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We present experimental results on polarization ellipse self-rotation (PSR) and polarization hole burning (PHB) in the acetylene-filled hole-core photonic crystal fiber for the P5, P7, and P9 vibrational-rotational Doppler broadened (~500MHz) lines at the gas pressures 0.4-4Torr and W-scale power. The experimental values of PHB and PSR effects are in good agreement between them and with predictions of the developed semi-classic model for the acetylene molecules as the saturable rotating dipoles (gyrators) with random orientations. The maximum experimental PSR value normalized to the gas initial absorbance proved to be significantly lower than that observed in alkali-metal vapors earlier..

We present results of the experimental investigations of noise characteristics of the self-referencing optical phase demodulator based on a bulk low-pressure acetylene cell at the wavelength 1530.37nm of P9 acetylene absorption line. The configuration is simple, does not need phase locking, and can be operated with high-etendue waves. While the intensity noise of the utilized semiconductor laser at frequency >250MHz was below the photonic noise, the demodulator resolution (i.e., the minimum detectable phase modulation amplitude) was significantly reduced by an excessive laser phase noise. To reduce the output noise, we propose and analyze different balanced detection configurations that increase the resolution to the standard quantum level.

Acousto-optic frequency shift modulators are widely used for well-known heterodyne signal processing algorithms in interferometric sensors. Output signal stability is very important for such modulators applications. For this reason temperature dependences of the polarization mode conversion peak frequency and efficiency of those modulators was tested in a climate chamber. It was shown that the shift of the polarization mode conversion peak frequency was about 0.1 MHz per 1 ℃ temperature change. Such behavior was theoretically explained by the temperature dependence of the difference between the effective refractive indices for polarization modes and the temperature dependence of the surface acoustic wave velocity on the X-cut lithium niobate substrate. Also it was shown that the change in the polarization mode conversion efficiency with temperature was due to a change in the surface acoustic wave excitation efficiency with the frequency, characterized by the frequency dependence of the real part of the interdigital transducer admittance.

An adaptive optical fiber sensor/demodulator of an optical phase modulation with a Sagnac interferometer configuration is reported. The dynamic population grating recorded in ytterbium-doped fiber (YDF) at a wavelength of 1064 nm enables adaptive properties of this configuration with a high-pass transfer function and with the cut-off frequency of about 260 Hz at ∼ 10 m W cw recording power. A linear response with nearly 100% modulation depth is ensured by effective formation of the nonshifted phase dynamic grating with the amplitude one order of magnitude greater than can be expected from the saturation of the YDF absorption at the recording wavelength. This is associated with the photoinduced changes in the UV optical absorption of the YDF and enables minimal detected amplitude of the phase modulation ≈ 0.7 ∗ 10 − 7 H z in our experimental configuration. We believe that, in general, this mechanism of the phase grating formation can ensure the sensor resolution limited by the photonic noise of the utilized light power only.

We report experimental measurements of noises and resolution in a bulk self-referencing interferometric configuration based on quantum memory of acetylene (C2H2) molecules at the wavelength of 1530.37 nm of P9 absorption line.

We report polarization ellipse self-rotation and polarization hole-burning in the acetylene-filled hollow-core photonic crystal fiber in spectral range 1520–1540 nm. P5 oscillation rotation line demonstrated the strongest results that are in agreement with classical model.

Application of the phase memory of acetylene (C2H2) vibrational-rotational transitions in the 1520–1540 nm wavelength range for a self-referencing homodyne detection of a sub-nanosecond optical phase modulation is reported. In the proposed configuration the collinearly propagating coherent dipole radiation of the excited molecule acts like a phase-locked reference wave (local oscillator) that enables transformation of the initial phase modulation into the intensity one. This technique does not need high light intensity and can operate in a linear range of the medium optical absorption. The linear optical phase demodulation (i.e., transformation of the phase-to-amplitude light modulation) is interpreted as an introduction of an additional phase shift to the carrier frequency component of the modulated signal in the maximum of the dispersion curve of a narrow optical absorption peak. It has been experimentally demonstrated with the bulk 10 cm long cuvette filled with low pressure (∼2 Torr) acetylene at room temperature. Effective demodulation of the milliwatt-scale incident laser wave of a single- and multi-mode structure is shown. As expected, the response to the fast (

