Deterministic chaos in laser with injected signal

Dynamic behaviour of an homogeneously broadened laser with injected signal is analyzed for a model in which the polarization is adiabatically eliminated. Detuning between the atomic resonant frequency, the cavity resonance and the frequency of the external signal is considered. We show that a transition to chaos via intermittency is possible for parameters appropriate for CO₂ lasers.     

Development of two-color laser system for high-resolution polarization spectroscopy measurements of atomic hydrogen

We have developed a high-spectral-resolution laser system for two-photon pump, polarization spectroscopy probe (TPP-PSP) measurements of atomic hydrogen in flames. In the TPP-PSP technique, a 243-nm laser beam excites the two-photon 1S-2S transition, and excited n=2 atoms are then detected by polarization spectroscopy of the n=2 to n=3 transition using 656-nm laser radiation. The single-frequency-mode 243 and 656-nm beams are produced using injection-seeded optical parametric generators coupled with pulsed dye amplifiers. The use of single-mode lasers allows accurate measurement of signal line shapes and intensities even with significant pulse-to-pulse fluctuations in pulse energies. Use of single-mode lasers and introduction of a scheme to select nearly constant laser energies enable repeatable extraction of important spectral features in atomic hydrogen transitions.     

Lasers as Light Sources for Analytical Atomic Spectrometry

Abstract

Lasers have advantages compared to conventional light sources, which include high power, a monochromatic emission profile, stability, and rapid tuning across an atomic line. These advantages have resulted in superior analytical figures of merit and methods of background correction compared to conventional light sources. The most widely used lasers for atomic spectrometry include dye laser systems, optical parametric oscillator systems, and diode lasers. Three principal techniques employ lasers as light sources. Laser‐excited atomic fluorescence spectrometry (LEAFS) involves the use of laser light to excite atoms that emit fluorescence and serves as the analytical signal. Laser‐enhanced ionization (LEI) involves laser excitation of atoms to an excited state energy level at which collisional ionization occurs at a higher rate than from the ground state. Diode laser atomic absorption spectrometry (DLAAS) employs a DL as a source to excite atoms in an atom cell from the ground state to an excited state. The analytical signal is involves the ratio of the incident and transmitted beams. Recent applications of these techniques are discussed, including practical applications, hyphenated techniques employing laser‐induced plasmas, and work to characterize fundamental spectroscopic parameters.     

Two-color polarization spectroscopy of rubidium

We report on two-color, two-photon polarization spectroscopy in a room-temperature rubidium vapor. We use two separate lasers, a strong pump at 780 nm to induce an anisotropy in the atomic polarization and a weak probe at 776 nm to interrogate this anisotropy. The lasers are resonant with the 5²S_1/2 → 5²P_3/2 and 5²P_3/2 → 5²D_5/2 transitions in rubidium, respectively. Finally, we have used our polarization spectroscopy signal as an error signal to lock the 776 nm laser. This modulation-free locking scheme allows us to detune the lock point of the second laser by adjusting the detuning of the laser used for the first transition.     

The coherence and spectra of a Bose condensate generated by an atomic laser

The first-order coherence dynamics of a Bose condensate generated by a cw atomic laser with evaporative cooling is analyzed. For the atomic-laser multimode model, the coherence functions and atomic field spectra are calculated by the master equation technique. Elastic collisions in the trapped atomic gas lead to significant broadening of the atomic laser line, a shift of its center, and a multi peak structure of the spectra. The oscillatory time dynamics of the atomic-field coherence function is studied. For the atomic laser, the free phase diffusion of the field typical of optical lasers, and characterized by monotonically decreasing mean field with a constant mean phase, is absent due to elastic collisions.     

Suppression of self-pulsing in Tm:YAlO3 lasers via current feedback

Self-pulsing of continuous-wave Tm:YAlO₃ lasers limits their use for a variety of important applications. We demonstrate for the first time that the pulsing can be suppressed via feedback to the pump diode laser, a technique that is suitable for both external resonator and monolithic lasers. We also show that the optical transfer function of the laser is that of an unstable relaxation oscillator.     

