Surface plasmon-based 3 [mu] m wave band solid femtosecond laser

Abstract

The invention discloses a surface plasmon-based 3 [mu] m waveband solid femtosecond laser, comprising: a fiber laser pumping source for emitting a laser beam; the resonant cavity comprises an input mirror group and a surface plasmon light modulation element; the laser beam can be input into the surface plasmon light modulation element through the input lens group; and an output mirror; wherein the laser beam is reflected to the input mirror group through the surface plasmon light modulation element, so that the laser beam can be output through the output mirror. The laser prepared by the invention has the advantages of high damage threshold, strong nonlinear modulation characteristic, high stability and the like, and effectively breaks through the barrier in the prior art.

Description

Technical Field

[0001] The invention belongs to the field of ultrafast laser technology and semiconductor device technology, and in particular relates to a 3μm band solid femtosecond laser based on surface plasmon. Background Art

[0002] Ultrafast lasers in the mid-infrared 3μm band have shown broad application prospects in many fields and are one of the important development directions of laser technology. The ways to generate ultrashort pulses in the mid-infrared 3μm band mainly include indirect generation by laser nonlinear frequency conversion technology and direct generation by mode-locked laser technology.

[0003] Laser nonlinear frequency conversion technology is currently a relatively mature technical means, but ultrafast OPO and OPA require strict phase matching and precise synchronization within the wider frequency domain of picosecond / femtosecond pulses, and need to consider the optical damage of nonlinear crystal materials and optical components under high peak power. This increases the complexity of material and system design, resulting in a complex system structure, bulky size and high price.

[0004] In recent years, with the development of rare earth ion doped laser crystal and optical fiber preparation technology and the continuous innovation of laser technology, mid-infrared 3μm band mode-locked ultrafast lasers have become a research hotspot. The direct generation of mid-infrared 3μm band lasers is mainly based on optical fibers and crystals doped with rare earth ions such as erbium (Er3+), holmium (Ho3+) and dysprosium (Dy3+). Although China has made progress in the drawing process of rare earth ion doped sulfide and fluoride optical fibers, commercial products still rely mainly on imports, and some products are embargoed to China. In addition, the development of mid-infrared optical fiber functional devices such as combiners, couplers, isolators, circulators, and mode-locked devices is not yet mature, and the processing technology of high-quality fluoride optical fibers is not perfect, making it difficult to achieve full fiberization. At the same time, sulfide and fluoride glass optical fibers are fragile, have low melting points, are easily damaged, and have strong nonlinear effects, making it difficult to achieve high-power and high-energy mid-infrared 3μm band ultrafast laser operation. Therefore, although rare earth ion-doped optical fibers have made progress in mid-infrared 3μm band ultrafast lasers, core optical fiber gain materials and functional components rely on imports and are subject to foreign control.

[0005] In contrast, laser crystals prepared domestically using solid-state laser crystal growth and preparation technology have the advantages of high damage threshold, weak nonlinear effect, and low cost, providing an ideal and reliable platform for the further development of high-power, high-energy mid-infrared 3μm band mode-locked ultrafast laser technology.

[0006] Summarizing the current research status, the lack of saturable absorption mode-locked elements with high damage threshold, low saturation loss and excellent nonlinear optical properties is the main obstacle to achieving stable operation of all-solid-state mode-locked lasers in the 3μm band.

[0007] Therefore, it is urgent to propose a 3μm band solid-state femtosecond laser based on surface plasmons. Summary of the invention

[0008] In response to the technical problem of the lack of high-performance mode-locked elements for mid-infrared 3μm band solid-state mode-locked ultrafast lasers, the present invention proposes a 3μm band solid-state femtosecond laser based on surface plasmons. The laser has the advantages of high damage threshold, strong nonlinear modulation characteristics and high stability, so as to solve the problems existing in the above-mentioned prior art.

[0009] To achieve the above object, the present invention provides a 3μm band solid femtosecond laser based on surface plasmon, comprising:

[0010] A fiber laser pump source for emitting a laser beam;

[0011] The resonant cavity comprises an input mirror group and a surface plasmon light modulation element, wherein the surface plasmon light modulation element is prepared by an ultra-thin aluminum oxide nano-mask with hexagonal holes on a two-dimensional Bi2O2Se substrate. 3-x Array obtained Bi2O2Se-WO 3-x Surface plasmon materials, and then the Bi2O2Se-WO 3-x The surface plasmon material is transferred to the gold mirror; the laser beam can be input to the surface plasmon light modulation element through the input mirror group; and the output mirror;

[0012] The laser beam is reflected to the input mirror group by the surface plasmon light modulation element, so that the laser beam can be output through the output mirror.

