High Repetition Rate Femtosecond Laser Research Articles

Space-selective precipitation of functional crystals in glass by using a high repetition rate femtosecond laser

Nonlinear optical crystals Sr 2TiSi 2O 8 are written arbitrarily in a stoichiometric SrO–TiO 2–SiO 2 glass by using a high repetition rate femtosecond laser. The mechanism of nucleation and subsequent crystal growth is assumed to the thermal accumulation effect and the laser-induced reduction of Ti 4+ to Ti 3+. Additionally, the threshold time for inducing crystal formation decreases, while the corresponding dot size increases with increasing laser power. The threshold variation is also discussed according to the mechanism of nucleation. We suggest that this technique can be used in light-wave switching, 3D optical memory and laser display.

High repetition rate and low energy femtosecond laser ablation coupled to ICPMS detection: a new analytical approach for trace element determination in solid samples

A low energy and high repetition rate infrared femtosecond laser system was developed for direct trace elements analysis by laser ablation/ICPMS. This system provides improved analytical performances in terms of limits of detection, repeatability, elemental fractionation and depth profile analysis in comparison to conventional nanosecond UV laser ablation used so far in analytical chemistry. Preliminary results show that limits of detection are improved by more than one order of magnitude and the elemental fractionation reduced to negligible values. In addition, depth profile resolution better than 20 nm are easily achievable on a Cr-Ni multilayer material which opens new fields of application in surface analysis.

Raman spectroscopy and luminescent properties of ZnO nanostructures fabricated by femtosecond laser pulses

In this paper, we report the laser-induced periodic structure with different spatial characteristics on the surface of polished ZnO single-crystalline by high repetition rate femtosecond laser pulses. This study demonstrates that, using different laser parameters and irradiation conditions, ZnO nanoripples and nanorods were successfully prepared. We have investigated the surface by means of scanning electron microscope (SEM), Raman scattering and photoluminescence (PL). We propose that second-order harmonic has a strong influence on the formation of nanostructures.

Novel approach to RF photonic signal processing using an ultrafast laser comb modulated by traveling-wave tunable filters

The analogy between optical frequencies and RFs leads to a novel technique for RF photonic signal processing using a femtosecond laser comb modulated by a traveling-wave tunable filter, such as an acoustooptic tunable filter (AOTF) or a novel electrooptic tunable filter (EOTF). In this new scheme, the recent history of an applied RF waveform to-be-processed slides into the tunable filter and a femtosecond pulse train diffracts off the moving acoustooptically or electrooptically induced dielectric grating, producing a shaped optical pulse train with each shaped pulse as a compressed replica of the RF waveform contained within the device aperture that is sped up by the ratio between the center optical and RF frequency. For a CW RF tone input, only a narrowband group of the frequency comb lines in the incoming laser comb is spectrally filtered and modulated due to the phase-matching condition in the filter and is simultaneously Doppler shifted by that RF due to the traveling-wave grating obeying the conservation of energy. This allows us to use the traveling-wave tunable filter as a spectrally mapped Doppler-shifted modulator that encodes different RF components onto the corresponding optical frequency comb lines. RF signal processing can then be performed by using optical techniques to manipulate the spectrally modulated laser comb. To reconstruct the processed RF signal, the Doppler-shifted and optically processed pulse train is heterodyne detected by beating with a reference femtosecond pulse train from the same laser source. A high repetition rate femtosecond laser comb is modulated by an AOTF to experimentally demonstrate this novel RF photonic signal processing technique. We demonstrate an RF tunable bandpass/notch filter, an RF down-converter, and an RF jammer nuller as novel applications of ultrafast lasers.

Optical vibration sensor fabricated by femtosecond laser micromachining

We fabricated an optical vibration sensor using a high-repetition rate femtosecond laser oscillator. The sensor consists of a single straight waveguide written across a series of three pieces of glass. The central piece is mounted on a suspended beam to make it sensitive to mechanical vibration, acceleration, or external forces. Displacement of the central piece is detected by measuring the change in optical transmission through the waveguide. The resulting sensor is small, simple, and requires no alignment. The sensor has a linear response over the frequency range 20 Hz–2 kHz, can detect accelerations as small as 0.01m∕s2, and is nearly temperature independent.

Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for rapid writing of low-loss optical waveguides in transparent glasses. A novel femtosecond fiber laser system (IMRA America, FCPA muJewel) providing variable repetition rate between 0.1 and 5 MHz was used to study the relationship between heat accumulation and resulting waveguide properties in fused silica and various borosilicate glasses. Increasing repetition rate was seen to increase the waveguide diameter and decrease the waveguide loss, with waveguides written with 1-MHz repetition rate yielding ~0.2-dB/cm propagation loss in Schott AF45 glass. A finite-difference thermal diffusion model accurately tracks the waveguide diameter as cumulative heating expands the modification zone above 200-kHz repetition rate.

A femtosecond autocorrelator with internal calibration

We describe an autocorrelator which allows measurement of femtosecond pulse profiles in real time. The autocorrelator output is displayed on an oscilloscope screen. This profile contains all the information needed to measure the pulse duration. The autocorrelator is based on collinear second-harmonic generation optical arrangement. It allows for convenient alignment of high repetition rate femtosecond lasers in real time.