Papers by Keyword: Femtosecond Laser

Abstract: In the paper, the optical fiber F-P acoustic emission sensing probe has been proposed to monitor online space-time progress of femtosecond laser plasma shock wave for the first time, the structure of sensing probe is microstructure with full optical fiber probes without glue, it can measure weak acoustic emission high frequency signal on femtosecond laser plasma shock wave. In the process of femtosecond laser ablating copper, iron and aluminum, we research and analyze the plasma shock wave acoustic emission signal change regulation under different laser pulse energy and different distance between the laser and the optical fiber sensing probe, and we analyze the feature of the acoustic emission signal spectrum. Experiment establishes a kind of new optical fiber sensing measurement method for femtosecond laser plasma shock wave acoustic emission signal.

Abstract: A technique for ordered fabrication of periodic freestanding micro/nanostructures on the crystalline germanium (Ge) <100> surfaces with 1064 nm wavelength ultrashort laser pulses under ambient conditions is presented. The laser radiation fluence used for obtaining the structures is close to the melting threshold (0.1 J/cm²) of Ge. The dimensions of structures range from hundreds of nanometres to a few microns. The orientation of the periodic surface structures depends on laser beam polarization direction. Arrays of structures are formed in rows parallel to the sample movement direction for samples machined with s-polarized laser pulses, but formed in the direction perpendicular to the movement for p-polarized pulses. The structures are fabricated under variable temperatures on sample surface owing to the changed interference between incident and reflected laser beams. A micro-Raman analysis of the processed surfaces shows a minor change in the spectral intensity as compared to the unprocessed surface and the material retains its crystallinity after laser irradiation.

Abstract: In this paper, lapped C-face of single crystal SiC wafer was irradiated by femtosecond laser. Chemical mechanical polishing (CMP) was then carried out to polish the irradiated SiC C-face. The authors compared the results of femtosecond laser-assisted CMP process. A white-light interferometer was used to investigate the surface morphology of the processed SiC substrate before and after laser irradiation. It was found that the material removal rate (MRR) of the irradiated substrate is about 3 times higher than that of the substrate not treated by femtosecond laser. In addition, lower surface roughness was realized after femtosecond laser assisted CMP process.

Abstract: The femtosecond laser drilling for metal thin film is theoretically investigated in this paper. Femtosecond laser patterning of metal thin films is of technological significance because the fabrication of electrodes or metallization lines is a key process commonly required in the manufacturing of modern electronic devices. A femtosecond pulsed laser has a temporally short pulse that does not cause significant heat conduction in the material. This property of femtosecond laser pulse drilling makes sub-micron machining achievable with laser irradiation. Considering vaporization as the mechanism of the material removal, this paper employs two-temperature model to analyze the thermal process for femtosecond laser drilling of metal thin film. The variations of the drilling rate and squared diameter with laser fluence are compared with the available experimental data. This study also analytically validates that the drilling depth per pulse is governed by the optical penetration depth for low laser fluences and the squared crater diameter is linearly in proportion to the logarithm of laser fluence.

Abstract: This letter presents the morphology of femtosecond Bessel beams induced high-aspect-ratio structural change regions in bulk silicon carbide. An axion is engaged in transforming Gaussians beams to Bessel beams, which are then focused on the surface or below the surface of the sample by combination of a plano-convex lens and a microscope objective. The sample is scanned by the focused femtosecond Bessel beams at the preset patterns. Through this method, the high-aspect-ratio uniform laser induced structure change regions have been produced and the highest respect ratio can reach 206 with the depth of 330 μm, the width of 1.6 μm in optimized conditions of appropriate focusing position and pulse energy. This result is attributed to uniform energy distribution in the long propagation distance of Bessel beams with nondiffracting. This technique will have great potential applications to make high-aspect-ratio microgrooves in wide-gap and transparent materials.

Abstract: The result of direct ablation of silicon by an 800 nm Ti:Sa femtosecond laser pulses are presented. Obtained slice of silicon with submicron roughness with tilt focused femtosecond laser pulses. Yaw cut more due to mechanical vibrations of the entire installation on a pneumatic table, but not the physics of the ongoing process. During processing, possibly thinning the silicon sample from the opposite edge (sharpening) to submicron values ​​(tens of nanometers).

Abstract: Femtosecond laser is now widely used in micro holes drilling because of its unique advantages, such as high efficiency, high precision and non-contact. Femtosecond laser is the best choice to fabricate micro holes. This paper makes a systematic study of the influence of laser power and number of pulses on diameter and depth of micro holes on S136 die steel through the focusing lens with focal length of 35 cm. A series of high-precision micro holes with different diameter and depth are fabricated. The relationship between the dimension of fabricated micro holes and the process parameters is determined.

Abstract: This paper analyzes the micro-mechanism of interaction between femtosecond laser and one dimension material. It gets the figure of temperature change with time by calculating the Two Temperature Equation(TTE) in the process of the laser ablation. And it presents the surface characters of metal material. Additionally, the plasma is generated when the temperature of ion subsystem is far higher than the melting point of copper metal. The paper can give the laser ablation threshold by the numerical calculation. It will help the researchers ensuring the laser fluence for preparing the copper film better.

Abstract: This paper presents an experimental investigation into microfabrication of nickel template by femtosecond laser in air at atmospheric pressure. The laser pulses used for the study are 800 nm in wavelength, 100fs in pulse duration, and the repetition rate used is 1KHz. Micro-hole ablation experiments are carried out in air by focusing the femtosecond laser beam on the nickel target surface at normal incidence with the long-focus objective lens of enlargement factor 50 and NA=0.7. Dependence of the diameter, depth and depth-to-diameter ratio of the fabricated holes on the laser power and number of pulses are revealed experimentally. Microgrooves with good uniformity are fabricated on nickel template with femtosecond laser by optimizing the process parameters.

Abstract: A femtosecond laser pulse duration is shorter than many physical/chemical characteristic times, which makes it possible to control electron dynamics such as ionizations and electron densities. This study expermetally investigtes the effects of laser fluence on sub-wavelength periodic surface structuring based on ultrafast laser electron dynamics control. A quantum model for the sub-wavelength periodic surface structuring is also proposed, which considers both the wave properties in the photon particle-properties based plasma model for photon-electron interactions and transient localized changes of material properties. It shows that the laser fluence strongly affects the ablation crater shapes. The prediction of ablation crater shape and periodicity is in agreement with experimental data.