the transmission fiber is laser-welded to a so-called end block made of quartz. However, the end block used in conjunction with high-intensity forward-propagating pump light has proven highly problematic because it also reflects the incident light. The back-reflected light is directed toward the input port 102 ( Figure 5 The light propagates and damages the material sealing the port, such as epoxy resin. Therefore, the disclosed input collimator assembly 80 not only has a compact configuration, but is also configured with multiple components that minimize the propagation of back-reflected light, as discussed below.

[0078] Figure 7A , Figure 7B , Figure 8 , Figure 9A and Figure 9B An input collimator assembly 80 is shown, which is configured to be glued or preferably soldered to an EO PCB 75. Figure 6 The retainer 94 is made of ceramic material and is characterized in that the CTE substantially matches one of the EO PCBs. Functionally, Figure 7A The retainer 94 supports optical elements, which in particular include a collimating lens 108, an end block 110 made of quartz, a light-shielding block 112, and a transmission optical fiber 98. Structurally, the retainer 94 extends between a proximal end 104 and a distal end 106 that is thinner than the proximal end 104. The retainer 94 can be integral or have separate components coupled together.

[0079] The collimator assembly 80 is one of the main contributing factors to the overall miniaturized configuration of the disclosed head. Prior art collimator assemblies are typically 12mm to 15mm long. In contrast, the disclosed collimator assembly is at most 10mm long, a result of miniaturized component elements. For example, the cylindrical end block 110 has a diameter of 1mm to 2mm and a length of 3mm to 5mm. Conversely, in Figure 3 The diameter of the end blocks used in known laser heads ranges from 4 mm to 8 mm, while the length of the end blocks is a minimum of 6 mm.

[0080] End block 110 is part of the problem related to high light intensity. Typically, the IR pump light is guided within the fiber core. When fiber 98 transmits the pump IR light to end block 110, a portion of this light is partially coupled back into fiber 98, and specifically coupled to its cladding 118. Figure 7A In the cladding, the coupled light is guided backward to the sealed input port 102. Figure 5 This back-reflected light presents a double danger. First, as it propagates along cladding 118, it may detach from the cladding. If the decoupled light is incident on the sealed input port 102... Figure 5 On the laser head, the seals, typically made of epoxy resin, are easily damaged by high temperatures. Once the seals are damaged, the interior of the laser head near the seals is also damaged, which may irreversibly affect the entire operation of the laser head, and the fiber 98 may burn directly. Secondly, even before reaching port 102, back-reflected light guided along cladding 118 reaches a portion of the fiber 98 covered by the protective polymer layer 116. Figure 7A Similar to epoxy resin, layer 116 is susceptible to the high temperatures associated with the high power intensity of back-reflected light, and damage to it exposes fiber 98 to high temperatures. To handle the high intensity of back-reflected light, the input collimator assembly 80 is provided with a light-blocking component, as will be disclosed in detail below.

[0081] See Figure 7A The near end 104 of the retainer 94 has a channel 114 that receives a double-clad single-mode (SM) optical fiber 98, the double-clad single-mode (SM) optical fiber comprising a small-diameter core, a cladding 118, and a protective polymer layer 116. Preferably, the optical fiber 98 is made of Teflon. TM Fluoropolymer is used for cushioning. The main portion of the optical fiber 98 extending within the input collimator assembly 80 is stripped from the protective layer 116. The distal end of the optical fiber is laser-welded to the end block 110.

[0082] One component of the light-blocking assembly is a light blocker 112, which is mounted on a retainer 94 between an end block 110 and the proximal end 104 of the retainer. The light blocker 112 is configured with two plates 120 that slide inwards toward each other in a passage 124 perpendicular to the longitudinal axis of the retainer 94. The latter are formed in the retainer 94 between the distal end 106 and the proximal end 104, respectively. One or both plates 120 have a small slit 122 through which an optical fiber 98 passes and is formed inside the plate 120, such that it is aligned with a collimator 108, a channel 125 for supporting the optical fiber 98 disposed on the top surface of the proximal end 104 of the retainer, and a sealed input port 102. Figure 5 Alignment. Alignment allows fiber 98 to avoid undesirable bending within the laser head 100. The light-blocking surface of plate 120 effectively prevents most of the back-reflected light after decoupling from reaching port 102.

