Two-laser Scheme Research Articles

Spectroscopic study of the F[formula omitted] outer well state in H2, HD and D2

Two-photon UV-photolysis of hydrogen sulfide molecules is applied to produce hydrogen molecules in highly excited vibrational levels in the X1Σg+ electronic ground state, up to the dissociation energy and into the quasibound region. Photolysis precursors H2S, HDS and D2S are used to produce vibrationally hot H2, HD and D2. The wave function density at large internuclear separation is excited via two-photon transitions in the F1Σg+ - X1Σg+ system to probe ro-vibrational levels in the first F1Σg+ outer well state of gerade symmetry. Combining with accurate knowledge of the X1Σg+ (v,J) levels from advanced ab initio calculations, energies of rovibrational levels in the F1Σg+ state are determined. For the H2 isotopologue a three-laser scheme is employed yielding level energies at accuracies of 4×10−3 cm−1 for F(v=0,J) up to J=21 and for some low J values of F(v=1). A two-laser scheme was applied to determine level energies in H2 for F(v=0−4) levels as well as for various F levels in HD and D2, also up to large rotational quantum numbers. The latter measurements in the two-laser scheme are performed at lower resolution and the accuracy is strongly limited to 0.5 cm−1 by ac-Stark effects. For H2 a new quasibound resonance X1Σg+ (v=6, J=23) is detected through the Q(23) and O(23) transitions in the F0-X6 band. Also a quasi-bound resonance in D2 is assigned, for the first time in this species: X1Σg+ (v=17 , J=15). The experimental results on F(v,J) level energies are compared with previously reported theoretical results from multi-channel quantum-defect calculations as well as with results from newly performed non-adiabatic quantum calculations.

Assessing Security of Chaos Communications Against Eavesdropping by Pump Detection

In this paper, we numerically evaluate a method that could be tried by an eavesdropper to force the standard two-laser scheme of chaos private transmission. This method is based on the detection of the voltage arising across a semiconductor laser junction and uses two lasers: one is synchronized to the transmitter (thus, reproducing chaos and rejecting the message), the other is selected and trimmed to copy the transmitter (i.e., reproducing both chaos and the message). The message is then obtained by difference and chaos cancellation. By assuming the usual parameter mismatch, which is expected to be achieved by an eavesdropper, it is shown that the method does not represent a substantial threat to the privacy of the transmission system. The scheme is also briefly considered as an alternative, but less performant, scheme for chaotic cryptography. The simulations are based on the Lang-Kobayashi model.

Privacy in Two-Laser and Three-Laser Chaos Communications

In this paper, we compare the performances of the well-known two-laser and three-laser chaos communications schemes, in terms of privacy. It is found by numerical analysis that in optimized conditions both methods are well suited for private transmission. However, while the three-laser scheme gives its optimum performance with the twin laser pair, the two-laser scheme reaches its best performance using two slightly different lasers (the optimum pair). This results in an easier device selection and in a slightly higher privacy level of the three-laser scheme. Using a twin pair with the two-laser scheme still offers a good level of privacy in most cases; however, in principle the eavesdropper has a chance to extract the message, by selecting a suitable laser.

Characterization of an optical frequency-shift-keying transmitter based on carrier-suppressed phase modulation

We experimentally characterize an optical frequency-shift-keying transmitter based on optical carrier-suppressed phase modulation. Only one laser source is needed to generate an optical FSK signal. The demonstration of 10-Gb/s FSK signal generation and 50-km transmission verified the improved performance of the proposed transmitter, compared with the previous two-laser schemes. To further reduce the complexity of the transmitter, the phase modulator is omitted and a single MZM modulator is used for both optical carrier-suppression (OCS) and phase modulation. This simplified structure is verified by simulation, implying the feasibility that a FSK transmitter can be constructed with only one laser source and one modulator.

Multi-User Private Transmission With Chaotic Lasers

In this paper, we propose a scheme for private data transmission using chaotic lasers, which is derived from the well-known public key cryptography. With this new approach, it is possible to exchange data between any couple of subscribers in a network, while schemes based on chaotic lasers are usually restricted to transmission between two specific users, sharing a twin laser pair. This is possible by introducing a provider, who is responsible of the network security. For each subscriber a couple of twin chaotic lasers is required, one being held by the provider and the other by the subscriber himself. The basic two-laser scheme of chaotic transmission is then used for secure data exchange, both between two subscribers and between a subscriber and the provider. Several arrangements can be considered, based on this architecture, including the use of an electro-optical repeater, which is studied in detail in this paper. More advanced solutions can be also implemented, e.g., using a three-laser scheme. The Lang-Kobayashi model is used for simulations. Experiments are performed using InP-integrated modules.

The Internal Energy of Neutral Ethylene Glycol Molecules Created in the Laser Vaporization of Aerosol Particles

Although laser vaporization of aerosol particles plays an important role in aerosol mass spectrometry, relatively little is known about disposal of excess energy in the degrees of freedom of the gas-phase species. A two-laser scheme, in which an infrared laser vaporizes aerosol particles prior to ionization of the vapor plume by a vacuum-ultraviolet laser, permits the determination of the internal energy of the neutral molecules created in laser vaporization. In this work, the fragmentation patterns of vacuum UV (VUV) photoionization mass spectra of ethylene glycol, in conjunction with photoelectron-photoion coincidence (PEPICO) measurements, determines the internal energy of gas-phase molecules created in the CO2 laser vaporization of neat ethylene glycol particles and ethanol particles mixed with trace ethylene glycol. The internal energy ranges from 1300 to 10250 cm-1 for CO2 laser powers between 25 and 112 mJ/pulse. For neat ethylene glycol, the rate with which the internal and kinetic energy grows wi...

Collisionally enhanced isotopic selectivity in multiphoton dissociation of vibrationally excited CF3H

We have studied infrared multiphoton dissociation of CF3H pre-excited to the second C–H stretch overtone under collisional conditions in view of developing a laser isotope separation scheme for carbon-13. This single stage process results in a C2F4 product that has been enriched in carbon-13 to a level as high as 99% starting from a naturally abundant sample, implying an isotopic selectivity in excess of 9000. While most of the selectivity is gained at the pre-excitation step, it can be increased up to a factor of 16 by collisions of the pre-excited CF313H species with room temperature molecules. This collision-induced enhancement in selectivity becomes evident from the dependence of the isotopic enrichment on both the total sample pressure and the time-delay between the two lasers, and we propose two different models that can account for this behavior. Finally, we evaluate the practical relevance of this two-laser scheme for isotope separation.