In the laser phase-locked system, the most crucial part is the use of lock-in amplifier to achieve the test gas, reference gas two-way detection, or even to achieve the measured gas, reference gas and laser background three-way detection.
Spectral measurement system built by a lock-in amplifier and a chopper, only measures the light intensity with a modulated frequency, so as to avoid the influence of other external noise, which can achieve the detection of low light with high precision.
The traditional lock-in amplifier have many defects due to using analog technology to achieve coherent modulation which greatly limits the phase-sensitive detector accuracy, and also introduces a lot of background noise.
The basic function of the lock-in amplifier is to extract the target signal from the noisy environment. According to the cause of the noise, it can be roughly divided into two types: the internal noise of the system and the external noise.
Tensile tests are to be carried out when evaluating the strength of metallic materials. In order to detect small changes in metal cracks or shape, you can measure the AC resistance of sample (called AC potential method).
Samples of superconducting material applied by a weak alternating voltage can occur a weak current through itself, which can be measured by LIA in order to avoid the measurement error from thermoelectric EMF effect.
The light from the beam splitter is converted into an electrical signal by the sensor. The sample beam and the reference beam are analyzed by two lock-in amplifiers with respective cut-off frequencies as reference frequencies, and the ratio of the two beams is calculated by the comparator.
There are two basic methods for connecting a voltage signal to the lock-in amplifier- the single-ended connection is more convenient while the differential connection eliminates spurious pick-up more effectively.