Photoconductive Near-field Microprobes (PC-NFMs) for the THz-Range

Introducing TeraSpike, the next generation of high-performance microprobes for photo-conductive THz near-field imaging. Achieve superior signal quality and minimal invasiveness in surface-near electric THz field detection. Seamless integration with 800nm/1550nm pump/probe systems offers a cost-effective path to high-resolution THz imaging.

Key features

• Smallest photo-conductive THz microprobe on the market
• Patented design
• Spatial resolution up to 3 µm
• Accessible frequency range 0 .. >4 THz
• Many application specific optimization types available
• Adaptable to all laser-based THz-Systems with λ around 800 nm or 1550 nm
• Required optical excitation power only 1-4 mW (1-5 µJ/cm²)
• Integrated overvoltage protection circuit
• System integration accessories available

Standard Detector Overview 

Our standard probes are designed for pulsed time-domain (TD) THz spectroscopy. However, frequency-domain operation has also been successfully demonstrated for specific types. Please inquire for further information. Detector probes are grouped by: 

• Exitation wavelength type: 800 nm or 1550 nm
• Field polarization type: x- or z-polarisation (Transversal or longitudinal orientation)
• Optimization type:
  • HR: High spatial resolution
  • HRS: High spatial resolution plus resonant sensitivity enhancement
  • N: Non-resonant (Z-Probe)
  • A-500G: Axial-dipol, resonant at 500 GHz (Z-Probe)
  • WT: High spectral purity
  • HR-WT: High-resolution plus high spectral purity and bandwidth
  • HR-WT-XR and WT-XR: High-bandwith and increased mechanical robustness

In addition to our standard probes listed above we can also offer custom-specific microprobes (please inquire).

Electrical connection is done through a compact coaxial SMP plug. We recommend the use of our low-noise current amplifier TS Companion.

Exemplary THz measurement data

THz pulse transient (left) measured with the TeraSpike TD-800-X-HR-WT in a TeraCube M2 system. Signal-to-noise power spectrum (right) generated by Fast-Fourier-Transformation of the time-domain data. Measurement were conducted without purging the system with Nitrogen.

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.

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