Detection (or demodulation) of the phase modulation is a critical operation in different photonic applications, in particular, in interferometric fiber sensors, material evaluation via laser induced ultrasound, coherent communications etc. Different techniques were proposed to overcome the main problem of conventional interferometers: necessity of stabilization of the quadrature operation point and compensation of the complex spatial structure of the detected wave. Here one can mention, active operation point stabilization via external optoelectronic loop [1], adaptive dynamic gratings based systems [2], self-reference (i.e. without external reference wave) confocal Fabry-Perot cavities [3], and configuration based on quantum phase memory of an ensemble of two-level atoms/molecules [4]. All these seemingly different approaches have the same common feature — they are based on utilization of a narrow absorption/gain spectral profile, artificial, as in the first two above-mentioned techniques, or natural, as in the two last cases. Here we analyse a general case of passing of the phase modulated wave through a narrow absorption/gain spectral line as a technique for its demodulation (i.e. its partial transformation into the intensity modulation wave) with the following detection by conventional photodetector.

We report on the first experimental observation of the polarization ellipse self-rotation (PSR) and the polarization hole burning (PHB) nonlinear optical effects for the acetylene ( C 2 H 2 ) vibrational–rotational transitions in the 1520–1530 nm spectral range. The experiments were performed using a 1-m-long acetylene-filled hollow-core photonic crystal fiber cell at room temperature and gas pressure of 0.4–4 Torr. The PHB effect was experimentally observed as a photo-induced input polarization ellipticity change in the output light. Among all the investigated acetylene transitions P9, P7, P5, and P3, the maximum ellipticity change of ∼ 35 % was observed at zero detuning from the center of the P5 absorption line with the initial optical absorbance about 6. The obtained results are in good agreement with the theoretical predictions of a classical analysis based on the model of the acetylene molecules as gyrators (circular oscillators) with random orientations. For the inhomogeneously broadened acetylene absorption P5 line ( ∼ 500 M H z ), the PSR effect observed for tuning at the sides of the P5 line, as expected, proved to be by factor Δ ω i h / Δ ω h (inhomogeneous-to-homogeneous broadening ratio) lower than the maximum PHB. The PSR constant for these conditions proved to be about 0.1 m − 1 , which is about 2 orders of magnitude lower than that reported earlier for the alkali metal (K, Rb) vapors.

The delayed optical nutation effect has been used to evaluate the longitudinal relaxation time ( T 1 ) inside an acetylene-filled hollow-core photonic crystal fiber (HC-PCF) at room temperature. In this experiment, sequences of two short optical pulses of 30 ns and 15 ns in width, respectively, with the maximum peak power up to ∼2.5 W, were generated at a laser wavelength of 1530.37 nm, which corresponds to the acetylene ro-vibrational P9 absorption line. The gas pressure inside the 1 m-long HC-PCF varied in the range 0.1–1 Torr. Numerical simulations based on the optical Bloch equations allowed us to evaluate the longitudinal relaxation time as T 1 ∼ 9 ns, proving to be fundamentally limited by the transit-time broadening. Also, the obtained results revealed the influence of slow and fast molecules in the form of a non-exponential decay of the delayed-nutation signals.

Experimental results on the transient optical nutation effect inside an acetylene-filled hollow-core photonic crystal fiber (HC-PCF) are reported. The experiments used 15 ns optical pulses with peak powers up to 5 W. The light wavelength was centered at 1530.37 nm, which corresponds to the P9 acetylene ( 12 C 2 H 2 ) vibrational-rotational absorption line. The gas pressure inside the PCF, with hollow core diameter of ∼10.3 μm, was kept around 0.12 Torr. Comparison of the experimental data with numerical simulations using the Maxwell-Bloch equations allowed us to evaluate the characteristic longitudinal and transverse relaxation times around 10 ns, as well as the transition dipole moment (1.36 × 10 −32 Cm).

