Jean-Marc Halbout

Generation of subpicosecond electrical pulses on coplanar transmission lines

Electrical pulses shorter than 0.6 ps were generated by photoconductively shorting a charged coplanar transmission line with 80 fs laser pulses. After propagating 8 mm on the line the electrical pulses broadened to only 2.6 ps.

Silicon Mach–Zehnder waveguide interferometers based on the plasma dispersion effect

Silicon Mach–Zehnder waveguide modulators have been fabricated and operation characterized at the wavelength of 1.3 μm. Device operation is based on the free‐carrier‐induced change in the refractive index of silicon. Modulation depths of −4.9 dB and response times τresponse<50 ns have been achieved at λ=1.3 μm for an injected carrier density of 6.5×1017 cm−3.

12‐fs ultrashort optical pulse compression at a high repetition rate

We have produced 12‐fs (full width at half‐maximum), 0.5‐MW optical pulses at a 500‐Hz repetition rate by passing the amplified pulses from a colliding pulse, passively mode‐locked ring dye laser through an optical fiber pulse compressor.

Broad-band microwave measurements with transient radiation from optoelectronically pulsed antennas

A broadband microwave measurement technique based on picosecond transient radiation from optoelectronically pulsed antennas is described. It is performed with exponentially tapered coplanar stripline antennas which are integrated with the photoconductive devices used for ultrafast pulse generation and sampling. The signal analysis required for deriving the desired physical properties from the measured time-domain waveforms is discussed. This is a coherent technique that independently determines both the real and the imaginary parts of the dielectric constants of materials, from 10 to 130 GHz, in a single experiment. Some representative results are presented. >

Capacitance free generation and detection of subpicosecond electrical pulses on coplanar transmission lines

By reanalyzing an earlier experiment to generate subpicosecond pulses using photoconductive switches (M.B. Ketchen, et al., Appl. Phys. Lett., vol.48, pp.751-753, 1986), it is shown that to first order, the sliding-contact generation site has no capacitance. This conclusion is further supported by a double sliding-contact experiment where, to first order, neither the generation nor the detection site has any capacitance. This result removes the parasitic capacitance of the electrical circuit as one of the major difficulties to short electrical pulse generation using photoconductive switches. >

Noninvasive picosecond ultrasonic detection of ultrathin interfacial layers: CFx at the Al/Si interface

A picosecond ultrasonics technique has been used to detect interfacial fluorocarbon (CFx) layers as thin as 0.5 nm between aluminum and silicon. The presence of the CFx material reduces acoustic damping and heat loss from the Al film into the Si substrate. This provides a means for noninvasive identification of organic/polymeric contaminants at the buried interface and potentially for characterizing interfacial mechanical properties.

Silicon optical modulators at 1.3- mu m based on free-carrier absorption

Silicon optical waveguide modulators, appropriate for operation in the 1.3-1.55 mu m wavelength region, have been fabricated and their performance characterized at the wavelength of 1.3 mu m. The modulator structures consist of p-i-n diodes integrated with silicon waveguides; device operation is based on free-carrier absorption. Modulation depths of -6.2 dB and response times less than 50 ns have been measured. Experimental results are compared with the p-i-n diode theory. It is argued that the device is suitable for integration with silicon electronics and silicon optoelectronic devices. The response times measured for the current devices may be improved by reducing the transverse dimensions of the p-i-n structure.<<ETX>>

Noncontact high-speed waveform measurements with the picosecond photoelectron scanning electron microscope

The authors have replaced the electron gun and beam blanking system of a conventional voltage contrast scanning electron microscope by a pulse-laser/photocathode combination, resulting in a source producing electron pulses of order 1 ps in duration at a 100 MHz repetition rate and with a peak brightness of 3 10/sup 8/ A/cm/sup 2/ sr at 1.8 keV. This novel instrument has demonstrated stroboscopic noncontact waveform measurements on metal interconnect lines in different environments with a temporal resolution between than 5 ps, a voltage resolution of 3 mV/(Hz)/sup 1/2/, and a spatial resolution of 0.1 mu m. These measurements are achieved with extraction fields above the sample of about 1 kV/mm. >

Coherent broadband microwave spectroscopy using picosecond optoelectronic antennas

We describe coherent microwave transient spectroscopy experiments using picosecond optoelectronic integrated antennas. The effectiveness of the experimental setup for the measurement of the loss and dispersion properties of materials in the 10–125 GHz range is characterized using microwave filters of predictable behavior. We also present measurements of the absorption coefficient and refractive index of fused silica over this frequency band.

Picosecond photoelectron scanning electron microscope for noncontact testing of integrated circuits

A scanning electron microscope which uses an ultrashort pulsed laser/photocathode combination as an electron source produces electron pulses of order 1 ps in duration at a 100‐MHz repetition rate and with a peak brightness of 3×108 A/cm2 steradian at 1.8 keV. By using this instrument in the voltage contrast mode, without contact with the samples, we have been able to measure electrical pulses propagating on coplanar transmission lines with, simultaneously, a temporal resolution of 5 ps, a voltage resolution of 3 mV/(Hz)1/2, and a spatial resolution of 0.1 μm. These measurements are achieved with extraction fields above the sample of about 1 kV/mm.