F. Bretenaker

Dual-Frequency Laser at 1.5

We describe the stabilization of the beatnote of an Er,Yb:glass dual-frequency laser at 1.5 mum with and without an external microwave reference. In the first case, a classical optical phase-locked loop (OPLL) is used, and absolute phase noise levels as low as -117 dBrad2/Hz at 10 kHz from the carrier are reported. In the second case one or two fiber-optic delay lines are used to lock the frequency of the beatnote. Absolute phase noise levels as low as -107 dBrad2/Hz at 10 kHz from the carrier are measured, fairly independant of the beatnote frequency varying from 2 to 6 GHz. An analysis of the phase noise level limitation is presented in the linear servo-loop theory framework. The expected phase noise level calculated from the measurement of the different noise sources fits well with the predictions.

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Dual tunable wavelength operation of Er,Yb:phosphate glass laser is reported. The spatial separation of the laser eigenstates and the use of two properly designed intracavity etalons permit one to tune the two wavelengths independently from 1540.5 to 1562.7 nm. The generated beat note, monitored using a Michelson interferometer, is experimentally shown to be adjustable from dc to 2.7 THz. The linewidth of this beat note is found to be less than 10 kHz. Several applications are discussed.

m for Optical Distribution and Generation of High-Purity Microwave Signals

The Jones matrix of a tilted plate is theoretically and experimentally described, taking into account the contribution of the successive internal reflections of the incident fundamental TEM(00) Gaussian beam. This induces variations of up to 10% of the transmission coefficients of the Jones matrix with angle of incidence. The consequence of the influences on the walkoff and the internal interference effects of the characteristics ofthe plate and of the incident beam, especially its mode size and its radius of curvature, leads to important different variations of the Jones matrix. of such a plate however, we show that for a given Gaussian beam the Jones matrix of the plate does not depend on its position along the beam propagation axis, in spite of the variations of mode size and radius of curvature whose effects compensate mutually. The Jones matrix of such a plate used in a laser cavity containing a diffracting aperture is also investigated. In every case, good agreement is observed between theory and experiment.

Dual tunable wavelength Er,Yb:glass laser for terahertz beat frequency generation

It is well known that ultranarrow electromagnetically induced transparency (EIT) resonances can be observed in atomic gases at room temperature. We report here the experimental observation of another type of ultranarrow resonances, as narrow as the EIT ones, in a Λ-system selected by light polarization in metastable He at room temperature. It is shown to be due to coherent population oscillations in an open two-level system (TLS). For perpendicular linearly polarized coupling and probe beams, this system can be considered as two coupled open TLSs, in which the ground state populations exhibit anti-phase oscillations. We also predict theoretically that in case of two parallel polarizations, the system would behave like a closed TLS, and the narrow resonance associated with these oscillations would disappear.

Jones matrices of a tilted plate for Gaussian beams

The polarizations and frequencies of the two eigenstates of a vertical cavity surface emitting laser with an external cavity containing a quarter-wave plate are theoretically and experimentally analyzed. It is shown that the polarizations of these eigenstates are fixed by the neutral axes of the quarter-wave plate. The optical pulses at a frequency equal to a half of the free spectral range of the external cavity, observed through a linear polarizer, are due to beats between the two eigenstates. All these features show that such polarization self-modulated lasers oscillate in a single round trip.

Ultranarrow resonance due to coherent population oscillations in a Λ-type atomic system

Abstract High-gain quasi-isotropic lasers are shown to be very sensitive probes of the Earth magnetic field. The rate of rotation of the polarization is shown to exhibit an Adler-type evolution with the azimuth of the laser propagation axis, with a locking region depending on the controlled loss-anisotropies introduced in the cavity. The evolution of this rotation rate with the excitation and the detuning is also investigated. It is also shown that the sensitivity of the laser to the Earth magnetic field increases when extra losses are introduced in the cavity, leading to a sensitivity of a few hundredths of Gauss. In every case, a good agreement is observed between experiments and theory.

Experimental evidence of single round-trip oscillation in polarization self-modulated vertical-cavity surface emitting lasers

The existence of partially spatially-resolved laser eigenstates is proven, using the polarization walkoff provided by a uniaxial birefringent crystal. The coupling between the ordinary and extraordinary eigenstates is shown to depend greatly on the relative positions of the different elements in the cavity, leading to different eigenstates dynamics. Rotation and inhibition vectorial bistability and vectorial simultaneity are successively isolated, with the removal of the transversal degeneracy of the two eigenstates allowing a simple eigenstate selection. >

Study of the dynamical behaviour of the polarization of a quasi- isotropic laser in the earth magnetic field

The transverse displacement at total reflection of a laser beam is experimentally investigated for only one reflection of the circularly polarized beams. The differential experimental method uses the high sensitivity of the helicoidal eigenstates of a laser to measure, for the first time, the intracavity transverse shift for various angles of incidence. The measurements are consistent with our calculations of the transverse shift for circularly polarized light.

The dynamics of spatially-resolved laser eigenstates

Abstract A resonant technique, based on the sinusoidal modulation of the pump beam intensity, is demonstrated in the case of the precise measurement of the lifetime of the 4 I 13 2 level of erbium ions in fluorophosphate hosts. This intensity modulation is obtained via a rotation of the polarization of the pump beam. The large signal-to-noise ratio enables the use of low pump power and apparent lifetime shortenings due to ion-ion energy transfer processes and to amplification of spontaneous emission are circumvented. A parallel ith decay times deduced from usual fluorescence decay measurements is performed. Extension of the method to the spectroscopy of other rare-earth ions is discussed.

Measurement of the Transverse Displacement at Total Reflection by Helicoidal Laser Eigenstates

A macroscopic angular Goos-Hänchen effect at total reflection on curved interfaces is studied experimentally. The results are compared with the complex-angular-momentum model of quasi-critical scattering. An extremum in angular deflection, which has not yet been predicted by any theory other than exact Mie scattering computations, is identified at low size parameters.