An acousto-optic Q-switch with a high damage threshold

Abstract

The present invention relates to the field of optoelectronics technology and relates to an acousto-optic Q-switch with a high damage threshold. The acousto-optic Q-switch comprises a base, a water-cooling block disposed within the base, a water nozzle connected to the water-cooling block mounted at the bottom of the base, an acousto-optic medium mounted on the side wall of the water-cooling block, a welding layer disposed on the upper surface of the acousto-optic medium, a transducer mounted on the welding layer, and a surface electrode disposed on the upper surface of the transducer; the surface electrode is connected to a radio frequency socket via a matching network and a temperature relay; the acousto-optic medium is high-purity fused quartz or quartz crystal, and an anti-reflection coating for a short-wavelength spectrum is plated on the light-transmitting surface of the acousto-optic medium; the present invention uses high-purity fused quartz or quartz crystal instead of tellurium oxide crystal, thereby significantly improving the damage threshold of the short-wavelength acousto-optic Q-switch; and the use of high-purity gold or high-purity silver as the bonding layer material can improve the acousto-optic Q-switch's ability to withstand driving electric power and improve the diffraction efficiency of the acousto-optic Q-switch.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to an acousto-optic Q switch with a high laser damage resistance threshold. Background Art

[0002] The acousto-optic Q-switch is a key component that performs Q-switching within the laser cavity. It has been widely used in laser marking machines, laser cutting machines and other fields. It can quickly Q-switch continuous lasers into high-power pulsed lasers of the required frequency. It has the characteristics of high diffraction efficiency, strong shutdown capability, low insertion loss, high repetition frequency, easy control, and stable and reliable performance.

[0003] With the development of optoelectronics technology, short-wavelength lasers have developed rapidly in recent years. To meet the Q-switching requirements of short-wavelength lasers, acousto-optic Q-switches using tellurium oxide as the acousto-optic medium have been developed. However, such acousto-optic Q-switches are prone to laser damage during use.

[0004] The main reason for laser damage to the light-transmitting surface is that the damage threshold of tellurium oxide crystal is low and cannot withstand high laser power. Summary of the Invention

[0005] In response to the above technical problems, the applicant discovered that tellurium oxide crystals can be used to make short-wavelength acousto-optic Q switches because they have low light absorption and can meet the high transmittance requirements of acousto-optic Q switches. In addition, fused quartz and quartz crystals have high damage thresholds, but low optical transmittance at short wavelengths, which cannot meet the high transmittance requirements of acousto-optic Q switches. The reason for the low optical transmittance of fused quartz and quartz crystals is that the materials contain high levels of metal impurities such as aluminum, calcium, iron, and sodium, as well as hydroxyl (-OH) groups. By using a purification process to produce high-purity materials and reducing the metal impurities and hydroxyl (-OH) content in the materials, the optical transmittance of fused quartz and quartz crystals can be significantly improved, meeting the high transmittance requirements of acousto-optic Q switches. Therefore, the present invention provides an acousto-optic Q switch with a high damage threshold.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An acousto-optic Q-switch with a high damage threshold comprises a base, a water-cooling block disposed within the base, a water nozzle connected to the water-cooling block mounted at the bottom of the base, an acousto-optic medium mounted on the sidewall of the water-cooling block, a welding layer disposed on the upper surface of the acousto-optic medium, a transducer mounted on the welding layer, and a surface electrode disposed on the upper surface of the transducer; the surface electrode is connected to a radio frequency socket via a matching network and a temperature relay; the acousto-optic medium is high-purity fused quartz or quartz crystal, and an anti-reflection coating is plated on the light-transmitting surface of the acousto-optic medium.

[0008] Furthermore, the impurity content in the high-purity fused quartz or quartz crystal is less than 10 ppm, wherein the substance in the high-purity fused quartz or quartz crystal itself refers to silicon dioxide, and its impurities refer to elements other than silicon dioxide, mainly referring to impurities of metal elements such as aluminum, calcium, iron, and sodium.

[0009] Furthermore, the impurity content of metal elements such as aluminum, calcium, iron, and sodium in the high-purity fused quartz or quartz crystal is less than 10 ppm.

[0010] Preferably, the impurity content of metal elements such as aluminum, calcium, iron, and sodium in the high-purity fused quartz or quartz crystal is less than 2 ppm.

