AMO GmbH - THz Nearfield Microscopy

THz-Tip: Near Field Photoconductive electric-field probe-tip

: Fig. 1.: Mounted THz probe-tip

AMO offers a new THz near-field sensor based on a novel microstructure design.

The freely-positionable photoconductive probe-tip enables low-invasive measurements of the amplitude and phase of a broadband electric field within the THz frequency range.

The spatial resolution of the sensor is 5 µm within a frequency range from 100 GHz to 3 THz, which translates into a sub-wavelength resolution of up to lambda/600. The THz near-field probe has been developed at RWTH Aachen University (Institute for Semiconductor Technology) for error detection and design assistance of THz and microwave devices such as antennas, waveguides or integrated circuits.

Details on the performance of the THZ-Tip can be found in this recent publication: “Tapered photoconductive terahertz field probe tip with subwavelength spatial resolution“, M. Wächter, M. Nagel, and H. Kurz, Appl. Phys. Lett 95, 041112 (2009).

Applications

: Fig. 2.: 2D near field amplitude distribution on coplanar waveguide measured with THz tip

Time resolved terahertz near-field microscopy (THz-SNOM)
On-chip micro wave integrated (MMIC) testing
Radar / HF antenna near field testing
THz Time- and frequency-domain spectroscopy
Near & far field broadband THz detection

Key features

Patend pending design
Tapered electrodes for field-singularity enhanced sensitivity
PC probe-tip with unprecedented near-field spatial resolution (5µm)
Low-invasive probing through ultra-thin (1.3 µm) probe design
Easy to integrate into existing optical systems (cw or pulsed)
Convenient tip-sample approximation through probe mounting with
built-in tilt angle
Versatilely applicable for near- and far-field measurements
Polarization sensitivitve (10:1)

Utilisation example

: Fig. 3: Setup

The Thz-Tip is mainly dedicated to be used in fs second pump probe experiments. The figure 3 illustrates a typical setup where a THz radiation is sampled by the THz-Tip which is gated by the fs second probe beam.

Other configuration to measure in reflection, synchronized to HF devices in near or far field are possible, too.

Best results, especially in THz imaging, are optained using a fast sampling technique like AMO´s AixScan technology utilizing fast delay lines, ASOPS or ECOPS as a faster alternative to lock-in amplifiers with superior noise reduction also for low frequeny noise.

Technical Data

	Minimum	Standard	Maximum
Gap size at apex [µm]	1,5	3	4,5
Spatial resolution [µm] @100 GHz - 3 THz	5
Dark resistivity [MΩ]	50	100
Photocurrent ratio Ipower/Idark (UBias = 1 V, P = 5 mW)	5e4	1e5
Bias [V]		1	1,5
Excitation wavelength [nm]	700	800	850
Excitation power (λ=800 nm, frep = 80 MHz, τFWHM = 150 fs) [mW]		5	10

Specifications

: Fig 4.: Typical current-voltage characteristics

: Fig. 5: Typical THz field amplitude detected in the far-field

Test conditions:

Optical source: Ti:Sa oscillator at λ = 800 nm,
T_FWHM = 150 fs and f_rep= 80 MHz.
THz emitter: InAs surface field emitter, excitation power P = 300 mW.
THz detector: Thz-Tip, excitation power P = 3 mW.
Lock-in detection with mechanical chopper at 1.5 kHz and 100 ms integration time in ambient air.

Schematic

: Fig.6: Schematic

Pictures

Fig. 7.: Mounted THz probe-tip
(article no.: THz-tip)

Fig. 8.: Mounted THz probe-tip with translation and focusing
            mechanics for free-space excitation on a magnetic
            baseplate
            (article no.: THz-tip+Mount free1)

Fig. 9.: Mounted THz probe-tip with translation and focusing
            mechanics for fiber-coupled excitation on a magnetic
            baseplate
            (article no.: THz-tip+Mount fiber1)

Order Information

THz-tip	2.500 €
THz tip+Mount free1	3.900 €
THz-tip+Mount fiber1	4.100 €
	Discount: 10% for 3-5 pieces 20% for more than 6 pieces Note: Each delivered device is tested to insure optimal results

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