封闭和开放铯原子系统中的EIA效应

本文主要从实验上研究了封闭的简并二能级铯原子系统中的电磁感应吸收效应(EIA)。当泵浦和探测光作用于铯原子的6S1/2 F=4 à 6P3/2F′=5跃迁时，获得了EIA信号，同时研究了泵浦光的频率失谐和强度对EIA信号的影响。在6S1/2 F=4 à 6P3/2 F′=4和6S1/2 F=4 à 6P3/2 F′=3两个开放的二能级系统中也观察到了EIA信号。在6S1/2 F=3 à 6P3/2 F′=4的跃迁上增加一个repumping 激光,将使EIA信号增加。     

n2-measurements at 1.32 μm of some organic compounds usable as solvents in a saturable absorber for an atomic iodine laser

We have measured the nonlinear index of refraction n₂ of 12 organic compounds by means of a time integrating interferometric technique using pulses of about 0.7 ns duration from an atomic iodine laser working at 1.32 μm. The accuracy of the n₂-values obtained is ± 20%. The results may help to facilitate the proper choice of a solvent for a dye usable as a saturable absorber for an atomic iodine laser.     

Quantum memory in an orthogonal geometry of silenced echo retrieval

We experimentally realize a quantum-memory protocol based on retrieval of silenced echo (ROSE) in Tm³⁺:Y₃Al₅O₁₂ crystal in an orthogonal geometry of the signal and control light fields. The silenced echo signal revival efficiency of ~13% with 36 μs storage time is demonstrated. To achieve that we implemented a high-precision atomic coherence control via amplitude- and phase-modulated laser pulses. We also discuss capabilities of this configuration, ways to increase quantum efficiency and to combine it with a single-mode optical cavity.     

A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb

This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of ¹²⁷I₂. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.     

Manufacturing of Nd:Gd3Ga5O12 ridge waveguide lasers by pulsed laser deposition and ultrafast laser micromachining

Laser radiation is used both for the deposition of the laser active thin films and for the micro structuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of crystalline and amorphous neodymium doped Gd₃Ga₅O₁₂ are grown on single crystal yttrium aluminium garnet by pulsed laser deposition using excimer laser radiation.Manufacturing of the laser active waveguides by micro structuring is done using femtosecond laser ablation of the deposited films. The structural and optical properties of the films and the morphology of the structured waveguides are determined in view of the design and the fabrication of compact and efficient diode pumped waveguide lasers. The resulting waveguides are polished, provided with resonator mirrors, pumped using diode lasers and the waveguide lasers are characterized. The spectroscopic properties of the amorphous waveguide are investigated and an infrared waveguide laser is demonstrated. To our knowledge, there have been no reports by other groups of the successful operation of a structured waveguide laser fabricated by this technique or of a waveguide laser made from amorphous neodymium doped Gd₃Ga₅O₁₂.     

双通道原子相干性转移效率与拉曼单光子失谐的关系研究

研究了原子相干性在双通道间的转移效率与拉曼单光子失谐的关系。在冷原子四能级Tripod型系统中,首先利用EIT动力学过程将光信号存储在原子的一个记忆通道上。然后通过拉曼双光子过程,我们进行了原子记忆在两个通道间相干转移的研究,结果表明,在一定的拉曼光强下,原子相干性在双通道间的转移效率随着拉曼单光子失谐发生变化,最大的转移效率可达到94%。     

Solid-state laser system for laser cooling of sodium

We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with up to 800 mW output power. The laser relies on sum-frequency generation from two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a doubly resonant cavity. We obtain conversion efficiencies as high as 2 W/W² after careful optimization of the cavity parameters. The output wavelength is tunable over 60 GHz, which is sufficient to lock on the sodium D₂ line. The robustness, beam quality, spectral narrowness and tunability of our source make it an alternative to dye lasers for atomic physics experiments with sodium atoms.     

Quantum theory of noise in gas and solid state lasers with an inhomogeneously broadened line. I

We present a quantum mechanical nonlinear treatment of the phase and amplitude flucutations of gas lasers, i.e. lasers with moving atoms, and of solid state lasers with an inhomogeneously broadened line. The atoms may possess an arbitrary number of levels. As in our preceding papers the noise due to the pump, incoherent decay, lattice vibrations or atomic collisions, as well as due to the thermal and zero point fluctuations of the cavity is completely taken into account. The linewidth (due to phase diffusion), and the intensity fluctuations (due to amplitude noise) are essentially expressed by the threshold inversion, the unsaturated inversion and the saturated population numbers of the two atomic levels, which support the laser modes. Our results apply to the whole threshold region and above up to essentially the same photon number, to which the previous semiclassical theories of inhomogeneously broadened lasers were applicable. For the example of a two-level system we also demonstrate the application of a new technique which allows us to eliminate rigorously the atomic variables (operators), yielding a set of nonlinear coupled equations for the lightfield operators alone. If the elimination procedure is carried out only partially and additional approximations are made, we find essentially the rate equations ofMcCumber, in a form derived byLax. When we neglect noise, the nonlinear equation may be solved exactly in the case of single mode operation. By a suitable expansion of the exact multimode equations we find a convenient set of equations, which reduce in the noiseless case to those derived and used previously byHaken andSauermann as well asLamb.     