[0011] More preferably, the impurity content of metal elements such as aluminum, calcium, iron, and sodium in the high-purity fused quartz or quartz crystal is less than 1 ppm.

[0012] Furthermore, the high-purity fused quartz and quartz crystals contain a hydroxyl (-OH) content of less than 5 ppm.

[0013] Preferably, the high-purity fused quartz and quartz crystal contain a hydroxyl (-OH) content of less than 1 ppm.

[0014] Furthermore, the anti-reflection film is made of hafnium oxide and yttrium fluoride.

[0015] Furthermore, the thickness of the hafnium oxide is 80 nm to 120 nm, and the thickness of the yttrium fluoride is 300 nm to 500 nm.

[0016] Preferably, the thickness of the hafnium oxide is 100 nm, and the thickness of the yttrium fluoride is 400 nm.

[0017] Furthermore, a first conductive silver paste, an indium foil and a second conductive silver paste are sequentially installed between the acousto-optic medium and the base.

[0018] Preferably, a first conductive silver paste, an indium foil and a second conductive silver paste are sequentially installed between the side wall of the acousto-optic medium and the base wall. The base is electrically connected to the welding layer through the two layers of conductive silver paste, which can avoid welding a ground wire on the acousto-optic medium.

[0019] Furthermore, the welding layer includes a first electrode layer, a bonding layer and a second electrode layer; the bonding layer is located between the two electrode layers.

[0020] Preferably, the first electrode layer and the second electrode layer are both made of high-purity chromium, and the thickness thereof are both 45 nm to 55 nm.

[0021] Preferably, the bonding layer is a thin film made of high-purity gold or high-purity silver material with a purity greater than 99.9%, and its thickness is 1 μm to 3 μm.

[0022] Furthermore, a sound absorbing block for absorbing ultrasonic waves is installed on one end face of the acousto-optic medium.

[0023] Preferably, the sound absorbing block is made of ceramic or metal material.

[0024] Optionally, the transducer uses lithium niobate material that excites longitudinal waves.

[0025] Beneficial effects of the present invention:

[0026] The present invention uses high-purity fused quartz or quartz crystal instead of tellurium oxide crystal, which improves the transmittance of the material. Since the laser damage threshold of high-purity fused quartz or quartz crystal is one order of magnitude higher than that of tellurium oxide crystal, the damage threshold of the short-wave acousto-optic Q switch can be greatly improved.

[0027] Because gold and silver have high melting points, the present invention uses high-purity gold or silver as the bonding layer material. This improves the acousto-optic Q-switch's ability to withstand driving power. Increasing the driving power, in turn, improves the acousto-optic Q-switch's diffraction efficiency, thus overcoming the disadvantage that the acousto-optic figure of merit of using high-purity fused quartz or quartz crystal as the acousto-optic medium is lower than that of conventional technologies using tellurium oxide as the acousto-optic medium.

[0028] The base in the present invention is electrically connected to the welding layer through the conductive silver paste, which can avoid welding a ground wire on the acousto-optic medium, reduce the thickness of the acousto-optic medium, increase the speed of heat transfer from the transducer to the housing, and prevent the transducer or the welding layer from being burned due to excessive temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the acousto-optic Q-switch structure of the present invention;

[0030] Figure 2 A partial enlarged view of the acousto-optic Q switch of the present invention;

[0031] In the figure, 1. base, 2. acousto-optic medium, 3. matching network, 4. temperature relay, 5. RF socket, 6. first conductive silver paste, 7. indium foil, 8. second conductive silver paste, 9. surface electrode, 10. transducer, 11. second electrode layer, 12. bonding layer, 13. first electrode layer, 14. water cooling block, 15. sound absorbing block, 16. water nozzle. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] like Figure 1As shown, a structural diagram of an acousto-optic Q-switch facing a light-transmitting surface is provided; specifically, an acousto-optic Q-switch with a high damage threshold comprises a base 1, a water-cooling block 14 is provided in the base 1, a water nozzle 16 connected to the water-cooling block 14 is installed at the lower portion of the base 1, an acousto-optic medium 2 is installed between the base 1 and the water-cooling block 14; the acousto-optic medium 2 is connected to the acousto-optic medium 2 via a matching network 3, and the acousto-optic medium 2 is made of high-purity fused quartz or quartz crystal; a temperature relay 4 is provided between the matching network 3 and the high-frequency socket 5, and the temperature relay 4 is fixedly connected to the base 1.

