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Photoconductive antennas for THz pulse generation - request a quote

 

PCA - Photoconductive Antenna for terahertz waves
Del Mar Photonics - PCA brochure - buy online - PCA Q&A
  antenna
Geometrical antenna parameters:
  • l - length of the antenna, defines the THz resonance frequency.
  • g - gap distance, important for laser excitation.
  • w - gap width.
 
   
  PCA with LT-GaAs absorber for laser excitation wavelengths l £ 850 nm; optical absorption > 70%  
 
 
Part No. Delivery time l
(mm)
g
(mm)
w
(mm)
Description
PCA-44-06-10-800-x 1 week 44 06 10 PCA: resonance frequency 1 THz, l = 800 nm, gap distance 6 mm,
optimal detector antenna
PCA-44-16-16-800-x 1 week 44 16 16 PCA: resonance frequency 1 THz, l = 800 nm, gap distance 16 mm
PCA-44-34-100-800-x 1 week 44 34 100 PCA: resonance frequency 1 THz, l = 800 nm, gap distance 34 mm
PCA-30-10-10-800-x 1 week 30 10 10 PCA: resonance frequency 1.5 THz, l = 800 nm, gap distance 10 mm
PCA-30-14-14-800-x 1 week 30 14 14 PCA: resonance frequency 1.5 THz, l = 800 nm, gap distance 14 mm
 
  buy online
 
PCA with LT-InGaAs layer for laser excitation wavelength l = 990 .. 1060 nm; optical absorption ~ 50%  
 
 
Part No. Delivery time l
(mm)
g
(mm)
w
(mm)
Description
PCA-44-06-10-1030-x 1 week 44 06 10 PCA: resonance frequency 1 THz, l = 990 .. 1060 nm, gap distance 6 mm,
optimal detector antenna
PCA-44-16-16-1030-x 1 week 44 16 16 PCA: resonance frequency 1 THz, l = 990 .. 1060 nm, gap distance 16 mm
PCA-44-34-100-1030-x 1 week 44 34 100 PCA: resonance frequency 1 THz, l = 990 .. 1060 nm, gap distance 34 mm
PCA-30-10-10-1030-x 1 week 30 10 10 PCA: resonance frequency 1.5 THz, l = 990 .. 1060 nm, gap distance 10 mm
PCA-30-14-14-1030-x 1 week 30 14 14 PCA: resonance frequency 1.5 THz, l = 990 .. 1060 nm, gap distance 14 mm
 
  buy online
 
PCA with LT-InGaAs layer for laser excitation wavelength l ~ 1040 nm; optical resonant design with 97 % absorption @ 1040 nm  
 
 
Part No. Delivery time l
(mm)
g
(mm)
w
(mm)
Description
PCA-44-06-10-1040-x 1 week 44 06 10 PCA: resonance frequency 1 THz, l ~ 1040 nm, gap distance 6 mm,
optimal detector antenna
PCA-44-16-16-1040-x 1 week 44 16 16 PCA: resonance frequency 1 THz, l ~ 1040 nm, gap distance 16 mm
PCA-44-34-100-1040-x 1 week 44 34 100 PCA: resonance frequency 1 THz, l ~ 1040 nm, gap distance 34 mm
PCA-30-10-10-1040-x 1 week 30 10 10 PCA: resonance frequency 1.5 THz, l ~ 1040 nm, gap distance 10 mm
PCA-30-14-14-1040-x 1 week 30 14 14 PCA: resonance frequency 1.5 THz, l ~ 1040 nm, gap distance 14 mm
 
   buy online
 
 
Part No. example Description
 PCA-44-06-10-800-x   PhotoConductive Antenna
 PCA-44-06-10-800-x   length l = 44 mm
 PCA-44-06-10-800-x   gap distance g = 6 mm
 PCA-44-06-10-800-x   gap width w = 10 mm
 PCA-44-10-800-x   laser excitation wavelength l = 800 nm
 PCA-44-06-10-800-0   unmounted chip, area: 2 mm x 2 mm, thickness: 400 m,
  with 4 bond contact pads
 PCA-44-06-10-800-h   mounted on a hyperhemispherical Si lens, 25.4 mm diameter
  Al heat sink, 1 m long coaxial cable with BNC or SMA connector
 

