An analysis of laser action in a periodic structure is presented. A model two counter-running waves coupled by backward Bragg scattering used. The resonant frequencies and threshold criteria for the modes oscillation have been determined both index gain periodicities. Analytical approximations are given high- low-gain cases, computational results intermediate regimes.

We demonstrate that a combination of prisms and diffraction gratings can provide not only quadratic but also cubic phase compensation ultrashort optical pulses. obtain compressed pulses as short 6 fsec.

We report a novel passive mode-locking technique in which two synchronized counterpropagating pulses interact thin, saturable absorber to produce short pulse. Continuous stable trains of shorter than 0.1 psec are obtained using ring laser configuration.

The kinetics of the primary event in vision have been resolved with use femtosecond optical measurement techniques. 11-cis retinal prosthetic group rhodopsin is excited a 35-femtosecond pump pulse at 500 nanometers, and transient changes absorption are measured between 450 580 nanometers 10-femtosecond probe pulse. Within 200 femtoseconds, an increased observed 540 indicating formation photoproduct on this time scale. These measurements demonstrate that first step vision, 11-cis----11-trans...

We have investigated laser oscillation in periodic structures which feedback is provided by backward Bragg scattering. These new devices are very compact and stable as the mechanism distributed throughout integrated with gain medium. Intrinsic to these also a gratinglike spectral filtering action. discuss variations of refractive index give expression for threshold bandwidth. Experimentally we induced periodicities gelatin films into rhodamine 6G was dissolved. The observed characteristics...

Femtosecond synchrotron pulses were generated directly from an electron storage ring. An ultrashort laser pulse was used to modulate the energy of electrons within a 100-femtosecond slice stored 30-picosecond bunch. The energy-modulated spatially separated long bunch and generate approximately 300-femtosecond at bend-magnet beamline, with spectral range infrared x-ray wavelengths. same technique can be substantially higher flux brightness undulator. Such synchrotron-based femtosecond sources...

The use of self-phase modulation in a single-mode fiber to chirp an optical pulse, which is then compressed with grating-pair compressor, has been shown be practical technique for the production pulses at least as short 30 fsec. We report results theoretical analysis this process. Numerical are presented achievable compression and pulse quality functions length input intensity. These given normalized units such that they can scaled describe wide variety experimental situations used determine...

The reflectivity of silicon has been measured following excitation with intense 90-fsec optical pulses. These measurements for the first time clearly resolve in process energy transfer to crystal lattice and dynamics phase transition melted state.

We report the first observation of femtosecond photon echoes from band-to-band transitions in a bulk semiconductor. The time decay echo, found to vary 3.5 11 fs, has allowed us determine polarization dephasing rate GaAs. This was depend on carrier density experimental range covered, 1.5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ 7\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, indicating dominance carrier-carrier scattering as principal mechanism. observed...

An analysis is given of folded 3-mirror laser resonators with an internal cell set at Brewster's angle. A method described to compensate the astigmatic distortions introduced by both mirror and cell. This compensation achieved for a specific relation between thickness folding It allows formation tight intracavity focus as required in applications such CW dye lasers. discussion mode characteristics compensated cavities limitation on beam concentration Brewster

Pulses of x-rays 300 femtoseconds in duration at a wavelength 0.4 angstroms (30,000 electron volts) have been generated by 90° Thomson scattering between infrared terawatt laser pulses and highly relativistic electrons from an accelerator. In the right-angle geometry, x-ray burst is determined transit time pulse across ∼90-micrometer waist focused beam. The are directed (∼0.6° divergence) can be tuned energy. This source femtosecond will make it possible to combine techniques with ultrafast...

We describe the generation and measurement of optical pulses as short 30 fs. The are produced using self-phase modulation in a 15-cm fiber followed by grating compressor.

We obtain gigawatt white-light continuum pulses that permit spectroscopic measurements with a time resolution of 80 fsec. These extend continuously from 0.19 to 1.6 microm and have sweeps as small 10 fsec/1000 A. find temporal, spatial, spectral properties are consistent self-phase modulation having prominent role in generation the continuum.