[0034] In one embodiment, the acousto-optic medium 2 has a plurality of end surfaces, and a sound absorbing block 15 for absorbing ultrasonic waves is mounted on one of the end surfaces of the acousto-optic medium 2 .

[0035] In a preferred embodiment, the sound absorbing block 15 is made of ceramic or metal material.

[0036] In one possible implementation, the acousto-optic medium 2 may further have two sound-transmitting surfaces, the two sound-transmitting surfaces being perpendicular to each other, a heat dissipation surface being provided between the two sound-transmitting surfaces, the heat dissipation surface being in contact with the inner surface of the base 1; the heat dissipation surface may be at a certain angle to the two sound-transmitting surfaces respectively. Of course, the shape of the acousto-optic medium 2 is not the focus of the present invention and is not limited thereto.

[0037] In a preferred embodiment, the temperature relay 4 is of a normally closed type. Generally speaking, it can be fixed to the base by bonding, that is, it can be glued to the base 1. In addition, other fixing methods can be used, such as welding to fix it to the base. Of course, a corresponding groove can also be provided on the outer shell of the base 1 for embedding the temperature relay 4.

[0038] Since a temperature relay 4 is provided between the matching network 3 and the high-frequency socket 5, and the temperature relay 4 is of a normally closed type, the radio frequency signal must pass through the temperature relay 4 before it can be transmitted to the surface electrodes of the transducer. When there is no cooling water, the temperature of the base 1 rises, the temperature relay 4 is disconnected, and the radio frequency signal cannot be transmitted to the transducer 10, which can effectively prevent the transducer 10 from burning out.

[0039] When water cooling is used in this embodiment, the cooling water enters the water channel of the base 1 through the water nozzle 16 and enters the cooling block 14 to cool the cooling block 14. In this way, the heat on the sound-absorbing surface 15 can be transferred out in time, thereby preventing the transducer 10 from being burned due to the excessive temperature of the acousto-optic medium 2.

[0040] In one embodiment, Figure 2 As shown, Figure 2This is a partial enlarged view of the welding layer and conductive part of the acousto-optic Q-switch; the upper surface of the acousto-optic medium 2 is provided with a welding layer, and the transducer 10 is mounted on the welding layer. The upper surface of the transducer 10 is provided with a surface electrode 9; the surface electrode 9 is connected to the RF socket 5 through the matching network 3 and the temperature relay 4.

[0041] In one embodiment, the welding layer is composed of two electrode layers and a bonding layer 12 ; the welding layer includes a first electrode layer 13 , a bonding layer 12 and a second electrode layer 11 ; the bonding layer is located between the two electrode layers.

[0042] In a preferred embodiment, the upper surface of the acousto-optic medium 2 is sequentially provided with a first electrode layer 13, a bonding layer 12, a second electrode layer 11, a transducer 10 and a surface electrode 9. The surface electrode 9 is connected to the RF socket 5 through a matching network 3 and a temperature relay 4. The acousto-optic medium 2 is high-purity fused quartz or quartz crystal.

[0043] In a preferred embodiment, high purity fused quartz and quartz crystal materials are produced through a purification process, wherein S i The O2 content is greater than 99.9999%, the hydroxyl-OH content is less than 1ppm, and the impurity content of metal elements such as aluminum, calcium, iron, and sodium is less than 2ppm. The light absorption of these two materials at 2.7 microns is reduced from 5% before purification to 1%, which significantly improves the optical transmittance of fused quartz and quartz crystal, meeting the high transmittance requirements of acousto-optic Q switches.

[0044] S i High-purity fused quartz or quartz crystal with an O2 content greater than 99.9999% is the best solution of the present invention. Of course, in actual situations, due to the limitations of purification technology, the S content of high-purity fused quartz is i The O2 content may not be greater than 99.9999%; however, a slight deviation can also solve the technical problem of the present invention, so the present invention is not limited to strictly S i High purity fused quartz or quartz crystal with an O2 content greater than 99.9999%.

[0045] In a preferred embodiment, the thickness L of the acousto-optic medium 2 is 3-5 mm, preferably 3 mm or 3.5 mm.

