Papers by Keyword: Optical Feedback

Abstract: A frequency-stabilized diode laser is widely used for applications in laser cooling and high-resolution spectroscopy. In this work, the 780-nm external cavity diode laser was constructed and subsequently frequency-controlled by three parameters, i.e., temperature, injection current and optical feedback. The laser frequency was measured with respect to the 5S_1/2 → 5P_3/2 (D2-lines) transition of Rubidium, while the laser mode was characterized by a Fabry-Perot interferometer. The laser temperature was passively controlled to a single value between 20 ̊C and 25 ̊C while the injection current was investigated in combination with course and fine adjustments of optical feedback. Only data relevant to a single-mode laser operation was collected. It was found that as the current increased, the laser frequency shifted linearly with slopes approximately 0.5-0.8 GHz/mA. Optical feedback from the external cavity was tuned by the voltage applied to the piezoelectric transducer, yielding a linear frequency response of approximately 0.2 GHz/V. The measured parameters were rearranged to represent the island of stability of the laser, suggesting suitable conditions that yielded single-mode operation, at a desirable laser frequency. The results were important for a design of an active feedback, in order to further reduce the frequency linewidth and intensity noise of the laser.

Abstract: We demonstrate a method of displacement measurement based on Nd:YAG laser with birefringence external cavity. The measurement system is composed of Nd:YAG laser, a wave plate with phase retardation of 450 and an external feedback mirror. Due to the birefringence effect, the external cavity modulates the laser output intensities in the two orthogonal directions with a phase difference of 900, which is two times to that of the wave plate. Both the in-quadrature laser intensities vary one period, when the external cavity length changes λ/2. These two channel laser intensities with phase difference of 900 can be subdivided to λ/8 after 4-fold evaluation. The movement direction of external mirror can be distinguished by the lead or lag between these two channel signals. Our method can improve the resolution of displacement measurement 4 times that of conventional optical feedback, and reach 133nm for a laser wavelength of 1.064µm.

Abstract: This paper presents a novel laser feedback interferometer for metrology of large range displacement. A Birefringence-Zeeman dual frequency laser is applied in the system. Due to its strong optical feedback effects, the intensity modulation curves of the two polarized lights will have a zero intensity part in a period. A quartz crystal is used in the external feedback cavity as a birefringent element. And a phase difference between the two lights can be adjusted to π/2. Thus, the intensity modulation curves in a period can be divided into four polarization zones with equal width. When the displacement of the object to be measured is produced, the four polarization zones will appear in sequence. According to the appearance order of the four zones, the direction of the displacement can be discriminated without ambiguity and the resolution of the system can be greatly increased. It is confirmed that the laser feedback interferometer has a resolution of 79.1nm and with a linearity of 0.01% over the whole measurement range of 15mm.