We present a new concept of the homodyne interferometric adaptive detection of optical phase modulation. To ensure adaptivity, i.e. stabilization of the interferometer operation point, we utilize the phase memory of a two-level quantum system, resonantly illuminated with the information bearing signal wave. Phase modulation of the transmitted signal wave transforms into the intensity modulation via interference with the collinearly propagating dipole radiation of the excited two-level system. The latter acts like a reference wave since it has a phase corresponding to that of the signal wave but averaged over the transverse relaxation time T 2 of the quantum system. Experimental demonstration with the acetylene-filled hollow-core micro-structured optical fiber at the communication wavelength of 1530nm of the acetylene P9 absorption line is presented. It is shown that the response to the introduced phase modulation is quadratic when the acetylene inhomogeneously broadened absorption line is excited in its center and is a linear one if it is excited at one of the absorption line sides.

Lithium niobate (LN) is one of basic materials of integrated optics used, for example, for electro and acousto-optical modulators, switches, diffraction gratings, nonlinear optical wavelength converters, and others [1]. LN-based ion exchange or Ti-indiffused photolithographic techniques are established technologies, however, some modern applications, such as high-purity suppressed carrier synthesis or high extinction ratio pulse generation for precision measurement systems require the use of additional active trimming electrodes [2] and a corresponding servo loop because of finite tolerances of optical elements. Recently developed direct laser writing (DLW) with femtosecond/ultrafast laser pulses [3] can be employed to address the problem, but this method is problematic for mass production and suffer from high insertion loss in optical waveguides (typically ∼ 1 dB/cm compared to

Experimental results on pulsed excitation of electromagnetically induced transparency (EIT) in the acetylene-filled hollow-core photonic crystal fiber (HC-PCF) at pressures 0.1–0.4 Torr are reported. The EIT was observed both in Λ and V interaction configurations with the continuous probe wave tuned to R9 (1520.08 nm) acetylene absorption line and with the control pulses tuned to P11 (1531.58 nm) and P9 (1530.37 nm) lines, respectively. The utilized control pulses were of up to 40 ns duration with

Dynamic population Bragg gratings can be recorded in the rare-earth-doped (e.g. doped with erbium or ytterbium) optical fibers with mWatt-scale cw laser power. Two-wave mixing (TWM) via such gratings is utilized in single-frequency fiber lasers and in adaptive interferometric fiber sensors with automatic stabilization of the operation point. Slow and fast light propagation can also be observed in the vicinity of narrow (~20-200Hz) spectral profile of stationary no-degenerate TWM. In particular, slow light propagation is observed for the purely amplitude grating, recorded in the erbium-doped fiber in spectral range 1510-1550nm. In its turn, in ytterbium-doped fibers at 1064nm (or in erbium-doped fiber at the wavelength below 1500nm) the dynamic grating has significant contribution of the phase component, the TWM profile has essentially asymmetric form, and both slow and fast (superluminal) light propagation is possible at different frequency off-sets between the counter-propagating interacting waves.

Low-pressure acetylene in the hollow-core photonic crystal structure fibers is an excellent medium for the room-temperature investigation of the coherent quantum effects in communication wavelength region. Pulsed excitation enables observation of new coherent phenomena like optical nutation or photon echo and evaluation of important temporal characteristics of the light-molecule interactions. We also report original experimental results on the pulsed excitation of the electromagnetically induced transparency in co- and counter-propagation configurations.

