THz photomixing using photoconductive antenna at ... - BATOP GmbH

1/14 Instruction manual PCA-44-06-10-800-x 

BATOP GmbH 

Wildenbruchstraße 15 

D-07745 Jena 

Instruction manual and data sheet PCA-44-06-10-800-x 

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

PCA – Photocconductive Antenna 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 

E-mail: info@batop.de 

http://www.batop.de/ 

PCA-44-06-10-800-0 - unmounted antenna chip 2 mm x 2 mm with 4 bond contact pads 

PCA-44-06-10-800-h - mounted antenna on hyperhemispherical 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...........................................5 

5. Instructions for use of the PCA-44-06-10-800-h..............................................................7 

6. Time-domain measurements...........................................................................................9 

7. Photomixing measurements ..........................................................................................10 

8. Order information...........................................................................................................14 

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: 161/106/02514 

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 and as photomixing emitter or detector in tunable 

cw THz measurement systems in the frequency region from 0.1 to 3 THz. 

Main PCA data 

200 

2. Antenna design 

300 

PCA 

44-06-10 

001 

2000 



D-07745 Jena 

• Laser excitation wavelength λ ~ 800 nm 

• Antenna resonance frequency 1 THz 

350 300 

2000 

all dimensions in micrometers 

Photo PCA 44-06-10 (survey) Photo PCA 44-06-100 Photo PCA 44-06-10 (detail) 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


Dielectric cover 





10 

100 

6 

44 

VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



3. Antenna parameters 

Electrical parameters minimum ratings standard maximum ratings 

Dark resistance 20 MΩ 25 MΩ 30 MΩ 

Dark current @ 10 V 300 nA 400 nA 500 nA 

Voltage 20 V 30V 

Dark current voltage characteristic at T = 300 K 

Current (μA) 



D-07745 Jena 

2,0 

1,5 

1,0 

0,5 

PCA 44-06-10 

JAM 373 

0,0 

0 10 20 30 40 50 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


Voltage (V) 

Optical excitation parameters minimum ratings standard maximum ratings 

Excitation laser wavelength 500 nm 800 nm 850 nm 

Optical reflectance @ 1040 nm 7 % @ 500 nm 5 % @ 800 nm 7 % @ 850 nm 

Optical mean power 30 mW 80 mW 

Optical mean power density 100 kW/cm 2 

Carrier recovery time 400 fs 





200 kW/cm 2 

VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



Spectral reflectance 

Illumination dependent resistance R 



D-07745 Jena 

Reflection (%) 

25 

20 

15 

10 

5 

0 

400 500 600 700 800 900 1000 1100 

Wavelength (nm) 

GaAs 0° + 0,166Si + 0,697Ta @ 650nm 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



4. Mounted PCA on hyperhemispherical silicon substrate lens 

Photoconductive antenna substrate semi-insulating GaAs 



D-07745 Jena 

chip area 2 mm x 2mm 

thickness t 650 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° 

β 

divergence angle ß 15° 

virtual focus length L 26.4 mm 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


PCA 

hyperhemispherical Si lens 





L 

t 

d 

h 

α 

VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



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 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 178 and BNC connector 

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



D-07745 Jena 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



5. Instructions for use of the PCA-44-06-10-800-h 

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 

Photomixing setup 



D-07745 Jena 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



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 6 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 (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 6 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. 

• 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. 



D-07745 Jena 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



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. 

6. Time-domain measurements 

THz detector signal at 10 mW optical pulse 

THz pulse, measured by B. Pradarutti, Fraunhofer-Institut Angewandte Optik und Feinmechanik, Jena, 

Germany 



D-07745 Jena 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



7. Photomixing measurements 

The THz photomixing measurements have been done at the Institute of Applied Physics, Technische 

Universität Darmstadt by Dominik Blömer in the group of Prof. Wolfgang Elsäßer. 

Photomixing setup 

The setup for the measurement of the emitted THz power is shown in the figure below. The dipole 

antenna was optically excited by a semiconductor laser based dual-wavelength external cavity source 

(2λ-ECDL) with a laser chip from Dr. Andreas Klehr und Dr. Goetz Erbert from Ferdinand-Braun-Institut 

fuer Hochfrequenztechnik (FBH) Berlin. The laser power can be adjusted using a λ/2-plate together 

with a polarizer (P). An optical spectrum analyzer (OSA) and a Fabry-Perot-Interferometer (FPI) have 

been used for the characterization of the laser radiation. The laser beam with a mean wavelength of ~ 

830 nm was focussed via a microscope objective (10x, NA 0.16) on the gap of the photoconductive 

antenna. The emitted THz power was directed with two off-axis parabolic mirrors (PM) onto a liquid 

helium cooled Si-bolometer (B). 

The bolometer does not give a calibrated signal, but the THz signal level is very low in the region of 

some 100 pW. 



D-07745 Jena 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



2λ-ECDL Bias voltage 



D-07745 Jena 

ISO 

BS 

OSA 

FP 

λ/2 P 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


V ,I 

b p 





S 

THz 

Lock-In Amp. 

PM 

THz photomixing setup at the Darmstadt University of Technology 

The dependency of the emitted THz power PTHz on the antenna bias voltage V is shown in the next 

figure. From the slope of the measured points a quadratic dependency of the THz power on the bias 

voltage can be deduced according the formula 

PTHz ~ V 2 

This dependency can be expected, because it means a proportionality between the electric field 

strength in the antenna gap with the emitted THz field strength ETHz, which is correlated with the THz 

power PTHz according to 

PTHz ~ ETHz 2 

THz signal (a.u.) 

1 

0,1 

PM 

10 15 20 25 30 35 40 

Bias Voltage (V) 

THz power as a function of the antenna bias voltage 

B 

VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



Optical excitation power 

In the figure below the measured dependency of the emitted THz power PTHz on the optical excitation 

power Popt is shown. The data points show a quadratic dependency according to the relation 

2 

PTHz ~ Popt 

This dependency can also be expected because of the following relations between the optical power 

Popt, the excited free carrier density in the antenna gap ρ, the current density j, the emitted THz field 

strength ETHz and the THz power PTHz 



D-07745 Jena 

1/2 

Popt ~ ρ ~ j ~ ETHz ~ PTHz 


10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

10 15 20 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


optical power (mW) 

THz power as a function of the optical excitation power 





VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



Difference frequency 

The measured influence of the difference frequency f on the emitted THz power PTHz is shown below. A 

resonance peak at f = 1.4 THz can be seen. The expected resonance frequency fres of a dipole antenna 

with a length l = λ/2 = 44 µm in a semiconductor environment with the refractive index n ~ 3.4 can be 

estimated using the following relation: 


f res 

10 

1 

0,1 



D-07745 Jena 

c c 

= = = 

n ⋅ λ 2 ⋅n 

⋅l 

0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 


Frequency (THz) 

THz power as a function of the difference frequency 





VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 



8. Order information 

PCA-44-06-10-800-x Photoconductive antenna 



D-07745 Jena 

length l = 44 µm 

gap g = 6 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 2 mm x 2 mm with bond contact pads 300 µm x 650 µm 

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

substrate lens, 1m coaxial cable with SMA connector 

Tel: +49 3641 634009 - 0 

Fax: +49 3641 634009 - 20 






w 

g 

VAT Reg. No: DE 813698804 

Tax Acc. No: 161/106/02514 

Local Court Jena HRB 112769 

l

THz photomixing using photoconductive antenna at ... - BATOP GmbH

Create successful ePaper yourself

Delete template?

Save as template?