New x-ray radiographic systems based on large-area flat-panel technology have revolutionized our capability to produce digital x-ray images. However, these imagers are extraordinarily expensive compared to the systems they are replacing. Hence, there is a need for a low-cost digital imaging system for general applications in radiology. A novel potentially low-cost radiographic imaging system ba...

The near-field propagation behavior of terahertz (THz) pulses generated by a planar large-aperture photoconducting THz transmitter has been characterized. A simulation model based on Huygens-Fresnel diffraction theory has been developed that permits accurate prediction of the spatiotemporal profiles of the THz beam everywhere and gives excellent agreement with experimental measurements. Two key...

From classical charge transport equations and dipole radiation equations, we derive a simple analytical model for the signal detected in terahertz time-domain spectroscopy using photoconducting antennas. The validity of our model is checked by comparison to published calculated results and to experimental data we have measured. This expression depends mostly on the carrier lifetime in the anten...

We describe the principles of free-space terahertz waveform synthesis by using a programmable optical pulse shaper to drive a photoconducting dipole antenna. We illustrate this technique using several experimental examples, including manipulation of the amplitude and the phase of ultrafast terahertz waveforms as well as generation of ultrafast bit sequences at terahertz frequencies. We present ...

We compare the use of free-space electro-optic sampling ~FSEOS! with photoconducting antennas to detect terahertz ~THz! radiation in the range of 0.1–3 THz. For the same average THz power and low-frequency modulation, signal-to-noise ratio and sensitivity are better with antenna detection at frequencies smaller than 3 THz. When the modulation frequency is increased to more than 1 MHz in FSEOS, ...

Herein, we demonstrate the ability to optically tune mobility of electrically powered Janus particles (JPs) that are half-coated with various zinc oxide ($\mathrm{Zn}\mathrm{O}$) semiconducting layers, i.e., polycrystalline, amorphous, and amorphous a ${\mathrm{Si}\mathrm{O}}_{2}$ passivation layer. The $\mathrm{Zn}\mathrm{O}$ semiconductor photoresponse causes an increase in its electrical con...