We propose to use phase memory of an ensemble of two-level centers, irradiated by the resonantly tuned detected signal wave, for homodyne interferometric detection of fast optical phase modulation. Collinearly propagating dipole radiation of the excited two-level centers acts as a coherent reference wave (local oscillator) necessary to transform the phase modulation into the amplitude modulation behind the resonant medium. The phase of this radiation follows the average phase of the incident detected wave with the characteristic transverse relaxation time T 2 that ensures adaptive properties of this interferometric detection configuration to slowly varying environmental conditions. We present experimental demonstration with the acetylene-filled hollow-core microstructured optical fibers at a wavelength of 1530.37 nm of the acetylene P9 absorption line, which is inside the telecommunications wavelengths range. It is shown that the response is quadratic when the acetylene ~500 MHz inhomogeneously broadened absorption line is excited in its center, but can be essentially linearized for excitation at one of the line sides.

We present data on the polarization degree of the fluorescence, excited in erbium-doped fibers (EDF) by linearly polarized light at three essentially different wavelengths in the spectral range of the fundamental absorption of Er 3+ (1492, 1526, and 1568 nm). Experiments were performed in otherwise similar single-mode fibers with a broad range of erbium concentration (≈640–5600 wt ppm). The polarization degree of the fluorescence demonstrated expected decay with the incident light power and proved to be significantly weaker for the central excitation wavelength of 1526 nm. The maximum value of the experimentally observed effect (≤0.3%) is significantly lower than it is predicted by model of the randomly oriented non-interacting dipoles. This discrepancy is explained by the reduced anisotropy (to the value 0.7–0.8) of the erbium ions absorption/emission, the effect which was utilized to explain the experimentally observed weak polarization hole burning in EDF earlier. Additional reduction in the fluorescence polarization degree and accelerated depolarization relaxation which were experimentally observed in fibers with high erbium concentration are attributed to the spatial migration of the excited state.

Experimental results on observation of slow and fast light propagation via two-wave mixing (TWM) in ytterbium doped fibers (YDF) at the wavelength 1064 nm are reported. For ≈10 mW of the incident cw laser power the effective population dynamic gratings with sub-ms formation time τ g and dominating phase (refractive index) components are formed in YDF by two counter-propagating coherent waves. The TWM at the recorded not shifted phase gratings is characterized by absence of any energy exchange between two interacting counter-propagating waves if they have the same frequency. For the no-degenerated TWM (i.e. that with the frequency off-set Δ Ω between the interacting waves) the maximal energy exchange is observed when Δ Ω is approximately equal to τ g −1 and changes its sign with the inversion of ΔΩ . In the reported experiments an effective slow and fast light propagation with maximal fractional delay of about 0.04 for 3.5 ms pulses was observed for these two maxima located at the frequency off-set ≈±200 Hz.

Experimental investigations of the main noise sources that limit the sensitivity of the adaptive interferometric all-fiber sensors operating in the communication wavelength region are reported. Adaptive properties (i.e., the autostabilization of an optimal operation point of the interferometer) are enabled by the dynamic population grating recorded in a segment of the erbium-doped fiber (EDF) at milliwatt-scale cw power in the 1480-1560 nm spectral range. The utilized symmetric Sagnac configuration with low light internal reflections ensures reduced sensitivity of the sensor to phase noise of the laser, while intensity noise is reduced to an insignificant level by the balanced detection scheme. It is shown that the fluorescence from the erbium ions, excited by the counterpropagating waves recording the grating, increases the noise level from the fundamental shot noise approximately by a factor of 2-3 only. It is also shown that conventional communication distributed feedback (DFB) semiconductor lasers with megahertz linewidth are not suitable for high-sensitivity applications of such sensors. Because of inevitable backreflections from the output terminal devices (photodiodes, insulators, circulator), the above-mentioned fundamental noise level is increased by 2 orders of magnitude due to high phase noise of the DFB laser.

Studies of magneto-optic properties of Fe 3 O 4 ferrofluid (colloidal solution of nanosized particles) in a pulsed and AC magnetic field are reported. It is shown that a microstructured optical fiber with cladding holes filled with ferrofluid is sensitive to the external magnetic field vector and that operating speed of magnetically controlled optofluidic devices can be increased by using a transverse biasing.