[0083] Figure 7B An alternative configuration of the light blocker 112, including bottom and top blocks 115, is shown. The bottom block 115 has a channel 114 that receives an optical fiber 98 having a protective layer 116 that is removed along its length between the light blocker 112 and the end block 110. The top block 115 is mounted on a recessed top surface of the bottom block 115 and covers the channel 114, thereby defining a pathway through which the distal end of the optical fiber 98 stripped from the protective layer 116 passes. Alternatively, the channel 114 may be disposed within the top block. Similar to... Figure 7A The configuration, channel 114 and Figure 5 Input port 102, end block 110, and collimating lens 108 Figure 7A Alignment. Unfortunately, due to known limitations of cutting tools, Figure 7A slit 122 and Figure 7B Channel 114 is still too large, allowing a significant amount of back-reflected light to reach input port 102. Therefore, a single light blocker 112 may not always be sufficient for the intended light-blocking purpose.

[0084] Figure 8 An alternative or additional light-blocking element is shown – a collar 126, which is mounted on the sealed input port 102. Figure 5 The retainer 94 is located on the proximal end 104 between the retainer 94 and the end block 110. The collar 126 is made of ceramic and is drilled to have a central passage 128, which is only slightly larger than the outer diameter of the cladding 118, which is not protected by the layer 116. For example, for a cladding diameter of 125 μm, the diameter of the central passage 128 is 126 μm and its length is 3 mm. Although the collar 126 can be used alone, it is used in conjunction with... Figure 7A and Figure 7BThe combination of light-blocking elements 112 was found to be very effective, effectively preventing the entire decoupled back-reflected light from incident on the sealed input port 102. If the collar 126 and end block 110 are used together, the retainer 94 can be configured with an elongated U-shaped central recess 129 that receives two light-blocking elements such that they are coaxial with each other and further... Figure 7A collimator 108 and Figure 5 The input port 102 is coaxial.

[0085] Figure 9A and Figure 9B An alternative concept for the input collimator assembly 80 is shown. The retainer 94 can have a multi-stage configuration with a distal end 106 supporting the FAC and SAC 108. A unique feature of the retainer 94 shown in these figures includes multiple individual U-shaped spring clips 130, which can be attached to the proximal end 104 of the retainer 94 and glued to the EO PCB 75 of the input collimator assembly 80. Figure 5 The fiber optic cable is held in place beforehand. The miniature spring clamp 130, cut from sheet metal (such as copper, aluminum, etc.), is flexible and therefore can withstand high thermal loads even if the CTE of the corresponding sheet metal and the parts in contact with the spring clamp 130 is mismatched. (See Figure 7 and...) Figure 8 In contrast to the configuration shown, the retainer 94 is mounted on the EO PCB 75, with the spring 130 glued to the circuit board. In other words, in relation to... Figure 6 Before contact with the EO PCB75, the retainer 94 is flipped to the mounting position, as indicated by arrow A. In the mounting position, the fiber optic cable 98 is aligned with the input port 102. Figure 5 The spring clamps 130 extend between the fiber 98 and the end block 110. Once installed, the spring clamps 130 restrict displacement of the fiber 98 away from the bottom of the channel, which helps the fiber extend without undesirable bending. In the installed position, the spring clamps 130 are spaced apart, which reduces the contact surface between them and the EO PCB 75, which further improves the resistance of these clamps to high thermal loads.

[0086] return Figure 8To minimize the amount of back-reflected light, the surface 111 of the end block 110 welded to the far end of the optical fiber is covered with an anti-reflective (AR) coating. Typically, AR coatings effectively suppress light with relatively narrow spectral widths. However, if the disclosed laser head is used to output red light, a wide spectral width is desired. This is achieved by providing a laser pump source with a Raman converter (not shown here) that induces first, second, third, and fourth Stokes shifts in the pump light at 1112±5 nm, 1170±5 nm, 1226±2 nm, and 1290±2 nm, respectively. The “tail” of this spectrum extends beyond the first and fourth Stokes shifts. Such a wide spectral range would require an anti-reflective (AR) coating covering the end block 110 with an even wider wavelength range of 1000 nm to 1400 nm, which would be impractical even if the most well-known AR coatings were used here. Conversely, the antireflective surface 111 of end block 110 relies on the engineered design of surface texture and pattern to achieve efficient light capture or transmission. Using any known technology, the nanostructured surface of end block 110 has no problem effectively suppressing back-reflected IR light in the desired 400 nm spectral range.

