Two unstable oscillations in the multimode laser with modulated inversion

We present comprehensive results of numerical studies on the dynamical properties of a multimode ring laser under modulation of the population inversion in the bad-cavity condition. Incoherent properties of unstable oscillations in this system are investigated in detail as a function of two control parameters: the dc component of the population inversion and the modulation amplitude. Two kinds of optical chaos in two limiting regions reported in a previous paper are extensively studied to clarify their different characteristics from deterministic and stochastic points of view. The competition between their different origins is revealed. Statistical properties of their stochasticity are investigated to clarify their non-Gaussian natures. Comparison with analytical results for a single-mode laser with fluctuations is also made.     

Synchronization and clustering in a multimode quantum dot laser

We analyze experimentally the intensity oscillations of the longitudinal modes of quantum dot semiconductor lasers. We show that the modal intensities can oscillate chaotically with different average frequencies, but obey a highly organized antiphase dynamics leading to a constant total output power. The fluctuations are in the MHz range. We report the first experimental observation of frequency clustering associated with synchronization. We also observe the propagation of perturbations across the optical spectrum from blue to red.     

Antiphase dynamics of a multimode quantum well semiconductor laser

A novel multilongitudinal mode model of a semiconductor laser is presented. The model takes into account four-wave mixing of the longitudinal modes and is based on the correct procedure of simultaneous expansion of the population inversion in time and space series. It is shown that the model has antiphase regimes similar to those observed in experiment. Such behavior exists in a narrow range of the carrier diffusion coefficient, which allows us to estimate the value of this parameter.     

Variable reflectivity unstable resonators for a long pulse XeCl excimer laser

The divergence of a long pulse, low gain XeCl excimer laser has been improved using confocal positive branch unstable resonators with variable reflectivity mirrors as outcouplers. With variable reflectivity unstable resonators, nearly diffraction limited beams are obtained. Variable reflectivity resonators lead to high brightness beams (9.1 10 W/(cm sr)). Different reflection profiles were studied with respect to their influence on the beam quality and the energy extraction.     

High-quality lowest-loss-mode lasing in GaAs quasi-stadium laser diodes having unstable resonators

We obtained high-quality lowest-loss-mode lasing in quasi-stadium laser diodes having unstable resonators that consisted of two curved end mirrors and two straight sidewall mirrors. The laser diodes were fabricated by applying a reactive ion etching technique to a metal-organic chemical-vapor deposition-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The electrode contact area of the laser diodes was formed along unstable periodic orbits, along which the optical beams are localized. Highly directional fan-out beams corresponding to the numerically obtained lowest loss mode were emitted from the end mirrors under CW operation at room temperature.     

A nonradiative approach to single-mode dielectric resonators

The development of a single-mode dielectric resonator specifically designed for high-frequency paramagnetic resonance applications is discussed. The use of dielectric resonators is expected to give better performances in comparison to metallic cavities, as well established at low frequency. The relatively low dielectric constant of the common good-quality materials at high frequency requires the presence of a metallic shielding in order to obtain an efficient single-mode operation. The configuration proposed in this paper concerns a partially open structure in which the confinement of the radiation is guaranteed by the forbidden propagation around the dielectric region. By this way a single-mode resonator can be obtained for arbitrary values of the employed dielectric constant. The complex resonance frequencies and the field distributions and intensity can then be obtained even in the presence of a lossy sample. An efficient excitation scheme, fully compatible with the common electron paramagnetic resonance setups, has been developed exploiting the nonradiative nature of the proposed device. Preliminary measurements around 90 and 186 GHz have been then successfully realized. Finally, the specific benefits of the proposed resonator have been discussed and compared with the performances of a conventional metallic cavity.     

High brightness operation of a XeCl laser with negative branch unstable resonators

Confocal and non-confocal negative branch unstable resonators with an intracavity spatial filter have been applied to a high-gain short-pulse UV preionized XeCl laser. The near- and far-field radiation characteristics have been investigated in both configurations. Laser beams of larger brightness have been obtained with non-confocal schemes. A maximum beam brightness of 1.3×10¹⁴ Wcm^–2Sr^–1 has been achieved.     

