Terahertz (THz) impulse ranging is used to examine ceramic ball bearings for fractures. THz radiation is demonstrated to transmit through both unfired and fired ceramic targets. The electromagnetic scattering signature of commercial aluminum oxide bearings is measured and compared to identical bearings damaged by thermal stress. Two separate methods are used to determine the presence of fractures: late time impulse response and time domain angular modulation. Late time impulse response detects changes in temporally shifted scattering mechanisms, while time domain angular modulation allows rapid detection of fractures. This evaluation technique is non-contact, nondestructive, requires no liquid medium, and is insensitive to ambient temperatures.
Over the past decade the experimental technique of THz time domain spectroscopy (THz-TDS) has proved to be a versatile method for investigating a wide range of phenomena in the THz or far infrared spectral region from 100 GHz to 5 THz. THz-TDS has wide potential for sensing and imaging. The experimental technique is described along with recent results on THz beam propagation for long base-line THz measurements. THz imaging has been demonstrated using both quasi-optical and synthetic aperture approaches, results are presented including images of scatterers as well as non-destructive evaluation of ceramics. Two potential sensing applications of THz-TDS are discussed, thin film characterization and use of waveguides for sensing.
This contribution focuses on applying the unique optoelectronic THz beam system we have developed to THz time-domain spectroscopy (TDS). The work developing the system is first reviewed. The emerging technique of THz-TDS is introduced, and some past applications are described. We then present a theoretical and experimental comparison between THz-TDS and the well-established Fourier transform spectroscopy (FTS). The extraordinary dynamic range of THz-TDS allows the study of exceptionally optically dense materials; specific past examples and new opportunities are discussed. The topic of difficult samples is explored for samples, such as flames, posing exceptional problems for FTS, but which can be relatively easily measured with THz-TDS.
We have designed and demonstrated two wide bandwidth passive frequency doublers capable of second harmonic generation over the entire 100 nm cavity optics bandwidth of a passively modelocked Ti:Al2O3 laser with minimal loss in conversion efficiency. In addition, we demonstrate that focussing effects are extremely important in determining the bandwidth in sum frequency mixing of ultrashort pulses in the near VUV region. This effect is demonstrated with noncollinear sum frequency mixing performed between the fundamental and the third harmonic subpicosecond pulses of this laser source.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.