Svetlana Mansurova

Non-steady-state photoelectromotive force effect under linear and periodical phase modulation: application to detection of Doppler frequency shift.

Non-steady-state photoelectromotive force effect in the presence of periodical and linear phase shift was investigated both theoretically and experimentally. It was shown that superposition of oscillating and linear movements of the interference pattern leads to the appearance of the sharp peak in the frequency dependence of the photoelectromotive force output current when the frequency of periodical modulation matches the frequency of the linear phase shift. We demonstrated experimentally that this effect can be used for determination of a Doppler frequency shift between signal and reference beam.

Practical aspects of applying triple correlations to the characterization of high-frequency repetition trains of picosecond optical pulses

Practical feasibility of measuring the train-average parameters of picosecond optical pulses being arranged in highfrequency repetition trains is investigated. For this purpose we consider exploiting the triple auto-correlations, whose Fourier transformations give the bispectrum of a pulse train. The main merit of similar approach consists in the capability of recovering signals and revealing asymmetry of pulse envelopes. The triple auto-correlation can be shaped by a three-beam scanning interferometer with the following one- or two-cascade triple harmonic generation. The efficiencies of these processes depend on the number of cascades and differ in various modern materials. The key features of measuring the train-average parameters of pulses with possible frequency chirp are also discussed.

Adaptive detection of Doppler frequency shift using ac non-steady-state photo-EMF effect

Adaptive velocimeter based on the AC non-steady state photo-EMF effect induced by oscillating interference pattern has been investigated. The possibility to detect very low velocities (micrometer per second) using photoconductive polymer based detector was demonstrated.

Performing the triple auto-correlation of picosecond optical pulse train with a photo electromotive force detector

vHere, we consider the possibility of involving the photo-EMF detectors in registration of the parameters peculiar to ultrashort optical pulses, and it is compared whit the recently triple correlator via Direct and Cascade Third Harmonic Generation. Knowledge of triple auto-correlation function, whose Fourier transformation shapes the corresponding bispectrum, makes possible recovering such train-average parameters as, for instance, the pulse width and frequency chirp as well as revealing asymmetry of ultra-short pulse envelope. The main advantage of applying the photo-EMF detectors lies in an opportunity to detect triple correlations directly, without any intermediate frequency conversion with optical nonlinear processes in additional crystals. Then, the theory of three-beam-correlations at photosensitive layer of the photo-EMF detector is developed, so that principal possibility of registering the high-order-correlations is demonstrated. It can be done within schematic arrangement including the three-beam Michelson interferometer, so that the obtained high-order-correlations have non-traditional form and need rather specific algorithm for their further processing. Also, the experimental characterizations are presented for gallium arsenide (GaAs) semiconductor and the poly-fluoren 6-co-triphenyldiamine (PF6-TPD) photo-conductor-polymer, which both exhibit the photo-EMF-effect. They both exhibit high-pass transfer functions that give us high vibration stability. This novel approach provides more reliable analyzing train-average parameters of picosecond pulses due to significantly higher level of the output optical signals under processing.

Analysis of originating ultra-short optical dissipative solitary pulses in the actively mode-locked semiconductor heterolasers with an external fiber cavity

We present an advanced approach to describing low-power trains of bright picosecond optical dissipative solitary pulses with an internal frequency modulation in practically important case of exploiting semiconductor heterolaser operating in near-infrared range in the active mode-locking regime. In the chosen schematic arrangement, process of the active mode-locking is caused by a hybrid nonlinear cavity consisting of this heterolaser and an external rather long single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and small linear optical losses. Our analysis of shaping dissipative solitary pulses includes three principal contributions associated with the modulated gain, total optical losses, as well as with linear and nonlinear phase shifts. In fact, various trains of the non-interacting to one another optical dissipative solitons appear within simultaneous balance between the second-order dispersion and cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in a hybrid cavity. Our specific approach makes possible taking the modulating signals providing non-conventional composite regimes of a multi-pulse active mode-locking. Within our model, a contribution of the appearing nonlinear Ginzburg-Landau operator to the parameters of dissipative solitary pulses is described via exploiting an approximate variational procedure involving the technique of trial functions.

Characterizing the parameters of ultra-short optical dissipative solitary pulses in the actively mode-locked semiconductor laser with an external fiber cavity

We discuss specifically elaborated approach for characterizing the train-average parameters of low-power picosecond optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency domains. This approach had been previously applied to rather important case of pulse generation when a single-mode semiconductor heterolaser operates in a multi-pulse regime of the active mode-locking with an external single-mode fiber cavity. In fact, the trains of optical dissipative solitary pulses, which appear under a double balance between mutually compensating actions of dispersion and nonlinearity as well as gain and optical losses, are under characterization. However, in the contrast with the previous studies, now we touch an opportunity of describing two chirped optical pulses together. The main reason of involving just a pair of pulses is caused by the simplest opportunity for simulating the properties of just a sequence of pulses rather then an isolated pulse. However, this step leads to a set of specific difficulty inherent generally in applying joint time-frequency distributions to groups of signals and consisting in manifestation of various false signals or artefacts. This is why the joint Chio-Williams time-frequency distribution and the technique of smoothing are under preliminary consideration here.

Problem of Talbot self-images localization: adaptive photo-EMF based detector vs. CCD-based methods

Talbot self-images localization is important in many optical applications such as interferometry, metrology and nanolithography. Usually, the problem of self-images localization is reduced to the finding the planes of maximal light pattern visibility. There are several conventional techniques that determine the contrast of an intensity distribution generated by a periodical object, such as root mean square (RMS) method, and variogram-based method. In all these cases, a CCD camera is used to record the light patterns that are processed and analyzed in order to find the self-image position. Recently, it has been proposed the use an adaptive photo-detector based on the non-steadystate photo-electromotive force (photo-EMF) effect, which uses periodically oscillating light pattern to induce alternating current through the short-circuited photoconductive sample. Here we perform the theoretical analysis of the technique based on the photo-EMF effect against the conventional methods for the localization of the Talbot patterns.

Initial stage of the active mode-locking in semiconductor heterolasers

We make an attempt to develop a novel approach to describing the initial stage of the active mode-locking in semiconductor laser structures based on analyzing the properties of dispersion relations in terms of stability for small initial perturbations. Nonlinear process of shaping optical pulses is interpreted as manifesting instability of diffusion type. For the purposes of experimental investigations, the auto-manual opto-electronic measuring system detecting average time parameters inherent in ultra-short optical pulse trains has been designed. This system is able to register auto-correlation functions of the second order exploiting the interferometric technique as well as to identify a pulsed character of the incoming light radiation. Experimental confirmations of appearing the diffusive instability within the active mode-locking process in semiconductor laser structures operating in the near infrared range are presented.