A compact measurement system to measure four-degree-of-freedom (4-DOF) geometric errors of machine tools is presented in this paper. The angular errors and the straightness errors of the machine tools can be detected simultaneously by only one single laser beam, one position-sensitive detector (PSD) and one four-quadrant photodetector (QPD) through a simple optical configuration. The 4-DOF system has been calibrated and an API XD laser system is used as a reference. The straightness and angular measurement range of the system are ± 100 μm and ± 200 arc-sec, respectively. The resolution of straightness and angle measurement is 0.1 μm and 0.5 arc-sec, respectively. The developed measurement system was assembled on a machine tool with a carrier platform which has been moved 800 mm with an interval of 50 mm. A similar measurement was also conducted by the API XD laser system. The measuring results show that the maximum straightness residual is less than 2 μm and the maximum angular residual is less than 2 arc-sec. The experimental results show that the system have a straightness repeatability of ± 2 μm and an angular repeatability of ± 2 arc-sec. The developed 4-DOF measurement system can be easily assembled for geometric error measurement of machine tools in the industrial fields.
KEYWORDS: Semiconductor lasers, Diffraction gratings, Diffraction, Deep ultraviolet, High power lasers, Nonlinear frequency conversion, Polarization, Laser systems engineering, Second-harmonic generation, Crystals
We reported a high-power narrowband blue diode laser which is suitable for subsequent nonlinear frequency conversion into the deep ultraviolet (DUV) spectral range. The laser is based on an external cavity diode laser (ECDL) system using a commercially available GaN-based high-power blue laser diode emitting at 448 nm. Longitudinal mode selection is realized by using a surface diffraction grating in Littrow configuration. The diffraction efficiency of the grating was optimized by controlling the polarization state of the laser beam incident on the grating. A maximum optical output power of 3.1 W in continuous-wave operation with a spectral width of 60 pm and a side-mode suppression ratio (SMSR) larger than 10 dB at 448.4 nm is achieved. Based on the experimental spectra and output powers, the theoretical efficiency and output power of the subsequent nonlinear frequency conversion were calculated according to the Boyd– Kleinman theory. The single-pass conversion efficiency and output power is expected to be 1.9×10-4 and 0.57 mW, respectively, at the 3.1 W output power of the ECDL. The high-power narrowband blue diode laser is very promising as pump source in the subsequent nonlinear frequency conversion.
For many applications, laser diodes with very narrow and stable emission wavelength are needed. The realization of mode selection by an external cavity system with a grating is widely used. The influence of longitudinal mode selection by external grating on the filamentation and catastrophic optical mirror damage (COMD) of 970 nm broad area single emitters is studied in this paper. The emitters worked at three configurations: free running, with 10% mirror feedback (mirror lasers), and 10% grating feedback (grating lasers). The grating lasers showed very short lifetime caused by COMD, while the free-running lasers and mirror lasers show no power degradation. The COMD was confirmed by optical microscope showing cracking and melting of the optical antireflective (AR) coatings. By observing the near-field pattern of the three lasers, the COMD of the grating lasers was attributed to the pronounced filamentation induced by the grating feedback. What’s more, the filamentations vary when the locked wavelength change which indicates that the carrier dynamics thus the refractive index profile is very sensitive to the locked lasing wavelength.
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