[0046] In one embodiment, a first conductive silver paste 6, an indium foil 7, and a second conductive silver paste 8 are sequentially installed between the side of the acousto-optic medium and the base wall; the base 1 is electrically connected to the indium foil 7 and the welding layer through the two layers of conductive silver paste, which can avoid welding a ground wire on the acousto-optic medium 2.

[0047] In another embodiment, a first conductive silver paste 6, an indium foil 7, and a second conductive silver paste 8 are installed between the bottom surface of the acousto-optic medium and the upper surface of the base; the base is electrically connected to the indium foil and the welding layer through the two layers of conductive silver paste, which can avoid welding a ground wire on the acousto-optic medium and reduce the thickness of the acousto-optic medium 2.

[0048] To demonstrate that the present invention can reduce the thickness of the acousto-optic medium 2, a comparison was made with patent CN203299481U, "A High-Reliability Acousto-Optic Q-Switch," filed by our unit in 2013. The results show that the thickness of the acousto-optic medium 2 in that patent is 4 to 6 nm, while the thickness of the acousto-optic medium in the present invention can reach 3 to 5 nm. The present invention significantly reduces the thickness of the acousto-optic medium 2, thereby increasing the speed at which heat from the transducer 10 is transferred to the base 1 and the water-cooling block 14, thereby preventing the transducer 10 from overheating and burning the transducer 10 or the welding layer.

[0049] Because the present invention does not solder a ground wire to the acousto-optic medium 2, the thickness of the acousto-optic medium 2 can be reduced by approximately 1 to 2 mm. At a driver power of 100 W, the temperature of the transducer 10 is reduced by 5°C, increasing the reliability of the transducer 10 by 50%. This significantly reduces the chance of transducer 10 burning out and improves product reliability.

[0050] It is understandable that, since the shapes of the base 1 and the acousto-optic medium 2 are slightly different during the actual design process, no matter where the conductive silver paste and the indium foil 7 are specifically coated, as long as electrical conduction between the base 1 and the welding layer can be achieved, it should be within the scope of protection of the present invention.

[0051] In one embodiment, an anti-reflection film for the short-wavelength spectrum is plated on the light-transmitting surface of the acousto-optic medium 2. The film material is hafnium oxide and yttrium fluoride. The thickness of hafnium oxide is 100nm±20nm, and the thickness of yttrium fluoride is 400nm±100nm.

[0052] Preferred thicknesses of the hafnium oxide are 80 nm, 100 nm, and 120 nm.

[0053] The preferred thickness of the yttrium fluoride is 300 nm, 400 nm and 500 nm.

[0054] In a preferred embodiment, the order of coating the anti-reflection film is to first coat yttrium fluoride with a thickness of 100nm±20nm, and then coat hafnium oxide with a thickness of 400nm±20nm. In this way, the reflectivity at a wavelength of 2.7 microns is less than 0.3%, which effectively reduces the reflected light on the light-transmitting surface, thereby increasing the light transmittance of the acousto-optic medium 2 and achieving better resistance to laser damage.

[0055] In a preferred embodiment, the transducer 10 is a lithium niobate material that excites longitudinal waves. Lithium niobate (LiNbO3, abbreviated as LN) crystal is an important artificially synthesized multifunctional piezoelectric, ferroelectric and electro-optical crystal; it can cooperate with the device of the acousto-optic Q switch to realize the function.

[0056] The bonding layer 12 is a thin film made of high-purity gold or high-purity silver with a purity greater than 99.9%, with a thickness of about 2 microns, which can effectively improve the bonding layer's ability to withstand electrical power.

[0057] In a specific embodiment, since the acousto-optic figure of merit of fused silica is 1.51×10 -15 S 3 / kg, while the acousto-optic figure of merit of tellurium oxide is 34.5×10 -15 S 3 / kg, so the acousto-optic figure of merit of tellurium oxide is 22.8 times that of fused quartz. To achieve the same diffraction efficiency, the acousto-optic Q-switch made of fused quartz requires 22.8 times the driving power of tellurium oxide. To improve the ability of the fused quartz acousto-optic Q-switch to withstand higher driving power, the present invention adopts two measures:

[0058] (1) Using high melting point gold (melting point 1064℃) or silver (melting point 960℃) instead of tin (melting point 235℃) as the bonding layer material to improve the bonding layer's ability to withstand electrical power;

[0059] (2) Reducing the thickness of the acousto-optic medium 2 increases the speed of heat transfer from the transducer 10 to the housing, lowering the temperature of the transducer 10 and preventing the transducer 10 or the bonding layer 12 from being burned due to excessive temperature.

