Photoconductive THz devices

The microprobe series TeraSpike is the new generation of high-performance microprobes for the photo-conductive detection of electric fields in the THz frequency range. Surface-near electric THz fields can now be measured with unprecedented signal quality and low invasiveness. The microprobes seamlessly fit into systems with optical excitation wavelengths below 860 nm and are the most cost-efficient solution to turn an existing time-domain pump/probe-system into a powerful THz near-field system for high-resolution imaging.

Key features

• Smallest active THz probe-tip on the market
• Patented design
• Spatial resolution up to 3 µm
• Frequency range 0-4 THz
• Adaptable to all laser-based THz-Systems with λ < 860 nm
• Mounting compatible with standard opto-mechanical components
• Typical optical excitation power 1-5 mW (1-5 µJ/cm²)
• Integrated overvoltage protection circuit

Models

In addition to custom-specific microprobes (please inquire) the following standard models are offered for pulsed excitation:

• TD-800-X-HR/HRS/HS
• TD-800-Z-A500G

Electrical connection is done through a compact coaxial SMP plug. We recommend the use of a low-noise current amplifier with 10⁷-10⁸ V/A amplification (e.g. DLPCA200) and high-grade connection cables (e.g. our TS Cable) for optimum operation.

Microprobe cantilever design: 

Technical specifications: 

X-series microprobes are sensitive to THz field components oriented in transversal direction to the probe-tip axis as defined by the x-axis direction in the upper illustration. The HR-option does not include a resonant antenna element and provides a somewhat higher bandwidth. The HRS-option includes an antenna element for enhanced sensitivity around 1 THz.  

Each probe is individually tested and comes with a manual & test certificate. For further information please take a look at our brochure (PDF file, 2 MB) and FAQ section.

Microprobe cantilever design:

The microprobes from the new 1550-X-series are our first probes which can be directly sampled by telecom-wavelength (1500 .. 1600 nm) laser pulses. They are sensitive to electric vector field-components oriented in transversal direction to the probe-tip axis as defined by the x-axis direction in the upper illustration. The model TD-1550-X-HR-WT offers good spatial resolution and clean spectral response due to our patent-pending internal absorber ("wave-trap") structures. The model TD-1550-X-HR-WT-XR provides increased mechanical robustness with only moderate loss of spatial resolution and sensitivity. It is designed for rougher applications e.g. where the sample distance is more difficult to control.

Technical specifications:

 ^(*) For a focus diameter of circa 20 µm, bias voltage 1 V , average optical excitation power 3 mW.
^(#) For front-switch instead of main-switch excitation. Front-switch excitation mode is showing reduced SNR.

Each probe is individually tested and comes with manual and test certificate. For more information please refer to our product brochure (2 MB PDF-file) and take a look into our FAQ section.

Microprobe cantilever design: 

Technical specifications: 

Z-series microprobes are sensitive to THz field components oriented in longitudinal direction to the probe-tip axis as defined by the z-axis direction in the upper illustration. The N-option does not include a resonant antenna element and provides a somewhat higher bandwidth. The A-500G-option includes an antenna element for enhanced sensitivity around 0.5THz.  

Each probe is individually tested and comes with a manual & test certificate. For further information please take a look at our brochure (PDF file, 2 MB) and FAQ section.

Microprobe cantilever design:

The TeraSpike TD-1550-Y-BF is a microprobe emitter based on patent pending design (DE 10 2013 020 216.7) for the bias-free surface-near excitation of Terahertz pulses on planar waveguides, metallic surfaces or meta-materials. The optically generated THz field is polarized in y-direction.

Application example:

Configuration: THz pulse generation on a thin-film microstrip line using the bias-free TeraSpike emitter microprobe. For on-chip contact-free THz field detection a second TeraSpike probe from the TD-800-X or Z series can be applied. 

THz Emission scheme: THz pulse generation is based on optical excitation of the InGaAs micro-cantilever surface. Placing the excited tip close to a conductive structure or surface allows efficient capacitive coupling and pulse transmission.

Technical specifications:

Each probe is individually tested and comes with manual and test certificate. For more information please refer to our product brochure (2 MB PDF-file) and take a look into our FAQ section.

This kit is the ideal solution to start with. It includes the following components:

• TeraSpike microprobe from the X- or Z-series.
• TeraSpike phantom (dummy device)
• TS cable connection (SMP to SMA)
• SMA to BNC adapter
• Mount and post

With this set the orientation of the mounted TeraSpike microprobe can be freely chosen as required by the application. The use of the dummy device TeraSpike Phantom - as included in the starter kit -  is recommended during all mechanical set-up and construction works because the risk of an uncontrolled mechanical impact during such processes can be easily avoided. Each microprobe is delivered in a robust transport and storage box.

Each probe is individually tested and comes with a manual & test certificate. For more information please refer to our product brochure (2 MB PDF-file) and take a look into our FAQ section.

The standard design of the TeraSpike probe is optimized for highest spatial resolution, lowest field invasiveness and highest sensitivity. This is achieved through the free-standing semiconductor-based cantilever microstructure containing the active field sensor elements. The mechanical robustness of this standard design matches the requirements of long-term application in well controlled and automated systems such as the TeraCube Scientific allowing also pointed sample contact.

For application in rougher environments or where the sample distance is more difficult to control the new XR-design is an excellent choice with drastically further increased mechanical robustness combined with only low reduction of spatial resolution and sensitivity.

Comparison of cross-section designs - Standard vs. XR-option:

Time- and frequency-domain response - Standard vs. XR-option:

The XR-option is currently available for the following x- and z-field sensitive TeraSpike probes:

• TeraSpike TD-800-X-HR-WT-XR
• TeraSpike TD-800-Z-WT-XR

If you are interested in an XR-option for other TeraSpike models, please contact us.

TeraSpike near-field probes are used under different excitation conditions. Some configurations might generate THz modes which are able to propagate along the internal electrodes of the probe-tip. So far, these modes were observed in terms of reflection signals in the recorded time-domain transients.

Protemics has developed a new patent pending design* called “wavetrap” which is effectively slowing down and absorbing such probe-internal THz signal transmission.

Tip designs

The WT-option is currently available for the following x- and z-field sensitive TeraSpike probes:

• TeraSpike TD-800-X-HR-WT
• TeraSpike TD-800-Z-WT
• TeraSpike TD-800-X-HR-WT-XR
• TeraSpike TD-800-Z-WT-XR

 If you are interested in an WT-option for other TeraSpike models, please contact us.

*German patent application DE 10 2014 015 516.1