Observation of energetic terahertz pulses from relativistic solid density plasmas

We report the first experimental observation of terahertz (THz) radiation from the rear surface of a solid target while interacting with an intense laser pulse. Experimental and two-dimensional particle-in-cell simulations show that the observed THz radiation is mostly emitted at large angles to the target normal. Numerical results point out that a large part of the emission originates from a micron-scale plasma sheath at the rear surface of the target, which is also responsible for the ion acceleration. This opens a perspective for the application of THz radiation detection for on-site diagnostics of particle acceleration in laser-produced plasmas

Design and analysis of quasi-optical THz time domain imaging systems

A THz time domain imaging system is optimized and analyzed with ZEMAX. The requirements to the optical design of time domain imaging systems in the THz spectral region are deduced. A system is presented, which is diffraction-limited for wavelengths down to 838 µm and field points up to ±4 mm. In the optical system a 90° off-axis parabolic mirror is combined with an aspheric plastic lens. The lens was made from ZEONEX E48R®, and it was manufactured by ultraprecision machining. A resolution test of the system shows that on time domain analysis of the pulse maximum on-axis 1 LP/mm can be resolved with an intensity contrast of 0.22. The resolution of the outermost field point is 0.67 LP/mm with an intensity contrast of 0.23. An outlook of an optimized system for imaging a field of ±10 mm in x- and y-direction is given

Electrooptical sampling of ultrashort THz pulses by fs-laser pulses at 530 nm and 1060 nm

Electrooptical sampling (EOS) of ultrashort THz pulses with the help of fs-pulses at a wavelength of 1060 nm and (by second harmonic generation, SHG) of 530 nm is reported. ©2006 IEEE

THz tomography in transmission and reflection

A THz-system which can measure ultrashort THz-pulses simultaneously in transmission and in reflection under 0° and off-axis under 15° is presented. By combining the time resolved analysis of the three measurement directions, a high amount of information of the inner sample structure can be obtained. For first analysis concepts the main pulse amplitude and spectral information of transmittance measurements were evaluated

Intracavity terahertz generation inside a high-energy ultrafast soliton fiber laser

Intracavity terahertz emission inside a high-energy ultrafast Yb-doped fiber laser is presented. The terahertz radiation is generated by a transient photocurrent induced at the surface of a saturable InGaAs multiquantum well grown by molecular beam epitaxy on top of a semiconductor Bragg reflector. This device simultaneously works as the saturable absorber mirror for initiating and managing the passive mode locking required for the ultrashort pulse operation of the laser system. The maximum terahertz average power achieved is 4.2 mu W, which reveals a net conversion efficiency of 3.1x10(-5)

Multi-sensor evaluation of a wooden panel painting using terahertz imaging and shearography

Cultural heritage objects are increasingly being investigated using advanced non-destructive optical measurement techniques. Holographic and speckle interferometry based instrumentation allow dimensional measurement of objects at the tens of nanometer scale. For the structural diagnostics of artwork, double-exposure techniques are often used to locate defects, delaminations, voids and other structural features. Shearography is a speckle interferometry configuration that uses a close-to-common-path shearing interferometer configuration to give a direct sensitivity to displacement gradient at the object surface. This configuration is particularly useful for measurements outside the optical laboratory, as the stability requirements are much reduced compared with holography techniques. Terahertz imaging is a new category of sensor, used to investigate materials using electromagnetic radiation in the 0.1 to 10 THz frequency range. At these frequencies many materials become semi-transparent, so bulk structural diagnostics can be performed. Typically terahertz imaging is performed using a scanning pixel, or multi-pixel, sensor. In this manuscript shearography is first used to identify areas of interest of possible structural anomalies in the artwork. These regions of interest are then studied in more detail using the terahertz imaging instrument. Together the two instruments provide an analysis of both the surface and bulk structural features. The approach is demonstrated experimentally using a wooden panel painting.Structural Integrity & Engineering MechanicsAerospace Engineerin