[0060] This embodiment uses fused quartz as the acousto-optic medium of the acousto-optic Q switch. The thickness L of the fused quartz is selected to be 3 mm, the surface electrode width is 2 mm, and the acousto-optic interaction length is 40 mm. When the driving power is 100 W, the diffraction efficiency of the light with a wavelength of 2.7 microns reaches 50%, which can meet the short-wave Q-switching requirements.

[0061] In a preferred embodiment, the present invention deposits a 2.7 micron anti-reflection film on the light-transmitting surface of the fused silica acousto-optic medium. The film materials are hafnium oxide and yttrium fluoride. The thickness of hafnium oxide is 100nm±20nm, and the thickness of yttrium fluoride is 400nm±20nm. The damage threshold reaches 500MW / cm 2 , which is more than 10 times the damage threshold of tellurium oxide acousto-optic Q switch.

[0062] During the implementation process, the radio frequency electrical signal is loaded between the surface electrode 9 and the base 1 (the surface electrode 9 is the positive electrode of the electrical signal, and the base 1 is the ground electrode of the electrical signal). The transducer 10 absorbs the radio frequency electrical signal and converts the radio frequency electrical signal into ultrasonic waves. The ultrasonic waves are transmitted to the acousto-optic medium 2 through the welding layer, and the laser interacts with the acousto-optic medium 2 to generate diffracted light.

[0063] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium, which may include: ROM, RAM, disk or CD, etc.

[0064] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation plans of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An acousto-optic Q-switch with a high damage threshold, comprising a base, a water-cooling block disposed within the base, a water nozzle connected to the water-cooling block mounted at the bottom of the base, an acousto-optic medium mounted on the sidewall of the water-cooling block, a solder layer disposed on the upper surface of the acousto-optic medium, a transducer mounted on the solder layer, and a surface electrode disposed on the upper surface of the transducer; the surface electrode being connected to a radio frequency socket via a matching network and a temperature relay; characterized in that: The acousto-optic medium is high-purity fused quartz or quartz crystal, and an anti-reflection film is plated on the light-transmitting surface of the acousto-optic medium; a first conductive silver paste, an indium foil, and a second conductive silver paste are sequentially installed between the acousto-optic medium and the base, and the base is electrically connected to the welding layer through the first conductive silver paste, the indium foil, and the second conductive silver paste.

2. The acousto-optic Q-switch with a high damage threshold according to claim 1, characterized in that: The content of metallic element impurities in the high-purity fused quartz or quartz crystal is less than 10 ppm.

3. The acousto-optic Q-switch with a high damage threshold according to claim 2, characterized in that: The content of metallic element impurities in the high-purity fused quartz or quartz crystal is less than 1 ppm.

4. The acousto-optic Q-switch with a high damage threshold according to claim 1, wherein: The high-purity fused quartz or quartz crystal contains a hydroxyl group -OH content of less than 5 ppm.

5. The acousto-optic Q-switch with a high damage threshold according to claim 4, characterized in that: The high-purity fused quartz or quartz crystal contains a hydroxyl group -OH content of less than 1 ppm.

6. The acousto-optic Q-switch with a high damage threshold according to claim 1, characterized in that: The anti-reflection film is made of hafnium oxide and yttrium fluoride.

7. The acousto-optic Q-switch with a high damage threshold according to claim 1, wherein: A sound absorbing block for absorbing ultrasonic waves is installed on one end surface of the acousto-optic medium.

8. The acousto-optic Q-switch with a high damage threshold according to claim 1, characterized in that: The welding layer includes a first electrode layer, a bonding layer and a second electrode layer; the bonding layer is located between the two electrode layers, and the bonding layer is a thin film made of high-purity gold or high-purity silver material with a purity greater than 99.9%, and its thickness is 1μm~3μm.

9. The acousto-optic Q-switch with a high damage threshold according to claim 1, wherein: The thickness of the acousto-optic medium is 3-5 mm.

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