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An approach is reported to acquire an optical frequency standard based on precise frequency locking between optical frequency comb and continuous wave. A stabilized erbium-fiber-based frequency comb is created by locking to the two-photon absorption resonance of rubidium atoms. An Erbium-doped distributed-feedback narrow linewidth lasers is presented with an actively stabilized all fiber Mach–Zehnder interferometer. With this structure, many lines of the optical frequency comb can make a contribution to the error signal. The signal-to-noise ratio (SNR) is enhanced compared to traditional way which utilizes only one comb line. An acousto-optic modulator (AOM) is used to compensate the noise in fiber which is induced by environment. The relative frequency offset instability is 2 × 10 −13 at 1 s and 6 × 10 −15 at 1000 s. This stabilized system can be wisely used in optical communication at 1550 nm. The main advantage of this structure is the ability for long distance frequency transmission. Without dispersion, the stability and the robustness of the transmission is greater than the scheme only with the frequency comb. We transferred the signals along 10km optical fiber link with it. The relative frequency stability loss of the frequency signal is 1.1 × 10 −15 at 1 s and reaches 7.6 × 10 −19 at 1000 s. [ABSTRACT FROM AUTHOR]

A phenomenon of modal instability is investigated theoretically in some high power solid-state lasers with an unstable cavity. This modal instability is caused by a thermo-optic-thermo feedback coupled with an asymmetrical laser oscillation inside some unstable cavities. Numerical investigations indicate that this instability can appear in all lasers with Nd 3+ -doped disk scheme, Yb 3+ -doped disk scheme and direct-liquid-cooled slab scheme, but the physical mechanisms of optic-thermo feedback in the three schemes are completely different. It is shown that the modal instability can appear within a special power range only in the Nd- or Yb-doped disk lasers due to certain saturation phenomenon, but exhibits a power threshold in the direct-liquid-cooled slab lasers. Therefore different strategies to mitigate the modal instability in different lasers are suggested. Finally, the presence of transverse modal instability in the Nd:YAG thin-disk laser is confirmed qualitatively by an experiment. [ABSTRACT FROM AUTHOR]

A comparison between two methods of timing jitter calculation is presented. The integral method utilizes spectral area of the single side-band (SSB) phase noise spectrum to calculate root mean square (rms) timing jitter. In contrast the harmonic analysis exploits the uppermost noise power in high harmonics to retrieve timing fluctuation. The results obtained show that a consistent timing jitter of 1.2 ps is found by the integral method and harmonic analysis in gain-switched laser diodes with an external cavity scheme. A comparison of the two approaches in noise measurement of a diode-pumped Yb:KY(WO 4 ) 2 passively mode-locked laser is also shown in which both techniques give 2 ps rms timing jitter. [ABSTRACT FROM AUTHOR]

Abstract: A compact and rugged distributed feedback (DFB) laser system has been developed as online–offline injection seeder for the laser transmitter of a ground-based water vapor differential absorption lidar (WV DIAL) near 820nm. The frequency stability of this injection seeder system shows a standard deviation of only 6.3MHz and a linewidth of less than 4.6MHz during continuous operation of more than 14h. These values by far exceed the requirements for WV DIAL. By use of a novel technique based on an electro-optic deflector (EOD), alternating online–offline wavelength switching is achieved for each shot of the seeded laser with 250Hz with a response time of less than 10µs and very low crosstalk between the channels of only 33dB. As a result, a spectral purity of 99.95% is reached by the WV DIAL transmitter which again fulfills the requirements for WV DIAL measurements with high accuracy. Because moveable parts are not present in the seeding system, this setup is significantly less sensitive to acoustic vibrations and ambient temperature drifts during field experiments than other seeding systems which use external cavity diode lasers (ECDL) and mechanical switches. By our new seeding system not only the requirements for ground-based water-vapor DIAL are met but also for space-borne WV DIAL applications that pose even higher demands to the frequency stability and spectral purity of the laser transmitters. [Copyright &y& Elsevier]

Abstract: We present a simple and reliable optical setup for active stabilization of a diode laser. The method combines Doppler-free spectroscopy and magnetically induced dichroism in atomic vapor. The long- and short-term stability is achieved using a simplified optical and laser setup. We apply the setup to stabilize an external-cavity diode laser to the D2 atomic resonance in potassium vapor. With the laser locked we attain long-term stabilization to the atomic line with the reduction of laser frequency jitter down to 0.5MHz on a 50ms timescale. [Copyright &y& Elsevier]

Abstract: Fiber Bragg grating inscription with a deep ultraviolet (DUV) femtosecond laser and two-beam interferometry allows grating inscription in germanium-free fibers without classical UV photosensitivity. Therefore such a writing technology is a promising solution for the fabrication of fiber Bragg gratings in the active fiber material to realize a fully integrated all-fiber solution. In this paper we report on the use of the DUV femtosecond laser fiber Bragg grating technology to build a grating-stabilized fiber laser with high spectral purity. Output powers up to 158W at 1083nm and a slope efficiency of 76% have been demonstrated. [Copyright &y& Elsevier]

Abstract: We have developed a method of stabilizing multiple lasers based on double saturation spectroscopy. Compared with other laser-stabilization methods based on conventional saturation spectroscopy, ours provides numerous reference spectra constructed with several velocity groups of atoms. Two independent laser sources can be simultaneously stabilized by using combined optical-pumping processes associated with a single Rb reference. We analyzed the stability of the feedback loop taking the correlation effect of the saturation spectra into consideration. We experimentally demonstrated two stabilized laser sources with a frequency difference of 6,109MHz in the 87Rb D 2 line. The results were in good agreement with theory within errors in measurement. [Copyright &y& Elsevier]

We describe our system for frequency calibrating high resolution laser induced fluorescence spectra. The system utilizes two diode lasers that are spectrally narrowed with optical feedback from external resonators. One laser acts as a reference and is locked to a cesium transition with an external resonator containing a vapor cell in a Faraday filter configuration. Additional electronic feedback fixes the length of the resonator. The second laser receives its feedback from a confocal optical cavity and has the capability of scanning over several hundred megahertz. A portion of the scanning-laser output excites cesium atoms in a thermal atomic beam producing a fluorescence signal. Portions of each laser output are combined on a fast photo diode that produces a heterodyne signal. A counter reads the RF beat note between the laser frequencies and provides the frequency calibration. [Copyright &y& Elsevier]