We report experimental results on saturable absorption of acetylene (C2H2) confined to a hollow-core photonic crystal fiber (PCF). In our experiments, we utilized a 3-m long PCF with a 10-μm hollow core coupled to SMF-28 pigtails at both ends. The 30–70-ns laser pulses of the Watt scale peak power at the wavelength λ = 1528.015 nm of the P5 line of ν1 + ν3 combinational band of acetylene were used. The saturation power at the center of the Doppler broadened (≈520 MHz) absorption line was observed to grow in the range 0.15–1.2 W in the acetylene pressure interval 0.07–0.7 mbar which was evaluated from the cell optical absorption. The slow light propagation of the 30-ns saturating laser pulses with maximal fractional delay of ≈0.1 was experimentally observed. Optimal input pulse power in this experiment grew with the cell optical density following growth of the saturation power.

Experiments on slow/fast light propagation in the Bragg grating recorded in the optical waveguide formed in a photorefractive copper-doped lithium niobate wafer are reported. The change from slow to fast light propagation in the 8-mm-long grating with spectral FWHM of ≈0.14 nm and maximum Bragg reflection of ≈90% was achieved by tuning the carrier wavelength around the central Bragg value of ≈1553.36 nm. Effective electrooptical control of the 80-ps pulse shift (fractional delay/advancement of up to 0.4) was demonstrated by applying an external voltage of ≈80 V to the electrodes deposited on the waveguide sides.

We report effective formation of population gratings in ytterbium-doped fibers by coherent light at 976 nm, i.e. at the wavelength that is typically utilized for optical pumping of these fibers. The dynamic gratings need sub-mW cw laser power to be recorded and have comparable amplitude (absorption) and phase (refractive index) components. Given the spontaneous relaxation time of a Yb 3+ meta-stable level of ~ 0.8 ms, the grating formation time proved also to be in the sub-ms region with the phase grating component significantly slower than the amplitude one.

Dynamic population gratings recorded via local saturation of optical absorption/gain in rare-earth (Er, Yb) doped fibers demonstrate contributions of the amplitude and phase components. Quantitative comparison of the experimentally observed amplitude grating efficiency with that evaluated from spatially uniform saturation of the fiber optical absorption usually shows a significant discrepancy. The grating amplitude proves to be significantly weaker than its theoretical evaluation. The first results on quantitative comparison of the recorded phase grating amplitudes with spatially uniform photo-induced refractive index change in Er-doped fibers at three essentially different wavelengths (1485, 1526, and 1568 nm) are reported. As for the amplitude grating component, the experimentally observed phase grating amplitude is inferior to its theoretical evaluation; this discrepancy is spectrally dependent and is also significantly reduced in the short-wavelength region 1480–1490 nm on the Er3+ ion absorption.

We report linear polarization-insensitive detection of optical phase modulation in an adaptive interferometer based on transient two-wave mixing via dynamic population gratings in saturable Er-doped fiber (EDF). The proposed simple and robust configuration has an all-fiber design based on commercially available elements which makes it promising for applications in optical fiber interferometric sensors and coherent optical communication systems. The experimentally investigated single-mode polarization-maintaining EDF arrangement operated at 1492 nm and demonstrated efficient compensation of the polarization drifts below 100 Hz.

We report detailed experimental results on the optical nutation effect in acetylene-filled hollow-core photonic crystal fibers (HC-PCFs). This coherent quantum optical effect is manifested by the appearance of attenuated oscillations in the profiles of transmitted step-like coherent optical pulses. The experiments used 15 ns optical pulses with peak powers up to ∼4 W and centered at 1530.37 nm, which corresponds to the acetylene (12C2H2) vibration-rotation resonance absorption line P9. The all-fiber cell made from a HC-PCF with internal diameter ∼10.3 μm contained a gas pressure of about 0.12 Torr. The Maxwell-Bloch equations are used to analyze the influence of the homogeneous relaxation, the inhomogeneous Doppler broadening of the absorption line, and the random orientation of the acetylene molecules. By comparing the experimental results with numerical simulations, we obtain the longitudinal and the transverse relaxation times to be close to 10 ns and find that the transition dipole moment of the acety...

