Compact laser head

Abstract

The laser head for a high-power fiber laser system has a housing with a height of 5 to 10 mm provided at the bottom. The housing encloses an input collimator assembly that collimates single-mode pump light at a fundamental frequency and a maximum power of 2 kW. The housing further encloses multiple cascaded nonlinear frequency converters that accept the collimated pump light and convert the fundamental frequency to its higher harmonics, the converted light at the higher frequencies having a maximum power of 1 kW. Enclosed within the housing are electronic and light-guiding optical components mounted within the housing. At the bottom of the housing is an electro-optic printed circuit board (EO PCB), which directly supports the input collimator assembly, the multiple cascaded nonlinear frequency converters, and the electronic and optical components in their designated locations.

Description

Technical Field

[0001] The present disclosure relates to high-power lasers operating in the visible spectrum. In particular, the present disclosure relates to a small and cost-effective laser head for lasers of the above type.

Background Art

[0002] Visible light is typically defined as having wavelengths in the range between infrared (having longer wavelengths) and ultraviolet (having shorter wavelengths). Industrial laser applications that utilize visible light have conventionally included, but are not limited to, medical, material processing, science, and consumer goods. As the laser industry continues to mature with the availability of new nonlinear crystals used in frequency conversion schemes, lasers that generate visible light continuously find new applications (such as, for example, red-green-blue (RGB) light engines).

[0003] There are several laser types that output visible emission. One type includes short-wavelength semiconductor laser diodes. Another type of known device is represented by various gas lasers. Yet another type of solid-state laser is based on nonlinear frequency conversion, which includes generating the second and higher harmonics of the fundamental frequency, or utilizing sum frequency and parametric oscillation to obtain the desired frequency. Within the scope of the present invention, solid-state lasers that utilize nonlinear frequency conversion schemes (such as, for example, fiber lasers) are of particular interest. However, as will be recognized by those skilled in the art of laser technology, the main aspects of the present disclosure are applicable to other solid-state lasers that require frequency conversion as well.

[0004] Figure 1 illustrates a group of fiber lasers 10 utilizing nonlinear conversion techniques. Each laser 10 includes a continuous-wave (CW), quasi-CW (QCW), or pulsed pump source 12 that outputs infrared (IR) pump light in the 1 μm fundamental wavelength range, for example, between approximately 1030 nm and 1120 nm. The generated IR pump light further propagates through a delivery fiber 14 connected to a laser head 16. The laser head 16 is configured to include a frequency converter that generates visible laser output.

[0005] Patent Document 1 (which is incorporated in its entirety herein) discloses an exemplary QCW laser that generates red light at 615 nm, 635 nm, and longer wavelengths by utilizing a combination of a Raman converter and a frequency conversion scheme. The Raman converter includes a Raman fiber provided with a cavity consisting of one or more pairs (cascades) of fiber Bragg gratings. As is known to those skilled in the art, the Raman converter provides a wavelength shift from the fundamental frequency of the pump light in the Raman gain spectrum of the fiber. The pump light at the Raman-shifted fundamental frequency is converted into red output light by a frequency converter (e.g., a second harmonic generator (SHG) mounted on the laser head).

[0006] The subject of this disclosure is a laser head 16 (associated with a fiber laser operating in the visible spectral range). Compactness, automation, cost-effectiveness, cleanliness, optical efficiency, and stability against mechanical and thermal loads are all essential characteristics of a laser head. Each of these characteristics is defined by one or more specific components. Often, improving one characteristic can have adverse effects on others. Therefore, improving the operation of a laser head requires an integrated approach that involves modifications to multiple laser head components, as exemplified by the following development history of the laser head 16.

[0007] Figure 2 illustrates an exemplary laser head 16 configured to output red light, but those skilled in the art will readily recognize that the shown configuration is relevant to any fiber laser operating in any region of the visible spectrum, with or without minor variations. For example, the Raman converter may be omitted, as the frequency generator can utilize various nonlinear effects other than SHG. For example, the nonlinear optical process may include sum-frequency techniques and other techniques for determining the corresponding optical circuit diagram, as is well known to those skilled in the art in laser technology.

[0008] The architecture of the laser head 16 includes a combination of optical, fiber-related, and electrical / electronic components, all mounted on the bottom 18 of the laser head housing. A delivery fiber 14 extends into the interior of the laser head 16 through a fiber connector 30, where the distal end of the fiber is received by an input collimator assembly or objective lens 32.

[0009] Looking at Figure 3 in relation to Figure 2, the input collimator assembly 32 is provided with multiple elements, one of which is an end block 34, which is made of quartz and fused to the distal fiber end. The end block 34 minimizes damage to the distal fiber end and somewhat reduces the beam's power density. The expanded pump beam then propagates over free space and is collimated within the collimator 36.

[0010] The collimated pump beam interacts with a frequency conversion scheme 40 (Figure 2) including upstream and downstream nonlinear optical crystals (NLOs) 38 (e.g., lithium triborate (LBO)). As the pump light propagates through the upstream NLO 38, the Raman-shifted fundamental frequency is doubled. The light generated at the doubled frequency, 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, which, by interacting with the remaining pump light, generates additional converted light at the doubled frequency. A dichroic mirror 42 spectrally separates the converted and remaining IR pump beams, which are further decoupled from the head 16 through their respective output ports 44, 46.

[0011] Based on the above, as shown in Figure 3, the input collimator assembly or objective lens 32 includes a holder 45 and a collimator 36 in addition to the end block 34. The configuration of the collimator assembly 32 is bulky and therefore contributes to the large footprint of the laser head 16. Another major contributor to the overall large footprint of the laser head 16 is the frequency conversion scheme, which includes the nonlinear crystal 38, its respective crystal holder assembly, and guiding optics.

[0012] The miniaturization of the laser head 16 began by replacing the input fiber 14 with a fiber having a smaller core diameter, which resulted in a reduction in the beam diameter of the single-mode (SM) pump light. The reduced beam diameter created the possibility of using smaller optical components. However, the reduced beam diameter increased the IR pump light power density or intensity (I), where intensity (I) is the ratio of power (P) in watts (W) to the cross-sectional area of ​​the beam (I = W / cm²). 2The higher the optical power density of the light, the higher the optical efficiency of the NLO36. Therefore, the reduced beam diameter improves both compactness and frequency conversion efficiency. However, increasing the power density of the SM IR pump light at the desired wavelength in the 1 μm wavelength range also creates problems at high IR maximum pump light powers that reach approximately 2 kW or more.

[0013] For example, at relatively low IR power below 100W, the pump light presents little to no environmental hazard when it is reflected back from the end block 34. However, under the condition that the SM pump operates within the IR power range disclosed above, this all changes with high power density. In fact, high-density light caused more than a fair share of unexpected structural problems, as described below.

[0014] For example, when high-power IR pump light at a Raman-shifted wavelength is back-reflected from the end block 34, it is coupled into the cladding of fiber 14. Once guided through the silica cladding, the back-reflected light tends to decouple from it, damaging the polymer protective coating around the cladding, which makes the fiber vulnerable to environmental hazards. Particularly dangerous effects on the exposed fiber can be caused by rising temperatures, because the laser source continues to operate. Ultimately, the fiber can burn and be completely destroyed. Typical mechanisms for handling cladding modes, known as cladding mode strippers or mode filters, are made from silicon with a refractive index higher than or similar to that of silica. However, when used alone, the effectiveness of mode filters at the desired high power densities has been questionable.

