Output Of Lock-in Amplifier Research Articles

Single-beam low-frequency loss modulation technique for two-photon absorption measurement

We present a straightforward and reliable single-beam configuration designed for the assessment of two-photon absorption (2PA) through the utilization of the loss modulation technique. Mechanical rotation of a half-wave plate induces a sinusoidal modulation in the envelope of the probe pulse train. The elimination of spurious signals is achieved by determining the difference of the lock-in amplifier output at the focused and defocused positions of the sample. Our findings, based on measurements with dye solutions and crystalline silicon, demonstrate the feasibility of determining the 2PA coefficient, subject to preliminary calibration of the setup with reference samples. Remarkably, the acquisition of the 2PA signal in silicon at 1030 nm is accomplished with less than 200 pJ energy of the laser pulse, overcoming the challenge posed by concurrent linear absorption. Additionally, a signal of 3PA is revealed despite the presence of 2PA and linear absorption.

Precise determination of thermal parameters of a microbolometer

Determination of microbolometer thermal properties such as thermal capacitance, conductance, time constant, and IR responsivity is of the utmost importance as they directly influence microbolometer performance. Here we show a technique to measure them by using a minimized self-heating effect, thus leading to their precise determination via measurements based on an AC-biased Wheatstone bridge containing a microbolometer. The bridge outputs were subtracted from each other by a differential voltage preamplifier with its output processed by a lock-in amplifier. The lock-in amplifier output as a function of the amplitude of AC bias provided an amplitude of microbolometer thermal conductivity. A microbolometer temperature response to pulse irradiation of its membrane provided the value of its thermal time constant and, thus, its thermal capacitance. Finally, we also extracted microbolometer responsivity using a blackbody IR source. The method was experimentally verified using a micromachined bolometer, which showed excellent agreement with the analytical solution.

Gaussian Beams and Spatial Modulation in Nanopositioning

The kilogram is the last base unit of the systeme international d'unites (SI) that is still defined by an artifact. The watt-balance experiment is one of the promising methods that can produce a new definition of the kilogram based on fundamental constants. In this experiment, to compare an electromagnetic force and a gravitational force with a relative uncertainty of 10-9 by means of a beam balance, an absolute position sensor with nanometric resolution is needed. A novel method in position sensing based on the Gaussian beam propagation properties and their spatial modulation is presented. Two modulated and collimated Gaussian beams are focused into a slit. The slit is fixed to the object to be positioned. The resulting beams at the slit illuminate a photodetector whose signal is demodulated by a lock-in amplifier. The lock-in amplifier output signal is a function of the slit position with respect to the two modulated Gaussian beams. A resolution of 25 pm/(Hz)1/2 can be achieved. The long-term stability is 3.5 pm over 2 h and 20 min.

Limitations ofIn SituCurrent Density Mapping for Vibrating Electrodes Close to Metal Surfaces

The operation of the vibrating electrode measuring the current densities or field in solution, has been described based on the use of a lock-in amplifier. The analysis was developed to quantify the effects of a non-uniform field. This was achieved by considering the changes in lock-in amplifier output on increasing the ratio of the vibration amplitude to the distance of the vibrating electrode from a point current source. The results have shown that significant deviations from the true field occur when the ratio is greater than 0.3 and become 4 times too large at a ratio of about 0.95.

Change in optical activity of a lobster nerve associated with excitation.

1. To record the change in optical rotation of a nerve fibre associated with excitation, an optical apparatus was constructed using a polarizer, a photo-elastic modulator, an analyser and a lock-in amplifier. The apparatus was calibrated with the sucrose solution as the standard. 2. When a lobster leg nerve was dissected and mounted on the sample stage of the apparatus, stimulation elicited a transient change in the lock-in amplifier output. The signal (here called the 'R-signal') had a rapid time course, formed a peak during the rising phase of the birefringence signal, and often quickly returned to the base line, but sometimes showed a long-lasting later phase. 3. The R-signal arose at about the time when the compound action potential of slowly conducting fibres passed through the window of the chamber for the optical experiment, suggesting that it originates mainly in the smaller fibres. 4. The R-signal reversed its sign when the azimuth of the polarizer was changed by 90 deg, indicating that the R-signal was not due to electrical artifacts. Simultaneously recorded changes in the intensity of the transmitted light had a different time course and an amplitude too small to explain the appearance of the R-signal. 5. When the azimuth of the nerve was changed, the later phase of the R-signal changed its amplitude and direction, but the initial phase of the R-signal was much less influenced, suggesting that the birefringence signal was a component of the later phase. 6. The later phase of the R-signal could be reconstructed as a sum of an R-signal at a different azimuth and the birefringence signal, if the amplitude and direction of the latter were adjusted by multiplication of a factor. 7. Assuming that the nerve is a homogeneous, linearly and circularly birefringent and linearly and circularly dichroic material, the lock-in output was described by mathematical equations. From one of them the birefringence signal could be deduced from a series of R-signals observed at various nerve azimuths. The time course of the calculated birefringence signal agreed well with that of the experimentally recorded birefringence signals. 8. Utilizing the same equations, the contribution of the birefringence change to the R-signal was estimated and subtracted. The remaining part was independent of the nerve azimuth, and could be regarded as representing the time course of the change in optical rotation of the nerve.(ABSTRACT TRUNCATED AT 400 WORDS)