Bias-free large-area THz emitter

TeraBlast
THz emitter

An optically pumped THz source that works without a bias voltage. A nano-scale bi-metal grating on a large active area converts femtosecond pulses from 700 to 1600 nm into linearly polarized THz radiation — from low-power oscillators to amplified lasers. It is the recommended source for TeraSpike microprobe operation and an equally good emitter for far-field spectroscopy.

Request a quote Application notes (PDF)
TeraBlast · TD-1550-L-165 Bias-free
Photograph of the TeraBlast emitter in its black 1-inch housing with Protemics label, held in a mounting plate on an optical post with a blue post holder; the emitter chip is visible behind the front window.
700 – 1600 nm
Excitation wavelength
5 mW – 1 W
Average excitation power
> 2.5 µW
Average THz power
ca. 10 mm
Active area diameter
Working principle

THz pulses without a bias voltage.

TeraBlast emitters are based on bi-metallic grating structures on an InGaAs semiconductor (German patent application DE 10 2012 010 926 A1). Femtosecond excitation of the grating drives lateral photocurrents in the Schottky fields of the many asymmetric metal/semiconductor junctions; their sum is radiated as a THz pulse. No external voltage is applied. Because the active area is large, the emitter accepts average excitation powers from 5 mW to above 1 W without the saturation of conversion efficiency known from small-scale photoconductive antennas.

Schematic cross-section: semiconductor with a periodic grating of metal 1 and metal 2 stripes. Optical excitation pulses (red arrows) drive lateral photocurrents j_ph at the asymmetric metal/semiconductor junctions, all pointing in the same direction; THz pulses (blue arrows) are emitted.
Excitation scheme. Schottky-field induced lateral photocurrents jph at the asymmetric junctions of a bi-metal grating.
Average THz power versus NIR pump power from 0 to 500 mW: measured values rise to 2.5 µW at 370 mW and follow a parabolic fit that reaches about 4.7 µW at 500 mW.
THz power vs. pump power. Average THz power, measured with a pyroelectric detector (Spectrum Detector SPI-D-62-THz). The emitted power follows the square of the pump power.
Why bias-free

Robust, simple, and quiet next to a detector.

Near field

Works next to a photoconductive detector

When THz generation has to take place close to photoconductive detection — near-field detection with a TeraSpike microprobe or butt-coupled waveguide excitation — the modulated photocurrent of a biased emitter couples parasitically into the detector. TeraBlast has no such current.

Signal

No dark current, no offset

Without a bias there is no dark current and no parasitic offset signal in lock-in detection schemes.

Robustness

No failure on local defects

Bias-free operation makes the emitter extremely robust: a local short-circuit defect does not cause a device failure.

Power

Saturation-free large area

High emission power from the large active area: average excitation from 5 mW to above 1 W, from low-power oscillators to amplified lasers.

Handling

Virtually no alignment

No small gap to hit: illuminate the active area and the emitter radiates. Use it as an array emitter with a wide beam or as a point source with a focused one — for the highest bandwidth, focus the excitation to a spot smaller than 200 µm.

Emission

Linearly polarized

The emitted THz radiation is linearly polarized; a mark on the housing shows its direction. The excitation beam may have any polarization, and the nano-scale bi-metal design gives a high conversion efficiency. Excitation pulses shorter than 150 fs are recommended — the shorter, the better.

Measured emission

Near field and far field.

Space-time map of the THz field from −25 to +25 mm lateral position and 0 to 50 ps: the wavefront forms an arc whose bright, fast-oscillating apex lies at the emitter centre, with weaker slow components extending to both sides.
Near field

Emission profile at 15 mm distance.

The THz field is line-scanned in the time domain across the centre of the emitter at a distance of 15 mm in ambient air, without a back-surface aperture. The bright, fast-oscillating THz components are confined to an aperture of a few millimetres, while GHz components are emitted over a much wider range. Adjusting the focus of the excitation beam adapts the emission profile. For field detection closer than 20 mm, the HPF option blocks the low-frequency microwave emission.

Measured with a TeraSpike TD-800-X-HRS microprobe.

THz transient of the TeraBlast TD-1550-L-165 from −4.5 to 7.5 ps: a negative pre-pulse to −0.5 followed by the main peak with a width of 250 fs FWHM and small oscillations afterwards.
Time domain. Far-field THz transient, 250 fs pulse width (FWHM).
Power spectrum from 0 to 10 THz: maximum near 1 THz, falling to about −60 dB at 6 THz; the noise floor lies around −75 dB.
Frequency domain. Power spectrum of the same transient.

Far-field transmission through N2-purged free space, measured by ASOPS-based THz time-domain spectroscopy with electro-optic detection in a 400 µm thick GaP crystal. Excitation wavelength for all data on this page: 800 nm.

Technical specifications

Technical data.

ParameterTeraBlast TD-1550-L-165
Excitation wavelength range700 … 1600 nm
Typ. average excitation power range5 … 1000 mW
Max. excitation fluence for optimal efficiency220 nJ/mm²
Recommended excitation pulse duration< 150 fs (shorter is better)
Excitation beam polarizationarbitrary
Average THz emission power> 2.5 µW (a)
Active area diameterca. 10 mm (b)
THz polarizationlinear, marked on the housing
Bias voltagenone required
Mounting adapter1 inch

(a) Measured with a pyroelectric detector (Spectrum Detector Inc. SPI-D-62-THz) at 370 mW optical pump power.
(b) Larger active areas are possible — please ask.

Dimension drawing of the TeraBlast with 1-inch mount: front view with 10 mm active area, side view with diameters 25.40 mm and 30.48 mm and a length of 18.92 mm, and a perspective view.
Dimensions in mm, version with 1″ mount.
Options

Configured for your setup.

All options on request.

OptionDescription
HPF — high-pass filterA matching filter inside the housing blocks the low-frequency microwave emission. Recommended when the field is detected closer than 20 mm to the emitter.
AR — anti-reflection coatingVersion TD-1550-L-165-AR with anti-reflection coating.
Larger active areaActive areas beyond 10 mm diameter.
Unmounted chipThe emitter chip without housing and mount.
Bare InGaAs THz-TxInGaAs/InP chip without the Schottky-field inducing metal/semiconductor junctions; its THz field strength is significantly lower than that of the standard TeraBlast.
Documentation

Downloads.

PDF TeraBlast — application notesPDF · 0.7 MB · dimensions, installation, recommendations, options Download → PDF Protemics product brochurePDF · 5 MB · all probes, systems and components Download →
Ready to specify

Request a TeraBlast quote.

Tell us your laser and your application. Options such as the HPF filter, AR coating or larger active areas are available on request.

Request a quote Talk to an engineer