[0087] Back Figure 5 Another laser head element that primarily contributes to the small footprint of the head is the crystal holder assembly 82 of the frequency conversion scheme of the present invention. The configuration of the crystal holder assembly 82 is described below.

[0088] Figure 10 This actually illustrates a fully assembled (i.e., assembled) optoelectronic scheme mounted on the EO PCB 75 of the laser head of the present invention (which is configured to output red light). Along the path of the collimated IR light within the laser head, it propagates sequentially through upstream, two intermediate, and downstream frequency conversion stages or platforms, all based on corresponding SHGs. The SHGs are implemented by corresponding LBOs, which are supported by corresponding crystal holders 821, 822, 823, and 824. At the output of the first intermediate SHG 822, the red light generated in the upstream and first intermediate LBOs is guided outside the laser head 100 through the first red light output collimator assembly 234, while the red light converted in the second intermediate LBO and downstream LBOs exits the laser head 100 through the second red output collimator assembly 236. The unconverted IR light is guided through the clearing assembly 238. The output red and unconverted IR pump light can be coupled into corresponding output fibers or propagated in free space. The output collimator assemblies 234 and 236 each have a configuration similar to that of the input collimator 80.

[0089] refer to Figure 11A and Figure 11B , Figure 10 All crystal retainer assemblies 821-4 The common general structure includes a base 265 mounted on the EO PCB 75 and specifically configured with a thermoelectric cooler (TEC) 240. Based on ceramics (such as bismuth telluride (Bi2Te3)), the TEC 240 and EO PCB 75 have corresponding TCEs, and they are not completely mismatched. Instead of a single TEC 240, two separate TECs 2401 and 2402 ( Figure 11B It can be used to provide and control the desired thermal state. The TEC240 supports the thermal jacket 242 of the LBO244 package. The temperature detector (RTD) 252—another component of the crystal holder assembly 82—can be mounted on the base 265, or, as... Figure 11B As shown, it is mounted on top of the thermal sleeve 242. The latter configuration may be advantageous for frequency conversion schemes that generate green light. The latter requires only two conversion stages or cascades to convert IR light at the fundamental frequency into green light with a maximum power of approximately 1000 kW at a selected wavelength depending on the wavelength of the IR pump light.

[0090] refer to Figures 12A to 12C The configuration of the thermal jacket 242 takes into account the unique response of the LBO 244 to high temperatures along different crystal axes. Conceptually, the jacket 242 allows the LBO 244 to expand / contract in response to a thermal gradient without placing excessive load on the crystal, which could otherwise lead to mechanical and optical failure. This concept is achieved by forming multiple supports 246 (using laser-processed sheet metal as discussed below) Figure 12B and Figure 12C To achieve this.

[0091] Sheath 242 includes two rows (or half rows) of individual C-shaped supports 246, which are grouped such that along the longitudinal axis A-A' perpendicular to LBO 244... Figure 12A Each pair of supports 246 is aligned in the plane of the clamp 250. Figure 12B , Figure 12C The manufacture of bracket 246 includes, for example, laser cutting a sheet metal part into multiple spaced-apart individual / separate segments 248. Figure 12A and Figure 12D Then, it is shaped into a support 246 with a corresponding C-shaped profile.

[0092] like Figure 12C As shown, before the LBO 244 is inserted into the sheath 242, the vertical sides or bases 262 of the corresponding supports 246 of the clamp 250 converge. As a result, the top flanges 254 of the clamp 250 overlap each other. Therefore, as... Figure 12BAs shown, upon insertion, the LBO 244 presses against and unfolds the top and bottom flanges 258 of the corresponding supports 246 of each clamp 250. When fully inserted, the inner periphery of each clamp 250 conforms to the outer periphery of the closed portion of the LBO 244. Thus, on the one hand, the flexible supports 246 of each clamp 250 are in continuous contact with the crystal 244 regardless of whether the latter expands or contracts. On the other hand, there is no restriction on the expansion of the crystal 244 along its longitudinal axis A-A' because the opposite ends 255 of the sheath 242 ( Figure 12A It is open.