Multi-target ranging using an optical reservoir computing approach in the laterally coupled semiconductor lasers with self-feedback

We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays. Three radar probe signals are generated by driving lasers constructed by a three-element laser array with self-feedback. The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection, which are utilized as nonlinear nodes to realize the reservoirs. We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir, even when parameter mismatches exist between the response laser array and the driving laser array. Based on this, the three synchronous probe signals are utilized for ranging to three targets, respectively, using Hilbert transform. It is demonstrated that the relative errors for ranging can be very small and less than 0.6%. Our findings show that optical reservoir computing provides an effective way for applications of target ranging.     

Emission spectra of terahertz quantum cascade laser

We calculated energy levels, wave functions, and energies of radiative transitions in terahertz quantum cascade lasers based on GaAs/Al_0.15Ga_0.85As heterostructures. Current-voltage characteristics and current dependences of laser radiation intensity were measured, and the maximum operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade lasers were measured for different temperatures, and the effect of intensity “pumping” from low-frequency modes to high-frequency modes was found to happen in the case of an increase in the current and time delay of the signal capture, which is explained by heating of the sample during a pulse of the current. Application of the lasers for registration of impurity photoconductivity signals in semiconductor heterostructures was demonstrated.     

Preionization kinetics of an X-ray preionized XeCl gas discharge laser

The influence of preionization conditions on the performance of a XeCl gas discharge laser preionized by a short, high intensity x-ray pulse, has been studied. The laser output energy and optical pulse temporal characteristics have been used to determine the roles of initial electron density and of electron attachment to HCl and to impurities. Although the short pulse preionization technique functions well for XeCl when the laser voltage pulse has a short risetime (?20 ns), it is less well suited to XeCl lasers using slowly rising voltage pulses (>50 ns), or to F₂ containing gas mixtures (KrF and XeF lasers).     

A thermometry technique based on atomic lineshapes using diode laser LIF in flames

We report on the development of a novel diode laser thermometry technique permitting temperature measurements in flames based on the fluorescence lineshapes of an atomic tracer species. The technique, which we term OLAF (one-line atomic fluorescence) requires only a single diode laser source for excitation, is simple to implement, and has excellent spatial resolution. Temperatures are deduced from the 5²P_1/2 → 6²S_1/2 transition of atomic indium, the lineshape of which is highly sensitive to temperature changes at typical flame conditions. A rigorous validation is performed in a reference flame with comparisons to measurements by CARS and by Na-line reversal, and to numerical simulations.     

Frequency stabilised grating feedback laser diode for atom cooling applications

The free running linewidth of an external cavity grating feedback diode laser is on the order of a few megahertz and is limited by the mechanical and acoustic vibrations of the external cavity. Such frequency fluctuations can be removed by electronic feedback. We present a hybrid stabilisation technique that uses both a Fabry–Perot confocal cavity and an atomic resonance to achieve excellent short and long term frequency stability. The system has been shown to reduce the laser linewidth of an external cavity diode laser by an order of magnitude to 140 kHz, while limiting frequency excursions to 60 kHz relative to an absolute reference over periods of several hours. The scheme also presents a simple way to frequency offset two lasers many gigahertz apart which should find a use in atom cooling experiments, where hyperfine ground-state frequency separations are often required.     

Efficient multi and single line atomic fluorine lasers

Intense multi- and single-line laser operation is reported from semiconductively preionised atomic fluorine lasers employing an optimised capacitor transfer excitation circuitry. The performance and spectral characteristics of these lasers are discussed and compared to the characteristics of previously described atomic fluorine lasers. The efficiency of one of these lasers described, at optimum conditions, is reaching a value as high as 0.14%. To the best of our knowledge, this is the highest efficiency reported up date, for an atomic fluorine laser.