We demonstrate experimentally the detection, in a remote and noncontact manner, of human life signs using a high-sensitivity pulsed laser vibrometer. The high surface displacement detection sensitivity of the photo-electromotive-force (photo-EMF) pulsed laser vibrometer, combined with its tolerance to the presence and moderate temporal variations of optical speckles in the light beams, allows the detection of human heartbeats, breathing, and gross physical movement from essentially any part of a human subject's surface, even in the presence of clothing, all the while without limiting the interrogation points to specific locations like the chest and carotid areas. In contrast to conventional Michelson interferometer-based laser vibrometers, the photo-EMF pulsed laser vibrometer (PPLV) does not require the use of retroreflective tapes or special electronic filtering to retrieve vividly the biological subject's life signs. Experimental results demonstrating the detection of life signs from various parts of biological subjects' bodies, with or without the coverage of clothing are presented. We also demonstrate the monitoring of a human subject's heart movements by interrogating the back of his/her hand. Results from using PPLV to determine extremity blood circulation at various levels of proximal occluding pressures are also presented.

Experimental observation of phase (i.e. refractive index) component in the dynamic gratings recorded in erbium-doped optical fiber with saturation of optical absorption is reported. We utilized configuration of transient two-wave mixing with rectangular phase modulation of one of counterpropagating recording waves, where unshifted phase grating resulted in a transient energy exchange. The reported experiments were performed with heavily doped (≈5400 ppm erbium) fibers in a wide spectral range of Er3+ fundamental absorption at selected laser wavelengths 1492, 1526, 1549, and 1568 nm. Relative contribution of phase grating was especially large (up to ≈100% of the maximal amplitude component) at the opposite sides of the investigated spectral range and was significantly lower in its central part. The amplitude grating was found especially strong at short wavelength side of the spectrum (i.e. at 1492 nm), where the grating amplitude proved to be only two times lower than the theoretically predicted from consideration of two-level model.

We report on detailed investigation of the photo-electromotive-force (photo-EMF) effect in semiconductor with bipolar photoconductivity of impurity type in a spectral region close to the fundamental absorption edge, where both the photoconductivity and the photo-EMF response reach their maxima. The experiments performed with CdTe:V crystal (Δ E ≈ 1.51 eV) in the spectral range of 826–853 nm show that dynamics of the photo-EMF signal formation in this crystal is governed by relaxation of slow majority photocarriers–holes with the life-time which goes down from τ ≈ 9 μs at 850 nm to ≈6.5 μs at 826 nm. The minority photocarriers (electrons), which contribute approximately 10% of the total photoconductivity, also demonstrate significant wavelength dependence of their diffusion length with L D ≈ 8.5 μm at 850 nm and ≈6.3 μm at 830 nm. The reported results show significant improvement in responsivity of the bipolar CdTe:V photo-EMF detector when it is operated at λ = 840 nm (by factor ≈2.5 as compared with that at 852 nm).

Theoretical analysis of the transient two-wave mixing (TWM) of two continuous waves with rectangular phase modulation counter-propagating through the Er-doped optical fiber is presented. Approximate analytic solutions obtained for undepleted interacting waves of low power (neglecting large-scale saturation of the fiber optical absorption) and of high power (with significant spatially uniform large-scale absorption saturation) are complemented by numerical simulation for a broad region of the recording light power. The experimental dependence of the TWM efficiency on the recording power obtained for a single-mode fiber with ≃640 ppm erbium concentration and with initial optical density ≈8.4 at λ = 1526 nm demonstrated the initial, growing and decaying parts predicted theoretically. The maximum experimentally observed relative TWM signal amplitude proved to be approximately 3 times lower than expected.