[0015] Furthermore, as the temperature increases during laser operation, the refractive index of the cladding eventually equals that of the mode filter. As a result, instead of the back-reflected light being released from the cladding into the mode filter, it continues to propagate through the filter into the cladding towards the input port of the housing, and the fiber connector 30 extends into the laser head 16 through the input port. Typically, the gaps present in the input port around the fiber connector 30 are sealed by epoxy making the inside of the housing nearly airtight. When high-power back-reflected light strikes the epoxy, it is damaged and can burn due to its low resistance to rising temperatures. As a result, the encapsulated fiber can be easily damaged, and the inside of the laser head is exposed to the ambient environment, which often leads to very undesirable consequences. Moreover, the high optical power density and associated rising temperatures in experimental laser heads cause the adhesive to release chemical gases, gradually contaminating and eventually destroying the optical components. Clearly, all of the problems discussed above, associated with existing collimator assemblies positioned at the input of known laser heads, and with each collimator assembly at the output of laser heads, needed to be corrected.

[0016] Another issue associated with IR input and output (dump) collimator assemblies relates more to red lasers based on Raman converters than to lasers that generate other wavelengths in the visible spectrum. It is desirable to output red light over a wide wavelength range. For example, pump 12 in Figure 1 is capable of outputting light at a pump wavelength of 1060 ± 5 nm. SM fiber Raman converters can induce first, second, third, and fourth-order frequency Stokes shifts of pump light covering, for example, a very wide wavelength range. Typically, a "good" anti-reflective (AR) coating reflects less than 3% of the incident light, and even then, its optical effectiveness is questionable. Therefore, there is a need for improved AR structures that can effectively cover a spectral range of several hundred nanometers.

[0017] Figures 4A–4C illustrate an exemplary laser head 16 in one of the advanced development stages, highlighting a set of issues associated with the frequency conversion assembly, and more specifically, with the crystal holder assembly 50. The crystal holder assembly 50 includes a thermoelectric cooler (TEC) 52 and a resistance temperature detector (RDT) (e.g., a thermistor (not shown) supported by an optical bench 20, a C-shaped bracket 54, and an L-shaped jacket 56). The jacket 56 and bracket 54 are configured to hold the crystal 38 in place by a spring 60. A screw 58 (Figure 4B) rigidly connects the jacket 56 to the bracket 54. The entire assembly is mounted on the bottom 18 (Figure 4A) of the laser head housing. While the specific shapes and configurations of the bracket 54 and jacket 56 may vary, the combination of these elements with the relatively thick bottom 18 and optical bench 20 makes the assembly 50 too large, too tall, and too heavy. The fully assembled laser head 16 in Figure 4C has dimensions (W×L×H) mm corresponding to (105~115)×(215~220)×(60~75) mm, respectively. While these dimensions may vary from one type of conversion scheme to another according to the IR source parameters, the footprint of the laser head 16 disclosed above is rather typical, despite the fact that the laser head in Figure 4C operates with a reduced beam diameter of IR light. To reiterate one of the problems this disclosure seeks to solve, the footprint and weight of the frequency conversion assembly need to be reduced.

[0018] The housing base 18, optical bench 20, and crystal jacket 54 are all made from copper (Cu). The homogeneity of the material, characterized by a uniform coefficient of thermal expansion (CTE), helps minimize the inevitable displacement of the multiple components relative to each other during operation. However, other elements of the laser head (e.g., TEC52, LBO crystal 38 (Figure 2), and others) have their own CTEs that differ from the CTE of Cu. TEC52 continuously regulates the temperature of the crystal 38. It is necessary to cool the LBO crystal 38 during the generation of red light or to heat it during the generation of green light. This is because a uniform (constant) temperature is a prerequisite for efficient frequency conversion. The LBO crystal has a unique response to rising temperatures; it not only expands differently along two of its axes, but it also tends to contract along a third axis.

[0019] The expansion and contraction of LBO38 causes its displacement relative to the other components of the crystal holder assembly 50. This is because its CTE is different from that of all Cu components and TEC52. The displacement of the assembly components results in an increased thermal load that can deform the crystal 38, which reduces its conversion efficiency and often necessitates replacing the crystal 38.

[0020] To minimize the CTE mismatch between the TEC 52 and the crystal 38, the crystal holder assembly 50 (Figure 4A) uses a C-shaped bracket 54 configured to prevent direct contact between the TEC 52 and the crystal 38, as shown in Figures 4A and 4B. The bracket 54, along with the base 18 and the optical bench 20, raises the assembly 50, and as a result makes it mechanically unstable when in use. To minimize undesirable instability, the crystal holder assembly 50 utilizes a screw 58 and a spring 60 (Figure 4B), which securely fasten the C-shaped jacket 56 to the crystal 38. A plate 62 is obviously another element that contributes to the overall height of the assembly, and the plate 62 is placed between the crystal and the fasteners, and is designed to minimize deformation of the crystal 38 due to the bending moment generated by the screw 58 on the crystal. Such a relatively rigid connection between the crystal 38 and the jacket 56 is undesirable. The reason is that the crystal should "breathe" during temperature fluctuations. Rigidly restricting its expansion can lead to crystal failure. Based on the above, it becomes clear that CTE mismatch should be minimized, which can be done by carefully selecting materials for assembly components that have substantially similar CTEs. Based on the above, the configuration of all assembly components should be modified to reduce the laser head footprint, with particular emphasis on the height of head 16.

[0021] Traditionally, the laser head packaging process involves assembling fiber-related, optical, and electrical components separately from each other. Only after these groups of components are assembled does the packaging of the laser head 16 begin. For example, the electrical wires between the TEC 52 and the external power supply are routed into the laser head and manually connected to the TEC. Such a disassembled assembly method is too time-consuming and not cost-effective in mass production.

[0022] Moreover, as shown in FIGS. 4A-4C, the Cu bottom 18 and the optical bench 20 together define a height that is slightly less than half the height of the laser head 16. Using a thin base component that substitutes for both the bottom 18 and the optical bench 20 would be extremely advantageous from the perspective of mass production of the laser head 16. Moreover, the thin base / bench component should be configured to eliminate manual packaging of the laser head 16.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0024] Therefore, a high-power visible light laser configured with a lightweight and compact laser head, an electro-optical printed circuit board (EO PCB) functionally and structurally replaces the housing bottom and the optical bench of a known laser head, facilitating automated assembly of the laser head of the present invention, the input collimator assembly has a simple configuration that prevents retroreflected light from compromising the substantially sealed state inside the laser head, there is a need for a high-power visible light laser configured with a lightweight and compact structure in which the crystal holder assembly is configured to accommodate various components having different CTEs so as to minimize the thermal stress of the LBO crystal.

Means for Solving the Problems

[0025] These requirements are met by a modular visible fiber laser provided with an IR light source and a laser head configured with a frequency converter. Several structural aspects related to each laser head component and addressing each of the problems listed above are disclosed. Each aspect, individually or in any combination with other features of the same and other aspects, includes one or more features that contribute to a miniaturized, lightweight, easily automated, and cost - efficient laser head.

[0026] According to one aspect, the laser head of the present invention is configured with an electro - optical printed circuit board (EO PCB). The electro - optical printed circuit board (EO PCB) is made of ceramic and covered by a metallized layer, providing electrical paths and precisely designated locations for each optical and electrical component. Thus, the EO PCB functions as both the support base or bottom of the laser head and the optical bench. It is used as an alternative to the massive Cu housing bottom and Cu optical bench stacked on top of each other. The thin and lightweight EO PCB reduces the footprint and weight of the disclosed laser head and is important for the automation of the laser head assembly process.

