Ripple period adjustment on SiC surface based on electron dynamics control and its polarization anisotropy

We designed a femtosecond (fs) + picosecond (ps) double-pulse sequence by using a Mach-Zehnder-like apparatus to split a single 120 fs pulse into two sub-pulses, and one of them was stretched to a width of 2 ps by a four-pass grating system. Through observing the ripples induced on the ZnO surface, we found the ionization rate appeared to be higher for the sequence in which the fs pulse arrived first. The electron rate equation was used to calculate changes of electron density distribution for the sequences with different delay times. We suggest that using a temporally shaped fs+ps pulse sequence can achieve nonlinear ionization control and influence the induced ripples.

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“…We used the electron rate equation to calculate the maximum density (ρ) induced by an FPDPS [21,22] :…”

Section: Resultsmentioning

confidence: 99%

Nonlinear ionization control by temporally shaped fs+ps double-pulse sequence on ZnO

et al. 2023

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“…High-density plasmas are almost fully ionized and contain more positive ions and electrons than neutral particles [22]. Therefore, the first term in equation (3), which contains ∆N n , is negligible. The constant specific refractive indices of ions are typically negligibly small compared with those of neutral particles and electrons [23,24]; hence, the second term representing the ion density contribution can be ignored.…”

Section: Simulation Methodsmentioning

confidence: 99%

“…Plasmas are extensively used across a wide range of applications that include laser processing [1][2][3], plasma processing [4,5], welding [6], plasma acceleration [7], nuclear fusion [8], and medical treatments [9]. Controlling the electron densities in the plasmas is indispensable for the advancement and optimization of these technologies, because the electron density determines important plasma properties such as the plasma frequency and Debye length, as well as the energy transfer processes in particle collisions and the radiation and absorption mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Optical design of a laser wavefront sensor applicable under strong diffraction effects by irreproducible microscale high-density plasma

Shimada¹,

Inada²,

Ishijima³

et al. 2022

Meas. Sci. Technol.

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Accurate measurements of electron density in irreproducible microscale high-density plasmas are indispensable for improving laser processing and plasma processing technology because the dynamics of these plasmas are strongly influenced by their electron density. Because single-path laser wavefront sensors are capable of acquiring the two-dimensional electron density distribution with a single shot, the electron density of irreproducible millimeter-scale low-density plasmas has been measured by using such sensors. However, the strong diffraction effects caused by the irreproducible microscale high-density plasmas pose challenges for the measurement. In this study, we numerically and experimentally demonstrate a suitable optical configuration of single-path laser wavefront sensors for accurate measurements of irreproducible microscale high-density plasmas with minimal measurement errors. Our Fresnel diffraction-based numerical simulation indicates that the serious measurement errors caused by the strong diffraction effects can be significantly reduced through the use of relay lenses with high magnification and a short-wavelength laser source. In addition, we propose an alignment procedure for the optical setup to minimize the measurement errors and experimentally validated the procedure by measuring a laser wavefront shaped by a spatial light modulator. Finally, we applied the verified laser wavefront sensor to the measurement of a laser-induced plasma with a two-dimensional line-integrated electron density higher than 1 × 1021 m−2 in an approximately 40 × 50 μm region. This study provides a new strategy to rigorously analyze the dynamics of irreproducible microscale high-density plasmas using a laser wavefront sensor.

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“…Femtosecond laser-induced periodic surface structures (LIPSS) have been studied extensively for many types of materials, such as metals, semiconductors, dielectric solids, and thin films [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Owing to its versatility and flexibility, femtosecond LIPSS has become an efficient processing technique for fabricating functional devices, for structural color, absorption and luminescence enhancement, and large-area gratings [15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

High-Performance Birefringence of Periodic Nanostructures in FTO Thin Film Fabricated by IR-UV Femtosecond Laser

et al. 2022

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By using infrared to ultraviolet (IR-UV) femtosecond laser directing, periodic nanostructures were efficiently fabricated on an F-doped tin oxide (FTO) film with a thickness of 650 nm. The morphology of the nanostructures and duty cycle were studied in detail by changing the laser fluence and scanning speed, where three lasers with central wavelengths of 343, 515, and 1,030 nm were used in the experiments. Under the 515 nm laser irradiation with scanning speed of 0.01 mm/s and laser fluence of 23 mJ/cm2, the periods Λ is 172 nm, the ablated nanogroove with width w2 is 52 nm, the birefringence Δn reached a maximum of 0.21, and the phase retardance was up to 135 nm. The morphology of the nanostructures and the birefringence effects of the FTO film prepared by a femtosecond laser at wavelengths of 1,030 and 343 nm were also studied, where the phase retardance of the nanostructured FTO film was much lesser than for the 515 nm laser because the thickness of the nanoripples layer, and, thus, the duty cycle of periodic nanoripples was smaller. Finally, a large-area FTO film with periodic nanostructures was fabricated efficiently by direct laser writing using a 515 nm fs laser beam focused via a cylindrical lens, and demonstrated the characteristics of a quarter-wave plate for 532 nm light.

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Ripple period adjustment on SiC surface based on electron dynamics control and its polarization anisotropy

Cited by 9 publications

References 39 publications

Nonlinear ionization control by temporally shaped fs+ps double-pulse sequence on ZnO

Nonlinear ionization control by temporally shaped fs+ps double-pulse sequence on ZnO

Optical design of a laser wavefront sensor applicable under strong diffraction effects by irreproducible microscale high-density plasma

High-Performance Birefringence of Periodic Nanostructures in FTO Thin Film Fabricated by IR-UV Femtosecond Laser

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