Two-mode Emission Research Articles

Controlled two-mode emission from the interplay of driving and thermalization in a dye-filled photonic cavity

Two dimensional photon gases trapped in dye-filled microcavities can undergo thermalization and nearly ideal equilibrium Bose-Einstein condensation. However, they are inherently driven-dissipative systems that can exhibit an intricate interplay between the thermalizing influence of the environment given by the dye solution and the pump and loss processes driving the system out of equilibrium. We show that this interplay gives rise to a robust mechanism for two-mode emission, when the system is driven by an off-centered pump beam. Namely, after the system starts lasing in the dominantly pumped excited mode, in a second transition a photon condensate is formed in the ground mode, when the pump power is increased further. This effect is a consequence of the redistribution of excited dye molecules via the lasing mode in combination with thermalization. We propose to exploit this effect for engineering controlled two-mode emission and demonstrate that by tailoring the transverse potential landscape for the photons, the threshold pump power can be tuned by orders of magnitude.

Two-color surface-emitting lasers by a GaAs-based coupled multilayer cavity structure for coherent terahertz light sources

Two-color surface-emitting lasers were fabricated using a GaAs-based coupled multilayer cavity structure grown by molecular beam epitaxy. InGaAs/GaAs multiple quantum wells were introduced only in the upper cavity for two-mode emission in the near-infrared region. Two-color lasing of the device was successfully demonstrated under pulsed current operations at room temperature. We also observed good temporal coherence of the two-color laser light using a Michelson interferometer. A coherent terahertz source is expected when a wafer-bonded coupled cavity consisting of (001) and non-(001) epitaxial films is used for the two-color laser device, in which the difference-frequency generation can be enabled by the second-order nonlinear response in the lower cavity.

Amplitude-squeezed emission from a transverse single-mode vertical-cavity surface-emitting laser with weakly anticorrelated polarization modes

We discuss the polarization-resolved intensity noise characteristics of a transverse single-mode vertical-cavity surface-emitting laser (VCSEL). Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yield only an imperfect anticorrelation between the strong and the weak orthogonally polarized fundamental modes. Yet the total emission shows amplitude squeezing of 0.4 dB below the shot-noise level. Unlike for transverse two-mode emission, a perfect anticorrelation between the two polarization modes is not necessary for generation of amplitude-squeezed emission in a transverse single-mode VCSEL, in agreement with theoretical predictions.

Midinfrared surface-emitting PbSe/PbEuTe quantum-dot lasers

Midinfrared laser emission from self-organized PbSe quantum dots in a high-finesse vertical-cavity surface-emitting laser structure is reported. The structure was grown by molecular-beam epitaxy and consists of high reflectivity epitaxial EuTe/PbEuTe Bragg mirrors with a PbSe/Pb1−xEuxTe quantum-dot superlattice as the active region. Narrow laser emission at 4.2–3.9 μm induced by optical pumping is achieved at temperatures up to 90 K. The observation of simultaneous two-mode emission indicates a width of the inhomogeneously broadened PbSe dot gain spectrum of about 18 meV.

Study of an injection-seeded supra-atmospheric CO_2 laser operated below emission threshold with a ring cavity

The dynamics and tuning range of an injection-seeded supra-atmospheric CO(2) laser operated at a pressure of 10 atm with a ring cavity are studied theoretically and experimentally. When the losses of such a laser are sufficiently high, the short lifetime of the gain does not permit the buildup of intense pulses that start from spontaneous emission noise; the laser is then said to be operated below emission threshold. Under such circumstances, injection seeding with a few milliwatts of a single-mode signal permits nearly full extraction of the available power. The extraction efficiency is shown to depend in a sensitive manner on the frequencies of a cavity mode and of the injected signal. When these two frequencies are mismatched, a lower power is extracted, and two-mode emission takes place. The laser is shown to be tunable over 41 transition lines of the CO(2) spectrum.