[0027] The EO PCB supports the frame, which is made from Kovar or aluminum (Al) and generally extends along the edges of the EO PCB. One of the sides of the frame is formed with an inwardly recessed portion that provides a pocket on top of the EO PCB. The pocket is shaped and dimensioned to receive a USB cable plug. The USB cable plug provides an electrical connection between the electrical components of the laser head and external devices (e.g., power supply and controller). The recessed portion of the frame isolates the USB plug from the rest of the head's interior, eliminating the need for additional partitions and expandable materials, which are typically installed in known laser heads and isolate the plug from the inside of the laser head housing. The lid and frame can be manufactured as separate parts or as a one-piece part.

[0028] In another embodiment, the input and output IR collimator assemblies are mounted within a housing. Each collimator assembly includes a one-piece holder, which supports the distal end of a fiber, and the fiber is connected to an end block, collimator, and additional components made of quartz, as discussed below herein.

[0029] According to one feature of this embodiment, instead of bonding the distal fiber end and end block with adhesive in known collimator assemblies, these components are laser-welded to each other. In contrast to adhesives, welding has high resistance to the considerable thermal load created by the high-power light inside the housing.

[0030] Inevitably, as high-power IR light propagates through the housing, it partially strays and is reflected backward from the end block towards the input port. The input port accepts a fiber connector, which is sealed to the housing. The backward-reflected light jeopardizes the integrity of the seal, and when the seal is damaged, it exposes the inside of the housing to environmental hazards, sometimes causing the fiber to burn.

[0031] Therefore, another feature of this embodiment is that it helps minimize the propagation of stray, back-reflected light toward the seal. In particular, the light blocker is mounted on top of the holder between the end block and the input port. The location of the light blocker prevents the back-reflected stray light from further propagating toward the seal.

[0032] One possible configuration of the light blocker has a clamshell structure comprising a bottom slab and a top slab. The bottom slab is mounted on a holder and has a top surface that is in contact with the bottom surface of the top slab. One or both of the top and bottom surfaces are machined with their respective generally U-shaped recesses, which form channels traversed by fiber stretching when the top slab is mounted on the bottom slab. The channels are dimensioned so that back-reflected stray light is incident on the distal surface of each slab, which then acts as a protective barrier that minimizes the propagation of back-reflected light.

[0033] In another configuration of the optical blocker, two plates are mounted on a holder, with their respective inner sides in contact with each other. Similar to a slab, one or both of the contacting sides have small recesses, which are aligned with each other and thus form a channel. The fiber extends through the channel, which has an inner diameter slightly larger than the outer diameter of the fiber. The sides of each plate facing the end block stop the main portion of the back-reflected stray light from propagating further toward the seal.

[0034] Furthermore, back-reflected IR light is coupled into the fiber cladding, posing the same risk to the seal as stray light. To minimize the effect of back-reflected light guided by the cladding, the fiber may be configured with a cladding mode filter formed along the fiber stretch, which is peeled from the polymer protective layer and positioned between the optical blocker and the input port. The mode filter is made of silicon, and silicon releases back-reflected light from the cladding due to its different refractive index, with silicon having a higher refractive index than silica. The optical blocker and cladding mode filter, individually or in combination, significantly minimize the amount of high-power back-reflected light incident on the seal.

[0035] Another feature of this embodiment is the inclusion of a ferrule, which is mounted on a holder and traversed by a fiber peeled from its protective layer. The central bore of the ferrule is just larger than the outer diameter of the cladding and substantially smaller than the channel formed in the optical blocker. The ferrule may be paired with either an optical blocker or a mode filter, or any of these elements may be used individually or on their own.

[0036] Another feature of the collimator assembly of the present invention is related to red lasers, but it can, of course, be used with all types of visible light lasers. To output red light over a wide wavelength range as desired, the IR input light should preferably cover a wavelength range of 1000 to 1400 nm. Accordingly, according to this feature of the present invention, the surface of the end block (which is laser-welded to the fiber end) is provided with randomly arranged subwavelength-sized nanospikes. The structured surface of the end block has been found to be effective in the desired absorption spectrum.

[0037] All of the above characteristics become even more effective for the intended purpose when the fibers used in this invention are buffered with Teflon® fluoropolymer. Teflon® fluoropolymer provides the fibers with excellent resistance to high temperatures, chemical reactions, corrosion, and stress cracking.

[0038] Further embodiments relate to frequency conversion assemblies, and in particular to crystal holder subassemblies. The main difficulties associated with crystal holder subassemblies stem from the unique reaction of LBOs to temperature gradients and from multiple components having different CTEs.

[0039] According to one feature of this embodiment, the crystal holder subassembly includes a TEC connected to an EO PCB. The TEC is typically made from semiconductor n-type and p-type materials having a CTE that matches the CTE of the EO PCB. The subassembly further includes a thermal jacket and an RDT, the thermal jacket mounted on the TEC and sized to accept an LBO crystal.

[0040] The thermal jacket configuration takes into account the different CTEs of each LBO crystal and the thermal jacket. Since the CTE mismatch between these components is practically unavoidable, the disclosed thermal jackets have various modifications that allow the LBO crystals to expand substantially without limitation.

[0041] According to one modification of the thermal jacket, two identical metal sheets are structured as each half of the thermal jacket. Each metal sheet is first laser-cut to have a series of spaced slits extending from one longitudinal edge of the sheet toward the opposite longitudinal edge, but terminating at a predetermined distance from the opposite edge. Subsequently, each sheet is shaped to have either a generally C-shaped or Z-shaped cross-section. The shaped sheets are then mounted on a TEC or submount or any other pedestal structure so that their respective slotted edges face each other. The assembled sheets form an inner channel, which extends along the longitudinal axis and is dimensioned to receive a crystal.

[0042] Based on the above, the thermal jacket is constructed with multiple clamps, each having a pair of flexible arms that press against the respective sides and tops of the crystal. Such contact between the jacket and the crystal prevents displacement of the crystal relative to the jacket. However, the elastic arms do not substantially hinder the expansion of the LBO. As is known, the maximum CTE of an LBO crystal is observed along its longitudinal axis, but the jacket leaves open ends that are axially spaced on the opposite side, which allows the crystal to expand freely in the axial direction.

[0043] Another feature of the crystal holder is the jacket support structure, which may include a ceramic submount on the EO PCB. A heating layer is mounted on the submount and covers the dielectric insulation. The dielectric layer is then placed on top of the heating layer and the crystal jacket, and the crystal jacket is soldered to the dielectric layer by interposed solder pads. The dielectric layer between the heating layer and the crystal jacket provides electrical insulation between these components.

[0044] According to further feature embodiments of this disclosure, the majority of bulk optical components (e.g., lenses and mirrors) are supported by their respective cradles, which are mounted directly onto the EO PCB. One of the issues during laser head assembly involves optically aligning the optical components after they have been mounted on the head. Alignment is necessary to minimize light loss within the laser head. Alignment can involve tilting and rotating or yawing the cradles around an axis generally perpendicular to the plane of the EO PCB.

[0045] The cradle comprises a base that supports the optical components and a pair of sides that elastically press against each face of the optical elements. To provide tilting of the cradle, a pair of elastic leaves (cut outward from the bottom of the cradle and bent) are soldered to the EO PCB. Applying an external force directed to the EO PCB causes one of the leaves to yield. Yawing motion of the cradle is achieved by a boss, which, like the leaves, is formed on the outer surface of the bottom of the cradle and is connected to the EO PCB.

