Showing papers by "Gerard Mourou published in 1989"

Picosecond GaAs‐based photoconductive optoelectronic detectors

Abstract: A novel material deposited by molecular beam epitaxy at low substrate temperatures using Ga and As4 beam fluxes has been used as the active layer for a high‐speed photoconductive optoelectronic switch. The high‐speed photoconductive performance of the material was assessed by fabricating two devices: an Auston switch and a photoconductive‐gap switch with a coplanar transmission line. In a coplanar transmission line configuration, the speed of response is 1.6 ps (full width at half maximum) and the response is 10 to 100 times greater than that of conventional photoconductive switches. Since the material is compatible with GaAs discrete device and integrated circuit technologies, this photoconductive switch may find extensive applications for high‐speed device and circuit testing.

Short-pulse laser absorption in very steep plasma density gradients.

Abstract: We have measured the absorption of 1-ps laser pulses interacting with matter at intensities from ${10}^{10}$ to ${10}^{16}$ W/${\mathrm{cm}}^{2}$. The variations of absorption with incidence angle and polarization have been used to infer submicron plasma-density-gradient scale lengths. The results show a transition between a regime of laser interaction with sharply bounded dense cold matter ($I\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ W/${\mathrm{cm}}^{2}$), where absorption is by the usual skin depth effect, to a regime of interaction with a plasma of very steep density gradient ($\frac{L}{\ensuremath{\lambda}}\ensuremath{\le}0.2$) ($5\ifmmode\times\else\texttimes\fi{}{10}^{12}\mathrm{W}/{\mathrm{cm}}^{2}\ensuremath{\le}I\ensuremath{\le}{10}^{15}\mathrm{W}/{\mathrm{cm}}^{2}$).

Picosecond Electronics and Optoelectronics

Abstract: This book presents papers on semiconductor lasers. Topics considered include a mode-locked laser with a single-mode fiber output, a fast multiple quantum well absorber for mode locking, the suppression of timing and energy fluctuations in a mode-locked semiconductor laser by cw injection, and parametric oscillations in semiconductor lasers.

Chirped-pulse amplification of 100-fsec pulses

Abstract: Chirped-pulse amplification is used to generate 2-mJ pulses of 106-fsec duration in an alexandrite amplifier. Compression of the optical pulse is achieved by using a sequence of intracavity prisms in conjunction with diffraction gratings. This allows for the compensation of both linear and quadratic contributions to the dispersion from the amplifier.

Tunneling escape time of electrons from a quantum well under the influence of an electric field

Abstract: We have performed time‐resolved photoluminescence on GaAs/AlxGa1−xAs single quantum well structures with an electric field applied perpendicular to the well plane. The quantum wells are coupled to the GaAs continuum through a thin barrier; the escape time of the electrons in the well was measured by time‐resolved photoluminescence. The dependence of the decay time on applied bias was found to agree very well with a simple semiclassical model.

100 GHz traveling‐wave electro‐optic phase modulator

Abstract: Dramatic bandwidth enhancement has been achieved in a GaAs traveling‐wave electro‐optic phase modulator by the addition of a GaAs superstrate to suppress both velocity mismatch and electrical dispersion.

Chirped pulse amplification of 300 fs pulses in an alexandrite regenerative amplifier

Abstract: The amplification of femtosecond dye laser pulses up to the 3.5-mJ level in an alexandrite regenerative amplifier is discussed. An expansion/compression system using diffraction gratings allows chirped amplification techniques to be used to produce peak powers upwards of 1 GW. Limitations in the chirped pulse amplification of ultrashort pulses due to intracavity dispersive elements are discussed. >

Charge-transfer-state photoluminescence in asymmetric coupled quantum wells

Abstract: We have performed continuous and time-resolved photoluminescence experiments on novel double-quantum-well structures in Schottky diodes. We have directly observed the buildup of a charge-transfer (CT) state in which the electrons and holes are in separate wells because of the fact that they tunnel in opposite directions. We have studied the effect of an electric field on the CT state formation, and have observed a strong, linear Stark shift of the CT luminescence.

Theoretical and experimental investigations of subpicosecond photoconductivity

Abstract: Monte Carlo methods are used to study photoconductive transients in gallium arsenide. It is demonstrated that working with presently established ranges for the Γ‐L coupling coefficient, the existence of a velocity overshoot at moderate fields cannot be exactly predicted. The role of negative velocity electrons in the initial transient for short wavelength excitation is also demonstrated. Details of an actual experiment are described and evaluated against a model which incorporates the Monte Carlo simulation into a transmission line structure with a frequency‐dependent characteristic impedance. The results demonstrate that an appropriately designed experiment can observe subpicosecond carrier transport transients.

Absorption of an ultrashort laser pulse in very steep plasma density gradients

Abstract: The authors present calculations of the absorption of an ultrashort laser pulse in various plasma density profiles, with density scale lengths less than or comparable to the wavelength, for various angles of incidence, and for both s and p polarizations. This simple model is used to infer submicron plasma-density-gradient scale lengths from measurements of the variation of absorption with angle and polarization, for data obtained with plasmas created by 1-ps, 1.06- mu m laser pulses. These experimental results, obtained with a short pulse (1 ps) incident on solid matter, are analyzed between 5*10/sup 12/ W/cm/sup 2/ and 5*10/sup 14/ W/cm/sup 2/. It is found that in this intensity range, where the interaction is with a plasma of finite but very steep density gradient and where prepulse and nonlinear effects are weak or negligible, 3*10/sup -2/ >

Picosecond pulse formation by transmission line discontinuities

Abstract: We present a technique for transforming electrical step-like excitations into picosecond electrical pulses by using discontinuities embedded in a coplanar transmission line structure. We have experimentally demonstrated the formation of 3 ps pulses from photoconductively generated steps. Equations for the pulse amplitude/duration trade-off based on a lumped element approach are given and shown to be in agreement with the calculations of the element values.

