iPCA-21-05-1000-800-h
Broad area interdigital photoconductive THz antenna with microlens array and
hyperhemispherical silicon lens for laser excitation wavelengths λ ~ 800 nm
PCA applications
The PCA can be used as terahertz (THz) emitter or detector in pulsed laser gated broadband THz measurement systems for time-domain spectroscopy in the frequency region from 0.1 to 4 THz.The emitter conversion efficiency of optical laser power into THz power is very high.
The preferred application is as THz emitter antenna for mean optical laser power > 500 mW.
Main PCA data
· Laser excitation wavelength:λ ~ 800 nm
· Antenna resonance frequency:2 THz
· Active antenna area:1 mm x 1mm
· Emitted THz spectrum:0.1 THz … 4 THz
· Emitter conversion efficiency:100 µW THz / 1 W optical power
· Maximum mean THz power:200 µW @ 3 W laser power
· Recommended optical power:0.5 W … 3 W
iPCA working principle
Instead of a single small antenna gap an extended gap along the finger electrodes of the iPCA can be illuminated by a short pulse laser beam. By using the microlens array only every second gap between the finger structure is excited by the laser beam with a photon energy h larger than the energy gap Eg of the semiconductor antenna material. The fill factor of the lens array of 73.5 % ensures, that nearly the total optical laser energy is used for excitation of carriers. Despite of the large emitting area the needed voltage for the carrier excitation is low (~ 15 V) because of the small gap of only 5 µm.
The coherent excitation of the single emitters, located at every microlens spot results in a constructive interference of the radiated THz waves in the far field. The laser beam has to be adjusted in such a way, that the spots are on the GaAs surface between the finger electrodes (minimum electrical resistance of the antenna).
Antenna design
iPCA-21-5-1000-800 with lens array
Photoconductive antenna
substrate
semi-insulating GaAs
chip area
4 mm x 4 mm
thickness t
650 µm
active area
1 mm x 1mm
Hyperhemispherical lens
material
undoped HRFZ-silicon,
specific resistance ρ
>10 kΩcm
refractive index n
3.4
diameter
12 mm
height h
7.1 mm
distance d
7.7 mm
Terahertz beam
collection angle α
57°
divergence angle β
15°
virtual focus length L
26.4 mm
Aluminum mount
25.4 mm diameter, 6 mm thick
Coaxial cable
type RG178 B/U, impedance 50 Ω, capacitance 96pF/m, 1 m long
Connector type
BNC
- The iPCA chip is optically adjusted and glued on the hyperhemispherical silicon lens with a thermal conducting glue.
- The silicon lens is fixed on the aluminum mount with a thermal conducting glue.
- The two antenna contacts are wire bonded on a printed circuit board, which provides the connection to a 1m long coaxial cable with BNC or SMA connector
- A central hole in the aluminum mount allows the Terahertz radiation to escape from the hyperhemispherical silicon lens
Antenna parameters
Electrical parameters
value units
Dark resistance
1.5 MΩ
Dark current @ 15 V
10 µA
Maximum voltage
15 V
Resistance under illumination
≤0.5 MΩ
Photocurrent ³
≥30 µA
Optical excitation parameters
value units
Excitation laser wavelength
< 850 nm
Optical reflectance @ 800 nm
7 %
Maximum mean optical power
3 W
Carrier recovery time
200 fs
描述 [描述] • Dipol length l: 21 µm<br />• Gap distance g: 5 µm<br />• Gap width w: 1000 µm<br />• Array area: 1 mm x 1 mm<br />• Laser wavelength λ: ≤ 800 nm