THz pulse generation and single shot detection in a single ZnTe Crystal IRMMW- THz 2022

Single-cycle THz signal of few picoseconds duration, have been simultaneous generated via optical rectification and detected by electro-optic effect in the same ZnTe crystal. An unbalanced seemingly single shot detection scheme was performed to characterize the signal. The added simplicity of this scheme aided the independent analysis of the horizontal and vertical polarization arm of the chirped probe beam to explain the associated nonlinearities in the detected THz signal

THz Spectroscopic Characterization of Oil Shales, IRMMW-THz 2022

Grey to dark-grey samples reported to be oil shales have been analyzed under the THz reflection and transmission spectroscopy. In order to examine the organic and mineral stratification of the oil shales, samples at varying height above the ground level were excavated from stream banks and hilly terrains. The constituent of these aquatic and terrestrial-based oil shales were further correlated to investigate any correspondence or dissimilarities in their composition by examining the refractive index, absorption and optical path length maps of the samples

Near infrared few-cycle pulses for high harmonic generation

We report on the development of tunable few-cycle pulses with central wavelengths from 1.6 um to 2 um. Theses pulses were used as a proof of principle for high harmonic generation in atomic and molecular targets. In order to generate such pulses we produced a filament in a 4 bar krypton cell. Spectral broadening by a factor of 2 to 3 of a 40 fs near infrared input pulse was achieved. The spectrally broadened output pulses were then compressed by fused silica plates down to the few-cycle regime close to the Fourier limit. The auto-correlation of these pulses revealed durations of about 3 cycles for all investigated central wavelengths. Pulses with a central wavelength of 1.7 um and up to 430 uJ energy per pulse were employed to generate high order harmonics in Xe, Ar and N2. Moving to near infrared few-cycle pulses opens the possibility to operate deeply in the non-perturbative regime with a Keldysh parameter smaller than 1. Hence, this source is suitable for the study of the non-adiabatic tunneling regime in most generating systems used for high order harmonic generation and attoscience.Comment: 12 pages, 4 figure

Factorization of Numbers with the temporal Talbot effect: Optical implementation by a sequence of shaped ultrashort pulses

We report on the successful operation of an analogue computer designed to factor numbers. Our device relies solely on the interference of classical light and brings together the field of ultrashort laser pulses with number theory. Indeed, the frequency component of the electric field corresponding to a sequence of appropriately shaped femtosecond pulses is determined by a Gauss sum which allows us to find the factors of a number

Tunable ultra-fast infrared generation in a gas-filled hollow core capillary by a four-wave mixing process: erratum

This erratum reports corrections to the temporal axes in Figs. 12 and 13 of J. Opt. Soc. Am. B 39, 662 (2022)JOBPDE0740-322410.1364/JOSAB.444574

Etude et détection de polluants atmosphériques dans le domaine THz

Bourse financée par l'Agence de l'Environnement et de la Maîtrise de l'Energie (ADEME) et par la région Nord Pas de CalaisTerahertz or Far Infrared radiation extends from 100 GHz to 10 THz. This frequency range was consideredto be a "spectral gap" due to the considerable technological difficulties in producing a tunable source with reasonable emission powers. Two THz spectrometers have been developed and exploited. The first uses THz pulses and is based on Time Domain Spectroscopy. It is capable of providing a spectrum which extends from few GHz to 1.2 THz within few minutes and has a spectral resolution in the order of few GHz. The second instrument generates continous wave THz by photomixing and can reach up to 3 THz with a spectral purity of 5 MHz. After presenting the analytical descriptions and experimentally characterizations of the instruments, we focus on the monitoring and detection of atmospheric pollutants, illustrated by the analysisof cigarette smoke which represents an example of hostile medium. This study reveals the presences of the hydrogen cyanide (HCN), carbon monoxide (CO) and formaldehyde (H2CO) and allows their concentrations to be measured. This analysis is verified by comparison with standard chemical methods. The fundamentalpart of this work is the study of the gas response after a subpicosecond excitation : the free induction decay of carbonyl sulphide that consists of a series of uniformly spaced subpicosecond commensurate transients. A theoretical model is used to understand the classical phenomena. The quasi exponential decrease of the reemitted pulses is linked to the spectral width of the rotational transition while the anharmonicity influences the pulse shape due to the propagation, dispersion and centrifugal distortion.Le rayonnement Térahertz, ou infrarouge lointain, couvre la bande spectrale de 100 GHz à 10 THz. Cettepartie du spectre électromagnétique est encore peu exploitée et a souvent été qualifiée de "gap spectral" en raison des nombreuses difficultés à émettre ce rayonnement à des puissances exploitables. Deux spectromètres dans la gamme THz ont été développés et exploités. Le premier, basé sur la spectroscopie résolue en temps, utilise des impulsions THz et permet d'obtenir un spectre de quelques GHz à 1,2 THz en quelques minutes avec une résolution de l'ordre du GHz. Le second est un spectromètre continu basé sur le photomélange avecune extension spectrale de 3 THz et une pureté spectrale de 5 MHz. Après des descriptions analytiques et des caractérisations expérimentales des dispositifs, nous nous sommes intéressés à l'étude, à la surveillance et à la détection des polluants atmosphériques dans l'infrarouge lointain en exploitant les deux instruments pour l'analyse de la fumée de cigarette qui représente un excellent exemple de milieu hostile. Cette étude révèle la présence d'acide cyanhydrique (HCN), de monoxyde de carbone (CO), et de formaldéhyde (H2CO). Les concentrations de ces espèces ont été déduites des formes de raies puis confirmées et comparées à desmesures par méthodes chimiques. La partie fondamentale de ce travail est d'étudier la réponse d'un gaz suite à une excitation subpicoseconde : les signaux de précession libre dans le sulfure de carbonyle (OCS) qui consiste en une série d'impulsions transitoires. Un modèle théorique permet d'interpréter classiquement ces impulsions réémises. La décroissance quasi exponentielle des impulsions transitoires est liée à la largeur de raie des transitions de rotation et les informations d'anharmonicité sont observées sur les formes de cesimpulsions qui sont principalement dues à la propagation, à la dispersion et à la distorsion centrifuge

Modulation instability in a dispersion oscillating fibre pumped by a broad band pulse

International audienceWe numerically investigate the modulation instability generated in a dispersion oscillating fibre pumped by a chirped pulse with a broad bandwidth. We highlight that the side bands are wide, not symmetric in frequency about the pump and several instantaneous side bands can spectrally overlap with each other in one side, while they are well located in the other side. We also show that the spectral distribution can be intuitively explained with an analogy in which the fibre is pumped by a tuneable continuous wave

Fiber Optical Parametric Amplifier for Ultra-Short Pulses

International audienc

Near Infrared tunable source delivering ultra-short pulses based on an all normal dispersion fiber and a zero dispersion line

International audienceA tunable laser source (820-1200 nm) delivering ultra-short pulses in the range of 40-100 fs is investigated. It is based on the filtering of a continuum in the Fourier plane of a zero dispersion line without any phase compensator. The numerical simulations show the origin and the impact of the nonlinear chirp to guarantee ultra-short pulses