The new bias-free Terahertz emitter series TeraBlast from Protemics are optically pumped THz sources which can be used with a wide range of femtosecond laser sources (such as low power oscillators or amplified lasers with wavelengths in the range of 700..1600 nm). They are ideally suited and tested for near-field imaging applications including TeraSpike microprobe operation. The TeraBlast is however also a great emitter for far-field spectroscopy and other THz applications.
TeraBlast emitters are based on a patent pending technology (German patent application: DE102012010926 A1) utilizing bi-metallic grating structures for the optical bias-free generation of Terahertz radiation. The emitters offer a large active area and can be excited by pulsed Femtosecond lasers within a broad range of average power from 5 mW up to above 1 W without causing the typical signs of conversion efficiency saturation or device failures as known from small-scale photoconductive antennas. Furthermore, TeraBlast emitters are the ideal solution for applications where THz pulse generation needs to occur in close proximity to photoconductive detection (e.g. near-field detection or butt-coupled waveguide excitation). In such situations voltage-biased emitters are often unusable because of strong parasitic coupling effects from modulated photocurrents which are avoided for the bias-free TeraBlast emitters.
THz pulse emission is generated by optical excitation of the TeraBlast emitter through femtosecond near-infrared or infrared pulses. Pulse durations < 150 fs are recommended. The emitted Terahertz radiation is linearly polarized. The following plot is showing an exemplary measurment of the emitted THz field which is line scanned across the center of the TeraBlast emitter in time-domain using a TeraSpike microprobe (Model: TD-800-X-HRS). The bright fast oscillating THz frequency components are well confined to an aperture area of few millimeter size, whereas GHz radiation is emitted over a much wider range. The emission profile can be easily adapted by adjusting the focussing of the optical excitation beam.
Exitation scheme: The THz emission process is based on Schottky-field induced lateral photo-currents (jph) at the multiple asymmetric metal/semiconductor junctions.
Measurement example (TeraBlast TD-1550-L-165): Far-field transmission through N2-purged free-space measured with a femto-second laser from Laser Quantum („taccor") and electrooptic detection in a 400-µm-thick GaP crystal using ASOPS based time-domain spectroscopy.
|Excitation wavelength range||700 .. 1600 nm|
|Typ. average excitation power range||5 mW .. 1000 mW|
|Average THz emission power||> 2.5 µW (a)|
|Active area diameter||ca. 11 mm (b)|
|Adapter dimension (Outer diameter)||1/2 inch|
Anti-reflection coating (-AR)
For Terahertz emission spectra without Fabry-Perot signature THz pulse reflection at the emitter backside can be suppressed by this broadband anti-reflection coating. Please note, that the field amplitude of the emitted pulse is also reduced by approx. 30% through application of the AR-coating.
High-pass filter (-HPF)
In order to allow THz field measurements in close distance to the TeraBlast emitter without a dominating contribution of low-GHz-Range radiation the emitter can be equipped with an intergrated high-pass filter at the output facet.
(a) Measured with pyroelectric detector (Spectrum Detector Inc. SPI-D-62-THz) for 370 mW optical pump power
(b) Larger active areas possible. Please request!