Few-cycle pulse retrieval using amplitude swing technique.

Ultrashort pulses have garnered significant attention across various scientific disciplines and applications. In this paper, we demonstrate that the recently introduced amplitude swing technique is a robust method for characterizing pulses in the few-cycle temporal domain by analyzing compressed and chirped pulses from a Ti:Sapphire laser oscillator. The duration of the measured pulse for the case of best compression was 5.98 fs (Fourier limit 5.50 fs) corresponding to 2.2 cycles, while the chirped pulses were up to 15 times temporally stretched. The results obtained have been validated using the d-scan technique, showing excellent agreement in all situations. Therefore, the capability of the amplitude swing technique to measure ultra-broadband pulses in the few-cycle regime is demonstrated, as well as very far from optimum compression, while only being limited by the transparency and birefringence of its elements.

Towards the Standardization of Photothermal Measurements of Iron Oxide Nanoparticles in Two Biological Windows.

A systematic study on laser-induced heating carried out in two biological windows (800 nm and 1053 nm) for Fe3O4 nanoparticles in water suspension showed evidence of the strong dependence of the specific absorption rate (SAR) on extrinsic parameters such as the vessel volume or laser spot size. The results show that a minimum of 100 µL must be used in order to obtain vessel-size-independent SARs. In addition, at a constant intensity but different laser powers and spot size ratios, the SARs can differ by a three-fold factor, showing that the laser power and irradiated area strongly affect the heating curves for both wavelengths. The infrared molecular absorber IRA 980B was characterized under the same experimental conditions, and the results confirm the universality of the SARs' dependence on these extrinsic parameters. Based on these results, we propose using solutions of IRA 980B as a standard probe for SAR measurements and employing the ratio SARiron oxide/SARIRA 980B to compare different measurements performed in different laboratories. This measurement standardization allows us to extract more accurate information about the heating performance of different nanoparticles.

Nano-dispersion-scan: measurement of sub-7-fs laser pulses using second-harmonic nanoparticles.

We demonstrate the measurement and retrieval of sub-7-fs laser pulses from a broadband Ti:Sa oscillator using ensembles of commercially available second-harmonic nanoparticles (NPs) and dispersion scan (d-scan). Scattering adds an incoherent component to the d-scan trace, and our retrieval procedure allows for correctly weighting the coherent and incoherent contributions to the trace. Comparison with a thin crystal [beta barium borate (BBO)] gave consistent pulse durations (6.56±0.03 fs for BBO and 6.5±0.1 fs for the NPs). These results pave the way to using ensembles of NPs for the measurement of ultrashort light pulses with ultra-broadband spectra at room temperature with standard spectrometers, in any spectral range.

Simultaneous measurement of two ultrashort near-ultraviolet pulses produced by a multiplate continuum using dual self-diffraction dispersion-scan.

We present a new method based on self-diffraction dispersion-scan (SD d-scan) that enables the simultaneous measurement of two distinct ultrashort laser pulses in a region where they spatially and temporally overlap. This situation can arise when sampling and focusing two different spatial portions of a single inhomogeneous beam onto a medium. We demonstrate this new dual SD d-scan method by simultaneously characterizing two intense broadband ultraviolet pulses at 400 nm, with durations in the 10 fs range, originating from two different spatial portions of a beam produced by a multiplate continuum (MPC).

Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime.

We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations, and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.

Optical rotation of a uniformly, linearly polarized Bessel-like beam in free space.

We report on the observation of a light beam in air whose polarization state is uniform and linear at the transverse region where the intensity is high and rotates uniformly with propagation distance. The beam is obtained by interference of two circularly polarized Bessel beams of opposite helicities and very similar, but not equal, cone angles. The measured rotation rate is in agreement with that expected from theory.

Optical transmission properties of Pentelic and Paros marble.

Ancient Greek and Roman sources report that the statue of Zeus in Olympia had a head, and in particular eyes, similar to the description of Zeus by Homer, so we think that the statue was visible to the human eye. Since the temple was 12 m high, and had a small door and no windows, the illumination of the statue by conventional media is questionable. The aim of this paper is to characterize the optical transmission of Paros and Pentelic marble to demonstrate that it was possible to have the Zeus temple illuminated through the roof marble tiles. Spectral absolute transmittance measurements were taken in samples with different thicknesses using a calibrated spectrophotometer, as well as total transmittance measurements using a luxmeter. The results show that both types of marble transmit light and that Pentelic marble has a higher transmittance in the visible range than Paros marble in some cases and hence could have been one reason, among others, to change the type of marble in the roof in antiquity.

Characterization of broadband few-cycle laser pulses with the d-scan technique.

We present an analysis and demonstration of few-cycle ultrashort laser pulse characterization using second-harmonic dispersion scans and numerical phase retrieval algorithms. The sensitivity and robustness of this technique with respect to noise, measurement bandwidth and complexity of the measured pulses is discussed through numerical examples and experimental results. Using this technique, we successfully demonstrate the characterization of few-cycle pulses with complex and structured spectra generated from a broadband ultrafast laser oscillator and a high-energy hollow fiber compressor.

Generation of high-energy vacuum UV femtosecond pulses by multiple-beam cascaded four-wave mixing in a transparent solid.

The generation of ultrashort vacuum UV (VUV) pulses by nondegenerate cascaded four-wave mixing of femtosecond pulses in a thin slide of a large band-gap transparent solid is numerically demonstrated. Using a novel noncollinear multiple-beam configuration, cascaded four-wave mixing of amplified 30 fs Ti:sapphire laser pulses at 800 nm, and their second harmonic in lithium fluoride results in the generation of VUV radiation down to 134 nm with energies in the µJ range and durations comparable to those of the pump pulses. The proposed geometry is advantageous in large dispersion scenarios, namely for generating radiation close to absorption bands. Hence these results set this technique as a promising way to efficiently generate ultrashort VUV radiation in solids for several applications in science and technology.

Octave-spanning spectra and pulse synthesis by nondegenerate cascaded four-wave mixing.

We present a theoretical model and 2D numerical simulation of cascaded four-wave mixing of femtosecond pulses in bulk chi((3)) media, evidencing the importance of 2D interaction geometries in the efficient generation of frequency-converted pulses. Octave-spanning spectra and pulse synthesis down to the sub-two-cycle regime is demonstrated without the need for complex amplitude or phase control, in agreement with experimental measurements.