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Recently, we reported an experimental implementation of THz frequency sweeping with a kHz sweep rate and a THz sweep range using a wavelength-swept laser and a distributed feedback laser in THz photomixing. Frequency-domain THz interferograms can be rapidly measured by combining the THz frequency sweeping and coherent homodyne detection. We present fast thickness measurement based on this measurement...
We recently demonstrated high-speed time-domain and frequency-domain terahertz time-of-flight tomography. To investigate the applicability of these tomography systems to nondestructive inspection of composites, we have prepared glass fiber reinforced polymer samples. The samples have artificial internal defects such as delamination and inclusion, which have various sizes and thicknesses and lie at...
We present a simple data processing technique that effectively removes undesired signals and extracts hidden sample-induced echoes, accurately determining material parameters in ambient atmosphere. The method is validated by demonstrating refractive index and thickness calculations in transmission and reflection terahertz time-domain measurements.
High-speed frequency-domain terahertz (THz) coherence tomography is demonstrated using frequency sweeping of continuous-wave THz radiation and beam steering. THz frequency sweeping with a kHz sweep rate and a THz sweep range is implemented using THz photomixing in which an optical beat source consists of a wavelength-swept laser and a distributed feedback laser diode. During the frequency sweep, frequency-domain...
We present a new technical implementation of a high-speed broadband frequency sweep of continuous-wave terahertz (THz) radiation. THz frequency sweeping with a kHz sweep rate and a THz sweep range is implemented using THz photomixing in which an optical beat source consists of a wavelength-swept laser and a distributed feedback laser diode. During the frequency sweep, frequency-domain THz interferograms...
High-speed terahertz reflection three-dimensional imaging is demonstrated using electronically controlled optical sampling (ECOPS) and beam steering. The ECOPS is used for a 1 kHz axial scan and a transverse scan is performed using beam steering. Telecentric f-theta lenses essential for beam steering have been fabricated with axial and nonaxial symmetry. Using the imaging system, a volume of 100 ×...
We present experimental implementation of high-speed broadband frequency sweep of CW THz radiation applicable to high-speed THz spectroscopy and tomography. A wavelength-swept laser and a distributed-feedback laser diode constitute a high-speed frequency-swept optical beat source used for photomixing.
We demonstrate a frequency swept optical beat source for high speed continuous wave THz generation. The range of the sweeping bandwidth is about 2.16 THz (17.3 nm). And we observe CW THz waveforms for several static optical beat sources using a fiber coupled CW THz measurement system in order to confirm the feasibility of our frequency swept optical beat source as a CW THz radiation source.
We propose a high-speed frequency-scanning optical beat source using a wavelength swept laser and a tunable laser for continuous THz wave generation. The beat frequency is scanned at 1 kHz over a range with a 2.16 THz width.
We demonstrate a continuous THz emission using a low-temperature-grown InGaAs photomixer and a widely tunable dual-wavelength erbium-doped fiber laser as an optical beat source. The wavelength spacing can be tuned from 2.3 nm to 8.8 nm which corresponds to the CW THz frequency from 0.3 to 1.1 THz.
We present high-speed terahertz time-domain spectroscopy based on electronically controlled optical sampling (ECOPS). The time delay between the two laser pulses is demonstrated to be rapidly swept at a scan rate of 1 kHz on a time delay window of 77 ps. It is shown that a measurement time is shortened by a factor of 50 by using ECOPS compared to asynchronous optical sampling.
We propose a widely tunable injection-locked dual-wavelength Erbium-doped fiber laser using two micro-heater-integrated Fabry-Perot laser diodes and two fiber Bragg gratings. The wavelength spacing can be continuously tuned from 2.4 nm to 9.0 nm.
Terahertz birefringence of zinc oxide is investigated using terahertz time-domain spectroscopy. Birefringence is observed in the <10-10> orientation while not in the <0001> orientation. Dispersion of ordinary and extraordinary refractive indices are measured, and the refractive index difference is found to be -0.18 in the 0.25 ~ 1.35 THz frequency region. It is demonstrated through azimuthal...
Continuous-wave (CW) THz generation from InGaAs based photomixers has been demonstrated by using a tunable dual-wavelength 3-section DFB laser diode as the optical beat source. The wavelength of each lasing mode can be tuned by adjusting currents in micro-heaters which are fabricated on the top of the each DFB section. The CW THz frequency emitted from the InGaAs photomixers is continuously tuned...
We have found a modulation-limited behavior of interferometric THz spectra in the one-dimensional multilayer structures making up high/low refractive index material periods. These modulation-limited THz spectra are based on the fact that the degree of THz pulse broadening decreases with increasing the number of periods because some time-delayed and multiple reflected THz pulses are in-phase or out-of-phase...
We report on terahertz frequency and power measurements based on terahertz frequency comb and a bolometer. Terahertz frequency comb and its individual modes are measured through multiheterodyne beat detection by use of a bolometer. A power spectrum of terahertz frequency comb is measured over the frequency up to 1.7 THz, and the frequency and power of the comb modes spectrally resolved are measured...
It is shown that a wavelet power spectrum estimation technique can be applied to high-resolution terahertz time-domain spectroscopy using asynchronous optical sampling to effectively remove noises without sacrificing spectral features on a spectrum.
We demonstrate high-resolution Fourier-transform terahertz spectroscopy using two terahertz frequency combs with stabilized different repetition frequencies without a mechanical time delay tool.
All-optical clock recovery is performed using a multisection semiconductor laser that can generate two kinds of self-pulsation due to compound cavity mode beating and passive mode locking. To investigate factors to influence quality of optical clock, optical clocks recovered from an optical data are compared by using various self-pulsations with different characteristics. It is experimentally demonstrated...
All optical 3R regenerator based on semiconductor is a main building block in realizing all optical signal processing because of small compact, robust, and low cost compatible solution. Functional elements and architectures for building up to 40 Gbps all optical 3R regenerators will be discussed.
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