Fano resonances in prism-coupled multimode square micropillar resonators

We report Fano resonances in a multimode square glass micropillar resonator; the resonances were obtained by using angle-resolved prism coupling. Our experiments reveal characteristically asymmetric line shapes of high-Q resonances and of detuned low-Q resonances in multimode reflection spectra. The asymmetric resonance line shapes evolve for an approximately pi phase within a 0.5 degree range of reflection angles. We model our observed asymmetric multimode resonances by the far-field interference between a light wave that is evanescently coupled with a high-Q mode orbit and a coherent light wave that is refractively coupled with a detuned low-Q mode orbit.     

多元件共焦型非稳腔的特征

本文首次使用牛顿成像方程对多元件共焦型非稳腔的基模给出了公式化描述,揭示出这类光腔的重要特征.对本文所用方法和其它方法的比较亦作了讨论.     

High-power solid-state lasers with unstable resonators

The thermal lensing properties of stable and unstable resonators are compared and rules are given for the design of optimized unstable resonators containing a focusing rod. Experimental verification with a high-power Nd: YAG system proved that for unstable resonators the restricting relationship between beam quality and output power no longer holds. Careful resonator design enables high output power to be extracted with unstable resonators without destroying the output couplers.     

The use of confocal unstable resonators in a double Rogowski TEA CO2 laser

The use of positive branch confocal unstable resonators in a double Rogowski TEA CO₂ laser is described. Single mode energies have been achieved of up to 62% of the maximum obtained multimode under similar conditions. The resonator far fields have been measured and found to be within 1.1 times the diffraction limit predicted by simple theory.     

High-power solid-state lasers with unstable resonators

The thermal lensing properties of stable and unstable resonators are compared and rules are given for the design of optimized unstable resonators containing a focusing rod. Experimental verification with a high-power Nd: YAG system proved that for unstable resonators the restricting relationship between beam quality and output power no longer holds. Careful resonator design enables high output power to be extracted with unstable resonators without destroying the output couplers.     

A nonperturbative quantum electrodynamic approach to the theory of laser induced high harmonic generation

Using nonperturbative quantum electrodynamics, we develop a scattering theory for high harmonic generation (HHG). A transition rate formula for HHG is obtained. Applying this formula, we calculate the spectra of high harmonics generated from different noble gases shined by strong laser light. We study the cutoff property of the spectra. The data show that the cutoff orders of high harmonics are greater than that predicted by the “3.17” cutoff law. As a numerical experiment, the data obtained from our repeated calculations support the newly derived theoretical expression of the cutoff law. The cutoff energy of high harmonics described by the new cutoff law, in terms of the ponderomotive energy U_p and the ionization potential energy I_p, is 3.34U_p+ 1.83I_p. The higher cutoff orders predicted by this theory are due to the absorption of the extra photons, which participate only the photon-mode up-conversion and do nothing in the photoionization process.     

A quantum approach to paramagnetic resonance

In the semi-classical theory of the problem of interaction of radio-frequency (r.f.) field with electron or nuclear spin, the application of quantisation is restricted to the spin system only, the r.f. field being treated classically. In this paper, a purely quantum approach is discussed for a system with spin > 1/2 using a Glauber vector to describe coherent excitations of the r.f. field. It is illustrated here for the case of spin 3/2. One finds that this quantum approach contains the classical one. An erratum to this article is available at .     

A statistical approach to quantum mechanics

A Monte Carlo method is used to evaluate the Euclidean version of Feynman's sum over particle histories. Following Feynman's treatment, individual paths are defined on a discrete (imaginary) time lattice with periodic boundary conditions. On each lattice site, a continuous position variable x_i specifies the spacial location of the particle. Using a modified Metropolis algorithm, the low-lying energy eigenvalues, |ψ₀(x)|², the propagator, and the effective potential for the anharmonic oscillator are computed, in good agreement with theory. For a deep double-well potential, instantons were found in our computer simulations appearing as multi-kink configurations on the lattice.