[0093] Let's look again. Figure 12C It is easy to see that each bracket 246 has a Z-shaped cross-section. Figure 12C The sheath 242 is mounted on an optional base 260, which is typically made of Cu and TEC 240 respectively. Figure 11A The sheath 248 is made of mismatched materials between CTEs.

[0094] In terms of alternative structures, sheet metal can be machined to have multiple recesses 245 ( Figure 12A The plurality of recesses terminate at a distance from one of the opposing longitudinal edges of the sheet. In this configuration, when a C-shape or Z-shape is applied to the processed sheet, each row has multiple individual, spaced-apart segments 248 ( Figure 12A ) continuous base 265 ( Figure 12D ).

[0095] Figures 12E to 12F A variant of the thermal sleeve 242 is shown. Figures 12A to 12D Specifically, each bracket costs 246 ( Figure 12C and Figure 12D It has a base 262, which engages perpendicular to the bottom 75 of the housing. Figure 6 The side of the extended crystal 244, while the flange 254 is corresponding to the top and bottom of the crystal 244. Figure 12B ) or only the top ( Figure 12C (Parallel) For convenience, Figures 12A to 12D The sheath configuration is referred to as a horizontal structure. Once assembled, this horizontal structure is placed... Figure 12A The TEC240 is heated, which exposes the crystal to unnecessarily high thermal loads, resulting in reliability issues during and after reflow.

[0096] Figure 12E and Figure 12F The sheath 242 is configured to address this problem. In contrast to the horizontal structure, Figures 12E to 12CThe sheath 242 has a vertical structure, wherein the lower half 243 of the sheath 242 receives the crystal 244, and its top is covered by the upper half 247. This configuration firstly allows the lower half 243 ( Figure 12F Separate return to TEC / heater 240 ( Figure 12E On top of the sheath 242, without crystal 244 and upper half 243. Crystal 244 and upper half 247 are then installed at room temperature. In the assembled horizontal structure of the sheath 242, the bottom 249 of the crystal (… Figure 12F The crystal is placed on the base 262 of the corresponding support 246, while the side 251 of the crystal presses against the inner surface 253 of the corresponding flange 254 of the support half (e.g., the lower half 243), as discussed below.

[0097] The sheath 242 has halves 243 and 247 configured with micro-latch arrays. The latching assembly allows, for example, the outer surface 257 of the flange 254 of the upper half 247 to overlap with the corresponding flange 254 of the lower half 243. The latching assembly is configured with resilient protrusions or tongues 259 cut from the corresponding flange 254 of the support 246. However, the support of each half has a protrusion 259 on only one side, and these protrusions are positioned diagonally relative to each other when the sheath 242 is fully assembled. The other sides of the corresponding halves 243, 247 have corresponding openings 261 formed in the flanges 254. During final assembly, as the LBO 244 is placed within the lower half 243, the upper half 247 slides downwards such that the protrusion 259 of one half protrudes through the corresponding opening 261 of the other half and resiliently presses inward against the corresponding opposite side 251 of the crystal 244. Figure 12E As better illustrated, the flange 254 of one half spans across one flange of the other half. A slight modification to this structure involves forming a protrusion 259 in both flanges of one half 243, 247, while providing an opening 261 in the flange 254 of the other half. However, this modified structure is more... Figure 12E and Figure 12F The structure shown is less resistant to both external and internal loads.

[0098] Depending on whether the laser head of this invention is configured to emit green or red light, not only does the number of necessary optical frequency conversion stages—two for green and four for red—change, but also the TEC 240 ( Figure 12A The position of the TEC 240 can also be varied. Green light generation requires the TEC 240 to operate in a heated state, while red light is obtained when the TEC 240 operates in a cooled state. If the laser head of this invention is configured to emit green light, the TEC 240 should be safely spaced apart from both the crystal 244 and the EO PCB 75. Figure 10In this configuration, the TEC 240 is advantageously mounted on top of the thermal sleeve 242. Conversely, when the exposed laser head outputs red light, the TEC 240 is... Figure 11A This is part of the base 265 of the support sheath 242. Based on the maximum power of the IR pump light at the fundamental frequency, red light can achieve a maximum power of approximately 750 kW at the desired wavelength. Structural problems may arise at different locations of the TEC 240 generated by green and red light.

