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Study On Thermal Radiation Of Micronano Periodical Structure Fabricated By Femtosecond Laser

Posted on:2017-05-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:S LiuFull Text:PDF
GTID:1108330503992420Subject:Optical Engineering
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When the wavelength of the incident light is near to the structural period of material, fancy optical phenomena will occur as a result. In light by the structure color in the natural creatures, the manipulation of light by periodical surface structures is always a hot spot in scientific researches. The manipulation is not only restrained in the range of visible light, thermal radiation in the range of infrared light can be also achieved by modifying the surface structures. Many researches have already shown that manipulation of the thermal radiation with micro/nano structure can be widely applied in the areas of thermophotovoltaic devices and radiation cooling devices. While traditional researches are mostly restrained in the labs because even though ideal machining properties can be obtained with many micromachining techniques such as lithography, it possesses many deficiencies such as high environmental requirement, complicated machining procedures, limited machining materials and hard to fabricate a surface which large areas. Femtosecond laser micromachining techniques thus provide a new solution for resolving such problems. Study on the manufacturing of micro/nano periodical structures with femtosecond laser and the thermal radiation characters of the fabricated surface can broaden the applications of thermal-radiationcontrolled devices. Meanwhile, it exports a new application area of femtosecond laser micromachining techniques.This thesis mainly studied the manufacturing of micro/nano periodical structure with femtosecond laser and the thermal radiation characteristics of the manufactured surfaces. Based on the theory of surface plasmon resonance, he rigorous coupled wave analysis method is chosen as a simulation tools and femtosecond laser machining techniques is applied in experiment. In addition, Fourier transform infrared spectrometer is used for the measurement of thermal radiation spectrum of material.The main content and results is as follows:1. Femtosecond laser beam is oblique incident onto the metal tungsten target for the preparation of grating structure with subwavelength period. The gratings with subwavelength period among 349 ~ 620 nm are obtained. Experiments of femtosecond laser direct writing micron-level periodical structures were studied, the relations between the widths of periodical grooves and the average laser power are measured. This provides experiment basis for preparation of grating structures.2. The reflectivity of the periodical microstructure with a period of 10 μm and duty ratio 0.5 is simulated by through rigorous coupled wave analysis methods. The simulation results shows that when the grating depth is 1 μm, absorption enhancement phenomena is occurred when TM wave is incident. We also simulated the influence of reflectivity when using a micro/nano periodical grating structure with a depth of 1 μm and a duty ratio 0.5. The results shows that with the TM incident, there will be an absorption peaks when the center wavelength is similar to the grating period. Combining with the Kirchhoff’s law of thermal radiation, the simulation results can be extended to the emission enhancement phenomena of the materials. 3. By preparing one dimensional micro/nano gratings structure on the metal nickel, chromium, titanium alloy, the radiations under different grating period, viewing angles and temperatures were studied. The experimental results show that the grating structure can realize the enhancement of thermal radiation intensity at a percentage from 35% to 84%; the period of micro/nano grating structure is close to the central wavelength of the enhancement peak of the thermal radiation; the enhancement of thermal radiation with a micro/nano grating structure is thermal stable under 300 degrees Celsius, that is the central wavelength of the enhancement peak won’t change with the variation of the temperature. When observing with a certain viewing angle, the wavelength of the thermal radiation enhancement peak is decreased with the increase of viewing angle.Then we proposed a method that projecting the grating to the normal incidence plane to calculate the wavelength of the enhancement peak. The empirical formulas coincide well with the experimental data. Through double cycle thermal radiation enhanced spectrum of onedimensional grating structure we found that in one-dimensional grating structure with multiple grating period, each periodical structure is independent in thermal radiation enhancement effect. 4. Single period concentric rectangle structure can obtains a thermal radiation enhancement peak the same as a one-dimensional grating structure. Since there two grating structures in parallel and vertical direction on the surface, when the plasmon resonance enhancing the thermal radiation, distinguish images of the thermal enhancement with different optical structure can be clearly seen when using infrared imager and infrared polaroid. Since concentric dual cycle rectangular structure with two kinds of grating periods as 10 μm and 15 μm, when setting the polaroid with the polarization direction is parallel or perpendicular to the gratings, thermal radiation spectrum of 10 μm and 15 μm grating structures can be obtained. While if the polarizer is not applied, the thermal radiation spectrum is the sum of the two spectra. Thermal radiation spectrum of the structure of single period concentric rings are also studied. Thermal radiation enhancement peak under different polarization angles were measured. Study shows the concentric ring structures can provide a thermal radiation enhancement effect similar to the uniform natural light.
Keywords/Search Tags:Thermal radiation, Grating structure, Femtosecond laser, Surface plasma polaritons, Micromachining
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