We report on the experimental demonstration of semiconductor photo-electromotive force (photo-EMF) adaptive detector for laser ultrasonic applications with responsivity close to the theoretical limit for monopolar device of this type. The photo-EMF detector fabricated of a monopolar CdTe:V crystal was characterized in the spectral region 827–852 nm which is very close to the fundamental optical absorption edge of CdTe ( ≈ 825 nm). At λ = 833 nm the experimentally observed photo-EMF signal amplitude reached its maximal value, which corresponds to the theoretical limit for a monopolar photoconductor with quantum efficiency of photoconductivity 0.6–0.75.

Theoretical analysis of two-wave mixing (TWM) via reflection population grating, aiming to support current experimental investigations of dynamic gratings in Erbium (Er)-doped fibers, is presented. It is shown that for low recording intensities the stationary TWM via reflection saturated absorption gratings is well described in approximation of a spatially uniform grating amplitude. The analysis of the transient TWM is performed both for rectangular and for sinusoidal phase modulation of one of the recording waves and it is shown how the recorded grating amplitude and characteristic recording time can be obtained from the detected signals. It is pointed out that the majority of the existing experimental results on TWM in Er-doped fibers are qualitatively explained within the framework of the developed model.

We report on experimental observation of transient mixing of two mutually coherent waves of orthogonal polarizations collinearly propagating through birefringent Er-doped fiber. The dynamic grating responsible for this two-wave mixing (TWM) process is formed via effect of polarization hole burning (PHB) and has spatial period equal to the beat length of the fiber birefringence. Experiments were performed at the laser wavelength 1549 nm in 2-m long Er-doped fiber with 2-cm birefringence beat length without optical pumping. We observed that the transient collinear TWM has amplitude and characteristic relaxation time close to those of transient PHB effect measured for linearly polarized light and similar to corresponding characteristics of transient TWM observed for counter-propagating orthogonally polarized waves in the same fiber.

Summary Dynamic two-wave mixing of periodically phase modulated beams in liquids with thermal mechanism of optical nonlinearity for measurements of thermo-optical characteristics and, in particular, of optical absorption is proposed. Unlike conventional “pump-and-probe” technique, the configuration under consideration does not need an additional probe beam. This reduces problems with alignment and ensures an increased output signal, which proves to be proportional to the recorded photo-thermal grating amplitude. The method is illustrated with experiments performed at λ=633 nm using a model sample of acetone dyed with “methylene blue”. Evaluation of the limit sensitivity of the configuration for detection of low optical absorption is also given.

Simultaneous utilization of ac photoelectromotive (photo-EMF) and modulated photocarrier grating (MPG) techniques for characterization of bipolar transport in semi-insulating photorefractive GaAlAs multiple quantum well structure is reported. From the ac photo-EMF experiment the electrons were determined as the dominant photocarriers for interband optical excitation at λ=633 nm. From the self-consistent data obtained from photo-EMF and MPG experiments the diffusion length of the photoelectrons was evaluated as LD≃1.4±0.2 μm, and that of the photoholes (minority carriers)—as LDm≃0.6±0.1 μm. In the MPG configuration, the contrast of the illuminating interference pattern was controlled by electro-optic modulation of the signal beam polarization, which allowed us to measure dielectric relaxation time of the photoconductor as well. As evaluated by both techniques it proved to be about τdi≃0.05 μs for the average light intensity I0≃0.3 mW/mm2. The proposed combination of the characterization techniques seems to...

Detailed experimental data on the efficiency of two-wave mixing via population dynamic grating in erbium-doped fiber (EDF) with saturable optical absorption are presented. The measurements were performed for spectral region 1490–1560 nm of the EDF absorption/gain spectrum, both for absorption and for phase (refractive index) components of the dynamic grating. The reported data confirm the earlier results published for some particular recording wavelengths. In particular, the amplitude gratings recorded in EDF in the central part of this region (1520–1560 nm) are significantly less efficient (by more than 1 order of magnitude) than it can be estimated from measurements of a spatially uniform fiber absorption saturation. It is shown, however, that this effect cannot be explained by spatial migration of the Er3+ excited state. At the short-wavelength spectrum side around 1490 nm, the disagreement between the experimentally observed and the evaluated grating amplitude is minimum (∼0.3) and can, probably, be attributed to the polarization mismatch in the counterpropagating recording waves.

