Double modulated differential THz-TDS for thin film dielectric characterization

Abstract

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-mm-thick samples of silicon dioxide on silicon. q

Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy

“…In this way the whole THz transient was experiencing a constant delay from the pump pulse [13]. Double modulation is a well-known technique for both static and time-resolved terahertz spectroscopy [14,15], however to date this has only been used for noise reduction of the differential scan. The key element in simultaneous acquisition of reference and differential THz scans is the use of a two frequency chopper blade, which shape is shown on Fig 1(b).…”

A Review on Thin-film Sensing with Terahertz Waves

“…In DTDS, the optical chopper typically used to modulate the laser pump beam is discarded in favor of the galvanometer, and only one lock-in amplifier is necessary. Even though DTDS can decrease the effects of laser fluctuations, the modulation rate of the galvanometer is too slow to avoid 1/ f noise from the laser [40,41]. To further improve the dynamic range and reduce the minimum sample thickness, an optical chopper can be added to the system with an expense of a second lock-in amplifier [42][43][44], as depicted in Fig.…”

Label-free bioaffinity detection using terahertz technology

“…In this case, a pure avidin film acts as a reference to a film of biotin bound to avidin (figure 1). Double-modulated DTDS has been used for characterizing micron-thick films and is described elsewhere in detail (Jiang et al 2000, Brucherseifer et al 2000, Mickan et al 2002a. Figure 2 shows a schematic of a double-modulated DTDS spectrometer.…”