[0013] Optionally, the input mirror group includes a first input mirror, a second input mirror and a third input mirror;

[0014] Among them, the laser beam can be input to the surface plasmon light modulation element along the first input mirror, the second input mirror and the third input mirror in sequence, and the laser beam reflected by the surface plasmon light modulation element can be input to the output mirror along the third input mirror, the second input mirror and the first input mirror in sequence.

[0015] Optionally, a laser gain medium is further included, and the laser gain medium is arranged between the first input mirror and the second input mirror.

[0016] Optionally, a dispersion compensation mirror is further included, and the laser light beam reflected to the input mirror group by the surface plasmon light modulation element can pass through the dispersion compensation mirror and be input to the output mirror.

[0017] Optionally, the dispersion compensation mirror is CaF2 crystal.

[0018] Optionally, it further comprises an optical focusing coupling system, wherein the optical focusing coupling system is used to focus and collimate the laser beam emitted by the optical fiber laser pump source.

[0019] Optionally, the fiber laser pump source uses a 1150nm fiber laser.

[0020] Optionally, the focusing ratio of the optical focusing coupling system is 4:1.

[0021] Optionally, the laser gain medium is a Ho, Pr:YLF crystal, wherein Ho 3+ The ion doping concentration is 0.185at.%, Pr 3+ The ion doping concentration is 0.079 at.%.

[0022] Optionally, the first input mirror and the second input mirror are both concave mirrors with a curvature of 50 mm, and the third input mirror is a concave mirror with a curvature of 100 mm.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] The present invention utilizes Bi2O2Se-WO 3-x Surface plasmon materials are used as surface plasmon light modulators to modulate the reflected laser beam. Bi2O2Se-WO 3-x Surface plasmon materials have a large nonlinear absorption coefficient and ultrafast light modulation characteristics. By regulating their plasmon structure, the ultrafast carrier dynamics process and nonlinear absorption characteristics can be flexibly controlled, thereby optimizing the performance of mid-infrared 3μm band surface plasmon light modulation elements, achieving improved mode-locked laser performance and flexible switching of operating modes.

[0025] The present invention selects Ho, Pr: YLF crystal as the laser gain medium, which has low phonon energy, good light transmittance, high thermal conductivity coefficient, and Pr 3+ The introduction of Ho 3+ The "self-termination" problem of laser oscillation in the 3μm band of doped crystals is solved, which helps to achieve high-power, high-efficiency and high-stability ultrafast laser output in the 3μm band.

[0026] The laser prepared by the present invention has the advantages of high damage threshold, strong nonlinear modulation characteristics and high stability, and effectively breaks through the existing technical barriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0028] Figure 1 A 3μm band solid femtosecond laser based on surface plasmon according to an embodiment of the present invention;

[0029] Among them, 1. Fiber laser pump source; 2. Light focusing coupling system; 3. First input mirror; 4. Laser gain medium; 5. Second input mirror; 6. Third input mirror; 7. Surface plasmon light modulation element; 8: Dispersion compensation mirror; 9. Output mirror. DETAILED DESCRIPTION

[0030] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0031] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0032] In the existing technology, the mid-infrared 3μm band covers the intrinsic absorption peaks of many molecules and atoms, and the picosecond-femtosecond ultrafast laser has the characteristics of short pulse time, high peak power and wide spectral range, so it has wide applications in ultra-high precision molecular spectroscopy, polymer fine processing and ultrafast molecular imaging. This band is located in the "atmospheric transparent window" and has important prospects in free space optical communications and infrared remote sensing detection. In particular, the mid-infrared optical frequency comb is used for wavelength calibration of ultra-high resolution astronomical spectrometers to improve the accuracy of radial velocity measurement, and provide tools for the exploration of terrestrial planets, the study of cosmic expansion speed and the measurement of basic physical quantities. In addition, this band is strongly absorbed by substances containing hydroxyl and amino groups, suitable for laser surgery, with little trauma and fast hemostasis, and is known as the "golden scalpel". The mid-infrared 3μm band ultrafast laser can also be used as the excitation source of mid-infrared supercontinuum and optical parametric oscillator, and has potential application value in high-order harmonic generation and the study of ultrafast characteristics of carriers in semiconductor materials. In summary, mid-infrared 3μm band ultrafast lasers show broad application prospects in many fields and are one of the important development directions of laser technology.

