Narrow-line Dye Laser And Its Application On Spectroscopy

Being able to cover the visible spectral band of 550-600 nm, a wideband tunable continuous-wave dye laser with gain medium of the dye Rhodamine 6G has unique advantages in high-resolution laser spectroscopy such as the investigation of hyperfine spectrum of iodine molecules. Moreover, frequency stabilized narrow-line dye laser plays an important role in many precision measurements and metrology, such as optical lattice clocks and tests of fundamental physics.The narrow-line laser radiation can be obtained by using the Pound-Drever-Hall frequency locking method whose performance dependents on the stability of the optical resonator serving as a frequency reference as well as the noise property of the frequency feedback control system. This thesis discusses the temperature control of a thermal- and acoustic- insulated enclosure, the intensity noise suppression, the laser frequency stabilization, and the measurement of the absorption spectrum of the gaseous iodine molecules as an example to demonstrate the application of the narrow-line dye laser system to high-resolution laser spectroscopy.Firstly, we introduce the development of the thermal- and acoustic- insulated enclosure and the analysis of its temperature-control loop. To be used in the laser frequency stabilization, the enclosure is devoted to achieve two goals, which are making a stable environment with small temperature fluctuation and lower the impact of the acoustic wave on the reference cavity. We analyze the gain of the temperature-control loop in a stage-by-stage manner, laying a foundation for future improvements on the thermal control system. The measurements show that while the ambient temperature fluctuation is around 1 K, the thermal instability inside the enclosure is reduced to 3-4 mK.For reducing the laser intensity fluctuation and investigating the noise mechanism of the feedback control system, we implement a long-term and wideband laser intensity stabilization with electro-optic amplitude modulation. Usually, two strictly matched electro-optic crystals are needed for this purpose to compensate the drift caused by the crystal birefringence. Here we are able to use a single lithium niobate (LiNbO3) crystals to achieve a control bandwidth of 2.5 MHz and a long-term intensity stability of 8×10-4. Furthermore, the residual noise of the control system is analyzed in detail, providing useful guidance for further improvement. In addition, the current system can well be adopted to greatly reduce the residual amplitude modulation, which is a byproduct of the electro-optic modulation and is one of the major sources that affect the frequency stability of the laser.The frequency feedback control system is central to investigations introduced in this thesis. We employ two-stage Pound-Drever-Hall frequency stabilization to cope with the unfavorable frequency noise of a dye laser, which has strong low-frequency components as well as fast ones that extend to around 1 MHz. After the pre-stabilization, the linewidth of the laser is reduced from 670 kHz to 2 kHz (0.1 s measurement time).,which is suffice for high-precision laser spectroscopy. When the frequency noise is further suppressed by the second-stage frequency stabilization, the linewidth is further reduced to 1.4 Hz (beat measurement,2 s measurement time). The frequency instability of the beat note is 4×10-15 (3 s averaging time), with the thermal noise contributes to an instability of 1.2×10-15. At Fourier frequencies of 0.1-2 Hz, the frequency noise in the beat note exhibits a 1/f power law. Below 0.1 Hz, the noise follows a power law that is much steeper than a 1/f noise, a characteristic that is primarily caused by the drift of the cavity length. The current narrow-line dye laser meets the basic requirement for detecting the 1S0-3P0 clock transition in an ytterbium atom.One of the primary goals of developing the narrow-line dye laser system is to detect the spectrum of iodine molecules trapped in the sub-nanometer channels of a zeolite crystal. This spectroscopic investigation will have a positive impact on the experimental exploration of compact optical frequency references and on the investigation of spatial alignment of diatomic molecules. As a preparation of this spectroscopic investigation, an experimental system for saturated absorption spectrum of gaseous iodine is implemented. Also established is a high-sensitivity balanced detection system for probing optical absorption of zeolite-iodine structure. The dye laser after first-stage frequency stabilization is successfully used to detect the Doppler-free hyperfine spectrum of iodine molecules in free space.In the end, we discuss several possible ways that will further improve the frequency stability and also upgrade the functionality of the current system, making it more competent for applications of laser spectroscopy.