[0099] Figures 13A to 13C A structure is shown that is successfully used for both the heating and cooling states of the TEC 240, and can be combined. Figure 12A To be better understood. When the laser head of the present invention is part of a laser system that generates green light, it is highly desirable to limit the heat generated by the TEC240 from affecting adjacent components. To achieve the desired thermal protection, the ceramic base 264 of the base 265 is provided with a plurality of low-dielectric-conductivity ceramic pillars 266. Figure 13C The low-dielectric conductive ceramic pillar is attached to the bottom of the EOPCB 75.

[0100] The TEC 240 is mounted on top of a base 264, which has two heater pads 268 that engage with the EO PCB lines. The TEC 240 is soldered to the metallized top of the base 264 between the pads 268. To provide electrical insulation between the TEC and the sheath 242, a dielectric insulating layer 270 is sandwiched between the TEC and the sheath pad 275. A thermistor 252 is mounted on the pad 275 and electrically coupled to the EO PCB 75. Taking into account the heat in the green light state, nothing prevents the disclosed base from being effective when the illustrated structure is used to generate red light with a maximum power of approximately 750W.

[0101] Figure 14A The diagram shows optical elements 202 (such as a folding mirror 235, a focusing lens 237, a half-wave polarizer 239, and a dichroic mirror 241). Figure 10 An exemplary component 200 is directly soldered to the EO PCB 75. Component 200 includes an IR laser source 204 and a localized heat source 206 aligned with the optical element 202 to be soldered, facing the respective top and bottom of the EO PCB 75. The optical element 202 can be held in place by a temperature-controlled holder 210, which, acting as the laser source 204 and heat source 206, influences the active solder 208 between the element 202 and the EO PCB 75. A non-contact temperature sensor 215 is coupled to the solder 208 and outputs a signal received in a processor, which evaluates the received signal. If the received signal is outside the desired range, one or both of the heat sources 204 and 206 are adjusted appropriately.

[0102] See Figure 14B Optical element 202 is coupled to EO PCB 75 using ultrasonic solder activation. In the illustrated arrangement, a solder preform 212 or a non-removable or non-foldable elastomeric solder ball (not shown) is pre-bonded to EO PCB 75, and then element 202 is bonded to the preform or solder ball. Element 202 may optionally be metallized. However, even without metallization, element 202 can be reliably coupled to the preform / solder ball. The bonding process may include ultrasonic solder activation. Alignment of element 202, including yaw and tilt / tilt, may be performed before and / or during its soldering.

[0103] Figures 15A to 15C An alternative configuration for coupling optical element 202 to EO PCB 75 is shown. Instead of directly coupling optical element 202 to the board, the illustrated configuration includes a bump 280 for receiving optical element 202. Figure 15A The bump 280 is made of sheet metal material (such as copper) and has a pair of spaced-apart flanges 284. Figure 15B The C-shaped cross-section is defined by the bottom 286. The recessed flange 284 presses against the received optical element 202. Figure 15A ), to prevent its lateral displacement. The corresponding top segment 288 of flange 284 ( Figure 15B The element is bent inward to ensure reliable contact between the element 202 and the bottom 286.

[0104] A recess 282 is formed in each flange 284. Figure 15B During this process, a small portion of sheet metal was not removed, but instead bent out near the bottom 286 where the two flexible arms 292 are formed. Figure 15C The bottom 286 of the protrusion 280 is embossed at 290. This structure is welded to the preform 212. Figure 15A It also facilitates the optical alignment of the bump 280, thereby providing yaw and tilt motion for the bump.

[0105] The aspects disclosed herein, in their application, are not limited to the details of the construction and arrangement of the components set forth in the following description or shown in the accompanying drawings. These aspects allow for the assumption of other embodiments and can be practiced or implemented in various ways. The disclosed laser head is undergoing a range of experiments, thus often requiring modifications to the disclosed embodiments. Several possible variations of the laser head components are illustrated by the accompanying drawings, which are self-evident and intended to form part of this disclosure. Therefore, the examples of specific implementations provided herein are for illustrative purposes only and are not intended to be limiting.

