Effect Of Femtosecond Laser Pulses Research Articles

Effect of tunable femtosecond laser pulses on the sporulation of Eimeria species oocysts of chickens: An in vitro study

Parasitic Eimeria species infection is a severe disease in the poultry industry and a major cause of coccidiosis and disease-engendered financial losses. Increasing resistance to drug-based treatment presents a significant problem, as does the use of disinfectants to sanitize poultry farms, because of increasing oocyst resistance to chemical interventions and contamination of poultry products. Reducing the rate of sporulation of Eimeria species oocysts can minimize the spread of the disease. Therefore, we studied the effect of femtosecond laser pulses on oocysts sporulation rate with the goal of developing an effective light-based treatment for coccidiosis, as an alternative to pharmaceutical intervention. Eimeria species oocysts were harvested from the intestines of infected broiler chickens. Unsporulated oocysts obtained were distributed over 96 well plates and irradiated with pulsed femtosecond laser at various wavelengths and exposure times. Irradiation of the oocysts with pulsed 360 to 390 nm femtosecond laser significantly reduced their sporulation rate and altered their morphology compared to untreated controls. Compared to other wavelengths within the 360 to 390 nm spectra, treatment with pulsed 370 nm wavelength was most effective in decreasing oocyst sporulation rate, reducing sporulation to 17%, 15%, and 11%, after 5-, 10-, and 15-min exposure times, respectively. In contrast, irradiation with infrared 720 nm and 800 nm wavelengths had no significant effect on oocysts sporulation rate. These findings clearly show that irradiation with a pulsed 370 nm femtosecond laser effectively reduces Eimeria species oocyst sporulation and that it is possible to develop an effective light-based treatment for coccidiosis.

Pulsed far-infrared radiation of ferromagnetic heterojunction and its photothermal regulation

Under illumination of a femtosecond laser pulse on the Pt/CoFe/Ta trilayer heterostructure, an impulsive spin current can be generated in the ferromagnetic layer due to the ultrafast demagnetization. The spin current is super-diffusively transported and injected into the neighboring heavy metal layers, and is converted into the transversal charge current due to the spin-orbit coupling, which is named inverse spin Hall effect. The transient charge current on a time scale of sub-picosecond gives rise to the electromagnetic radiation in the far-infrared range to the free space. In this work, we demonstrate two kinds of experiments to investigate the modulation of far-infrared emission by photo-thermal effect, which is due to the thermal energy deposed by light pulses on a short timescales. First, the amplitude of the emitted far-infrared pulse as a function of an applied magnetic field is measured, which shows a far-infrared hysteresis behavior. The coercive field of the sample obtained by far-infrared hysteresis is smaller than that obtained by the <i>M</i>-<i>H</i> hysteresis through vibrating sample magnetometer. In addition, the coercive field decreases with pump laser fluence increasing. Second, the control of spin polarization on an ultrafast timescale in the presence of a small magnetic field applied oppositely to that of the magnetization of the ferromagnetic sample. The amplitude of far-infrared time-domain signal reaches a maximum value at a pump fluence of 1.43 mJ/cm<sup>2</sup>. For the pump fluence larger than 1.43 mJ/cm<sup>2</sup>, the far-infrared pulse experiences a phase reversal. After the reversal, a decrease of the laser pump fluence cannot restore the original phase of the far-infrared pulse. The above two experimental results not only elucidate the photothermal effect of femtosecond laser pulses, but also provide a new method for controlling the far-infrared radiation pulses based on ultrafast spintronics. These results demonstrate that far-infrared emission spectroscopy can be used as an ultrafast optical method to investigate magnetic properties, such as the coercive field and anisotropy field of the samples.

Study of domain wall dynamics in GdFeCo using double high-speed photography

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km/s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization. Keywords: ferrimagnetism, domain wall dynamics, high-speed photography method, Faraday effect.

Исследование динамики доменной границы в GdFeCo методом двукратной высоко скоростной фотографии

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km / s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization.