Ultrafast response of superconducting transmission lines

Abstract: The authors report investigations of picosecond transient propagation on normal and superconducting transmission lines and results of a variety of lines that include YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coplanar lines, a superconducting coaxial cable, and a dielectric-matched gold-line structure. A previously developed algorithm for analyzing transient propagation was used to identify the dominant mechanisms for signal distortion in most of these cases, and the essential properties of all tested to date are summarized for a direct comparison. >

External electro-optic probing of millimeter-wave integrated circuits

Abstract: An external, noncontact electrooptic measurement system, designed to operate at the wafer level with conventional wafer probing equipment and without any special circuit preparation, has been developed. Measurements have demonstrated the system's ability to probe continuous and pulsed signals on microwave integrated circuits on arbitrary substrates with excellent spatial resolution. In addition, it has been shown that the electrooptic probe tip can measure voltage values on an integrated circuit chip, even in areas where physical contact made by a test instrument would be inappropriate. Experimental measurements on a variety of digital and analog circuits, including a GaAs selectively doped heterostructure transistor prescaler, an NMOS silicon multiplexer, and a GaAs power amplifier MMIC (monolithic microwave integrated circuit) are reported. >

External electro-optic probing of millimeter-wave integrated circuits

Abstract: An external, noncontact electrooptic measurement system, designed to operate at the wafer level with conventional wafer probing equipment and without any special circuit preparation, has been developed. Measurements have demonstrated the system's ability to probe continuous and pulsed signals on microwave integrated circuits on arbitrary substrates with excellent spatial resolution. In addition, it has been shown that the electrooptic probe tip can measure voltage values on an integrated circuit chip, even in areas where physical contact made by a test instrument would be inappropriate. Experimental measurements on a variety of digital and analog circuits, including a GaAs selectively doped heterostructure transistor prescaler, an NMOS silicon multiplexer, and a GaAs power amplifier MMIC (monolithic microwave integrated circuit) are reported. >

Ultrafast optical modulator

Abstract: An ultrafast traveling wave optical modulator capable of functioning at frequencies greater than 100 GHz having an optical waveguide parallel to a transmission line. The optical waveguide is in a substrate of electro-optic material (GaAs with GaAlAs layers forming the optical waveguide). The transmission line is a pair of coplanar electrodes on the substrate. A superstrate having an effective dielectric constant substantially equal to the square of the index of refraction of the substrate (a GaAs body in which the electric field on the line is substantially confined) eliminates the mismatch in velocity of propagation of the traveling electrical and optical signals thereby increasing the response time of the modulator so that it can function when the electrical modulating signal on the line exceeds 100 GHz in bandwidth.

Amplification of 100-fs pulses in alexandrite using chirped pulse techniques

Abstract: The advent of chirped pulse amplification (CPA)1 has led to renewed interest In the development of solid state amplifiers for ultrashart pulses. The broad bandwidths and high energy storage capabilities of solid state materials such as alexandrite and Ti: sapphire point to the potential for these materials in the production of high energy femtosecond pulses. Recently, we reported on the generation of 300-fs pulses at the millijoule level in an alexandrite regenerative amplifier.2 We present new results extending the CPA technique to the generation of 106-fs pulses with peak powers of 20 GW.

Optical Oscilloscope Capable Of Measuring Picosecond Electrical Waveforms

Abstract: We have developed a new system for measuring picosecond electrical waveforms, where the advantages of electro-optic sampling are maintained, but the need for a complex short-pulse-laser is eliminated. The system utilizes two advanced technologies; an optical oscilloscope which is a conceptually new optical waveform analyzer with picosecond time resolution, and an electro-optic modulator for electric to optical signal convertor. Using this system, the waveform of the driving current and optical pulses from a laser diode have been simultaneously measured with the temporal resolution of < 25 ps.

Amplification of 100-fs Pulses in Alexandrite Using Chirped Pulse Techniques

Abstract: Chirped pulse amplification is used to generate 2 mJ pulses of 106 fs duration in an alexandrite amplifier. Compression of the optical pulse is achieved by using a sequence of intracavity prisms in conjunction with diffraction gratings. This allows for the compensation of both linear and quadratic contributions to the dispersion from the amplifier.

Subnanosecond Time-Resolved Electron Diffraction from Thin Crystalline Gold Films

Abstract: A 100-ps-resolution electron pulse was used to study a 25-nm thick gold single crystal irradiated by a synchronized infrared optical pulse. The change in electron diffraction intensity following laser heating (the Debye-Waller effect) was measured as a function of delay time. The relaxation of a crystal lattice distortion in the surface region appears to explain an observed oscillation in time of the scattered electron intensity. This novel technique provides a sensitive structure probe for short-time dynamics and is, we believe, the fastest lattice temperature probe.