[0106] Furthermore, the wording and terminology used herein are for descriptive purposes and should not be considered restrictive. Any reference to examples, embodiments, components, elements, or actions of systems and methods mentioned herein in the singular may also include embodiments comprising a plural, and any plural reference to any embodiment, component, element, or action herein may also refer to embodiments comprising only a singular. References in singular or plural form are not intended to limit the systems or methods, components, actions, or elements of this disclosure. The use of “comprising,” “including,” “having,” “containing,” “configuration,” and variations thereof herein is intended to encompass the terms listed thereafter and their equivalents, as well as additional terms. References to “or” may be interpreted as inclusive, such that any term described using “or” may refer to a single, more than one, and any term in all described terms. Furthermore, in the event of inconsistencies in the use of terminology between this document and documents incorporated herein by reference, the use of terminology in the incorporated references is supplementary to the use of terminology in this document; for irreconcilable (i.e., contradictory) inconsistencies, the use of terminology in this document shall prevail.

[0107] Therefore, having described at least one example, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. For instance, the examples disclosed herein can also be used in other situations. Thus, the foregoing description and figures are merely illustrative.

Claims

1. A laser head for a high-power fiber laser system, comprising: A housing with a height of 5 mm to 10 mm, the housing having a bottom; An input collimator assembly is mounted to the housing and is operable to collimate single-mode pump light at the fundamental frequency and a maximum power of 2kW. A multi-cascaded nonlinear frequency converter, located within the housing and receiving collimated pump light, converts the fundamental frequency into its higher harmonics, wherein the converted higher frequency light has a maximum power of 1 kW. Multiple electronic and light-guiding optical components are installed in the housing. The bottom of the housing is an electro-optic printed circuit board, which directly supports the input collimator assembly, the multi-cascaded nonlinear frequency converter, and electronic and optical components at designated locations. The single-mode pump light is coupled to the input collimator assembly at a desired fundamental wavelength within a 1 μm spectral range, and the converted second-harmonic light is either green light at the desired wavelength or red light at the desired wavelength.

2. The laser head as described in claim 1, wherein, The multi-cascaded nonlinear frequency converter includes two or more sequentially positioned second-harmonic generator components, each of which is operable to generate a second harmonic of the fundamental frequency.

3. The laser head as described in claim 1, wherein, The green light has a maximum power of 1 kW or the red light has a maximum power of 750 W.

4. The laser head as described in claim 1, wherein, The input collimator assembly is configured with: A retainer extending along the longitudinal axis; A collimator, which is mounted on the distal end of the retainer and is coaxial with the retainer; A quartz end block, which is mounted on the retainer between the collimator and the proximal end of the retainer and extends along the block axis; as well as A ferrule is mounted on the retainer between the quartz end block and the proximal end of the retainer. The ferrule has a coaxial path with the quartz end block and collimator, through which a single-mode transmission fiber passes, the distal end of which is directly coupled to the proximal end of the quartz end block. The transmission optical fiber guides the pump light at the fundamental frequency, the pump light is incident on the quartz end block and partially back-reflected from the quartz end block, and the size of the ferrule is designed to minimize the propagation of back-reflected light toward the near end of the support.

5. The laser head as described in claim 4, wherein, The input collimator assembly includes a light blocker mounted on the retainer between the collar and the end block, the light blocker having a distal side facing the quartz end block and configured to reflect the back-reflected light.

6. The laser head as described in claim 5, wherein, The light blocker includes two plates mounted to the retainer and capable of being displaced perpendicularly to the longitudinal axis of the retainer toward each other in a mounting position. The plates are configured in the mounting position to define a recess between corresponding opposite sides of each other, the recess through which the transmission optical fiber passes and is coaxial with the passage of the collimator, end block and ferrule.

7. The laser head as described in claim 5, wherein, The light blocker is configured with two blocks mounted on each other such that corresponding sides opposite each other in the mounting position define a longitudinal path coaxial with the collimator, end block and collar and through which the transmission optical fiber passes.