[0046] The above and other embodiments will become more readily apparent when considered in conjunction with the following drawings. [Brief explanation of the drawing]

[0047] [Figure 1] This diagram illustrates several known fiber laser assemblies, each including a laser head. [Figure 2] This is a top view of a laser head, shown without its cover, configured according to known prior art. [Figure 3] This is an axial cross-sectional view of one known collimator assembly. [Figure 4A] This is a top-down perspective view of a known prior art crystal holder subassembly. [Figure 4B] Figure 4A is a cross-sectional view of the crystal holder subassembly. [Figure 4C] Figures 4A and 4B show perspective views of a known laser head including a crystal holder subassembly. [Figure 5] This is a diagram illustrating the laser head of the present invention. [Figure 6] Figure 5 is a top view of the bottom of the laser head of the present invention. [Figure 7A] This diagram illustrates the individual components of the input collimator assembly of the laser head according to the present invention. [Figure 7B] This diagram illustrates the individual components of the input collimator assembly of the laser head according to the present invention. [Figure 8] This is a top-down perspective view of another configuration of the disclosed input collimator assembly. [Figure 9A] This diagram illustrates yet another configuration of the disclosed input collimator assembly. [Figure 9B] This diagram illustrates yet another configuration of the disclosed input collimator assembly. [Figure 10] Figure 6 is a top view of the EO PCB, accompanied by an exemplary electro-optical circuit diagram of the laser head of the present invention shown in Figure 5. [Figure 11A] Figure 5 is an illustrative cross-sectional side view of the laser head of the present invention. [Figure 11B]Figure 5 is another exemplary cross-sectional side view of the laser head of the present invention. [Figure 12A] This is a top view of the crystal holder assembly. [Figure 12B] Figure 12A shows front views of the crystal holders, each featuring the respective configurations of the crystal clamp or thermal jacket. [Figure 12C] Figure 12A shows front views of the crystal holders, each featuring the respective configurations of the crystal clamp or thermal jacket. [Figure 12D] Figures 12B and 12C illustrate one half of the thermal jacket. [Figure 12E] Figures 12B to 12D show assembly diagrams of modified thermal jackets. [Figure 12F] Figures 12B to 12D are exploded views of modified thermal jackets. [Figure 13A] Figure 12A is an exploded view of the pedestal supporting the crystal holder subassembly. [Figure 13B] Figure 12A is a top view of the pedestal supporting the crystal holder subassembly. [Figure 13C] Figure 12A is a bottom view of the pedestal supporting the crystal holder subassembly. [Figure 14A] Figure 6 shows schematic diagrams illustrating different techniques for mounting optical components onto the EO PCB. [Figure 14B] Figure 6 shows schematic diagrams illustrating different techniques for mounting optical components onto the EO PCB. [Figure 15A] These are top-down views of each bulk component holder. [Figure 15B] These are top-down views of each bulk component holder. [Figure 15C] These are top-down views of each bulk component holder. [Modes for carrying out the invention]

[0048] Herein, the disclosed subject matter will be referred to in detail. Wherever possible, the same or similar reference numbers are used in the drawings and descriptions to refer to the same or similar parts or steps. The drawings are in a simplified form and are far from precise scale. For convenience and clarity purposes only, the terms “connect,” “join,” “combine,” and similar terms with their refractive morphemes are used not necessarily to indicate direct and direct connections, but also to connections through mediated elements or devices.

[0049] Figure 5 illustrates the compact laser head 100 of the present invention, which has a footprint comparable to that of a typical iPhone 70. While the dimensions of the laser head 100 may vary somewhat, the smallest known laser head 16 (shown in Figures 4A–4C) has dimensions of 75 mm in width (W), 120 mm in length (L), and 22 mm in height / thickness (H). By comparison, the disclosed laser head 100 (which has undergone laboratory testing) is 75 mm (W) × 112 mm (L) × 8 mm (H). Depending on the structure of the present 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 present invention is a result of the reconfiguration of a small number of key head components (including, among other things, the housing 78, the input collimator assembly 80, the output collimator assembly, and the crystal holder assembly 82).

[0050] Referring to Figure 6 in combination with Figure 5, the housing 78 comprises a bottom 75 (Figure 6), a frame 84, and a lid 86 (Figure 5). Based on the dimensions of the laser head 100 disclosed in the previous paragraph, it is its height / thickness that has been dramatically reduced compared to the known laser heads of Figures 4A-4C. There were two main elements that needed to be redesigned to provide a smaller structure for the laser head 100 (the bottom 75 of the housing 78 and the crystal holder assembly 82 (Figure 5)).

[0051] In contrast to known laser heads characterized by a combination of a large Cu base and an optical bench, the base 75 is fabricated from a ceramic (e.g., aluminum nitride (AlN) or beryllium oxide (BeO)) and also functions as an optical bench. Conceptually and functionally, the base 75 is an electro-optical printed circuit board (EO PCB) with precisely defined locations 76 for each optical component and electrical traces 74 for electrical components. The electro-optical printed circuit board (EO PCB) is one of the notable features of this disclosure, given the maximum power of the pump and the converted light, which will be specified later. The 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 critically important for the fully automated assembly of the laser head 100.

[0052] The frame 84 (Figure 5) can be made from Kovar, or preferably aluminum (Al), or any other lightweight, durable material having desired thermal and electrical properties that substantially match those of the bottom / EO PCB 75. It can be bonded, blazed, soldered, or laser-welded to the EO PCB and covered by a lid 86, which is preferably made from the same material as the frame 84. The frame 84 and lid 86 can be two separate parts (which are joined together during head assembly) or a one-piece monolithic part.

[0053] One of the sides of the frame 84 has a portion of it that is recessed inward to provide a pocket 88 (Figure 5). The pocket 88 is shaped and sized to receive a USB cable plug, commonly indicated as 92. The plug 92 provides an electrical connection between the TEC and RDT and an external device (e.g., a power supply and controller) via their respective electrical traces 74 (Figure 6). The recessed portion of the frame isolates the USB plug 92 from the rest of the inside of the head.

[0054] The miniaturization of the disclosed laser heads is based on beam diameter. For example, the current delivery fiber has a 14 μm core that outputs a beam with a beam diameter of 14 μm, which is four times smaller than that of known laser head designs. Core diameter is generally inversely proportional to light intensity, which means that in the disclosed laser head 100, the light intensity is four times higher than that in known designs. Given that single-mode pumped IR light can have a maximum power in the range of 1-2 kW at selected wavelengths within the 1 μm spectral range, the light intensity at the distal end of the delivery fiber raises safety concerns. Moreover, such high-intensity light damages the degassing adhesive at rising temperatures, affecting the elements, optical components, and, of course, the connections between the fiber ends. To reduce the risks associated with high-intensity light, the distal end of the delivery fiber is laser-welded to a so-called end block made of quartz. However, it has been found that an end block combined with high-intensity forward-propagating pumped light is highly problematic because it also reflects incident light. The light reflected from the back propagates toward the input port 102 (Figure 5), destroying the material (e.g., epoxy) sealing this port. Therefore, the disclosed input collimator assembly 80 not only has a compact configuration, but it is also configured to include multiple components that minimize the propagation of the light reflected from the back, as will be discussed shortly.

[0055] Figures 7A, 7B, 8, 9A, and 9B illustrate an input collimator assembly 80, which comprises a holder 94 bonded (or preferably soldered) to an EO PCB 75 (Figure 6). The holder 94 is made from a ceramic material characterized by CTE that substantially matches that of the EO PCB. Functionally, the holder 94 in Figure 7A supports optical elements (including, among other things, a collimator lens 108, an end block 110 made of quartz, a light shielding block 112, and a delivery fiber 98). Structurally, the holder 94 extends between a proximal end 104 and a distal end 106, with the distal end 106 being thinner than the proximal end 104. The holder 94 can be monolithic or it can have separate pieces that are joined together.

