Diamond NV color center laser and preparation method thereof

Abstract

The invention discloses a diamond NV color center laser and a preparation method thereof, and the preparation method comprises the following steps: preparing a diamond color center sample through a high-pressure and high-temperature method, carrying out the ultrasonic cleaning of the diamond color center sample, carrying out the spin coating of photoresist, carrying out the exposure of the photoresist through a double-beam interference exposure system, and carrying out the development of the sample. A patterned photoresist is obtained; plating a metal nickel mask layer on the surface of the patterned photoresist; stripping the photoresist and the nickel layer on the photoresist to form an arrayed metal nickel layer; performing thermal chemical etching to obtain a micron column; removing a nickel layer to obtain a color center diamond micron column resonant cavity array; and finally, laser emission of the NV color center is realized by utilizing a laser pumping single micron wire. Compared with the traditional electron beam exposure and dry etching combined process, the method has the advantages of large-area preparation, deep etching, low preparation cost and the like, and meanwhile, the device has the advantages of compact structure, small size, small optical loss and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of diamond NV - center lasers, and particularly relates to a diamond NV - center laser and a preparation method thereof. Background Art

[0002] Diamond NV - centers have excellent optical properties, including a wide emission spectrum, low absorption loss, large absorption and emission cross - sections, high quantum efficiency, etc., and have important application prospects in quantum information processing, quantum sensing, etc. Developing laser devices based on diamond NV - centers will further promote the realization of the above - mentioned applications. The reported diamond NV - center laser devices mostly use Fabry - Perot (F - P) resonators. This type of resonator has problems such as large volume and large optical loss on the cavity surface, which is not conducive to realizing high - performance NV - center laser devices. With the rapid development of micro - nano processing technology, micro - nano structures have been widely used in the laser field. Compared with traditional F - P resonators, micro - nano resonators can achieve extremely high quality factors (Q - values), enhance the interaction between light and matter, thus significantly reducing the threshold of laser emission, and their small size also helps to achieve high - degree integration of optical systems. Moreover, by adjusting parameters such as the size, shape, and material of the micro - nano resonator, its optical resonance mode and spectral characteristics can be flexibly regulated to meet the requirements of specific wavelengths and modes in different application scenarios.

[0003] Although various resonator structures such as micro - and nano - wires, rods, disks, and rings have been reported, due to the extremely high hardness and extremely stable chemical properties of diamond, precision processing faces greater challenges, resulting in no good solutions for large - area and low - cost preparation of diamond NV - center micro - nano wires and laser devices.

[0004] Diamond has extremely high hardness and extremely stable chemical properties. It is difficult to directly fabricate a high - quality resonator on the diamond surface. Therefore, people usually use external mirrors to form a resonator (such as the F - P resonator composed of plane - plane mirrors mentioned above) to achieve laser output.

[0005] Structurally: The reported diamond NV - center laser resonators include those based on plane - plane or plane - concave mirrors, as well as fiber F - P resonators that use the fiber end face as one of the cavity mirrors. Since large - size mirrors are used in all of them, the overall volume of the resonator is large.

[0006] Technologically: The F - P resonator usually requires the diamond - color - center sample to be placed at a specific position between two mirrors at the Brewster angle, with high requirements for fine operation. And high - reflection coatings need to be deposited on both the fiber end face and the external mirror of the fiber F - P resonator, resulting in a high manufacturing cost.

[0007] That is to say, the cavities of existing diamond NV - center lasers generally have problems such as large volume, high optical loss, difficult adjustment, and high preparation cost. Summary of the Invention

[0008] In view of the above - mentioned problems existing in the prior art, the present invention provides a preparation method for a diamond NV - center micro - pillar resonant cavity array.