[0033] The main ways to generate ultrashort pulses in the mid-infrared 3μm band include indirect generation by laser nonlinear frequency conversion technology and direct generation by mode-locked laser technology. Laser nonlinear frequency conversion technology uses nonlinear conversion processes such as optical parametric oscillation (OPO) and optical parametric amplification (OPA) to convert mature 1μm band ultrashort pulses to the mid-infrared 3-5μm band. This is a relatively mature technical means at present, but ultrafast OPO and OPA need to achieve strict phase matching and precise synchronization in the wider frequency domain of picosecond / femtosecond pulses, and need to consider the optical damage of nonlinear crystal materials and optical components at high peak power, which increases the complexity of material and system design, resulting in a complex system structure, bulky volume and high price.

[0034] In contrast, mode-locked laser technology produces coherent superposition by locking the phase of the longitudinal mode in the laser resonator, thereby forming a stable and reliable Fourier transform-limited ultrashort pulse. This is the most direct and effective technical means to generate ultrafast lasers, with the advantages of simple system design, compact structure, high conversion efficiency, and high frequency and power stability. In recent years, with the development of rare earth ion-doped laser crystal and optical fiber preparation technology and the continuous innovation of laser technology, mid-infrared 3μm band mode-locked ultrafast lasers have become a research hotspot. The direct generation of mid-infrared 3μm band lasers is mainly based on erbium (Er 3+ ), holmium (Ho 3+ ) and dysprosium (Dy 3+ ) and other rare earth ion doped optical fibers and crystals. Rare earth ion-doped optical fibers have the advantages of good heat dissipation, high gain, and wide bandwidth, and can effectively avoid water absorption loss, making them ideal gain materials. Although China has made progress in the drawing process of rare earth ion-doped sulfide and fluoride optical fibers, commercial products still rely mainly on imports, and some products are embargoed to the domestic market. In addition, the development of mid-infrared optical fiber functional devices such as combiners, couplers, isolators, circulators, and mode-locked devices is still immature, and the high-quality fluoride optical fiber processing technology is imperfect, making it difficult to achieve full fiberization. At the same time, sulfur-based and fluoride glass optical fibers are fragile, have low melting points, are easily damaged, and have strong nonlinear effects, making it difficult to achieve high-power and high-energy mid-infrared 3μm band ultrafast laser operation. Therefore, although rare earth ion-doped optical fibers have made progress in mid-infrared 3μm band ultrafast lasers, core optical fiber gain materials and functional components rely on imports and are subject to the control of others.

[0035] In contrast, China is in the leading position in the world in the growth and preparation technology of solid laser crystals. Laser crystals have the advantages of high damage threshold, weak nonlinear effect and low cost, which provides an ideal and reliable platform for the further development of high-power and high-energy mid-infrared 3μm band mode-locked ultrafast laser technology.

[0036] Surface plasmon resonance (SPR) is a collective oscillation phenomenon of free electrons in metal nanostructures under the excitation of resonant wavelength. SPR can bind the energy of light field in the subwavelength scale and realize the high localization of electromagnetic field. In addition to enhancing the interaction between light and matter, the non-radiative decay of surface plasmons can also generate hot carriers, and their generation rate increases significantly at the laser resonance wavelength. High kinetic energy hot carriers can overcome the potential barrier and transfer from the surface of metal nanoparticles to heterojunction semiconductors. This process occurs in the ultrafast time scale of tens of femtoseconds to several picoseconds. Surface plasmons provide new opportunities for enhancing the ultrafast nonlinear optical properties of two-dimensional materials. At present, two-dimensional material-metal nanoparticle plasmon structures have been successfully applied to solid-state pulsed lasers and have achieved remarkable results. However, the high scattering loss of noble metals such as Au and Ag greatly increases the unsaturated loss of saturable absorption devices, which is not conducive to pulsed laser performance. The plasmon resonance absorption peak of metals is usually located near the visible light band, which limits their application in optoelectronic devices in the near-infrared to mid-infrared bands. In contrast, semiconductor nanoparticles have smaller scattering losses, and their LSPR absorption peaks can cover the range from near-infrared to mid-infrared, filling the gap in metal LSPR and laying the foundation for achieving low-threshold, high-power all-solid-state mode-locked laser output in the 3μm band.

[0037] Summarizing the current research status, there are still many problems to be solved. In addition to the strong absorption loss of water vapor in the air to the 3μm band, especially the 2.7μm laser, and the thermal effect of the gain medium caused by the large quantum loss, the lack of saturable absorption mode-locked elements with high damage threshold, low saturation loss and excellent nonlinear optical properties is the main obstacle to the stable operation of the 3μm band all-solid-state mode-locked laser. In order to solve such problems, the present invention proposes a 3μm band solid-state femtosecond laser based on surface plasmon.

