Investigation On CW Single-frequency Tunable Ti: Sapphire Laser With Its Intensity Noise

All-solid-state continuous-wave single-frequency tunable Ti:sapphire lasers with compact configuration, high stabilization and high efficiency have been extensively applied to high-precision interferometry, high-sensitive laser spectroscopy, gravity-wave detection, quantum communications, atom cooling and so on owing to their broad tunable wavelength range from 700 nm to 1000 nm, high output power and low intensity noise. It has been demonstrated that the Ti:sapphire laser with high-efficiency and high-stabilization can be achieved by analyzing the characteristic of the Ti:sapphire crystal, designing and optimizing the resonant cavity and inserting the necessary optical devices into the laser cavity. However, when Ti:sapphire lasers are used in the experimental researches for laser cooling of atoms, quantum optics and quantum information, more and more attentions have to be paid in reducing intensity noises of their output light since the extra noises of laser sources will severely influence the experimental results. During the period of my Ph. D study, we designed and constructed a CW Ti:sapphire laser firstly. Then, we experimentally analyzed the noise characteristics of the Ti:sapphire laser. The accomplished main works are as following:1. Based on analyzing the absorption and emission spectra of Ti:sapphire crystal, we design a ring laser resonantor with four mirrors, in which the optical astigmatism is compensated. Using the transmission matrix the stable operation conditions of the laser and the properties of the beam-waist are calculated. By optimized the parameters of the laser resonantor the unidirectional operation of the laser can be realized in the required tunable range.2. The dependences of the Ti:sapphire laser output power on the intracavity losses and the transmission of the output coupler are theoretically analyzed and experimentally investigated. According to the experimentally measured intracavity losses and the given transmission of the output coupler, the design of the laser is optimized and the stable laser output with higher power is obtained. In order to improve further the frequency stability of the Ti:sapphire laser, a confocal reference cavity and an electronic servo-system are used for the laser frequency locking on.3. The tuning properties of the Ti:sapphire laser are analyzed. The maximum tuning wavelength range is limited by the bandwidth of the Ti:sapphire crystal. A set of BRF inserted in the resonant cavity serves as the tuning element of the laser. The tuning range and the tuning precision are determined by the thinnest and the thickest plate of the BRF, respectively. Besides, an etalon inserted in the resonant cavity can improve further the tuning precision in a noncontinuous tuning fashion. In order to achieve the continuous tuning, we change the voltage of the PZT attached on a cavity mirror to adjust the resonant frequency of the cavity, continuously.4. To research the intensity noise of the built Ti:sapphire laser, its intensity-noise dependence on the longitudinal-mode structure of the pumping source is experimentally studied, firstly. We find that the intensity noise is significantly reduced when a single-longitudinal-mode green laser is utilized as pumping source instead of the multi-longitudinal-mode green laser. Then the influences of the pumping rate and the wavelength of the laser on the intensity noise of the Ti:sapphire laser are studied. Increasing the pumping rate, the frequency of the relaxation resonant oscillation (RRO) moves toward higher frequency and the amplitude of RRO peak decreases. Finally, we theoretically analyzed the spectra of the intensity noise of the output laser and the theoretical calculation and the experimental result are in good agreement. The theoretical model can be applied to calculate the intensity noise spectra of the laser pumped by a pumping source with a noise distribution.5. In order to suppress the intensity noise at the low frequencies of the all-solid-state continuous-wave single-frequency tunable Ti:sapphire laser, the characteristic of the optoelectronic feed-forward is theoretically analyzed. The calculated result shows that the best gain of the feedback circuit depends on the injected noise. Then, the characteristic of the intensity noise suppression at the low frequencies by means of the optoelectronic feed-forward is experimentally investigated. By tuning carefully the gain of the feedback circuit the suppression of the intensity noises can be optimized. The decrease of the amplitude of the intensity noise from 8.7 dB to 1.4 dB is experimentally observed, and the maximum noise suppression of 7.3 dB is obtained at 1.125 MHz. It has been demonstrated that by selecting the best delay time and feed-forward gain, the intensity noise can be suppressed almost to the quantum noise level at any sideband frequency.The creative works are as following:A. We designed and built an all-solid-state CW single-frequency tunable Ti:sapphire laser.B. The Ti:sapphire laser was optimized by inserting a silicon plate to measure the intracavity losses and studying the relationship bwtween the output power and transmission of the output coupler.C. The tuning precision was improved by designing and selecting a suitable tuning device.D. Influences of the longitudinal-mode structure of the pumping source and a variety of factors on the intensity noise of the Ti:sapphire laser were studied and a method for theoretically calculating the intensity noise spectra was applied. E. Intensity noise at the low frequencies of the Ti:sapphire laser was suppressed by optoelectronic feed-forward control.