[0009] The object of the present invention is achieved in the following manner: A preparation method for a diamond NV - center laser, comprising the following steps: Step 1, preparing a diamond color - center sample by the high - pressure and high - temperature method Mix high - purity graphite powder (99.99 wt.%) and high - purity nitride sodium azide (NaN3: 0.01 - 0.5 wt.%) evenly and press them into a column as the carbon source for diamond growth. Use FeNi as the alloy catalyst, and then place it in a high - pressure and high - temperature six - face anvil device. Synthesize for 12 - 72 h at a pressure of 5.0 - 6.0 GPa and a temperature of 1500 - 1850 K to obtain Ib - type diamonds with different nitrogen contents. The maximum area of the diamond is 10 mm×10 mm, and the thickness is between 0.1 - 0.5 mm. Subsequently, irradiate the sample with a 10 MeV electron beam for 10 - 30 h, and the total irradiation dose is 100 - 300 MGy; after irradiation, anneal the sample in vacuum at 800 - 900 °C for 2 - 4 h to obtain a diamond color - center sample with a color - center concentration of 1 - 10 ppm; Step 2, polishing the diamond color - center sample and preparing a micro - pillar resonant cavity on it. The specific steps are as follows: (1) Ultrasonically clean the diamond color - center sample; (2) Spin - coat a photoresist on the diamond color - center sample; (3) Use a two - beam interference exposure system to perform a first exposure on the photoresist for 1 s. After rotating the sample by 90°, perform another exposure for 1 s. Subsequently, develop the sample for 20 s to obtain a patterned photoresist. The diameter range of a single cylinder in the pattern is 500 nm - 1.5 μm; (4) Use a magnetron sputtering coater to deposit a metal nickel mask layer with a thickness of 300 - 500 nm on the surface of the patterned photoresist; (5) Put the sample coated with the metal nickel mask layer into acetone and ultrasonically clean it until the photoresist is completely peeled off, and the nickel layer on the photoresist is also removed, forming an arrayed metal nickel layer on the diamond; (6) Thermochemically etch the above sample using microwave plasma, where the H2 flow rate is 200 - 500 sccm, the temperature of the vacuum chamber is 850 - 1000 °C, the air pressure is 3.0 - 13 kPa, the plasma power is 1.5 - 11 kW, and the etching time is 2 - 10 h to obtain micron columns with a depth of 1 - 5 μm; (7) Immerse the sample obtained by thermochemical etching in aqua regia until the nickel layer on the surface is completely removed, and repeatedly rinse with deionized water to obtain a color center diamond micron column resonator array; (8) Pump a single micron wire using a 532 nm laser, and when the energy reaches more than 500 mJ∙cm-2, laser emission of the NV color center can be achieved.

[0010] In step two (2), when spin-coating the photoresist, the rotation speed of the spin coater is 4000 rpm, the coating time is 60 s, and annealing is performed at 115 °C for 60 s.

[0011] In step two (3), the power density of the interference spot of the double-beam interference exposure system is 0.6 mW∙mm-2.

[0012] In step two (3), the pattern is an array with a diameter of 1 μm and a spacing of 1 μm.

[0013] In step two (6), the H2 flow rate is 300 sccm, the temperature of the vacuum chamber is 900 °C, the air pressure is 8 kPa, the plasma power is 5 kW, and the etching time is 5 h.

[0014] A diamond NV color center laser is prepared by the above method. Compared with the prior art, compared with the diamond NV color center laser device with an externally added cavity mirror forming a resonator in the prior art, we provide a more integrated micro-nano device structure and preparation method. This method uses double-beam exposure combined with thermochemical etching process, which has the advantages of large-area preparation, deep etching, and low preparation cost compared with the traditional electron beam exposure combined with dry etching process. At the same time, the device has the advantages of compact structure, small volume, and low optical loss. The diamond NV color center laser device based on this structure has the advantages of low threshold, high coherence, and high conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flowchart for the preparation of a diamond NV color center sample.

[0016] Figure 2 is the NV-color center concentration distribution of irradiated HPHT diamond.

[0017] Figure 3 is a comparison photo of a diamond NV color center sample before and after ultraviolet light excitation.

[0018] Figure 4 It is the emission spectrum of a diamond NV color center sample under 532 nm laser pumping.

