We demonstrate high speed scanning of a time-domain terahertz pulse by a rotary optical delay line (RODL) incorporated into a photoconductive antenna based terahertz system. The delay line of RODL consists of six rotating convex reflective blades with a rotating speed controlled for a wide range of scan repetition rates. It can perform path length scans of 2.1 cm at a scanning speed of 8.4 m/s while maintaining linearity. The comparison of the terahertz temporal waveform and the frequency spectrum measured by using the RODL and a linear stage optical delay line confirms the linearity of the RODL up to 140 ps at high scan repetition rates of 400 scan/s. A high signal-to-noise ratio, up to a few thousand, can be obtained by averaging multiple terahertz pulses at a high scan speed.
We report the first measurement of terahertz pulse using a rotary optical delay line (RODL). The delay line uses a rotating reflective surface that gives a linear delay length with respect to the rotation angle. Operation principles and the profile of the reflective surface are examined and the optical path as a function of the radius and the rotating angle is calculated. A comparison of the temporal waveform and frequency spectrum obtained by using the RODL and the linear stage optical delay line (LODL) confirms that the linearity of the RODL is up to 500 ps corresponding to a delay scan length of 7.5 cm, and the difference in time delay is less than 0.2 ps. The RODL is suitable for the high-speed scanning of terahertz pulses up to 400 Hz.
An alternative stress-inducing method, a lowenergy pulsed electric field (LE-PEF), was used to improve the lipid productivity of microalgae cultures. A large shift in the Nile-Red-stained peaks toward a higher intensity in fluorescent-activated cell sorting, suggestive of an increased neutral lipid content, was observed when 10 kV LE-PEF pulses were applied to 800 mL batch cultures of Acutodesmus dimorphus. The optimal LE-PEF on-off cycle treatment for A. dimorphus was 10 s on-60 s off for 15 min with 6 cycles per day. Under these optimal LE-PEF treatment conditions, A. dimorphus showed an overall 28.8 % increase in lipid productivity. Therefore, based on these results, LE-PEF can be regarded as a promising tool to avoid the lipid content and growth rate trade-off and improve the lipid productivity of microalgae in various cultivation systems.
We describe a fast measurement of a pulsed terahertz signal generated by a femtosecond laser and a photoconductive antenna using an oscillating optical delay line. The method to measure the amplitude of the retroreflector in the oscillating optical delay line is proposed and the displacement of the retroreflector is exactly calculated to acquire the optical delay time in the fast scan mode. With the different oscillation frequency and amplitude of the retroreflector, the pulsed terahertz signals are measured and analyzed. The comparison of the temporal waveform and frequency spectrum between the fast scan mode and the slow scan mode shows a good agreement with the decrease in the scanning time from 60 to 1 s at a signal to noise ratio of 430.
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