A high-speed high-resolution heterodyne interferometer using a laser with low beat frequency is developed. The interferometer has two spatially separated parallel beams with different frequencies. Two interference signals with opposite Doppler shift are optically generated by the interferometric optics. The measurement electronics uses two identical phasemeters for the two opposite interference signals. The two interference signals are selectively used according to the speed of the target, which makes sure that the Doppler shift of the selected signal is always positive, so that the measurable speed is no longer limited by the beat frequency of the laser source. Experimental results show that the measurement resolution is 0.62 nm. The measurable speed can exceed the restriction determined by the beat frequency. Compared with a commercial interferometer, the displacement difference is less than 40 nm in a travel range of 900 mm.

A method has been developed for the stabilization of an internal mirror He-Ne laser to achieve a high frequency reproducibility that is mainly influenced by the temperature of the stabilized laser. However, it is difficult to achieve a reproducible temperature in a short time under different ambient temperatures. In this paper, the He-Ne laser is stabilized based on the relationship between the laser mode number and the laser cavity temperature where a reproducible temperature can be rapidly achieved under different ambient temperatures, resulting in a high frequency reproducibility. Experiments have demonstrated that the He-Ne laser used can be stabilized in approximately 10 min, typically 6 min; the frequency stability is less than 2×10(-10); the frequency reproducibility is less than 1×10(-9).

A multi-wavelength absolute distance measurement method based on synchronous occurrence and phase measurement of coarse and refined synthetic wavelength is proposed to remove the effect of vibration on the measurement distance. The phase value of refined synthetic wavelength is monitored to see if half-synthetic wavelength error occurs by judging whether it is near to 2π or 0. If yes, a new suitable refined synthetic wavelength is generated to re-measure the distance with phase near π. A measuring system has been built with a He–Ne laser source and three acousto-optic frequency shifters for implementation of this method. A comparative measurement has been performed using a counting laser interferometer at a distance of 20 m. Actual measurements indicate that half-synthetic wavelength error has been identified and eliminated with uncertainty of smaller than 60 µm under laboratory conditions.

No abstract

BACKGROUND: Emotional intelligence plays a vital role in human-computer interaction, and EEG signals are an objective response to human emotions. OBJECTIVE: We propose a method to extract the energy means of detail coefficients as feature values for emotion recognition helps to improve EEG signal-based emotion recognition accuracy. METHOD: We used movie clips as the eliciting material to stimulate the real emotions of the subjects, preprocessed the collected EEG signals, extracted the feature values, and classified the emotions based on them using Support Vector Machine (SVM) and Stacked Auto-Encoder (SAE). The method was verified based on the SJTU emotion EEG database (SEED) and the self-acquisition experiment. RESULTS: The results show that the accuracy is better using SVM. The results based on the SEED database are 89.06% and 79.90% for positive-negative and positive-neutral-negative, respectively. The results based on the self-acquisition data are 98.05% and 89.83% for the same, with an average recognition rate of 86.57% for the four categories of fear, sad (negative), peace (neutral) and happy (positive). CONCLUSION: The results demonstrate the validity of the feature values and provide a theoretical basis for implementing human-computer interaction.