Del Mar Photonics - PCA brochure - buy online

 Model   Product Name+   Buy Now 
 iPCAp-21-05-1000-800   iPCAp, 800 nm, 21x5x1000 microns  Buy Now 
 iPCAp-21-05-300-800-   iPCAp, 800 nm, 21x5x300 microns  Buy Now 
 iPCAs-21-05-1000-104   iPCAs, 1040 nm, 21x5x1000 microns  Buy Now 
 PCA-44-16-16-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 6 m  Buy Now 
 PCA-44-16-16-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 6 m  Buy Now 
 PCA-44-16-16-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-1040-u   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-1040-u   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 6 m  Buy Now 
 PCA-30-10-10-800-h   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-800-u   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-800-u   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-800-h   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 14 m  Buy Now 
 PCA-30-10-10-1030-u   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-1030-h   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-1030-h   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-1030-u   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 14 m  Buy Now 
 PCA-30-10-10-1040-h   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-1040-u   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-1040-u   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-1040-h   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 14 m  Buy Now 

 

800 nm
 
PCA with LT-GaAs absorber for laser excitation wavelengths λ ≤ 850 nm; optical absorption > 70%
 Model   Product Name+   Buy Now 
 PCA-44-16-16-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-800-u   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-800-h   PCA: resonance frequency 1 THz, λ = 800 nm, gap distance 6 m  Buy Now 
 PCA-30-10-10-800-h   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-800-u   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-800-h   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-800-u   PCA: resonance frequency 1.5 THz, λ = 800 nm, gap distance 14 m  Buy Now 

 

990-1060 nm
 
PCA with LT-GaAs absorber for laser excitation wavelengths λ = 990 .. 1060 nm; optical absorption ~ 50%
 Model   Product Name+   Buy Now 
 PCA-44-16-16-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-1030-u   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-1030-h   PCA: resonance frequency 1 THz, λ = 990 .. 1060 nm, gap distance 6 m  Buy Now 
 PCA-30-10-10-1030-u   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-1030-h   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-1030-u   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-1030-h   PCA: resonance frequency 1.5 THz, λ = 990 .. 1060 nm, gap distance 14 m  Buy Now 

 

1040 nm
 
PCA with LT-GaAs absorber for laser excitation wavelengths λ ~ 1040 nm; optical resonant design 97% absorption @ 1040 nm
 Model   Product Name+   Buy Now 
 PCA-44-16-16-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 16 m  Buy Now 
 PCA-44-16-16-1040-u   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 16 m  Buy Now 
 PCA-44-34-100-1040-u   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 34 m  Buy Now 
 PCA-44-34-100-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 34 m  Buy Now 
 PCA-44-06-10-1040-h   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 6 m  Buy Now 
 PCA-44-06-10-1040-u   PCA: resonance frequency 1 THz, λ ~ 1040 nm, gap distance 6 m  Buy Now 
 PCA-30-10-10-1040-u   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 10 m  Buy Now 
 PCA-30-10-10-1040-h   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 10 m  Buy Now 
 PCA-30-14-14-1040-h   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 14 m  Buy Now 
 PCA-30-14-14-1040-u   PCA: resonance frequency 1.5 THz, λ ~ 1040 nm, gap distance 14 m  Buy Now 

Del Mar Photonics - PCA brochure - buy online - PCA Q&A

PCA - Photoconductive Antenna for THz Applications

Del Mar Photonics - PCA brochure - PCA models - buy online

  Contents  
   
How does a PCA work?  
  A photoconductive antenna (PCA) for terahertz (THz) waves - working principle

