AIR-COUPLED PHOTOCONDUCTIVE ANTENNAS

Transcription

1 AIR-COUPLED PHOTOCONDUCTIVE ANTENNAS Report: Air-Coupled Photoconductive Antennas In this paper, we present air-coupled terahertz photoconductive antenna (THz-PCAs) transmitters and receivers made on high-resistive ultra-fast semiconductor substrates packaged in TeTechS patent pending sensor enclosure modules. The enclosure modules house the sensor chip dye with a collimating high-resistive silicon lens attach to the back side of the THz-PCA chip. The devices are excited by focusing laser beams through air.

2 Air-Coupled Photoconductive Antennas A I R - C O U P L E D P H O T O C O N D U C T I V E A N T E N N A S Air-Coupled Photoconductive Antennas INTRODUCTION Terahertz photoconductive antennas are among the most promising devices that are used to harness the unique properties of terahertz waves for variety of applications, such as manufacturing process control, security, biology and medicine, medical imaging, material spectroscopy and sensing, and monitoring and spectroscopy in pharmaceutical industry. Since their demonstration as practical terahertz sources and detectors, THz-PCAs have been the subject of a vast amount of scientific and industrial reports investigating their applications as terahertz wave transmitters and receivers. Using THz-PCAs for generation and detection of terahertz signals, one can achieve relatively high signal-to-noise ratio and perform fast scan for imaging and spectroscopy applications. The possibility of fabricating THz-PCAs on photoconductive materials with the band gap energy equal to the energy of the photons at the telecommunication wavelengths makes THz-PCAs attractive for several real-world applications. The air-coupled THz-PCAs are excited by femtosecond optical pulses to generate and detect terahertz pulses with bandwidth of up to 5 THz. TETECHS AIR-COUPLED T-ERA THZ-PCAS Researchers and technologists in diverse fields of science and engineering need THz-PCAs to build their terahertz spectroscopy measurement setups to perform terahertz imaging and sensing experiments. They often demand for pre-packaged and easy to use THz-PCAs both for wide bandwidth and high frequency resolution applications. TeTechS T-Era series THz-PCAs are built to address this need. TeTechS air-coupled T-Era series THz-PCAs are used for emitting and detecting terahertz waves. Figure 1 shows the drawing of an air-coupled T-Era THz-PCA. The device is made on high resistive ultra-fast epitaxially grown low-temperature GaAs (LT-GaAs) substrates packaged in TeTechS patented chip enclosure module. The enclosure module houses the THz-PCA with a collimating high-resistive silicon lens attach to the back side of the THz-PCA chip. The device is packaged in a modular format so that it is easy to change the THz-PCA chip dye inside the enclosure at a fraction of cost. The silicon lens can be re-aligned after changing the THz-PCA chip dye using a silicon lens setting fixture. The standard Ø1 threaded body makes it convenient to attach the module to other standard optical components or mount it on an optical bench. When excited by 800 nm, 100 fs optical pulses with 20 mw average optical power, a pair of T-Era-100A-800-air (transmitter) and T-Era- 20D40P-800-air (receiver) generate more than 30 na peak terahertz photocurrent on the receiver antenna with more than 5 THz bandwidth and 70 db power spectrum dynamic range. Page 1

3 Figure 1: Exploded Drawing of an Air-Coupled Terahertz Photoconductive Antenna. Figure 2 shows the fabricated air-coupled T-Era-20D40P-800-Air terahertz photoconductive antenna chip dye on LT-GaAs substrate. The device is used to detect wideband terahertz pulses in terahertz time-domain systems. Figure 2: Image of a Fabricated Terahertz Photoconductive Antenna Chip Dye. Page 2

4 Figure 3 shows a typical terahertz time-domain measurement setup with a pair of T-Era THz-PCAs used to generate and detect a terahertz wave. The laser beam is focused on the THz-PCAs through an opening on the back side of their enclosures. The outgoing beam from the transmitter device is collected using a parabolic mirror and focused on the receiver using a similar mirror. Figure 3: A Typical terahertz time-domain measurement setup with a pair of T-Era THz-PCAs as the terahertz transmitter and the receiver modules. 1. Femto-second laser 2. Transmitter antenna 3. Receiver antenna 4. Terahertz beam focus for transmission measurement 5. Terahertz beam focus for reflection measurement 6. Linear scanning stage. Page 3

5 Figure 4 shows a typical terahertz pulse and its corresponding power spectrum generated by a T-Era-100A- 800-Air transmitter module and detected by a T-Era-20D40P-800-Air receiver module in a terahertz timedomain system. Figure 4: A Typical wide bandwidth terahertz pulse and its corresponding power spectrum generated and detected by a pair of T-Era terahertz photoconductive antennas. CONCLUSION In this paper, we present TeTechS air-coupled T-Era terahertz photoconductive antennas for generating and detecting wideband terahertz signals. These devices are used extensively in terahertz time-domain systems. The key components in terahertz time-domain measurement setups are the THz-PCA transmitter and receiver modules, where the laser beam is coupled to the THz-PCAs to generate and detect terahertz pulses. Page 4