Instruction manual and data sheet PCA-40-05-10 ... - BATOP GmbH

1/15 Instruction manual PCA-40-05-10-800-x 

BATOP GmbH 

Wildenbruchstraße 15 

D-07745 Jena 

Instruction manual and data sheet PCA-40-05-10-800-x 

Photoconductive THz antenna for laser excitation wavelengths λ ~ 500 nm … 850 nm 

PCA – Photocconductive Antenna 

PCA-40-05-10-800-0 - unmounted antenna chip 4 mm x 4 mm with 2 bond contact pads 

PCA-40-05-10-800-h - mounted antenna on hyperhemispherical silicon substrate lens 

PCA-40-05-10-800-a - mounted antenna on aspheric focusing silicon substrate lens 

PCA-40-05-10-800-c - mounted antenna on aspheric collimating silicon substrate lens 

Table of contents: 

1. PCA applications ........................................................................................................................... 2 

2. Antenna design.............................................................................................................................. 2 

3. Antenna parameters ...................................................................................................................... 3 

4. Mounted PCA on hyperhemispherical silicon substrate lens: PCA-40-05-10-800-h..................... 5 

5. Mounted PCA on aspheric silicon substrate lens: PCA-40-05-10-800-a ...................................... 7 

6. Instructions for use of the PCA-40-05-10-800-x......................................................................... 11 

7. Time-domain measurements....................................................................................................... 13 

8. Order information......................................................................................................................... 15 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 

E-mail: info@batop.de 

Deutsche Bank Jena 

Bank Code: 82070024 

Account No: 3922655 

Germany IBAN: DE49 8207 0024 0392 2655 00 

VAT Reg. No: DE 813698804 

Tax Acc. No: 162/106/01639 

Local Court Jena HRB 112769


1. 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 5 THz. 

Main PCA data 

2. Antenna design 



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• Laser excitation wavelength λ ~ 800 nm 

• Antenna resonance frequency 1 THz 

Photo PCA 40-05-10 (survey) Photo PCA 40-05-10 Photo PCA 40-05-10 (detail) 

Dielectric cover 








VAT Reg. No: DE 813698804 




3. Antenna parameters 

Electrical parameters minimum ratings standard maximum ratings 

Dark resistance 2 MΩ 2.5 MΩ 3 MΩ 

Dark current @ 10 V 3 µA 4 µA 5 µA 

Voltage 20 V 30V 

Dark current voltage characteristic at T = 300 K 

Optical excitation parameters minimum ratings standard maximum ratings 

Excitation laser wavelength 500 nm 800 nm 850 nm 

Optical reflectance @ 1040 nm 32 % @ 500 nm 7 % @ 800 nm 8 % @ 850 nm 

Optical mean power 40 mW 80 mW 

Carrier recovery time 300 fs 



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Spectral reflectance 

Reflection (%) 



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35 

30 

25 

20 

15 

10 

Illumination dependent resistance R 

5 

0 

500 600 700 800 900 1000 1100 1200 

Wavelength (nm) 








VAT Reg. No: DE 813698804 




4. Mounted PCA on hyperhemispherical silicon substrate lens: PCA-40-05-10-800-h 

Photoconductive antenna substrate semi-insulating GaAs 

chip area 4 mm x 4 mm 

thickness t 600 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° 



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β 

divergence angle ß 15° 

virtual focus length L 26.4 mm 

Aluminum mount 25.4 mm diameter, 9 mm thick 

Coaxial cable type RG174 /U, impedance 50Ω, capacitance 101pF/m, 1 m long 

Connector type BNC or SMA 




PCA 

hyperhemispherical Si lens 





L 

t 

α 

d 

h 

VAT Reg. No: DE 813698804 




• The PCA 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 

PCA with hyperhemispherical silicon lens, coaxial cable RG 174 and BNC connector 

Front view on mounted PCA (laser side) Back view on mounted PCA (THz side) 



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VAT Reg. No: DE 813698804 




The antenna can be used as terahertz emitter or detector in pulsed laser gated broadband THz 

measurement systems for time-domain spectroscopy and as photomixing emitter or detector in tunable 

cw THz measurement systems in the frequency region from 0.1 to 3 THz (see schematics below). 

Schematic of a time-domain spectroscopy setup 

5. Mounted PCA on aspheric silicon substrate lens: PCA-40-05-10-800-a 

Photoconductive antenna substrate semi-insulating GaAs 

chip area 4 mm x 4 mm 

thickness t 600 µm 

Aspheric lens material undoped HRFZ-silicon 

specific resistance ρ >10 kΩcm 

refractive index n 3.4 

diameter 12 mm 

height h 8 mm 

distance d 8.6 mm 

rough AR surface 

Terahertz beam focal length f 50 mm 



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collection angle α 57.6° 

convergence angle ß 6.8° 








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Airy disc diameter at 300 GHz 5 mm 

optical 

beam 

t 

α 

h 

d 



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at 1 THz 1.5 mm 

at 3 THz 0.5 mm 

β 

Aluminum mount 25.4 mm diameter, 9 mm thick 

Coaxial cable type RG174 B/U, impedance 50Ω, capacitance 101pF/m, 1 m long 

Connector type BNC or SMA 

• The PCA chip is optically adjusted and glued on the aspheric silicon lens 

• The silicon lens is glued on the aluminum mount. 