A photoconductive antenna (PCA) for terahertz (THz) waves consists of a highly resistive direct semiconductor thin film with two electric contact pads. The film is made in most cases using a III-V compound semiconductor like GaAs. It is epitaxially grown on a semi-insulating GaAs substrate (SI-GaAs), which is also a highly resistive material.
The important difference between the SI-GaAs substrate and the film is the relaxation time for excited carriers. In a SI-substrate the carrier lifetime is about 500 ps, but in the film shorter than 1 ps.

down
 
 

A short laser puls with puls width < 1 ps is focused between the electric contacts of the PCA. The photons of the laser pulse have a photon energy E = h× n larger than the energy gap Eg and are absorbed in the film. Each absorbed photon creates a free electron in the conduction band and a hole in the valence band of the film and makes them for a short time electrical conducting until the carriers are recombined.

The PCA can be used as THz transmitter as well as THz receiver.

  • In case of a transmitter a voltage V is connected on the electrical contacts and the excited carriers are accelerated by the electric field during the optical pulse, which results in a short broadband electromagnetic pulse with a time-dependent electrical field E(t) and frequencies in the THz region.
  • In case of a receiver a current amplifier is connected on the electrical contacts. During the optical pulse the excited carriers are accelerated by the electric field component of the incident terahertz pulse with the time-dependent electrical field E(t). This leads to a measurable current signal in the outer circuit.
 
 
  Photoconductive Antenna PCA energy band diagramm

To get the needed short carrier lifetime, the film must include crystal defects. These defects can be created by ion implantation after the film growth or alternatively by a low temperature growth. Low temperature grown GaAs (LT-GaAs) between 200 and 400 C contains excess arsenic clusters.
These clusters create defect levels within the band gap Eg and lead to a fast non-radiative recombination of the electron-hole pairs within a time interval < 1 ps.

down
 
PCA applications up
 

As mentioned above, a PCA can be used as a THz emitter or detector in pulse laser gated broadband THz measurement systems for time-domain spectroscopy.
Because THz waves penetrate dielectric materials like paper or plastic, are reflected by materials with free electrons like metals and are absorbed by moleculs with certain vibration levels within the terahertz band, they have a lot of applications in the fields of time-domain spectroscopy and and imaging:

down
  Security checks:
  • Screening passengers for explosives and weapons
  • luggage screening
  • mail drug screening
  • mine detection
  • locating water marks in currency
  • reading text in envelopes or beneath paint.
 
  Medical imaging for brest and skin cancer detection and for teeth testing in dentistry. Terahertz waves offers medical benefits:
  • Terahertz radiation is nonionizing. That means, it is safe.
  • It can penetrate epithelial tissues.
  • Laterally image resolution of 250 m is possible.
  • 3-D imaging using amplitude and phase information is possible.
 
  Process control for:
  • polymeric compounding
  • examining circuit interconnects in packaged ICs
  • final control of packaged products
  • quality control in food processing
  • rapid characterisation of the stability and polymorphic forms of drugs.
 
 
Frequency and wavelength  
  electromagnetic spectrum up
  Antenna

The photoconductive antenna can be considered as a dipole of the length L, which is in resonance with the electromagnetic wavelength ln inside the semiconductor.
The resonance condition is L = m ln/2 with m = 1, 2, 3,..- integer.
The wavelength ln in the material with the refractive index n is given by ln = l/n. Using the wave relation c = l . f and m = 1, the resonance frequency of the antenna f is given by f = 2×c×n/L
with
c = 3×108 m/s - speed of light in the vacuum
n - refractive index of the semiconductor antenna material
L - length of the antenna.