[0019] Figure 5 It is the process flow chart of forming a micron column by thermochemical etching of a diamond NV color center sample.

[0020] Figure 6 It is a schematic diagram of thermochemical etching treatment.

[0021] Figure 7 It is the surface topography map of a diamond NV color center micron column array measured by a 3D profiler. Specific embodiments

[0022] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. After reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present invention.

[0023] A method for preparing a diamond NV color center laser, comprising the following steps: Step 1, preparing a diamond color center sample As Figure 1 shown, 99.99 wt.% high-purity graphite powder and 0.01 - 0.5 wt.% high-purity nitride sodium azide NaN3 are mixed evenly and pressed into a column as the carbon source for diamond growth. FeNi is used as an alloy catalyst, and then it is placed in a high-pressure and high-temperature six-sided top device. It is synthesized for 12 - 72 h at a pressure of 5.0 - 6.0 GPa and a temperature of 1500 - 1850 K to obtain Ib-type diamonds with different nitrogen contents, with a maximum area of 10 mm × 10 mm and a thickness between 0.1 - 0.5 mm. Subsequently, the sample is irradiated with a 10 MeV electron beam for 10 - 30 h, and the total irradiation dose is 100 - 300 MGy. The irradiated sample is vacuum annealed at 800 - 900 °C for 2 - 4 h to obtain a diamond color center sample with a color center concentration of 1 - 10 ppm.

[0024] Figure 2 To measure the NV-color center concentration distribution map of the diamond NV color center sample, it can be seen from the figure that the NV-color centers of this sample are uniformly distributed and maintain an NV-color center concentration of about 1.0 ppm. Figure 3 It is a comparison diagram of the diamond NV color center sample before and after ultraviolet light excitation. Figure 4 It is the spectrum of NV-color center diamond collected under 532 nm laser pumping. From Figure 3 and Figure 4It can be seen that the diamond NV color center samples prepared by the high-pressure and high-temperature method have a uniform color center distribution and exhibit typical NV color center luminescence.

[0025] Step 2: Polish the diamond color center sample and fabricate a microcylinder resonator on it, as Figure 5 shown. The specific steps are as follows: (1) Ultrasonically clean the diamond color center sample; (2) Spin-coat photoresist on the diamond color center sample. When spin-coating the photoresist, the rotation speed of the spin coater is 4000 rpm, the coating time is 60 s, and anneal at 115 °C for 60 s; (3) Use a two-beam interference exposure system (the power density of the interference spot is 0.6 mW∙mm -2 ) to perform a single exposure on the photoresist for 1 s. After rotating the sample by 90°, perform another exposure for 1 s. Subsequently, develop the sample for 20 s to obtain a patterned photoresist. The diameter range of a single cylinder in the pattern is 500 nm - 1.5 μm; the optimal pattern is an array with a diameter of 1 μm and a spacing of 1 μm; The diameter range of a single cylinder in the pattern is 500 nm - 1.5 μm. The minimum diameter is determined by the lithography system. The emission spectrum of the NV color center is mainly concentrated in the range of 600 - 850 nm (see Figure 4 ). To achieve whispering gallery mode (WGM) output in the microcylinder, it is necessary to ensure that the optical path difference in the cavity is an integer multiple of the optical wavelength, that is: mλ = 2πn eff R , where m is the mode number (a positive integer), λ is the resonance wavelength, n eff is the effective refractive index, R is the radius of the microcylinder cavity. The depth of the microcylinder cavity will affect the effective refractive index, mode quality factor, mode distribution, etc. to a certain extent; (4) Use a magnetron sputtering coater to deposit a metal nickel mask layer with a thickness of 300 - 500 nm on the surface of the patterned photoresist; (5) Immerse the sample coated with the metal nickel mask layer in acetone and ultrasonicate until the photoresist is completely peeled off, and the nickel layer on the photoresist is also removed, forming an arrayed metal nickel layer on the diamond; (6) Use microwave plasma to perform thermochemical etching on the above sample (see Figure 6), where the H2 flow rate is 200 - 500 sccm, the temperature of the vacuum chamber is 850 - 1000 °C, the air pressure is 3.0 - 13 kPa, the plasma power is 1.5 - 11 kW, and the etching time is 2 - 10 h, to obtain micro-columns with a depth of 1 - 5 μm; preferably, the H2 flow rate is 300 sccm, the temperature of the vacuum chamber is 900 °C, the air pressure is 8 kPa, the plasma power is 5 kW, and the etching time is 5 h; under the above conditions and the catalytic action of nickel, the carbon element in diamond will combine with hydrogen element to form methane, which is then etched. By controlling appropriate conditions, an etching effect with a high aspect ratio and a smooth surface can be obtained; (7)Immerse the sample obtained by thermochemical etching in aqua regia until the nickel layer on the surface is completely removed, and rinse it repeatedly with deionized water to obtain a color center diamond micro-column resonator array. The results can be seen Figure 7 ; (8)Pump a single micro-wire with a 532 nm laser, and when the energy reaches 500 mJ∙cm -2 or more, the laser emission of the NV color center can be realized.

