iPCA-21-05-300-800-h
Broad area interdigital photoconductive THz antenna with microlens array and hyperhemispherical silicon lens for laser excitation wavelengths λ ~ 800 nm
iPCA – interdigital Photoconductive Antenna
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 3 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 > 100 mW.
Main iPCA data
• Laser excitation wavelength
λ ~ 800 nm
• Antenna resonance frequency
2 THz
• Active antenna area
300 µm x 300 µm
• Emitted THz spectrum
0.1 THz … 3 THz
• Emitter conversion efficiency
2 µW THz / 100 mW optical power
• Maximum mean THz power
10 µW @ 500 mW laser power
• Recommended optical power
50 mW … 500 mW
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 hν 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 (~ 25 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-21-5-300-800 with lens array
Photoconductive antenna
substrate
semi-insulating GaAs
chip area
4 mm x 4 mm
thickness t
650 µm
active area
300 µm x 300 µm
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 ß
15°
virtual focus length L
26.4 mm
Aluminum mount
25.4 mm diameter, 6 mm thick
Coaxial cable
type RG178 B/U, impedance 50Ω, 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
50 ± 10
kΩ
Dark current @ 10 V
200
µA
Maximum voltage
20
V
Dark current voltage characteristic at T = 300 K
Optical excitation parameters
value
units
Excitation laser wavelength
< 850
850 nm
Optical reflectance @ 800 nm
7
%
Maximum mean optical power
1
W
Carrier recovery time
200
fs
Spectral reflectance of the iPCAwithout the microlens array
Illumination dependent resistance R
描述 [描述] • Dipol length l: 21 µm<br />• Gap distance g: 5 µm<br />• Gap width w: 300 µm<br />• Array area: 300 µm x 300 µm<br />• Laser wavelength λ: ≤ 800 nm