Numerical simulation and parameters estimation of the time fractional dual-phase-lag heat conduction in femtosecond laser heating

In this paper, considering the heat flux and the temperature gradient approximated by the fractional Taylor's series expansions with different orders in dual-phase-lag (DPL) model, we propose the time fractional DPL heat conduction model for thin gold films heating by femtosecond laser pulses. The solutions of the model are investigated analytically and numerically. Firstly, the semi-analytical solution is presented by the Laplace transform method and the Fourier cosine transform method. With the L1 approximation of the Caputo fractional derivative, the finite difference scheme is derived to describe the effects of femtosecond laser pulses on the temperature distributions of the gold films. The effectiveness of the numerical algorithm is examined by the comparison with the semi-analytical solution. And then based on the numerical algorithm and the experimental datasets of femtosecond laser pulses heating on gold films of various thicknesses, the estimations of the model parameters are considered by the modified hybrid Nelder–Mead simplex search and particle swarm optimization (MH-NMSS-PSO). Using the optimal values of the parameters estimation, we verify the consistencies between the semi-analytical solutions of the model and the datasets. It proves the accuracy of the time fractional DPL heat conduction model in characterizing the temperature distributions of thin gold films. Finally, the varieties of temperature distribution with time and position are considered and then the effects of the model parameters on the temperature distribution are also discussed.

High-precision cutting of polyimide film using femtosecond laser for the application in flexible electronics

The experimental results of cutting a polyimide film on the optical glass substrate by means of femtosecond lasers are given. Two modes of laser cutting of this film without damages to a glass base are determined. The first is the photo graphitization using a high repetition rate femtosecond laser. The second is ablative, under the effect of femtosecond laser pulses with high energy and low repetition rate. Cutting of semiconductor chips formed on the polyimide film surface is successfully demonstrated.

Linear electro-optic effect for femtosecond laser pulses in linear chirped MgO:LiNbO3 and its compensation for phase mismatch and group-velocity mismatch

For linear electrooptic (EO) effect of femtosecond laser pulses that propagates along the direction of non-optical axis in linear-chirped and periodically poled MgO:LiNbO3 (LCPPLMN), we explore the compensation scheme for the phase mismatch and the group-velocity mismatch between the o- and e-light, and discuss the effect of the linear chirp parameter of the LCPPLMN on the waveform of the output o- and e-light. It is found that, for any input pulse duration, the phase mismatch and the group-velocity mismatch can be simultaneously compensated by the optimization of the linear chirp parameter. As a result, high conversion efficiency of linear EO effect can be performed. In addition, we discuss the influence of the linear chirp parameter on the temporal evolutions of the output o- and e-light pulse.

Femtosecond Laser Photodisruptive Effects on the Posterior Human Corneal Stroma Investigated with Atomic Force Microscopy

To analyze the effects of femtosecond laser pulses on the posterior human corneal stroma with atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). A femtosecond laser (IntraLase iFS, Abbott, USA) was programmed to create a full posterior lamellar dissection in 9 human corneal tissues, using 3 different pulse energies (1.00 µJ, 0.75 µJ, and 0.50 µJ). Three corneal tissues were prepared in a similar fashion using a mechanical microkeratome (Moria Evolution 3, Moria, France). Six corneal tissues received an 8.00-mm diameter full cylindrical resection using either the femtosecond laser or the Barron trephine (Katena Products Inc., USA). The posterior corneal lenticules were first examined at AFM (Autoprobe CP, Veeco, USA). Both the posterior lenticules and the trephined corneal samples were scanned by ESEM (FEI Quanta 400, USA). Granules and crater-like features were observed on the stromal interface of all the laser dissected tissues, likely due to a secondary thermal effect of femtosecond laser dissection. Collagen fibers were seen only on samples treated with the 0.50 µJ pulse energy. Images of an even stromal surface were observed on the posterior stroma of mechanically dissected corneal samples. Mechanical and thermal effects, induced by femtosecond laser pulses on the human corneal stroma, were seen with AFM. Surface regularity of the photodisrupted stroma was inversely and non-linearly related to the pulse energy. The femtosecond laser provided high surface quality for lamellar resection of the posterior stroma comparable to those provided by mechanical devices.