[0056] The collimator assembly 80 is one of the main contributors to the overall miniaturization of the disclosed head. Prior art collimator assemblies are typically 12–15 mm in length. In contrast, the disclosed collimator assembly is at most 10 mm in length, which is a result of miniaturized assembly elements. For example, the cylindrical end block 110 has a diameter of 1–2 mm and a length of 3–5 mm. In contrast, the end block used in the known laser head of Figure 3 has a diameter of 4–8 mm, while the length of the end block is at least 6 mm.

[0057] The end block 110 is part of the problems associated with high light intensity. In most cases, the IR pump light is guided through the fiber core. When fiber 98 delivers the pump IR light to the end block 110, a portion of this light returns partially coupled into fiber 98 and, above all, into its cladding 118 (Figure 7A), which guides the coupled light backward to the sealed input port 102 (Figure 5). This backward reflected light poses a double hazard. Firstly, as it propagates along the cladding 118, it can become detached from the cladding 118. If the detached light enters the sealed input port 102 (Figure 5), the seal (which is typically made of epoxy) can easily break due to the rising temperature. Damage to the seal compromises the nearly sealed interior of the laser head, which can have an irreparable impact on the overall operation of the laser head, and fiber 98 can simply burn out. Secondly, even before reaching port 102, the back-reflected light guided along the cladding 118 reaches a portion of the fiber 98 covered by the protective polymer layer 116 (Figure 7A). Similar to epoxy, layer 116 is vulnerable to the rising temperature associated with the high power intensity of the back-reflected light, and if damaged, it exposes the fiber 98 to the rising temperature. To deal with the high intensity of back-reflected light, the input collimator assembly 80 is provided with a light-blocking assembly, as will be disclosed in detail shortly thereafter.

[0058] Referring to Figure 7A, the proximal end 104 of the holder 94 has a channel 114 for receiving a double-clad single-mode (SM) fiber 98, which comprises a small-diameter core, cladding 118, and a protective polymer layer 116. Preferably, the fiber 98 is buffered with Teflon® fluoropolymer. The main portion of the fiber 98 extending into the input collimator assembly 80 is stripped from the protective layer 116. The distal fiber end is laser-welded to the end block 110.

[0059] One of the elements of the light-blocking assembly is a blocker 112, which is mounted on the holder 94 between the end block 110 and the proximal end 104 of the holder. The blocker 112 comprises two plates 120, which slide inward toward each other perpendicular to the longitudinal axis of the holder 94 within a passage 124. The passage 124 is formed within the holder 94 between the distal end 106 and the proximal end 104 of the holder, respectively. One or both plates 120 have a small slit 122, which is traversed by a fiber 98 and is formed on the inner side of the plate 120, so as to be aligned with a collimator 108, a channel 125 (which is provided in the upper surface of the proximal end 104 of the holder to support the fiber 98), and a sealed input port 102 (Figure 5). This alignment allows fiber 98 to avoid undesirable bending inside the laser head 100. The light-shielding surface of plate 120 effectively prevents the main portion of the released back-reflected light from reaching port 102.

[0060] Figure 7B illustrates an alternative configuration of the optical blocker 112, including a bottom block and an upper block 115. The bottom block 115 has a channel 114 for receiving a fiber 98, the fiber 98 having a protective layer 116, which is removed along its length between the entry point into the optical blocker 112 and the end block 110. The upper block 115 is mounted on the grooved upper surface of the bottom block 115 and covers the channel 114, which thus defines a passage traversed by the distal end of the fiber 98 stripped from the protective layer 116. Alternatively, the channel 114 may be provided within the upper block. Similar to the configuration in Figure 7A, the channel 114 is aligned with the input port 102, end block 110, and collimator lens 108 (Figure 7A) of Figure 5. Unfortunately, due to known limitations of the cutting tool, the slit 122 in Figure 7A and the channel 114 in Figure 7B remain too large, allowing a considerable amount of back-reflected light to reach the input port 102. Therefore, the light blocker 112 alone may not always be sufficient for its intended light blocking purpose.

[0061] Figure 8 illustrates an alternative or additional light-blocking element (ferrule 126), which is mounted on the proximal end 104 of the holder 94 between the sealed input port 102 (Figure 5) and the end block 110. The ferrule 126 is made of ceramic and drilled to have a central passage 128, which is slightly larger than the outer diameter of the cladding 118, which is not protected here by layer 116. For example, for a cladding diameter of 125 μm, the central passage 128 is 126 μm in diameter and 3 mm in length. The ferrule 126 can also be used alone, but it has been found that its combination with the light blocker 112 in Figures 7A and 7B is very effective, practically blocking all of the unblocked back-reflected light from entering the sealed input port 102. When the ferrule 126 and end block 110 are used together, the holder 94 may be configured to have an elongated U-shaped central groove 129, which receives both light-blocking elements and makes them coaxial with each other, and further coaxial with the collimator 108 in Figure 7A and the input port 102 in Figure 5.

[0062] Figures 9A and 9B illustrate alternative concepts of the input collimator assembly 80. The holder 94 can have a multi-level configuration with a distal end 106 supporting the FAC and SAC 108. A notable feature of the holder 94 shown in these figures is the inclusion of multiple separate U-shaped spring clamps 130, which are attached to the proximal end 104 of the holder 94 and capable of holding the fibers in place before the input collimator assembly 80 is bonded to the EO PCB 75 (Figure 5). Cut from sheet metal (e.g., copper, aluminum, and others), the small spring clamps 130 are flexible and therefore capable of withstanding high thermal loads even if the CTEs of the respective sheet metal and parts (which are in contact with the spring clamps 130) are mismatched. In contrast to the configurations shown in Figures 7 and 8, the holder 94 is mounted on the EO PCB 75 with the springs 130 bonded to the substrate. In other words, the holder 94 is flipped into the installation position as indicated by arrow A before contacting the EO PCB 75 in Figure 6. In the installation position, the fiber 98 extends between the matched input port 102 (Figure 5) and the end block 110. Once installed, the spring clamp 130 restricts the displacement of the fiber 98 from the bottom of the channel, which helps the fiber extend without undesirable bending. In the installation position, the spring clamps 130 are spaced apart, which reduces the contact surface between them and the EO PCB 75, and which further improves the resistance of these clamps to high thermal loads.

[0063] Returning to Figure 8, to minimize the amount of back-reflected light, the face 111 of the end block 110 (which is welded to the distal fiber end) is covered with an anti-reflective (AR) coating. Typically, AR coatings effectively suppress light with a relatively narrow spectral width. However, if the disclosed laser head is used to output red light, it is desirable that the red light has a broad spectral width. This is achieved by providing a laser pump source having a Raman converter (not shown here), which induces first, second, third, and fourth-order frequency Stokes shifts of the pump light at 1112±5 nm, 1170±5 nm, 1226±2 nm, and 1290±2 nm, respectively. This spectral "tail" extends far beyond the first and fourth-order Stokes shifts. Such a broad spectral range requires an anti-reflective (AR) coating on the end block 110 that covers an even broader wavelength range of 1000–1400 nm (which is impractical even if the best known AR coatings were used here). Instead, the anti-reflective surface 111 of the end block 110 relies on the engineering of surface textures and patterns to enable efficient capture or transmission of light. Using any known technique, the nanostructured surface of the end block 110 has no problem effectively suppressing back-reflected IR light over the desired 400 nm spectral range.

[0064] Returning to Figure 5, another laser head element that greatly contributes to the small footprint of the head is the crystal holder assembly 82 of the present invention in the disclosed frequency conversion scheme. The configuration of the crystal holder assembly 82 is discussed below.