[0026] Example 1 A method for preparing a diamond NV color center laser, comprising the following steps: Step 1, prepare a diamond NV color center sample As Figure 1 shown, mix 99.99 wt.% high-purity graphite powder and 0.01 wt.% high-purity nitride sodium azide NaN3 evenly and press them into a column as the carbon source for diamond growth. Use FeNi as the alloy catalyst, and then place it in a high-pressure and high-temperature six-sided top device. Synthesize for 12 h at a pressure of 5.0 GPa and a temperature of 1500 K to obtain Ib-type diamond with a size of 10 mm × 10 mm × 0.1 mm. Subsequently, irradiate the sample with a 10 MeV electron beam for 10 h, and the total irradiation dose is 100 MGy; the irradiated sample is annealed in vacuum at 800 °C for 3 h to obtain a diamond NV color center sample with a color center concentration of ~1 ppm. The color center concentration distribution of this sample can be seen Figure 2 ; Step 2, polish the diamond NV color center sample and prepare a micro-column resonator on it. As Figure 5 shown, the specific steps are as follows: (1)Ultrasonically clean the diamond-color center sample; (2)Spin-coat a photoresist (model S1813) on the diamond-color center sample, with the spin coater rotating at 4000 rpm for 60 s and annealing at 115 °C for 60 s; (3)Use a double-beam interference exposure system, and the power density of the interference light spot is 0.6 mW∙mm-2 Perform one exposure on the photoresist with an exposure time of 1 s. After rotating the sample by 90°, perform another exposure with an exposure time of 1 s. Subsequently, develop the sample for 20 s to obtain a patterned photoresist. The pattern is an array with a diameter of 1 μm and a spacing of 1 μm. (4)Deposit a 300-nm-thick metal nickel mask layer on the surface of the patterned photoresist using a magnetron sputtering coater. (5)Place the sample with the deposited metal nickel mask layer in acetone and ultrasonically clean it until the photoresist is completely stripped, and the nickel layer on the photoresist is also removed, forming an arrayed metal nickel layer on the diamond. (6)Perform thermochemical etching on the above sample using microwave plasma (see Figure 6 ). Among them, the H2 flow rate is 300 sccm, the temperature of the vacuum chamber is 900 °C, the air pressure is 8 kPa, the plasma power is 5 kW, and the etching time is 2 h to obtain micron pillars with a depth of 1 μm. (7)Immerse the sample obtained by thermochemical etching in aqua regia until the nickel layer on the surface is completely removed, and rinse it repeatedly with deionized water to obtain an array of diamond micron pillar resonators with color centers (see Figure 7 ); the diameter (and depth) of the resonator has been designed according to the emission wavelength of the NV color center. Pump a single micron wire with a 532-nm laser with an energy of 1500 mJ∙cm -2 to achieve laser emission of the NV color center.