Saturated optical absorption, electromagnetically induced transparency, and slow/fast light propagation on their basis have recently been reported for the acetylene (C2H2) filled Hollow Core Photonic Crystal Fibers (HC-PCF) in the 1530nm spectral region (see e.g. [1-3]). Here we report experimental observation of the nonstationary coherent effects, such as optical nutation and free induction, in the acetylene filled HC-PCF. For experiments we used an allfiber pumped-through setup [3] with a 2.6 m-long HC-PCF with the capillary core diameter 10 μm. The gas pressure was 0.35 Torr, and the wavelength (1530.37 nm) corresponded to the P9 acetylene absorption line. Fig.1 presents typical profiles of the 15 ns input and output pulses observed for different incident light peak powers. The ratio between the output and input profiles (i.e., transmission coefficient) demonstrates pronounced temporal oscillations, which we attribute to the optical nutation effect caused by coherent Rabi oscillations [4]. The trailing edges of the input/output pulses shown in the inset to Fig.1 demonstrate another coherent effect i.e. the free optical induction [4].

A single-detector adaptive configuration for polarization-insensitive homodyne detection of optical phase modulation is proposed. Experiments were performed at a HeNe laser wavelength ( λ =633 nm) and employed GaAs photo-EMF adaptive detectors. It has been shown that residual fluctuations in the output signal are basically due to nonlinearity of the adaptive photodetector response to the intensity of the polarization-modulated signal wave.

Measurements of non-steady-state photocurrents and of time-modulated conductivities for homogeneous illumination of varying intensity are performed with a photorefractive iron-doped barium–calcium titanate crystal of the congruently melting composition (Ba 0.77 Ca 0.23 TiO 3 , BCT). The diffraction efficiency and the two-beam coupling gain are determined from conventional holographic experiments. Debye screening and diffusion lengths are found to be of the order of 0.1 μm. The response-time of the material is 2 s (light intensity 0.2 W/cm 2 , wavelength 514 nm) and the dark storage time is 6 s. The measured refractive index changes are only one third of the values, which are expected from the known electrooptic coefficients and space-charge fields.

Original experiments on measurements of the coherence length of diffusely scattered CW laser beams using GaAs adaptive photodetectors based on the photo-EMF effect are presented. Simplicity of the configuration, capability to detect aberrated speckle-like wavefronts with high signal-to-noise ratio, and potentially high speed of operation make this configuration potentially useful for Optical Coherence Tomography and Laser Ranging.

We present experimental results which demonstrate that non-steady-state photo-EMF, induced by vibrating interference fringes in Bi12SiO20 photorefractive crystal can be dramatically (by a factor of 103 in our experimental conditions) enhanced in a resonance regime under application of an external DC field. We show that for increasing applied electric field the resonance maximum moves from the dielectric relaxation frequency towards the low frequency end. Its magnitude grows as E02 for low values of the field, for high external field significant broadening of the resonance peak and linear growth of the signal resonance amplitude is observed. This effect and non-trivial dependence of the resonance signal amplitude on the spatial frequency of the pattern is explained by saturation of the space charge grating. Finally, the sensitivity of the biased resonance adaptive photo-EMF detector is estimated.

Measurements of non-steady-state holographic photocurrents and conventional modulated photocurrents are performed with a n-type photorefractive strontium-barium niobate crystal at light wavelength of 532 nm. The effective charge carrier density and the photocarrier diffusion lengths for two orthogonal directions in the crystal are deduced. A ratio of the photoelectron mobilities along the c and a axis of 2.4 is obtained. The dependence of the photocurrent signals on the modulation frequency points to an essential contribution of shallow traps to the charge transport.