A theoretical study of the dynamical behavior of single quantum-well semiconductor lasers

The used numerical model takes into account two quantized energy levels, n = 1, 2 for electrons and heavy holes in the conduction and valence bands of a single quantum-well laser where spontaneous emission. Auger recombination, and nonlinear gain suppression are considered. The time evolution of photon densities, P 1 and P 2, connected with first and second quantized state lasing at subband transition energies E 1 and E 2, respectively, has been investigated for large-signal modulation of the injection current at various cavity losses. Within a relatively small interval of cavity loss pronounced two-mode emission ( P 1, P 2) with inclusion of period-doubling bifurcations has been found. Period-doubling routes to chaos with a period-3 window in the chaos, and bistable pairs of period-1/period-3 as well as period-2/period-6 attractors have been obtained in case of single-mode operation at photon energies E 1 and E 2, respectively.

Operating regimes of a linear gas laser with a phase-anisotropic resonator

The method of the Jones vectors and matrices is used in a theoretical analysis and calculations of the parameters of single- and two-mode emission at λ = 0.63 μm from an He–Ne laser with an anisotropic resonator and orthogonally polarized modes. A study is made of the dependence of the lasing regimes on the polarization of an electromagnetic field in the resonator and on the spatial overlap of the mode fields. The calculations are carried out allowing for the elastic depolarizing collisions between the atoms of the active medium. The results of the calculations are presented graphically. The graphs identifying the stability regions of the different lasing regimes demonstrate clearly the influence of the type of polarization of the radiation and of the spatial overlap of the fields on the mode competition processes. The results obtained can be used in the development of lasers with anisotropic resonators generating two orthogonally polarized modes whose frequencies differ by an amount that can be varied in a wide range.

Competition between high-intensity modes of different polarizations in a gas laser

A theoretical analysis is made of the stability range of stimulated emission of two modes with orthogonal and parallel polarizations. The case of transitions between active levels of momenta ja = jb = 1 in a relatively strongly excited medium is considered. It is found that, in contrast to the case of parallel polarizations, emission of two modes with orthogonal polarizations is possible even when the mode spacing is small. Investigation is made of the influence of the quadrupole polarization of the medium on the width of the two-mode emission range. It is shown that the results obtained by calculating the polarization of the medium to within terms cubic in respect of the field amplitude describe correctly relatively highly excited active media.

Limits of stability of two-mode emission in a strong field

A theoretical analysis is made of the two-mode emission from a gas laser in the vicinity of the symmetric position of the modes relative to the center of the gain profile when the intensities of the modes in the symmetric position cannot be regarded as low. The example of a homogeneously broadened spectral line is used in an investigation of the range of stable two-mode emission as a function of the relative excitation of the medium.

Fluctuations of two-mode emission from a ring laser

An investigation was made of natural fluctuations of the intensities and difference frequencies emitted from a helium-neon ring laser in the two-mode (four-wave) self-locked regime. It is shown that the combination interaction, resulting in the self-locking of the difference frequencies, reduces the level of their fluctuations. A comparison is made with the emission of one mode.

Two-mode emission from a ring gas laser with a twoisotope active medium

A theoretical analysis is made of steady-state two-mode (two- and four-wave) emission from a ring gas laser with a two-isotope active medium. The interaction coefficients of traveling waves are calculated for two longitudinal linearly polarized modes. Two cases are considered: Modes polarized in one direction and at right-angles to one another. The limits of stability of the two-mode (two- and four-wave) emission are investigated as a function of the following parameters of a ring gas laser: mode spacing, positions of modes on the gain curve, longitudinal dimensions and relative positions of tubes with the active medium, lifetimes and total momentum of the active levels, and width of the spontaneous emission line.

Interaction of modes with orthogonal and parallel polarizations in a gas laser

An investigation was made of the interaction of the modes with orthogonal and parallel polarizations in a gas laser emitting two axial modes. The behavior of the critical frequency and stability region of the two-mode emission was determined as a function of various parameters. The calculated and experimental results were compared.