Characterization Of Ultrashort Optical Pulses Research Articles

Ultrashort Pulse Retrieval from Experimental Spectra Transformed in Chalcogenide and Silica Fibers

The characterization of ultrashort optical pulses is a highly requested task. The most popular commercially available hardware/software systems are based on interferometric measurements and second-harmonic generation, leading to some ambiguities and limitations. Here we experimentally test the non-interferometric method of pulse retrieval from three spectra: the fundamental spectrum and two spectra that transformed in an element with Kerr nonlinearity and accumulated different nonlinear phases (different Β-integrals). This method has no ambiguities related to time direction, and allows simple hardware/software implementation. We test a novel simple algorithm for experimental data processing based on the search for a polynomial-approximated spectral phase. Two experimental cases are considered. In the first one, we retrieved 160 fs pulses using a chalcogenide arsenic sulfide glass fiber as a nonlinear Kerr element. In the second case, we retrieved 670 fs pulses with a complex spectrum using a piece of silica-based fiber. The results are confirmed by independent measurements using a standard SHG-FROG technique (Second-Harmonic Generation Frequency-Resolved Optical Gating).

Complete characterization of ultrashort optical pulses with a phase-shifting wedged reversal shearing interferometer

The ability of an interferometer to characterize the spatial information of a light beam is often limited by the temporal profile of the beam, with femtosecond pulse characterization being particularly challenging. In this study, we developed a simple, stable, controllable shearing and vectorial phase-shifting wedged reversal shearing interferometer that is able to characterize all types of coherent and partially coherent light beams. The proposed interferometer consists of only a single beam splitter cube with one wedged entrance face and is insensitive to environmental vibration due to its common path configuration. A near zero-path length difference of the proposed interferometer ensures its operation for ultrashort pulses, providing, for the first time, a simple and stable interferometric tool to fully characterize sub-100 fs laser pulses. All common beam characterization can be carried out with the interferometer, such as the amplitude, phase, polarization, wavelength, and pulse duration. Furthermore, this technique is sensitive to the wavefront tilt and can be used for precise beam alignment. Therefore, this interferometer can be an essential tool for beam characterization, optical imaging, and the testing required for a wide range of applications, including astronomy, biomedicine, ophthalmology, optical testing and imaging systems, and adaptive optics.

Noninstantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for the generation and characterization of ultrashort optical pulses. One particular characterization method is frequency-resolved optical gating, which can be based on a large variety of third-order nonlinear effects. Any of these variants presupposes an instantaneous temporal response, as it is expected off resonance. In this paper we show that resonant excitation of the third harmonic gives rise to surprisingly large decay times, which are on the order of the duration of the shortest oscillator pulses generated to date. To this end, we measured interferometric third-harmonic frequency-resolved optical gating traces in TiO2 and SiO2, corroborating polarization decay times up to 6.5 fs in TiO2. This effect is among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrodinger equation are in excellent agreement with experimental observations. Our work (experiments and simulations) corroborates that a noninstantaneous polarization decay may appear in the presence of a 3-photon resonance. In turn, pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect.

Development of a nonlinear nanoprobe for interferometric autocorrelation based characterization of ultrashort optical pulses

Near-field scanning can achieve nanoscale resolution while ultrashort pulse diagnostic tools can characterize femtosecond pulses. Yet currently it is still challenging to nonperturbatively characterize the near field of an ultrashort optical pulse with nanofemtoscale spatiotemporal resolution. To address this challenge, we propose to develop a nonlinear nanoprobe composed of a silica fiber taper, a nanowire, and nonlinear fluorescent spheres. Using such a nanoprobe, we also report proof-of-principle characterization of femtosecond optical pulse through interferometric autocorrelation measurement.

