Arthur L. Smirl

Picosecond photorefractive and free-carrier transient energy transfer in GaAs at 1 mu m

The strength, formation, and decay of photorefractive and free-carrier gratings written in GaAs by 43-ps pulses at a wavelength of 1 mu m are investigated using picosecond-time-resolved two-beam coupling, transient grating, and degenerate-four-wave-mixing techniques. Photorefractive weak-beam gains of a few percent are measured at fluences of a few pJ/ mu m/sup 2/ (0.1 mJ/cm/sup 2/), and gain from transient energy transfer is observed at fluences larger than approximately 10 mJ/cm/sup 2/ in the beam-coupling experiments. The roles of saturation and two-photon absorption in determining the final electron, hole, and ionized-donor populations and the roles of drift and diffusion in determining the quasi-steady-state photorefractive and free-carrier index modulations are discussed. >

Picosecond photorefractive beam coupling in GaAs

We report the first observation to our knowledge of the photorefractive effect on picosecond time scales. Photorefractive beam coupling in GaAs with picosecond, 1.06-microm pulses is observed owing to charge separation between electrons and the ionized defect EL2(+) at low fluences and to separation between free electrons and holes created by two-photon interband absorption for high fluences. The accompanying processes of linear absorption, two-photon absorption, and transient energy transfer are also observed.

A hybridly mode-locked CW dye laser with brewster prisms

Abstract Stable pulses as short as 69 fs duration have been generated by a linear-cavity, synchronously-pumped cw rhodamine 6G dye laser incorporating a pair of Brewster-angled quartz prisms and the saturable absorbers DQOCI and DODCI.

Picosecond photorefractive effect in BaTiO(3).

We report the observation of photorefractive index gratings written and read out in BaTiO(3) using single pulses of 30-psec duration and fluences of 1 to 15 mJ/cm(2) at a wavelength of 0.532 microm. While the photorefractive gratings are masked during formation by large free-carrier grating, they are clearly seen from 50 psec to many minutes following the peak in the writing beams. The rapid and complete formation of the photorefractive grating and the complete decay of the free-carrier grating on a scale of 50 to 100 psec indicate either that the carrier-recombination time in our sample of BaTiO(3) is less than 100 psec or that the mobility of the carriers is >23 cm(2)/V sec.

Cavity-length detuning effects and stabilization of a synchronously pumped femtosecond linear dye laser

We report on the cavity-length detuning characteristics of a synchronously pumped femtosecond linear-resonator cw dye laser. The severe cavity-matching requirement (to within 0.2 μm) for optimum short-pulse generation is addressed by an active cavity-length stabilization scheme based on second-harmonic generation. This allows pulses ~100 fsec in duration to be maintained for periods of several hours.

Femtosecond pulse generation in the red/deep red spectral region

Optical pulses as short as 55 fs in duration have been generated near 675 nm in a synchronously pumped, hybridly mode-locked, sulforhodamine 101 dye laser. Hybrid mode locking of rhodamine B in the same cavity arrangement yielded 187 fs pulses at 650 nm.

Photoreflectance of GaAs doping superlattices

Abstract We have performed room-temperature photoreflectance measurements on two GaAs doping superlattices having considerably different built-in potentials (1.2 eV and 85 meV). The first sample exhibits Franz-Keldysh oscillations, the period of the oscillations corresponding to the large built-in dc field . A second dc pump beam has been used to change the electron-hole concentration and hence the built-in field. The spectrum of the second sample displays a number of features corresponding to quantized electron and hole states. There is qualitative agreement between experiment and theoretical calculation based on a two-band tight-binding model. In both samples the dependence of the amplitude of the photoreflectance signal on pump chopping frequency yields the minority carrier lifetime.

Variable intracavity spectral windowing in a synchronously pumped femtosecond cw dye laser

An aperture of variable width has been placed within an intracavity prism sequence in a synchronously pumped femtosecond dye laser. This is shown to permit direct control of the output pulse width in the range approximately 100-500 fsec. Wavelength tunability is achieved by translating the aperture transversely.

Nonlinear refraction in silicon induced by one-micron picosecond pulses

Abstract We use self-defocusing of 25 ps pulses of 1 μm radiation to quantify the optically-induced changes in the refractive index of Si. We find that a model based on external self-action and a Drude polarization can accurately describe our results. The model assumes linear generation of electron-hole pairs but also includes free-carrier absorption. We measure a peak phase distortion at 2.25 GW/cm 2 that is roughly 60 times larger than produced by the same thickness of CS 2 at this irradiance.

Nonlinear optical properties of the electron-hole plasma in Al0.52Ga0.48As

A dense electron‐hole plasma is created in Al0.52Ga0.48As using picosecond excitation with high excess energy. Its properties are studied by time‐resolved photoluminescence and transient transmission spectroscopy. Simultaneous emission out of the indirect X and the direct Γ band is observed. Alloy disorder strongly influences the bimolecular recombination by allowing for quasidirect transitions and stimulated emission out of the indirect X band. The electron‐hole plasma, whose electrons reside mainly in the X valleys, causes strong optical nonlinearities at the direct absorption edge. A persistent absorption bleaching and large induced refractive‐index changes due to band filling of the valence band and induced absorption due to band‐gap renormalization are observed.