Nanostructure Formation in Silicon Photovoltaic Cells by Femtosecond Laser Pulses

The experimental evidence of the effect of femtosecond laser pulses on the spectral response of a Silicon photovoltaic cell is demonstrated and investigated. The response of this device is covering the visible to near infrared spectral region. The responsivity of the photovoltaic cell is enhanced from 0.18A/W (0.5A/W to 0.85 A/W) to 0.25A/W, this means that the conversion efficiency increases from about 9% to about 14% due to irradiation effect. All treatments and measurements have been done at room temperature. The observed enhancement is related to the appearing of nano-structured groves in the 700-900 nm range.

Nanostructure formation in Silicon photovoltaic cell surface by femtosecond laser pulses

The experimental evidence of the effect of femtosecond laser pulses on the spectral response of a Silicon photovoltaic cell is demonstrated and investigated. The response of this device is covering the visible to near infrared spectral region. The responsivity of the photovoltaic cell is enhanced from 0.18A/W (0.5A/W to 0.85 A/W) to 0.25A/W, this means that the conversion efficiency increases from about 9% to about 14% due to irradiation effect. All treatments and measurements have been done at room temperature. The observed enhancement is related to the appearing of nano-structured groves in the 700-900 nm range. Keywords: Silicon photovoltaic cell, nanostructure, femtosecond laser pulse, irradiation, infrared

Nanostructure formation in Silicon Photovoltaic Cell Surface by Femtosecond Laser Pulses

The experimental evidence of the effect of femtosecond laser pulses on the spectral response of a Silicon photovoltaic cell is demonstrated and investigated. The response of this device is covering the visible to near infrared spectral region. The responsivity of the photovoltaic cell is enhanced from 0.18A/W (0.5A/W to 0.85 A/W) to 0.25A/W, this means that the conversion efficiency increases from about 9% to about 14% due to irradiation effect. All treatments and measurements have been done at room temperature. The observed enhancement is related to the appearing of nano-structured groves in the 700-900 nm range.

Femtosecond optical trapping of cells: Efficiency and viability

The femtosecond optical trapping capability and the effect of femtosecond laser pulses on cell viability were studied. The maximum lateral velocity at which the particles just failed to be trapped, together with the measured average trapping power, were used to calculate the lateral trapping force (Q-value). The viability of the cells after femtosecond laser trapping was ascertained by vital staining. Measurement of the Q-values shows that femtosecond optical tweezers are just as effective as continuous wave optical tweezers. The experiments demonstrate that there is a critical limit for exposure time at each corresponding laser power of femtosecond optical tweezers, and femtosecond laser tweezers are safe for optical trapping at low power with short exposure time.

Formation of nanoparticles on the silicon surface under the effect of femtosecond laser pulses

Nanoparticles were formed on the surface of single-crystal silicon as a result of irradiation of this surface with femtosecond laser pulses. According to the data of the atomic-force microscopy, the height of these nanoparticles ranges from 2 to 30 nm and their transverse size varies from 70 to 200 nm.

Decomposition of CF 2HCl molecules by femtosecond laser radiation

Studied in this Letter is the decomposition of the CF 2HCl molecules under the effect of femtosecond laser pulses at wavelengths of 0.4, 0.8, and 1.3–1.8 μm. The CF 3H molecule is the only decomposition product found, no matter what the radiation intensity in the range 40–200 TW/cm 2 and the wavelength used. This result differs substantially from the results of the pyrolysis and dissociation of CF 2HCl under the effect of nanosecond IR or UV laser pulses. The field ionization of the CF 2HCl molecule is believed to be its main decomposition mechanism.

Motion of an atom under the effect of femtosecond laser pulses: From chaos to spatial localization

The spatial localization of an atom in a field of periodic femtosecond laser pulses is considered. It has been shown that the atom can be localized with absolute accuracy in the nanometer range. The time interval during which the atom is situated in the laser field is only 10−7–10−8 of the total localization time interval.