Linear Characterization of Optical Pulses With Durations Ranging From the Picosecond to the Nanosecond Regime Using Ultrafast Photonic Differentiation

In this paper, we extend the recently introduced linear technique for temporal phase reconstruction using optical ultrafast differentiation (PROUD) to achieve full characterization of ultrashort optical pulses with durations down to the picosecond regime using a well-characterized temporal stretcher (e.g., dispersive optical fiber). The proposed method is experimentally demonstrated by precisely characterizing the amplitude and phase temporal profiles of microwatt-power picosecond pulses ranging from 4 to 20 ps with both continuous and discrete temporal phase variations. Using this simple mechanism, the same PROUD setup can be used to characterize optical pulses with durations ranging from the picosecond to the nanosecond regime. We provide a comprehensive mathematical analysis of this general PROUD technique: we evaluate in detail the influence of the key specifications (e.g., different sources of noise) of the used components and instruments, namely, optical differentiator, linear temporal stretcher, and time-domain intensity test equipment, on the performance of the PROUD measurement system, particularly in terms of phase sensitivity in the optical pulse characterization.

Spatiotemporal Amplitude and Phase Retrieval of Bessel-X pulses using a Hartmann-Shack Sensor

We propose a new experimental technique, which allows for a complete characterization of ultrashort optical pulses both in space and in time. Combining the well-known Frequency-Resolved-Optical-Gating technique for the retrieval of the temporal profile of the pulse with a measurement of the near-field made with an Hartmann-Shack sensor, we are able to retrieve the spatiotemporal amplitude and phase profile of a Bessel-X pulse. By following the pulse evolution along the propagation direction we highlight the superluminal propagation of the pulse peak.

Characterization of ultrashort optical pulses with third-harmonic-generation based triple autocorrelation

We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.

Precision and consistency criteria in spectral phase interferometry for direct electric-field reconstruction

We define and study precision and consistency criteria for spectral phase interferometry for direct electric-field reconstruction (SPIDER), an interferometric technique for the characterization of ultrashort optical pulses. Precision quantifies the similarity of different estimates of the electric field reconstructed from a single experimental data set. Consistency is a measure of the match between the reconstructed field and the data. These powerful experimental criteria allow one to monitor the fidelity of the reconstruction of the electric field from the experimental data by tracking systematic errors and random noise. Because of such imperfections, such criteria are necessary even for pulse characterization methods based on a direct algebraic inversion. In the case of SPIDER, the redundancy of data in each interferogram and the principle of shearing interferometry allow simple calculation of the precision and consistency measures.

Measurement of the root-mean-square width and the root-mean-square chirp in ultrafast optics

Based on two theorems, the importance of the root-mean-square (rms) width for the characterization of ultrashort optical pulses is demonstrated. First, it is shown that one can directly determine the rms width from the autocorrelation without making any assumptions about the specific form of the pulse envelope. Second, it is shown that a bandwidth-limited (unchirped) wave packet has the smallest possible rms time–bandwidth product. This reveals a natural definition for a rms chirp that is easily accessible to experimental measurement and that presents a useful measure for the quality of pulse compression techniques.

Spectrotemporal technique for enhancement of resolution in studies of ultrashort pulses

A new technique is proposed for the characterization of ultrashort optical pulses. The technique includes a simple mathematical treatment of the time-resolved spectrum of the signal that is obtained using an image converter camera. The theoretical description of the technique and several numerical examples modeling the ultrashort pulse reconstruction are presented. The dependence of the reconstruction result on the noise level is evaluated. It is shown that the temporal resolution of the technique can be up to two orders of magnitude higher than that for the used electro-optic device.

Linear filter analysis of methods for ultrashort-pulse-shape measurements

We analyze the properties required of a linear interferometer composed of time-stationary and time-nonstationary filters and a square-law, integrating detector in order that it may be used for the complete characterization of ultrashort optical pulses. Some general conditions for measurements are formulated for various schemes, and, in particular, time-nonstationary filtering is shown always to be necessary. The roles of both phase-only time nonstationarity and amplitude time gating are investigated in the context of known measurement schemes, and the known nonlinear schemes are shown to be members of a larger class of methods that use amplitude time-nonstationary filters.

A new triple correlator design for the measurement of ultrashort laser pulses

A measurement device, a triple correlator, is proposed for the characterization of ultrashort optical pulses. The proposed triple correlator uses two consecutive nonlinear optical interactions, a sum frequency generation followed by a difference frequency generation, to produce a triple correlation output a the same optical frequencies as the input pulse. Phase matching for the triple correlator is greatly simplified by using the given design. The operation of the triple correlator is described and examples of expected output signals are given. The reconstructed optical pulse is quite insensitive to noise, as shown by computer simulations.