Improved terahertz two-color plasma sources pumped by high intensity laser beam

We investigate the intensity dependent spatial drift of two-color plasma based terahertz (THz) sources. A simple scheme that uses an off-axis parabolic mirror is presented to overcome this shifting. In addition, the THz energy and electric field measurements are related via the real time images of the THz spot size

Printing accuracy tracking with 2D optical microscopy and super-resolution metamaterial-assisted 1D terahertz spectroscopy

Abstract Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices, ranging from displays to active wear. It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process. However, this process is still not being subjected to a quality control method that is both non-invasive and in situ. To address this issue, we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz (THz) waves. The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression, or expansion factor, for a pattern printed on a flexible plastic substrate. The pattern, which is carefully selected, has Babinet’s electromagnetic transmission properties in the THz frequency range. To validate our choice, we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy. Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission. Notably, under specific conditions, one-dimensional (1D) THz information from a resonant pattern can be more accurate than two-dimensional (2D) microscopy information. This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production

Contactless In Situ Electrical Characterization Method of Printed Electronic Devices with Terahertz Spectroscopy

Printed electronic devices are attracting significant interest due to their versatility and low cost; however, quality control during manufacturing is a significant challenge, preventing the widespread adoption of this promising technology. We show that terahertz (THz) radiation can be used for the in situ inspection of printed electronic devices, as confirmed through a comparison with conventional electrical conductivity methods. Our in situ method consists of printing a simple test pattern exhibiting a distinct signature in the THz range that enables the precise characterization of the static electrical conductivities of the printed ink. We demonstrate that contactless dual-wavelength THz spectroscopy analysis, which requires only a single THz measurement, is more precise and repeatable than the conventional four-point probe conductivity measurement method. Our results open the door to a simple strategy for performing contactless quality control in real time of printed electronic devices at any stage of its production line

Room-Temperature and Selective Triggering of Supramolecular DNA Assembly/Disassembly by Nonionizing Radiation

International audienceRecent observations have suggested that nonionizing radiation in the microwave and terahertz (THz; far-infrared) regimes could have an effect on double-stranded DNA (dsDNA). These observations are of significance owing to the omnipresence of microwave emitters in our daily lives (e.g., food preparation, telecommunication, and wireless Internet) and the increasing prevalence of THz emitters for imaging (e.g., concealed weapon detection in airports, skin cancer screenings) and communication technologies. By examining multiple DNA nanostructures as well as two plasmid DNAs, microwaves were shown to promote the repair and assembly of DNA nanostructures and single-stranded regions of plasmid DNA, while intense THz pulses had the opposite effect (in particular, for short dsDNA). Both effects occurred at room temperature within minutes, showed a DNA length dependence, and did not affect the chemical integrity of the DNA. Intriguingly, the function of six proteins (enzymes and antibodies) was not affected by exposure to either form of radiation under the conditions examined. This particular detail was exploited to assemble a fully functional hybrid DNA-protein nanostructure in a bottom-up manner. This study therefore provides entirely new perspectives for the effects, on the molecular level, of nonionizing radiation on biomolecules. Moreover, the proposed structure-activity relationships could be exploited in the field of DNA nanotechnology, which paves the way for designing a new range of functional DNA nanomaterials that are currently inaccessible to state-of-the-art assembly protocols

High-intensity single-cycle THz source driven by a high-power fiber laser

International audienceHigh-intensity THz sources driven by ultrafast lasers are attractive for a wide range of applications such as time domain spectroscopy, molecular dynamics and THz-matter interactions in the nonlinear regime, to cite a few. Recent advances in the development of high-average power ytterbium lasers have enabled the development of high-repetition rate THz-sources using different generation schemes. The best performances have been reached in a two-colour plasma generation setup driven by a state-of-the-art Yb fibre laser system and producing 640 mW THz average power at 500 kHz repetition rate [1]. However, this facility is complex and expensive as it implies few-cycle pump pulses with high average powers. The second promising approach for high power THz generation is based on optical rectification in lithium niobate (LiNbO3) nonlinear crystals [2]. In particular, it has been demonstrated that optimization of the pump pulse duration to few hundred femtoseconds in a tilted-pulse front pumping scheme in lithium niobate using a step-stair echelon is a relevant approach for optical-to-THz conversion efficiency scaling [3,4]. Single-cycle THz pulses with 74 mW average power and 400 kV/cm peak intensity have then been produced using a 10W-class pump laser delivering 240 fs pulses at 25 kHz repetition rate [4]

High-Intensity THz Pulses Generation In Lithium Niobate Using A Reflective Echelon Scheme

International audienceThis work analyzes how the beam size and the repetition rate affect the THz generation efficiency in lithium niobate (LiNbO3) using the RES (Refractive Echelon Mirror) configuration. Our THz source is driven by an ytterbium-fibre-based chirped-pulse amplifier system. The system delivers ultrashort pulses of 300fs duration with a maximum energy of 240 μJ at 330 kHz. It is found that by optimizing the pump beam size on the LiNbO 3 crystal, we measure a THz power of 114 mW for 44.5 W pump power at 205 MHz repetition rate, corresponding to a total optical-to-THz efficiency of 0.25%

High-intensity single-cycle THz source driven by a high-power fiber laser

International audienceHigh-intensity THz sources driven by ultrafast lasers are attractive for a wide range of applications such as time domain spectroscopy, molecular dynamics and THz-matter interactions in the nonlinear regime, to cite a few. Recent advances in the development of high-average power ytterbium lasers have enabled the development of high-repetition rate THz-sources using different generation schemes. The best performances have been reached in a two-colour plasma generation setup driven by a state-of-the-art Yb fibre laser system and producing 640 mW THz average power at 500 kHz repetition rate [1]. However, this facility is complex and expensive as it implies few-cycle pump pulses with high average powers. The second promising approach for high power THz generation is based on optical rectification in lithium niobate (LiNbO3) nonlinear crystals [2]. In particular, it has been demonstrated that optimization of the pump pulse duration to few hundred femtoseconds in a tilted-pulse front pumping scheme in lithium niobate using a step-stair echelon is a relevant approach for optical-to-THz conversion efficiency scaling [3,4]. Single-cycle THz pulses with 74 mW average power and 400 kV/cm peak intensity have then been produced using a 10W-class pump laser delivering 240 fs pulses at 25 kHz repetition rate [4]

The measurement of students performance. The use of an extended Rasch model for the analysis of predictors of high educational performance

Characteristics of the higher educational programs (e.g. non systematic variability of course’s difficulty among and within programs and over times) make observed  data (e.g. number of credits acquired) poorly informative indexes of the students’ performance. As alternative, it is proposed an extended version of Rasch model (the Three Facets Model, TFM). TFM conceptualizes student’s performance the expression of a three-component latent variable to be esteemed.  In so doing, TFM is able to take into account  the non-systematic sources of variation characterizing higher educatonal settings, thus avoiding limits entailed in the use of indexes based on observed data. An exemplificative longitudinal  case study has been performed, aimed at detecting predictors of performance within an undergraduate program of psychology of an Italian university. Two regression models have been compared: one using a traditional index of performance based on observed data versus one using the TFM estimation