8. The laser head of claim 5 further includes an optical fiber connector, the optical fiber connector being coaxially mounted to the input port of the housing along with the passage of the corresponding ferrule and light blocker, wherein, The transmission optical fiber extends to the gap length between the optical fiber connector and the quartz end block. The input port has a seal that is shielded from back-reflected light by the light blocker and the ferrule and maintains the near-sealed interior of the housing.

9. The laser head as described in claim 4, wherein, The near end of the quartz end block has a surface with a plurality of randomly arranged anti-reflective nanospikes, each of which has a size smaller than the fundamental wavelength of the pump light.

10. The laser head as claimed in claim 4, wherein, The quartz end block has a cylindrical cross-section and its dimensions are designed to be 1 mm to 2 mm in diameter and 3 mm to 5 mm in length.

11. The laser head as claimed in claim 2, wherein, The multi-cascaded nonlinear frequency converter is equipped with crystal holders mounted on the electro-optic printed circuit board, each crystal holder including a sheath. The sheath is configured with two longitudinal halves of a flexible support, the flexible support being made of sheet metal and arranged to define internal channels with open ends, the internal channels receiving a nonlinear crystal, the nonlinear crystal being lithium triborate. Each of the flexible supports elastically presses against the adjacent surface of the lithium triborate, so that the flexible support remains in contact with the lithium triborate regardless of whether the lithium triborate expands or contracts.

12. The laser head as claimed in claim 11, wherein, Each row of flexible supports is either completely separate from each other or has a common support.

13. The laser head as claimed in claim 11, wherein, The lithium triborate has opposite sides, a top, and a bottom, the bottom facing the electro-optical printed circuit board. The corresponding halves of the flexible support each have a base and opposing flanges. The base of each support and the opposing flange together define a C-shaped cross-section and resiliently press against the corresponding sides, top, and bottom of the lithium triborate, or The base and opposing flange of each support together define a Z-shaped cross section and elastically press against the corresponding side and top of the lithium triborate.

14. The laser head as claimed in claim 11, wherein, The lithium triborate has opposite sides, a top, and a bottom, the bottom facing the electro-optical printed circuit board. Each flexible support has a base that together defines a C-shape and opposing flanges. The base of each C-shaped support in one half engages with the top of the lithium triborate, while the flange faces the corresponding side of the lithium triborate. The base of each support in the other half engages with the bottom of the lithium triborate, while the flange of each flexible support in the other half faces the corresponding side of the lithium triborate.

15. The laser head as claimed in claim 14, wherein, In each half of the sheath, one flange of the corresponding support has a corresponding protrusion, and the other flanges of the corresponding support in each half have corresponding openings. The flanges of the corresponding halves overlap each other at the assembly position of the sheath. In the assembled position, the bump protrudes through the corresponding opening toward the opposite side of the lithium triborate and elastically presses against the opposite side.

16. The laser head as claimed in claim 11, wherein, The crystal holder further includes: A base having a plurality of pillars extending from the bottom of the base to be mounted on the electro-optical printed circuit board; Thermoelectric cooler mounted on the base; A dielectric insulating layer is sandwiched between the thermoelectric cooler and the sheath, wherein the base and the thermoelectric cooler are made of a material having a coefficient of thermal expansion that matches that of the electro-optic printed circuit board.

17. The laser head of claim 1, further comprising a plurality of clamps, each clamp being made of sheet metal and having a C-shaped cross-section defined by a pair of recessed flanges bridged at the bottom, the clamps being sized to receive corresponding optical components such that the flanges press against the optical components and prevent the optical components from actively detaching.

18. The laser head as claimed in claim 17, wherein, The flanges of the respective clamps each have corresponding pointed portions that converge to each other in order to press against the top of the inserted optical component.

19. The laser head as claimed in claim 17, wherein, The bottom of each clamp is equipped with: A protrusion extending from the outer side of the bottom and soldered to an electro-optical printed circuit board; and A pair of arms, located on the side of the protrusion and soldered to the electro-optical printed circuit board, the protrusion and the arms being soldered to enable the clamp to yaw and tilt.

20. The laser head of claim 1, further comprising a plurality of output collimator assemblies and a clearing assembly, the plurality of output collimator assemblies guiding higher frequency light to the outside of the housing, and the clearing assembly guiding unconverted pump light to the outside of the housing.

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