[0065] Figure 10 practically illustrates a fully assembled optoelectronic scheme mounted on the EO PCB 75 of the laser head of the present invention, configured to output red light. Following the path of collimated IR light inside the laser head, it propagates sequentially through upstream, two intermediate, and downstream frequency conversion stages, all based on their respective SHGs. The SHGs are realized by their respective LBOs, supported by their respective 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 out of the laser head 100 through the first red light output collimator assembly 234, while the red light converted in the second intermediate and downstream LBOs leaves the laser head 100 through the second red light output collimator assembly 236. Unconverted IR light is guided through the damp assembly 238. The output red and unconverted IR pump light can be coupled into their respective output fibers or propagated over free space. Output collimator assemblies 234 and 236 can each have a configuration similar to that of the input collimator 80.

[0066] Referring to Figures 11A and 11B, all crystal holder assemblies 82 in Figure 10 1~4A common general structure includes a base 265, which is mounted on an EO PCB 75 and, in particular, is configured with a thermoelectric cooler (TEC) 240. Based on ceramics (e.g., bismuth telluride (Bi2Te3)), the TEC 240 and EO PCB 75 have their respective TCEs, and they are not dramatically mismatched. Instead of a single TEC 240, two separate TECs 2401 and 2402 (Figure 11B) may be used to provide and control the desired thermal regime. The TEC 240 supports a thermal jacket 242, which surrounds the LBO 244. A resistance temperature detector (RTD) 252 (another element of the crystal holder assembly 82) may be mounted on the base 265 or on the thermal jacket 242, as shown in Figure 11B. The configuration of the thermal jacket 242 may be advantageous for frequency conversion schemes that generate green light. It requires only two conversion stages or cascades to convert IR light at the fundamental frequency to green light, and the green light has a maximum power of approximately 1000 kW at a selected wavelength that depends on the wavelength of the IR pump light.

[0067] Referring to Figures 12A to 12C, the configuration of the thermal jacket 242 takes into account the intrinsic response of the LBO 244 to rising temperatures along different crystal axes. Conceptually, the jacket 242 allows the LBO 244 to expand / contract in response to a temperature gradient without imposing an excessive load on the crystal (which could otherwise lead to mechanical and optical failure of the crystal). This concept is realized by a laser that processes a sheet metal piece to form multiple brackets 246 (Figures 12B and 12C), as discussed below.

[0068] The jacket 242 includes two rows (or half-bodies) of individual C-shaped brackets 246, which are grouped so that each pair of brackets 246 (they are aligned in a plane perpendicular to the longitudinal axis A-A' of the LBO 244 (Figure 12A)) defines the clamp 250 (Figures 12B, 12C). The fabrication of the brackets 246 involves, for example, laser cutting sheet metal pieces into multiple spaced-apart individual / separated segments 248 (Figures 12A and 12D), which are then shaped into the respective C-shaped contours of the brackets 246.

[0069] As shown in Figure 12C, before the LBO 244 is inserted into the jacket 242, the vertical sides or bases 262 of each bracket 246 defining the clamp 250 converge. As a result, the upper flanges 254 of the clamps 250 overlap each other. Thus, as shown in Figure 12B, during insertion, the LBO 244 presses and expands the upper and lower flanges 258 of each bracket 246 of each clamp 250. When fully inserted, the inner circumference of each clamp 250 coincides with the outer circumference of the enclosed part of the LBO 244. Thus, on the one hand, the flexible bracket 246 of each clamp 250 is in continuous contact with the crystal 244, regardless of whether the crystal 244 expands or contracts. On the other hand, there is nothing to restrict the expansion of the crystal 244 along its longitudinal axis A-A'. This is because the opposite end 255 of the jacket 242 (Figure 12A) is open.

[0070] Referring again to Figure 12C, it is easy to see that each bracket 246 has a Z-shaped cross-section. The jacket 242 in Figure 12C is mounted on an optional pedestal 260, which is made of a material that can mitigate the mismatch between the CTE of jacket 248 and the CTE of TEC 240 (Figure 11A), each of which is typically made of Cu.

[0071] In an alternative structural embodiment, the sheet metal may be processed to have a plurality of recesses 245 (Figure 12A) terminating at a predetermined distance from one of the longitudinal edges on the opposite side of the sheet. In this configuration, when applied to the processed sheet in a C-shape or Z-shape, each row has a continuous base 265 (Figure 12D), the base 265 supporting a plurality of individual spaced-apart segments 248 (Figure 12A).

[0072] Figures 12E–12F illustrate modified examples of the thermal jacket 242. In Figures 12A–12D, in particular, each bracket 246 (Figures 12C and 12D) has its base 262 engaging with the side of the crystal 244 that extends perpendicularly to the bottom 75 of the housing (Figure 6), while the flange 254 is positioned alongside the respective top and bottom of the crystal 244 (Figure 12B), or simply alongside the top only (Figure 12C). For convenience, the jacket configurations in Figures 12A–12D are referred to as horizontal structures. When assembled, this horizontal structure is placed on top of the TEC 240 in Figure 12A and heated, which exposes the crystal to an unnecessarily high thermal load, raising reliability concerns during and after reflow.

[0073] The jacket 242 in Figures 12E and 12F is configured to solve this problem. In contrast to the horizontal structure, the jacket 242 in Figures 12E-12C has a vertical structure, in which the bottom half 243 of the jacket 242 receives the crystal 244 with the top of the crystal 244 covered by the upper half 247. Such a configuration allows the bottom half 243 (Figure 12F) to be reflowed alone onto the TEC / heater 240 (Figure 12E) without the crystal 244 and the upper half 247. The crystal 244 and the upper half 247 are then installed at room temperature. In the assembled horizontal structure of jacket 242, the bottom 249 of the crystal (Figure 12F) rests on the base 262 of each bracket 246, while the sides 251 of the crystal press against the inner surface 253 of each flange 254 of the bracket of one of the halves (e.g., the bottom half 243, as discussed below).

[0074] The jacket halves 243 and 247 are configured with micro-latching arrays, for example, a latching assembly that allows the flange 254 of the bracket of the upper half 247 to overlap the outer surface 257 of each flange 254 of the lower half 243. The configuration of the latching assembly includes elastic tongues 259 cut from each flange 254 of the bracket 246. However, only one side of each bracket of the half has a tongue 259, and these are positioned obliquely to each other when the jacket 242 is fully assembled. The other side of each half 243, 247 has a respective opening 261 formed within the flange 254. During the final assembly, when the LBO 244 is placed inside the bottom half 243, the upper half 247 slides down, and one tongue 259 of the half protrudes through the respective openings 261 of the other half, elastically pressing inward against the opposite sides 251 of the crystal 244. As seen better in Figure 12E, the flange 254 of one half straddles one of the flanges of the other half. A slight modification of this structure involves forming the tongue 259 in both flanges of one half of the halves 243, 247, and on one side providing an opening 261 in the flange 254 of the other half. However, the structure thus modified is less resistant to external and internal loads than that shown in Figures 12E and 12F.

[0075] Depending on whether the laser head of the present invention is configured for green light or red light, not only does the number of required optical frequency conversion stages change (two for green and four for red), but the position of the TEC240 (Figure 12A) may also change. The generation of green light requires the TEC240 to operate in a heated regime, while red light is acquired with the TEC240 operating in a cooled regime. If the laser head of the present invention is configured to laser green light, the TEC240 should be safely spaced away from both the crystal 244 and the EO PCB 75 (Figure 10). In this case, the TEC240 is advantageously mounted on the thermal jacket 242. In contrast, when the disclosed laser head outputs red light, the TEC240 is part of the base 265 in Figure 11A supporting the jacket 242. Depending on the maximum power of the IR pump light at the fundamental frequency, the red light can reach a maximum power of approximately 750 kW at the desired wavelength. The different locations of the TEC240 based on the generation of green and red light present a structural problem.