 
 
  The refractive index n of GaAs at terahertz frequencies is n = 3.4. With this value the first resonant frequency and wavelength of the antenna with the length L can be calculated as follows: down
 
  f (THz) l (m) L (m)  
   0.3 1000 147  
   0.5   600   88  
   1.0   300   44  
   1.5   200   29.4  
   3.0   100   14.7  
 
 
Substrate lens for PCA transmitter  
  PCA without substrate lens  
  substrate without lens

Because of the high refractive index n ~ 3.4 of the semiconductor PCA the outgoing terahertz waves are strongly diffracted at the substrate-air interface. The boundary angle a for the total reflection can be calculated with

     a = arcsin(n-1) ~ 17.1

Only the THz waves emitted in the solid angle W with

 
 
  formula solid angle  
 

can escape the substrate. For GaAs with n = 3.4 the escape solid angle is W = 0.28. This is only 4.4% of the forward directed intensity.

 
 
  Aplanatic hyperhemispherical lens  
aplanatic hyperhemispherical lens
 

To increase the escape cone angle a , a hemispherical lens with the same refractive index n as the PCA can be used. To decrease the divergence in air, a hyperhemispherical lens with a certain distance d from the emitter to the tip of the lens is common. If this distance d is

 
  formula d hyperhemispherical lens up
 

the hyperhemispherical lens is aplanatic, that means without spherical and coma aberration. For a silicon lens with almost the same refractive index n ~ 3.4 as GaAs at therahertz frequencies the distance is d = 1.29 r with the lens radius r. The height h of the aplanatic hyperhemispherical lens is therefore h = d - t with the thickness t of the semiconductor PCA.
The length L from the lens tip to the virtuell focus behind the lens is given by

 

 
  L = r (n+1)

 
 
  For silicon is L = 4.4 r. With this hyperhemispherical lens nearly all the forward directed terahertz intensity can escape the PCA. The problem left is the beam divergence, which requires a further focussing element like a lens or mirror.  
 

 

Terahertz systems, set ups and components
New band pass and long pass THz optical filters based on porous silicon and metal mesh technologies.
Band pass filters with center wavelengths from 30 THz into GHz range and transmissions up to 80% or better. Standard designs
with clear aperture diameters from 12.5 to 37.5 mm.
Long pass filters with standard rejection edge wavelengths from 60 THz into GHz range. Maximum transmission up to 80% or
better, standard designs at 19.0 and 25.4 mm diameters.
Excellent thermal (from cryogenic to 600 K) and mechanical properties
THz products:
Portable Terahertz Source
THz Spectrometer kit with Antenna
THz transmission setup
THz time domain spectrometer Pacifica fs1060pca
THz time domain spectrometer Pacifica fs780pca
THz detectors: Golay cell and LiTaO3 piroelectric detectors
PCA - Photoconductive Antenna as THz photomixer
Pacifica THz Time Domain Spectrometer - Trestles Pacifica
Holographic Fourier Transform Spectrometer for THz Region
Wedge TiSapphire Multipass Amplifier System - THz pulses generation
Terahertz Spectroscopic Radar Mobile System for Detection of Concealed Explosives
Band pass filters with center wavelengths from 30 THz into GHz range
Long pass filters with standard rejection edge wavelengths from 60 THz into GHz range
Generation of THz radiation using lithium niobate
Terahertz crystals (THz): ZnTe, GaAs, GaP, LiNbO3 - Wedge ZnTe
Silicon Viewports for THz radiation - sample specs
Aspheric collimating silicon lens - Aspheric focusing silicon lens
more

iPCA - interdigital Photoconductive Antenna for terahertz waves
Large area broadband antenna with lens array and high emitter conversion efficiency
iPCA with LT-GaAs absorber, microlens array for laser excitation wavelengths
l £  850 nm, adjusted hyperhemispherical silicon lens with a high power conversion efficiency of 0.2 mW THz power / W optical power. The iPCA can be used also as large area THz detector. The two types iPCAp and iPCAs have the same active interdigital antenna area but different contact pad directions with respect to the electrical THz field.
Interdigital Photoconductive Antenna for terahertz waves generation using femtosecond Ti:Sapphire laser

THz books