Generation of ultrahigh and tunable repetition rates in CW injection-seeded frequency-shifted feedback lasers

We show both theoretically and experimentally that frequency-shifted feedback (FSF) lasers seeded with a single frequency laser can generate Fourier transform-limited pulses with a repetition rate tunable and limited by the spectral bandwidth of the laser. We demonstrate experimentally in a FSF laser with a 150 GHz spectral bandwidth, the generation of 6 ps-duration pulses at repetition rates tunable over more than two orders of magnitude between 0.24 and 37 GHz, by steps of 80 MHz. A simple linear analytical model i.e. ignoring both dynamic and non-linear effects, is sufficient to account for the experimental results. This possibility opens new perspectives for various applications where lasers with ultra-high repetition rates are required, from THz generation to ultrafast data processing systems.

Acousto-optic laser optical feedback imaging

We present a photon noise and diffraction-limited imaging method combining an imaging laser and ultrasonic waves. The laser optical feedback imaging (LOFI) technique is an ultrasensitive imaging method for imaging objects through or embedded within a scattering medium. However, LOFI performances are dramatically limited by parasitic optical feedback occurring in the experimental setup. In this Letter, we have tagged the ballistic photons by an acousto-optic effect in order to filter the parasitic feedback effect and to reach the theoretical and ultimate sensitivity of the LOFI technique. We present the principle and the experimental setup of the acousto-optic laser optical feedback imaging technique, and we demonstrate the suppression of the parasitic feedback.

Lambda/2 fringe-spacing interferometer

The precision of interferometry is directly linked to the fringe spacing of the recorded interferogram. Whereas all interferometric devices show a fringe spacing equal to a wavelength of the laser light we present a novel scheme of a two-beam interferometer exhibiting a fringe spacing reduced by a factor of 2; the direct detection of the beat signal is replaced with the monitoring of the fluorescence of a twofold degenerate atomic system resonant with the laser. The lambda/2 fringe spacing in the fluorescence signal is demonstrated with a hot sodium vapor excited by a broadband laser tuned to the D1 line. In the saturation regime, the dark fringes are expected to be extremely narrow, leading to the possibility of nanoscale displacement measurements or atom localization.

Static and dynamic profile of the electric field within the bulk of fused silica glass during and after thermal poling

We use the electric-field-induced second-harmonic (EFISH) technique to characterize, for the first time to our knowledge, the profile of the electric field induced within the bulk of fused silica glass samples both during and after thermal-poling treatment. During thermal poling, the initially homogeneous electric field decays exponentially from the anodic to the cathodic surface. After the poling treatment, a permanent electric field is induced within the bulk of the sample. It also decays exponentially from a positive value on the anodic surface to a negative value on the cathodic surface. The exponential decay constant depends on the thickness of the sample, the poling time, and the temperature. The temperature evolution of this constant makes it possible to retrieve the activation energy of the rapidly moving ionic species. This ensemble of observations indicates that modifications to models previously proposed are necessary.

Characterization and dynamics of gratings induced in glasses by femtosecond pulses

We characterize the gratings induced in commercial SF57 glass by femtosecond pulses. A simple technique enables us to measure both the real and the imaginary parts of the refractive index and shows that the induced grating is mainly a phase grating. An index variation of as much as 6x10(-3) is reported. Then we study the diffraction efficiency of the grating with respect to the intensity of the femtosecond pulse. Permanent structures are induced above the damage threshold. Below this threshold, the grating relaxes. The long-time dynamics of the decay is studied and described by two models. The formation of transient and permanent gratings in various other glasses is observed.

Measurement of the third-order susceptibility of glasses by EFISH of femtosecond pulses

We propose a simple technique based on electric field induced second harmonic (EFISH) generation of femtosecond pulses to measure the third order susceptibility x ;(3) (2 omega,0,omega,omega) in glasses. First we present the principle of the method, then we validate our experimental set-up and develop unexpected aspects of EFISH technique. Finally, we give a numerical value of the third order susceptibility in various glasses and discuss these results.

Laser-induced quasi-phase matching in thermally poled glasses

Quasi phase matching was induced within a few minutes by optical means in a thermally poled glass sample. The spatial modulation of chi((2)) that was induced by two-photon absorption of the sample subjected to an intense sinusoidal pump intensity pattern resulted in a chi((2)) grating. The second-harmonic generation produced by a probe beam was diffracted in specific directions by this chi((2)) grating, thus providing a way to monitor its inscription inside the glass. This chi((2)) grating is extremely stable at room temperature and in ambient laboratory conditions. During the process of inscription, a linear index grating was also induced. It was not stable, and it relaxed rapidly.