[0027] Example 2 A method for preparing a diamond NV color center laser, comprising the following steps: Step 1, prepare a diamond NV color center sample As Figure 1 shown, mix 99.99 wt.% high-purity graphite powder and 0.3 wt.% high-purity nitride sodium azide NaN3 evenly and press them into a column as the carbon source for diamond growth. Use FeNi as the alloy catalyst, and then place it in a high-pressure and high-temperature six-sided top device. Synthesize for 24 h at a pressure of 5.5 GPa and a temperature of 1750 K to obtain type Ib diamond with a size of 10 mm×10 mm×0.4 mm. Subsequently, irradiate the sample with a 10-MeV electron beam for 20 h, and the total irradiation dose is 200 MGy; the irradiated sample is vacuum annealed at 900 °C for 2 h to obtain a diamond NV color center sample with a color center concentration of ~5 ppm. Step 2, polish the diamond NV color center sample and prepare a micron pillar resonator on it. The specific steps are as follows: (1)Ultrasonically clean the diamond-color center sample. (2) Spin coat a photoresist (model S1813) on the diamond-color center sample, with the spinner speed at 4000 rpm for 60 s, and anneal at 115 °C for 60 s; (3) Use a dual-beam interference exposure system with the power density of the interference spot being 0.6 mW∙mm -2 , perform one exposure on the photoresist for 1 s. After rotating the sample by 90°, perform another exposure for 1 s. Subsequently, develop the sample for 20 s to obtain a patterned photoresist. The pattern is an array with a diameter of 900 nm and a spacing of 900 nm; (4) Use a magnetron sputtering coater to deposit a metal nickel mask layer with a thickness of 400 nm on the surface of the patterned photoresist; (5) Immerse the sample coated with the metal nickel mask layer in acetone and sonicate until the photoresist is completely stripped, and the nickel layer on the photoresist is also removed, forming an arrayed metal nickel layer on the diamond; (6) Use microwave plasma to perform thermochemical etching on the above sample (see Figure 6 ), where the H2 flow rate is 200 sccm, the temperature of the vacuum chamber is 1000 °C, the pressure is 13 kPa, the plasma power is 11 kW, and the etching time is 5 h to obtain micron columns with a depth of 3 μm; (7) Immerse the sample obtained by thermochemical etching in aqua regia until the nickel layer on the surface is completely removed, and rinse repeatedly with deionized water to obtain an array of color center diamond micron column resonators; the diameter (and depth) of the resonator has been designed according to the emission wavelength of the NV color center. A 532 nm laser with an energy of 1000 mJ∙cm -2 is used to pump a single micron wire, and the laser emission of the NV color center can be achieved.

[0028] Example 3 The difference between this example and Example 1 is as follows: In step one, the material dosage: 99.99 wt.% high-purity graphite powder and 0.5 wt.% high-purity nitride sodium azide NaN3; pressure: 6.0 GPa, temperature: 1850 K, synthesis time: 72 h, size: 10 mm×10 mm×0.5 mm, electron beam irradiation time: 30 h, total irradiation dose: 300 MGy; the irradiated sample is vacuum annealed at 900 °C for 2 h to obtain a diamond NV color center sample with a color center concentration of ~8 ppm.

[0029] In step two (2), the spinner speed for spin coating the photoresist is 4000 rpm for 60 s, and anneal at 115 °C for 60 s; (3) The power density of the interference spot is 0.6 mW∙mm -2, the pattern is an array with a diameter of 800 nm and a spacing of 800 nm; (4) The thickness of the nickel metal mask layer is 500 nm; (6) The flow rate of H2 in the thermochemical etching is 500 sccm, the temperature of the vacuum chamber is 850 °C, the air pressure is 3.0 kPa, the plasma power is 1.5 kW, and the etching time is 10 h, resulting in micro-columns with a depth of 5 μm; (7) Using a 532 nm laser with an energy of 500 mJ∙cm -2 to pump a single micro-wire, the laser emission of the NV color center can be achieved.