[0076] Figures 13A–13C illustrate structures that are well used in both the heating and cooling regimes of the TEC240 and can be better understood in combination with Figure 12A. When the laser head of the present invention is part of a laser system that generates green light, it is very desirable to limit the heat generated by the TEC240 to affect adjacent elements. To achieve the desired thermal protection, the ceramic pedestal 264 of the base 265 is provided with a number of low dielectric constant conductive ceramic studs 266 (Figure 13C) attached to the bottom of the EO PCB 75.

[0077] The TEC240 is mounted on a provided pedestal 264, with two heater pads 268 wire-bonded to the EO PCB. The TEC240 is soldered to the metallized top of the pedestal 264 between the pads 268. To provide electrical insulation between the TEC and the jacket 242, a dielectric insulating layer 270 is sandwiched between the TEC and the jacket soldering pad 275. A thermistor 252 is mounted on the soldering pad 275 and electrically coupled to the EO PCB 75. Since heat in the green light regime has been addressed, there is nothing preventing the disclosed base from becoming effective when the shown structure is used to generate red light, which may have a maximum high power of approximately 750 W.

[0078] Figure 14A illustrates an exemplary assembly 200 for directly soldering optical elements 202 (e.g., a folding mirror 235, a focusing lens 237, a half-wavelength polarizing plate 239, and a dichroic mirror 241 (Figure 10)) to an EO PCB 75. The assembly 200 includes an IR laser source 204 and a localized heat source 206, which are matched to the optical elements 202 that will be soldered facing the top and bottom of the EO PCB 75, respectively. The optical elements 202 can be held in place by a temperature-controlled gripper 210, because the laser source 204 and the heat source 206 affect the active solder 208 between the elements 202 and the EO PCB 75, respectively. A non-contact temperature sensor 215 is connected to the solder 208 and outputs a signal, which is received by 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.

[0079] Referring to Figure 14B, the optical element 202 is bonded to the EO PCB 75 using ultrasonic solder activation. In the shown configuration, a solder preform 212 or a non-collapsible elastomer solder ball (not shown) is pre-bonded to the EO PCB 75, and then the element 202 is bonded to the preform or solder ball. The element 202 may optionally be metallized. However, even without metallization, the element 202 can be reliably bonded to the preform / solder ball. The bonding process may include ultrasonic solder activation. Alignment of the element 202, including yawing and / or chipping / tilting, may be performed before and / or during its soldering.

[0080] Figures 15A–15C illustrate an alternative configuration for connecting the optical element 202 to the EO PCB 75. Instead of directly connecting the optical element 202 to the substrate, the illustrated configuration includes a C-shaped tongue 280 (Figure 15A) to receive the optical element 202. The C-shaped tongue 280 is fabricated from a sheet metal material (e.g., copper) and has a C-shaped cross-section defined by a pair of spaced-apart flanges 284 (Figure 15B) and a base 286. The recessed flanges 284 are pressed against the received optical element 202 (Figure 15A) to prevent its lateral displacement. The upper segment 288 (Figure 15B) of each flange 284 is bent inward to ensure reliable contact between the element 202 and the base 286.

[0081] During the formation of the recesses 282 (Figure 15B) within each flange 284, small pieces of sheet metal material are not removed but bent outward near the bottom 286 to form two flexible arms 292 (Figure 15C). The bottom 286 of the C-shaped tongue 280 is embossed at 290. This formed portion is soldered to the preform 212 (Figure 15A) to facilitate optical alignment of the C-shaped tongue 280 and provide yawing and tilting motion to the C-shaped tongue.

[0082] The embodiments disclosed herein in accordance with the present invention are not limited in their application to the construction details and component arrangements described below or illustrated in the accompanying drawings. These embodiments may envision other embodiments and may be practiced or implemented in various ways. The disclosed laser heads have generally undergone a series of experiments requiring modifications of the disclosed embodiments. Some of the possible variations of the laser head components are illustrated in the accompanying additional drawings, which are readily apparent and intended to be part of this disclosure. Thus, examples of specific implementations are provided for illustrative purposes only and are not intended to limit the scope.

[0083] Furthermore, the expressions and terminology used herein are for illustrative purposes only and should not be considered limiting. Any singular reference to an example, embodiment, component, element, or act of a system or method herein may encompass a plural embodiment, and any plural reference to any embodiment, component, element, or act herein may encompass a singular embodiment. References in the singular or plural form are not intended to limit the systems or methods, their components, acts, or elements currently disclosed. The use of “including,” “comprising,” “having,” “containing,” “composed of,” and their variations herein means that they encompass the items listed thereafter and their equivalents, as well as any additional items. References to “or” may be interpreted as inclusive, so that any term described using “or” may refer to one, two or more, or all of the terms described. In addition, if there are inconsistent uses of terminology between this document and any document incorporated herein by reference, the use of terminology in the incorporated reference is supplementary to that in this document. In cases of incompatible inconsistencies, the terminology used in this document shall prevail.

[0084] Having thus described several aspects of at least one example, it should be recognized that various alternatives, modifications, and improvements will readily come to mind for those skilled in the art. For example, the examples disclosed herein may be used in other contexts. Such alternatives, modifications, and improvements. Therefore, the above description and drawings are merely illustrative. [Explanation of Symbols]

[0085] 10 Fiber laser 12. Pulse pump supply source 14 Delivery Fibers 16 laser heads 18 Bottom 20 Optical Benches 30 Fiber Connectors 32 Input Collimator Assembly, Objective Lens 34 End Blocks 36 Collimator 38 Upstream and Downstream Nonlinear Optical Crystals (NLOs) 40 Frequency Conversion Schemes 41 1 / 2 wave plate 42 Dichroic Mirror 44 output ports 45 holders 46 output ports 50 Crystal Holder Assembly 52 Thermoelectric cooler (TEC) 54 Brackets 56 Jacket 58 Screw 60 Spring 62 plates 74 Electrical traces 75 Bottom, EO PCB 76. Precisely defined location 78 Housing 80 Input Collimator Assembly 82 Crystal Holder Assembly 821, 822, 823, 824 Crystal Holder Assembly 84 frames 86 Lid 88 pockets 92 USB Cable Plugs 94 holder 98 Fiber 100 laser heads 102 Input Ports 104 Proximal end 106 Distal end 108 Collimator 110 End Blocks 111 Anti-reflective surface 112 Blocker 114 channels 115 Upper block, bottom block 116 Protective polymer layer 118 Cladding 120 Plate 122 slits 124 Passage 125 channels 126 ferrules 128 Central aisle 129 Central groove 130 Spring Clamp 200 assemblies 202 Optical Elements 204 IR laser source 206 Heat source 208 Solder 212 Solder Preform 215 Non-contact temperature sensor 234 First red light output collimator assembly 235 Folding Mirror 236 Second red light output collimator assembly 237 Focusing lens 238 Dump Assembly 239 Half-wavelength polarizing plate 240 Thermoelectric cooler (TEC) 241 Dichroic Mirror 242 Thermal Jacket 243 Bottom half 244 Lithium triborate (LBO) crystal 245 recess 246 Bracket 247 Upper half 248 Jacket 249 Bottom 250 clamps 251 Side 252 Resistance Temperature Detector (RTD) 253 Inner surface 254 Flange 255 Opposite end 257 Outer surface 258 Upper and lower flanges 259 Tongue 260 pedestals 261 Opening 262 base 264 Pedestal 265 base 266 Low dielectric constant conductive ceramic studs 268 Heater Pad 270 Dielectric insulating layer 275 solder pads 280 Tongue 282 recess 284 Flange 286 Bottom 288 Upper segment 292 Flexible Arm