We report the first direct observation of nonthermal photoexcited carrier distributions in GaAs quantum-well structures. present experimental studies which show that these thermalize within 200 fs. In addition we are able to near band edge effect long-range Coulomb screening on bleaching two-dimensional-exciton resonances is much weaker than Pauli exclusion principle.

The dynamics of the structural changes that take place on a silicon surface following excitation with an intense optical pulse are observed 90-fs time resolution. threefold rotational symmetry $〈111〉$ becomes rotationally isotropic within picosecond after consistent transition from crystalline to liquid molten state.

Time-resolved measurements of optically induced changes in the near-band-gap transmission spectrum GaAs at 80\ifmmode^\circ\else\textdegree\fi{}K, following excitation with an ultrashort laser pulse, provide a means directly monitoring hot-carrier distribution as it cools to lattice temperature time constant 4 psec. Exciton screening and band-gap renormalization are observed occur less than 0.5

In a distributed feedback (DFB) laser with spatial index modulation, an antisymmetric taper of the parameter, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> , removes threshold degeneracy, which is characteristic uniform structures, and leads to one mode particularly low threshold. Exact solutions are presented for special case step . An approximate perturbation method developed gives simple expressions gains, external...

Efficient broadly tunable dye-laser action with a narrow line output has been demonstrated mirrorless laser system using distributed feedback. The feedback was obtained from spatial modulation of both gain and index refraction, induced by pumping liquid organic dye solution fringes formed the interference two coherent light beams. device over 640 Å either varying angle between interfering pump beams or refractive solvent. Linewidths less than 0.01 were measured peak power 36 kW observed.

Passive mode locking of a cw Rhodamine 6G laser is reported. A stable continuous output picosecond pulses has been achieved. Correlation measurements using second-harmonic generation (SHG) have determined the to be as short 1.5 psec. The are transform limited and wavelength tunable over range 5900–6100 Å.

We investigate the effect of excess excitonic populations created by resonant ultrashort excitation on optical-absorption properties GaAs quantum wells. find that under these conditions at room temperature excitons produce more absorption bleaching than equal densities free-carrier pairs. This partly recovers as ionize to give free carriers. Hence, we directly measure thermal ionization time for first time, and $\ensuremath{\tau}\ensuremath{\sim}300$ fs.

We report the first observation of laser-induced free-free transitions in primary photoelectron spectra gaseous helium ionized by ultrashort soft x-ray pulses. Measured transition amplitudes are well described projecting initial electronic state onto a Volkov wavefunction. Additionally, we direct measurements on temporal duration femtosecond high order harmonic radiation. The pulse is observed to exhibit strong dependencies upon both laser intensity and position generating medium relative focus.

Femtosecond photon-echo techniques are used to probe the dynamics of quantum-confined excitons in nanocrystals CdSe. Using three-pulse photon echoes, modulation echo signal from LO-phonon mode is effectively suppressed, and both electronic dephasing couplings lattice vibrations probed directly. Detailed measurements reported as a function nanocrystal size temperature. The times vary 85 fs 20-\AA{} diameter 270 40-\AA{} crystals. These rates determined by several dynamical processes, all...

A model calculation is presented that describes the features of spectral-hole burning measurements performed under conditions femtosecond transient excitation and probing. Pump-induced changes in spectrum probe transmittance arise not only from level population (hole burning), but also presence pump polarization during probe, perturbations decay polarization. These latter effects give rise to oscillating differential spectra when (shorter) pulse arrives prior peak noise. Only follows bulk...

Chirped ultrashort pulses are used to selectively excite vibrationally coherent populations in the ground and excited electronic states of a molecule liquid solution. Negatively chirped shown enhance nonstationary state component, while positively discriminate against its formation. Separation contributions signal allows us obtain state-specific information about vibrational dephasing.