A laser terahertz-emission microscope (LTEM) system is proposed and developed for inspecting electrical faults in integrated circuits (IC). We test a commercial operational amplifier while the system is operating. Two-dimensional terahertz-emission images of the IC chip are clearly observed while the chip is scanned with a femtosecond laser. When one of the interconnection lines is cut, the damaged chip has a LTEM image different from that of normal chips. The results indicate that the LTEM system is a potential tool for IC inspection.

Planar metamaterials consisting of subwavelength resonators have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by more than a factor of two compared to the far-field measurement. Moreover, for a film with a thickness of λ/375 the minimal area can be as small as 0.2λ × 0.2λ. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.

Ultrashort electromagnetic waves (600 fs width) from superconducting YBCO thin films have been observed by irradiating current-biased samples with femtosecond optical laser pulses (80 fs width). The Fourier component of the pulse extends up to ∼2 THz. The characteristics of the radiation are studied and the radiation mechanism is ascribed to the ultrafast supercurrent modulation by the laser pulses, which induce the nonequilibrium superconductivity.

We have observed ultrashort electromagnetic pulse radiation from YBa2Cu3O7-δ thin-film dipole antennas. The supercurrent transient is created by the excitation of the supercarriers into quasiparticles with a femtosecond laser pulse, and freely propagated electromagnetic pulses are measured and characterized. A pulse with 0.5 ps full width at half-maximum was obtained, containing frequency components up to 2.0 THz. A femtosecond time-resolved characterization of the spectra revealed that they strongly depend on the excitation conditions, and the quasiparticle recombination time becomes longer with increase in the excitation intensity. It is also observed that the radiation power increases in proportion to the square of both the bias current and the laser power in the region of weak excitation, which is consistent with the classical theory based on a two-fluid model. In the region of strong excitation, deviation from the classical theory was observed.

THz time-domain spectroscopy was used to directly probe the low-energy (0.5-5 meV) electrodynamics of the charge-ordered manganite Pr0.7Ca0.3MnO3. We revealed the existence of a finite peak structure around 2-3 meV well below the charge gap ∼ 300 meV. In analogy to the low-energy optical properties of the well-studied low-dimensional materials, we attributed this observed structure to the collective excitation mode arising from the charge-density-wave condensate. This finding provides the importance role of the quasi-one dimensional nature of the charge and orbital ordering in Pr0.7Ca0.3MnO3.

A system for measuring transmittance of electromagnetic waves in the sub-THz region is proposed. The electromagnetic radiation is generated by the excitation of a photoconductive antenna with a commercially available multimode laser diode. The spectral coverage of the radiation is increased by defocusing the light spot on the photoconductive antenna. Transmitted radiation is detected by a hot-electron bolometer through a Martin–Puplett-type interferometer. Transmittance is measured for n-type Si wafers with various doping levels. The carrier densities calculated from the transmittance agree well with those obtained from the dc conductivity measurement.

We have developed a supercurrent distribution imaging system for high T c superconductive thin films and demonstrated the visualization of the supercurrent distribution in the vortex-penetrated YBa 2 Cu 3 O 7Ϫ␦ thin film strips. The terahertz ͑THz͒ radiation and detection system with a scanning femtosecond laser was employed to visualize the distribution. The imaging system utilizes the principle that the femtosecond optical pulses excite THz radiation into the free space by optical supercurrent modulation, and the radiation amplitude is proportional to the local supercurrent density at the optically excited area. Prior to the observation of the supercurrent distribution, we studied optical excitation effects on the vortices trapped in the strips, calibration of the current density from the THz radiation amplitude, temperature dependence of the THz radiation properties, etc. The laser power dependence of the THz radiation in the remanent state revealed that the excitation with powers larger than the relatively weak finite value ͑about 10 mW in the present case͒ strongly affects the vortices trapped in the films. We attributed this behavior to the optically excited depinning effect. We derived a calibration function from the THz radiation images into the supercurrent density distributions by observing the bias-current dependence of the THz radiation, and applied it for the diagnosis of the distributions in the vortex-penetrated strips. The THz radiation images were successfully transferred into the supercurrent density distributions with quantitative agreement. The minimum magnetic flux resolution at the optically excited area was roughly estimated to be 3 0 where 0 is a single flux quantum. The measurement of the laser beam profile indicated that the spatial resolution of the THz radiation images is limited by the laser beam diameter: 25 m in our case. The observed distributions revealed that the vortices easily penetrate into the strip under an external magnetic field B EX of 0.9 mT, and the persistent supercurrent exists only near the strip edges in the remanent state after removal of the field. The calculations of the convolution between the observed laser pattern and the trial functions suggested that the supercurrent distribution width in the remanent state after removal of the field of 0.9 mT is estimated to be less than 1 m. The temperature dependence of the supercurrent distributions revealed that, below 60 K, the thermal activation produces no significant effects on the penetrated vortices at B EX ϭ0.9 mT, whereas, the vortices in the remanent state after removal of the field of 15 mT were strongly affected by the thermal activation. The decreasing rate of the supercurrent density at the edge with increasing temperature was larger than that inside the strip. This suggested that the vortices trapped near the edges exhibit rather different behavior from the ones that penetrated into the inner part of the strip.

We have demonstrated that the supercurrent distribution in current-biased YBa2Cu3O7−δ thin films can be obtained by measuring the radiation power of THz electromagnetic pulses excited with femtosecond laser pulses. As the radiation power is proportional to the square of the bias current density at the laser spot position, the two-dimensional current distribution can be obtained from the intensity distribution of THz radiation by scanning the laser spot. The characteristic supercurrent distribution is analyzed by using the critical-state model.