[0030] Compared with the existing diamond NV color center laser device with an externally added cavity mirror to form a resonant cavity, we provide a more integrated micro-nano device structure and preparation method. This method uses a double-beam exposure combined with a thermochemical etching process, which has the advantages of large-area preparation, deep etching, and low preparation cost compared with the traditional electron beam exposure combined with dry etching process. At the same time, the device has the advantages of a compact structure, small volume, and low optical loss. The diamond NV color center laser device based on this structure has the advantages of low threshold, high coherence, and high conversion efficiency.

[0031] The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the overall concept of the present invention, several changes and improvements can still be made, and these should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a diamond NV color center laser, characterized in that: The following steps are included: Step 1: Prepare diamond color center samples using high pressure and high temperature method 99.99 wt.% high-purity graphite powder and 0.01-0.5 wt.% high-purity nitride sodium azide NaN3 are mixed evenly and pressed into a column as a carbon source for diamond growth. FeNi is used as an alloy catalyst, and then placed in a high-pressure and high-temperature hexagonal top device, synthesized at a pressure of 5.0-6.0 GPa and a temperature of 1500-1850 K for 12-72 h to generate Ib-type diamonds with different nitrogen contents. The diamond area is up to 10 mm×10 mm and the thickness is between 0.1-0.5 mm. Subsequently, the sample is irradiated with a 10 MeV electron beam for 10-30 h, with a total irradiation dose of 100-300 MGy. The irradiated sample is vacuum annealed at 800-900 °C for 2-4 h to obtain a diamond color center sample with a color center concentration of 1-10 ppm. Step 2: polish the diamond color center sample and prepare a micron column resonant cavity thereon. The specific steps are: (1) Ultrasonic cleaning of diamond color center samples; (2) Spin coating photoresist on the diamond color center sample; (3) The photoresist was exposed once using a dual-beam interference exposure system for 1 s. The sample was rotated 90° and then exposed again for 1 s. The sample was then developed for 20 s. After development, a patterned photoresist was obtained. The diameter of a single cylinder in the pattern ranged from 500 nm to 1.5 μm. (4) using a magnetron sputtering coating machine to coat a metal nickel mask layer with a thickness of 300-500 nm on the patterned photoresist surface; (5) placing the sample coated with the metal nickel mask layer in acetone and ultrasonicating it until the photoresist is completely stripped off, and the nickel layer on the photoresist is also removed, forming an arrayed metal nickel layer on the diamond; (6) using microwave plasma to perform thermochemical etching on the above sample, wherein the H2 flow rate is 200-500 sccm, the vacuum chamber temperature is 850-1000 °C, the gas pressure is 3.0-13 kPa, the plasma power is 1.5-11 kW, and the etching time is 2-10 h, to obtain micron columns with a depth of 1-5 μm; (7) The sample obtained by thermochemical etching is immersed in aqua regia until the nickel layer on the surface is completely removed, and then repeatedly rinsed with deionized water to obtain a color center diamond micro-column resonant cavity array; (8) Using 532 nm laser to pump a single micrometer wire, the energy reaches 500 mJ∙cm -2 The above can realize the laser emission of NV color center.

2. The method for preparing a diamond NV color center laser according to claim 1, characterized in that: Step 2 (2) Spin-coat the photoresist at a speed of 4000 rpm, coating time of 60 s, and annealing at 115°C for 60 s.

3. The method for preparing a diamond NV color center laser according to claim 1, characterized in that: Step 2 (3) The power density of the interference spot of the dual-beam interference exposure system is 0.6 mW∙mm -2 .

4. The method for preparing a diamond NV color center laser according to claim 1, characterized in that: Step 2 (3) The pattern is an array with a diameter of 1 μm and a spacing of 1 μm.

5. The method for preparing a diamond NV color center laser according to claim 1, characterized in that: Step 2 (6) The H2 flow rate is 300 sccm, the vacuum chamber temperature is 900 °C, the gas pressure is 8 kPa, the plasma power is 5 kW, and the etching time is 5 h.

6. A diamond NV color center laser, characterized in that: Prepared by the method according to any one of claims 1 to 5.

Images