[0038] like Figure 1 As shown, in this embodiment, a 3μm band solid femtosecond laser based on surface plasmon is provided, including: a fiber laser pump source 1 that emits a laser beam, an optical focusing coupling system 2 that focuses and collimates the laser beam, a laser gain medium 4 that receives and transmits the focused laser beam, an input mirror group that reflects the focused laser beam, and a surface plasmon light modulation element 7 that modulates the reflected laser beam. The laser resonant cavity of the fiber laser pump source adopts an X-type resonant cavity, the laser gain medium 4 is Ho, Pr: YLF crystal; the surface plasmon light modulation element 7 is Bi2O2Se-WO 3-x Surface plasmon materials.

[0039] The laser also includes a dispersion compensation mirror 8, which is a CaF2 crystal. The dispersion compensation mirror 8 is used to perform dispersion compensation on the modulated laser beam reflected by the first input mirror 3 to obtain a target laser beam.

[0040] The laser further comprises an output mirror 9, and the output mirror 9 is used to output the target laser beam.

[0041] As an optional implementation, the fiber laser pump source 1 is focused and collimated by the optical focusing coupling system 2, focused to the center of the laser gain medium 4 after passing through the first input mirror 3, and then reflected to the third input mirror 6 and the surface plasmon light modulation element 7 in sequence through the second input mirror 5, and then reflected to the third input mirror 6, the second input mirror 5 and the first input mirror 3 in sequence through the surface plasmon light modulation element 7, and finally outputs the laser beam through the dispersion compensation mirror 8 and the output mirror 9.

[0042] As an optional implementation, the fiber laser pump source 1 has an output power of 0-50W, a central wavelength of 1150nm, an optical focusing coupling system 2 ratio of 4:1, and a pump light radius focused on the laser gain medium 4 of about 50μm. Compared with LD pumping, this embodiment uses a 1150nm fiber laser as a pump source, and the characteristics of high power, high beam quality, and high brightness of the fiber laser can effectively reduce the laser oscillation threshold and improve the output power and efficiency.

[0043] As an optional embodiment, the laser gain medium is Ho, Pr:YLF crystal, Ho 3+ The ion doping concentration is 0.185at.%, Pr 3+ The ion doping concentration is 0.079at.%, and the crystal is wrapped with indium foil and placed in a copper water-cooling fixture, and the water-cooling temperature is set to 18°C. This embodiment uses Ho, Pr: YLF crystal laser gain medium, which has low phonon energy, good light transmittance, high thermal conductivity coefficient, and Pr 3+ The introduction of Ho 3+ The "self-termination" problem of laser oscillation in the 3μm band of doped crystals is solved, which helps to achieve high-power, high-efficiency and high-stability ultrafast laser output in the 3μm band.

[0044] As an optional implementation, the first input mirror 3 and the second input mirror 5 are both concave mirrors with a curvature of 50 mm, and the coating parameters are: AR@1150nm and 2.8-3.1μm@HT. The third input mirror 6 is a concave mirror with a curvature of 100 mm, and the coating parameters are: AR@1150nm and 2.8-3.1μm@HT. The output mirror 9 has a transmittance of 1% at 2.8-3.1μm.

[0045] In the experimental process, this embodiment uses a hexagonal pore ultrathin aluminum oxide (Al2O3) nanomask to prepare WO on a two-dimensional Bi2O2Se. 3-x The array was made of 100 nm pores. First, the Al2O3 nanomask supported by the PMMA layer was immersed in acetone for 10 minutes to dissolve the PMMA. Then, the AAO nanomask was transferred to a quartz substrate with two-dimensional Bi2O2Se. Next, WO3 was deposited on the substrate using thermal evaporation, and the deposition rate was kept at about 100 nm by controlling the heating current. After the deposition is completed, the Al2O3 mask is peeled off with tape, and finally a WO3 nanostructure array is formed on the two-dimensional Bi2O2Se surface. Subsequently, the prepared sample is annealed in an oxygen atmosphere at 300°C for 2 hours to adjust the surface oxygen vacancy density, and the gas flow rate is fixed at 50sccm. Finally, the sample is taken out of the tube furnace and cooled to room temperature to prevent re-oxidation in the air. 3-x The surface plasmon sample was transferred to a gold mirror to prepare Bi2O2Se-WO 3-x Surface plasmon light modulation element 7.

