Systematic comparison of commercial devices for temporal characterization of few-cycle laser pulses in the 500-1000†nm spectral range.

We compare multiple temporal pulse characterization techniques in three different pulse duration regimes from 15 fs to sub-5 fs, as there are no available standards yet for measuring such ultrashort pulses. To accomplish this, a versatile post-compression platform was developed, where the 100 fs near infrared pulses were post-compressed to the sub-two-cycle regime in a hybrid, three-stage configuration. After each stage, the duration of the compressed pulse was measured with the d-scan, TIPTOE and SRSI techniques and the retrieved temporal intensity profiles, spectrum and spectral phases were compared. Spectral homogeneity was also measured with an imaging spectrometer to understand the input coupling conditions of the temporal measurements. Our findings suggest that the different devices give similar results in terms of temporal intensity profile, however they are extremely sensitive to alignment and to beam quality, especially in the case of the shortest pulses. We address specific steps of measurement procedures, which paves the way towards the standardization of pulse characterization in the near future.

A comparative study of femtosecond pulsed laser ablation of meloxicam in distilled water and in air.

The increasing prevalence of water insoluble or poorly soluble drugs calls for the development of new formulation methods. Common approaches include the reduction of particle size and degree of crystallinity. Pulsed laser ablation is a clean technique for producing sub-micrometre sized drug particles and has the potential to induce amorphization. We studied the effect of femtosecond pulsed laser ablation (ELI ALPS THz pump laser system: λc = 781 nm, τ = 135 fs) on meloxicam in distilled water and in air. The ablated particles were characterized chemically, morphologically and in terms of crystallinity. We demonstrated that femtosecond laser ablation can induce partial amorphization of the particles in addition to a reduction in particle size. In the case of femtosecond pulsed laser ablation in air, the formation of pure meloxicam spheres showed that this technique can produce amorphous meloxicam without the use of excipients, which is a unique result. We also aimed to describe the ablation processes in both investigated media.

Single thin-plate compression of multi-TW laser pulses to 3.9 fs.

Post-compression of 12-fs laser pulses with multi-TW peak power from an optical parametric chirped pulse amplification (OPCPA) system was performed by using a single thin fused silica plate in a vacuum. By optimizing the input pulses in both spatial and temporal domains, after compression with customized chirped mirrors, we achieved pulses as short as 3.87 fs, in combination with 12-mJ energy. The spatio-spectral quality of the post-compressed pulses was thoroughly analyzed. The generated 1.4-cycle pulses pave the way for next generation attosecond and particle acceleration experiments.

The petawatt laser of ELI ALPS: reaching the 700 TW level at 10†Hz repetition rate.

Performance of the novel high repetition rate HF-PW laser system of ELI ALPS is presented in its first operation phase at 400 TW and 700 TW levels. Long-term operation was tested at 2.5 and 10 Hz repetition rates, where an exceptional 0.66% and 1.08% shot-to-shot energy stability was demonstrated, respectively. Thorough spatio-spectral and temporal measurements confirmed high quality output pulses with a Strehl ratio of >0.9 after compression at both repetition rates. Amplified pulses with an unprecedentedly high 240 W average power were reached for the first time from a PW-class amplifier chain by using novel pseudo-active mirror disk amplification-based pump lasers.

Sub-7 fs radially-polarized pulses by post-compression in thin fused silica plates.

We experimentally demonstrate the post-compression of radially polarized 25 fs pulses at 800 nm central wavelength in a multiple thin plate arrangement for the first time, to the best of our knowledge. Sub-7 fs pulses with 90 µJ energy were obtained after dispersion compensation, corresponding to a compression factor of more than 3.5. Preservation of radial polarization state was confirmed by polarized intensity distribution measurements. Linear projections of the radially polarized pulses were also fully characterized in the temporal domain.

Age-Related Absorption of the Human Lens in the Near-Ultraviolet Range.

The purpose of the present study was to determine the age dependence of the ultraviolet (UV) absorption of the different parts of the human crystalline lens. Cryostat sections of human cadaveric lenses (60 µm) were cut. The UV absorbance of nine samples, derived from different parts of the lens, was determined using a Shimadzu scanning spectrophotometer. The absorbance of the anterior and posterior lens capsules was measured separately. The absorption coefficients were calculated from the measured absorbance and values taken at 280 as well as at 360 nm were compared statistically. ANCOVA analysis of the values taken at 280 and at 360 nm wavelengths shows that correlation between the absorption coefficients and age can be found only in the case of the posterior layers. These results suggest a differential age-dependent increase of the UV absorption of the posterior layers compared to the anterior ones and can be related to the differential protein expression in the anterior and posterior parts. Posterior crystalline lens capsules have higher absorption coefficients than the anterior ones regardless of age.

The molecular background of the differential UV absorbance of the human lens in the 240-400 nm range.

The ultraviolet (UV) absorption of various sections of the human lens was studied and compared with protein expression paralleling differential UV absorbance in anterior and posterior lenticular tissue. The UV absorbance of serial lens cryostat sections (60 µm) and that of lens capsules was determined using a Shimadzu scanning spectrophotometer, and the absorption coefficients were calculated. Two-dimensional gel electrophoresis was performed using two pooled lenticular protein extracts (anterior and posterior sections). Protein spots were quantified and significantly different spots were identified by mass spectrometry following in-gel digestion with trypsin and chymotrypsin. The UV-C and UV-B absorption of the human lens increased toward the posterior parts of the lens. The anterior and posterior lens capsules also effectively absorbed UV radiation. Levels of molecular chaperone proteins Beta-crystallin B2 (UniProtKB ID:P43320), A3 (UniProtKB ID:P05813) and of glyceraldehyde 3-phosphate dehydrogenase (UniProtKB ID:P04406) were significantly higher in the anterior part of the lens, whereas lens proteins Beta-crystallin B1 (UniProtKB ID:P53674) and Alpha-crystallin A chain (UniProtKB ID:P02489) were higher in the posterior sections. These results provide evidence that differential UV absorption in the anterior and posterior lens is accompanied by differential protein expression.