Claims

1. A laser head for a high-power fiber laser system, wherein the laser head is A housing with a base and a height of 5 mm to 10 mm, An input collimator assembly, the input collimator assembly being mounted in the housing and operable to collimate single-mode pump light at the fundamental frequency and a maximum power of 2 kW, A multi-cascade nonlinear frequency converter, the multi-cascade nonlinear frequency converter is located within the housing, receives collimated pump light, and converts the fundamental frequency to higher harmonics thereof, the converted light at higher frequencies having a maximum power of 1 kW, and the multi-cascade nonlinear frequency converter Multiple electronic components and optical components that guide light are mounted inside the housing. Includes, The bottom of the housing is an electro-optical printed circuit board (EO PCB), which directly supports the input collimator assembly, a multi-cascade nonlinear frequency converter, and electronic and optical components at their respective designated locations, in a laser head.

2. The laser head according to claim 1, wherein the multi-cascade nonlinear frequency converter includes two or more sequentially positioned second harmonic generator assemblies, each capable of generating a second harmonic of the fundamental frequency.

3. The laser head according to claim 1, wherein the pump light is coupled into the input collimator assembly at a desired fundamental wavelength within the 1 μm spectral range, and the converted light at the second harmonic is green light at a desired wavelength with a maximum power of 1 kW, or red light at a desired wavelength with a maximum power of 750 kW.

4. The aforementioned input collimator assembly is A holder extending along the longitudinal axis, A collimator is mounted on the distal end of the holder and is coaxial with the holder, A quartz end block, wherein the quartz end block is mounted on the holder between the collimator and the proximal end of the holder and extends along the block axis, A ferrule mounted on the holder between the quartz end block and the proximal end of the holder, the ferrule having a passage, the passage being coaxial with the quartz end block and collimator, and traversed by a single-mode (SM) delivery fiber, the single-mode (SM) delivery fiber having its distal end directly connected to the proximal end of the quartz end block, It is configured to include, The laser head according to claim 1, wherein the single-mode (SM) delivery fiber guides the pump light at the fundamental frequency, which is incident on the quartz end block and partially back-reflected therefrom, and is provided with an anti-reflective (AR) coating covering the distal end of the quartz end block, and the ferrule is sized to minimize the propagation of the back-reflected light toward the proximal end of the holder.

5. The laser head according to claim 4, wherein the input collimator assembly includes an optical blocker, the optical blocker is mounted on the holder between the ferrule and the end block, and the optical blocker has a distal side facing the quartz end block and is configured to reflect the back-reflected light.

6. The laser head according to claim 5, wherein the optical blocker comprises two plates, which are mounted on the holder and are displaceable toward each other toward an installation position perpendicular to the longitudinal axis of the holder, and the plates are configured to define a recess between each of their opposing sides in the installation position, the recess being traversed by the single-mode (SM) delivery fiber and coaxial with the collimator, end block, and the passage of the ferrule.

7. The laser head according to claim 5, wherein the optical blocker comprises two blocks, the upper of the two blocks mounted on the lower of the two blocks at the longitudinal mounting position of the optical blocker, the longitudinal passage formed between the two blocks is defined by a recess formed on the surface of the lower block that is in contact with the upper block, and the single-mode (SM) delivery fiber is arranged in the longitudinal passage so as to be coaxial with the collimator, end block, and ferrule.

8. The laser head according to claim 5, further comprising a fiber connector mounted at the input port of the housing coaxially with the passages of the respective ferrules and optical blockers, the single-mode (SM) delivery fiber extending to have a straight length between the fiber connector and the quartz end block, the input port having a seal, the seal being shielded from the back-reflected light by the optical blockers and ferrules, and maintaining a substantially sealed interior of the housing.

9. The laser head according to claim 4, wherein the proximal end of the quartz end block has a surface provided with a plurality of randomly arranged anti-reflective nanospikes, each of which is sized to be smaller than the fundamental wavelength of the pump light.

10. The laser head according to claim 4, wherein the quartz end block has a cylindrical cross-section, is dimensioned to have a diameter of 1 to 2 mm, and has a length of 3 to 5 mm.

11. Each of the multi-cascade nonlinear frequency converters comprises a crystal holder mounted on the EO PCB, each crystal holder including a jacket, the jacket comprising two longitudinal halves of a flexible bracket made of sheet metal material and positioned to define an open-ended inner channel for receiving a nonlinear crystal, the nonlinear crystal being lithium triborate (LBO), The laser head according to claim 2, wherein the flexible brackets are elastically pressed against adjacent surfaces of the LBO, so that the flexible brackets and the LBO are in contact with each other regardless of the expansion or contraction of the LBO.

12. The laser head according to claim 11, wherein the flexible brackets in each row are either completely isolated from one another or have a common support.

13. The LBO has opposite side portions, an upper portion, and a bottom portion, the bottom portion facing the EO PCB, and each half of the flexible bracket has a base and an opposite flange, respectively. The base and the opposite flange of each bracket define a C-shaped cross-section and are elastically pressed against the respective sides, top, and bottom of the LBO, or The laser head according to claim 11, wherein the base and the opposite flange of each bracket define a Z-shaped cross-section and are elastically pressed against the respective sides and top of the LBO.

14. The LBO has opposite sides, a top, and a bottom, the bottom facing the EO PCB, and the flexible bracket has a base and an opposite flange, each defining a C-shape together. The laser head according to claim 11, wherein the base of each C-shaped bracket of one half of the head engages with the upper part of the LBO while the flange faces each side of the LBO, and the base of each bracket of the other half of the head engages with the bottom of the LBO while the flange faces each side of the LBO.

15. The laser head according to claim 14, wherein one of the flanges of each bracket of each half of the jacket has a tongue, and the other flange of each bracket of each half has an opening, and the flanges of each half are superimposed on each other in the assembled position of the jacket, and in the assembled position, the tongues protrude through the corresponding openings toward the opposing sides of the LBO and are elastically pressed toward them.

16. The aforementioned crystal holder is A base provided with multiple studs, wherein the studs extend from the bottom of the base and rest on the EO PCB, A thermoelectric cooler (TEC) mounted on the aforementioned base, A dielectric insulating layer sandwiched between the TEC and the crystal jacket, wherein the base and the TEC are made of a material having a coefficient of thermal expansion that matches that of the EO PCB, The laser head according to claim 11, further comprising:

17. The laser head according to claim 1, further comprising a plurality of clips, each made from a sheet metal material and having a C-shaped cross section defined by a pair of recessed flanges bridged by a bottom, the clips being sized to receive their respective optical components, the flanges being pressed against the optical components to prevent the optical components from spontaneously disengaging.

18. The laser head according to claim 17, wherein the flanges of each clip each have respective tip portions that converge toward each other to press against the top of the inserted optical component.

19. The bottom of each clip is A protrusion extending from the outer side of the bottom and soldered to the EO PCB, A pair of arms located on the side of the protrusion and soldered to the EO PCB, wherein the protrusion and the arms are soldered together such that the clip yaws and tilts, The laser head according to claim 17, comprising the following:

20. The laser head according to claim 1, further comprising: a plurality of output collimator assemblies that guide the light at a higher frequency outside the housing; and a damp assembly that guides unconverted pump light outside the housing.

Images