Research On The New High-resolution Laser Spectroscopy

With the rapid development of modern science and technology, demand for higher-resolution spectrometer has been growing rapidly for its wide use from scientific research to commercial purpose. However, the optical dispersing systems and the photo detectors have confined the spectral resolution limit of the normal spectrometers. In this article, a high resolution measurement has been realized with a 2-dimension (2-D) dispersing CCD spectrometer and a new method for hyperfine spectrum measurement based on it is put forward and experimentally demonstrated. Ultra-high-resolution spectrometry is obtained through incorporating a 2-D dispersing CCD spectrometer and a tunable Fabry-Perot (F-P) filter. Spectra resolution as high as 37.5 MHz (0.08 pm @800 nm) was achieved in a ～17.4 nm spectral range.First, a 2-D dispersing array detector-based spectrometer has been designed and built. A fiber-pigtailed laser diode (LD) was used to help system building and spectral calibration. It takes the virtually imaginary phased array (VIPA) as the prime dispersion element while the ordinary diffraction grating as the assistant, and disperses in two vertical directions, which can thus be called as an orthogonal dispersion spectrometer. Spectra resolution as high as 0.7 GHz (1.5 pm @800 nm) was achieved in the spectral range of 792-809.4 nm.Second, the experimental system incorporating the orthogonal dispersion spectrometer and the tunable F-P-based scanning interferometer has been established based on the orthogonal dispersion spectrometer described above. In the part of the tunable F-P scanning interferometer, the tunable F-P was used as the filter to choose the output wavelengths by controlling the voltage applied onto the tunable F-P. By synchronizing the recording of each spectrum casted onto the CCD with the change step of electric voltage applied onto the tunable F-P, the whole picture of the high-resolution spectrum can thus be obtained by integrating those spectra all the time. Spectral resolution higher than 37.5 MHz was achieved in a ～17.4 nm spectral range.Finally, the laser spectrum of the mode-locked Ti:sapphire laser has been measured with the spectrometer we built, proving that its longitudinal mode with the spacing of 76.3 MHz can be distinguished clearly.