[0046] In this embodiment, Bi2O2Se-WO 3-x Surface plasmon materials are used as surface plasmon light modulation elements 7, namely solid mode-locked switching devices. Excellent performance of saturable absorber mode-locked switching devices is the key to breaking through the key technology of solid mode-locked ultrafast laser in the mid-infrared 3μm band. Bi2O2Se-WO 3-x Surface plasmon materials have a large nonlinear absorption coefficient and ultrafast light modulation characteristics. By regulating their plasmon structure, the ultrafast carrier dynamics process and nonlinear absorption characteristics can be flexibly controlled, thereby optimizing the performance of solid-state mode-locked switching devices in the mid-infrared 3μm band, achieving improved mode-locked laser performance and flexible switching of operating modes.

[0047] In this embodiment, Bi2O2Se-WO 3-x WO on the surface plasmon light modulation element 7 3-xThe arrangement period of the surface plasmon light modulation element 7 and the position and angle of the output mirror 9 are adjusted, the dispersion compensation amount is reasonably controlled, and the transmittance of different output mirrors is explored to achieve a stable mode-locked state, thereby obtaining a stable mode-locked laser with an average output power of more than 400mW and a pulse width of less than 20ps. When the pump light power is low, the intensity of the emitted light in the cavity is weak, and the mode-locked element absorbs weak light strongly, resulting in large losses in the cavity and failure to form laser oscillation. With the increase of the pump light power, the number of inverted particles in the resonant cavity gradually increases, and the fluorescence intensity in the cavity also increases accordingly. When the energy in the cavity is several times the saturation flux of the mode-locked element, its absorption intensity is significantly reduced, and the loss in the cavity is reduced, thereby achieving laser oscillation, and finally obtaining a stable output of 3μm pulsed laser.

[0048] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A 3μm band solid femtosecond laser based on surface plasmon, characterized in that: include: A fiber laser pump source (1) for emitting a laser beam; The resonant cavity comprises an input mirror group and a surface plasmon light modulation element (7). The surface plasmon light modulation element (7) is prepared by an ultra-thin aluminum oxide nano-mask with hexagonal holes on a two-dimensional Bi2O2Se substrate. 3-x Array obtained Bi2O2Se-WO 3-x Surface plasmon materials, and then the Bi2O2Se-WO 3-x The surface plasmon material is transferred onto the gold mirror; the laser beam can be input into the surface plasmon light modulation element (7) through the input mirror group; and the output mirror (9); The laser beam is reflected to the input mirror group by the surface plasmon light modulation element (7), so that the laser beam can be output through the output mirror (9).

2. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 1, characterized in that: The input mirror group comprises a first input mirror (3), a second input mirror (5) and a third input mirror (6); The laser light beam can be sequentially input to the surface plasmon light modulation element (7) along the first input mirror (3), the second input mirror (5) and the third input mirror (6), and the laser light beam reflected by the surface plasmon light modulation element (7) can be sequentially input to the output mirror (9) along the third input mirror (6), the second input mirror (5) and the first input mirror (3).

3. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 2, characterized in that: It also comprises a laser gain medium (4), wherein the laser gain medium (4) is arranged between the first input mirror (3) and the second input mirror (5).

4. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 1, characterized in that: It also includes a dispersion compensation mirror (8), and the laser light beam reflected to the input mirror group by the surface plasmon light modulation element (7) can pass through the dispersion compensation mirror (8) and be input to the output mirror (9).

5. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 4, characterized in that: The dispersion compensation mirror (8) is CaF2 crystal.

6. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 1, characterized in that: It also comprises an optical focusing coupling system (2), and the optical focusing coupling system (2) is used to focus and collimate the laser light beam emitted by the optical fiber laser pump source (1).

7. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 1, characterized in that: The fiber laser pump source (1) adopts a 1150nm fiber laser.

8. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 6, characterized in that: The focusing ratio of the optical focusing coupling system (2) is 4:

1.

9. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 3, characterized in that: The laser gain medium (4) is a Ho, Pr:YLF crystal, wherein Ho 3+ The ion doping concentration is 0.185at.%, Pr 3+ The ion doping concentration is 0.079 at.%.

10. The 3 μm band solid femtosecond laser based on surface plasmon according to claim 2, characterized in that: The first input mirror (3) and the second input mirror (5) are both concave mirrors with a curvature of 50 mm, and the third input mirror (6) is a concave mirror with a curvature of 100 mm.

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