• 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 aspheric silicon 

lens as a collimated beam with a focus 50 mm away and an Airy disc diameter dependent on the 

THz frequency. 








f 

THz 

beam 

VAT Reg. No: DE 813698804 






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PCA with aspheric silicon lens, coaxial cable RG 174 and BNC connector 

Front view on mounted PCA (laser side) Back view on mounted PCA (THz side) 








VAT Reg. No: DE 813698804 



M 

10/15 Instruction manual PCA-40-05-10-800-x 

Terahertz time-domain spectrometer with two photoconductive antennas on aspheric lenses 

Components of the THz time-domain spectrometer: 

BB – breadboard, BS – beam splitter, CA – connector to amplifier, CB – connector to bias, DL - delay 

line, DA – detector antenna, EA – emitter antenna, M – mirror, OL – optical lens, PLB – pulsed laser 

beam, TB – Terahertz beam 

Bias voltage of the emitter antenna: 

• dc voltage: In this case the dc output voltage of the detector antenna (typical in the region of 1 

.. 100 mV) can be measured using a dc voltage amplifier. 

• ac voltage: As a result of the emitter square wave bias voltage between –V .. +V the detector 

antenna delivers an ac voltage, which can be phase sensitive measured using a lock-in 

detector 



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M OL DA TB EA OL 

BB CA CB 








BS 

PLB 

VAT Reg. No: DE 813698804 


Local Court Jena HRB 112769 

M 

DL


6. Instructions for use of the PCA-40-05-10-800-x 

Emitter: 

The pulsed laser beam (in case of time domain spectroscopy) or the mixed cw laser beam (in case of 

cw THz emitter) has to be focussed onto the antenna gap using an appropriate lens or objective with a 

beam diameter of about 5 µm to bridge the antenna gap with photo-excited carriers within the 

semiconductor. At the same time a voltage U of ~ 20 V (maximum 30 V peak voltage) has to be 

supplied on the gap by connecting the BNC connector cable to a voltage source. The recommended 

optical mean laser power Popt is 30 mW (maximum 80 mW). 

Receiver: 

The pulsed laser beam has to be focussed onto the antenna gap using an appropriate lens or objective 

with a beam diameter of about 5 µm to bridge the antenna gap with photo-excited carriers within the 

semiconductor. The phase of the laser beam with respect to the beam on the emitter site has to be 

adjusted by using of an optical delay line in such a way, that the measured value of the THz field on 

the antenna meets a maximum of the optical beam. By changing the phase difference between the 

emitter and receiver antenna the time-dependent shape of the THz field can be measured. 

The cable with the BNC connector must be connected with a sensitive electronic current amplifier. 

Attention: Please be sure, that the focusing lens or the lens mounting parts does not touch the 

antenna chip or the tiny gold contact wires between the antenna chip and the PCB. See figure “front 

view on mounted PCA (laser side)” above. 

Lock-in detection 

Because of the very small detector signal a lock-in detection scheme is recommended. The following 

two possibilities for lock-in detection can be used: 

• An optical chopper can be used in front of the emitter antenna to chop the optical beam with a 

frequency ~ 1 kHz. The result is a chopped emitted THz signal, which meets the detector 

antenna. The output of the detector antenna is than a chopped current, which can be amplified 

using an ac amplifier and rectified using a standard lock-in system. The disadvantage of this 

system is the loss of 50 % of the optical excitation power on the emitter antenna. 



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• A square wave voltage generator with an output voltage U of maximum +/- 30 V and a 

frequency of some kHz can be used as supply for the emitter antenna. The result is an emitted 

alternating THz signal, which meets the detector antenna. The output of the detector antenna 

is than an alternating current, which can be amplified using an ac amplifier and rectified using a 

standard lock-in system. This setup is shown in the figures above. 

Direct voltage detection 

If the THz signal is large enough, a direct dc voltage detection scheme can be used. In this case the 

emitter antenna has to be supplied by a dc voltage U of up to 30 V. The detector antenna rectifies the 

THz signal like in a lock-in system using the delay line for adjusting the optical reference signal. The 

maximum antenna output voltage is in the region of ~ 10 mV and the current ~ 1 nA. In this case a low 

drift dc current amplifier is needed to increase the signal level for registration. 



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VAT Reg. No: DE 813698804 




7. Time-domain measurements 

PCA-40-05-10-800-h emitter using optical pulse of 220 fs duration 



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PCA-40-05-10-800-h detector signal using optical pulse of 25 fs duration 

THz pulse, using the PCA-40-05-10-800 as detector, measured by Michael Williams of the 

Schmuttenmaer Research Group, Department of Chemistry, Yale University, U.S.A. 



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VAT Reg. No: DE 813698804 




8. Order information 

PCA-40-05-10-800-x Photoconductive antenna 

length l = 40 µm 

gap g = 5 µm 

width w = 10 µm 

laser wavelength λ = 800 nm 

(500 nm … 850 nm) 

x denotes the type of mounting as follows: 

x = 0 unmounted chip 4 mm x 4 mm with 2 bond contact pads 500 µm x 400 µm 

x = h mounted on an Al disc with 25.4 mm ∅ and hyperhemispherical silicon 

substrate lens, 1m coaxial cable with BNC connector 

x = a mounted on an Al disc with 25.4 mm ∅ and aspheric focusing silicon substrate 

lens with 50 mm focus length, 1m coaxial cable with BNC connector 

x = c mounted on an Al disc with 25.4 mm ∅ and aspheric collimating silicon 

substrate lens with 12 mm diameter, 1m coaxial cable with BNC connector 



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w 

g 

VAT Reg. No: DE 813698804 


Local Court Jena HRB 112769 

l

Instruction manual and data sheet PCA-40-05-10 ... - BATOP GmbH

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