We demonstrate frequency stabilization of DFB laser via modulation transfer spectroscopy, which avoids the interference of Doppler absorption spectrum. By modulating the frequency of laser beam(pump laser beam), the other laser beam(probe laser beam) overlap pump laser beam is modulated as the same frequency by nonlinear interaction. By demodulating the signal from detection beam, an error signal is generated through the low pass filter. The frequency is stabilized at the 0 point position of the MTS frequency discrimination curve by PID loop which shows frequency fluctuation is less than 149 kHz, and the relative frequency stability is improved by nearly two orders of magnitude.
We demonstrate the high-gain of two double-pass Ho:YLF amplifiers with high-energy seed pulses injection via a modified population inversion Frantz-Nodvik model by numerical simulation. From the numerical simulation results, 26.2 mJ/1 kHz amplified pulses can be obtained by two double-pass amplifiers with 20 μJ/1 kHz, 40 nm (FWHM) bandwidth seed pulses injection. Due to ~1300 gain, the bandwidth of the amplified pulse decreases to about 3.5 nm (FWHM), corresponding to 466 fs pulse duration near 2 μm wavelength. Therefore, the spectrum shaping of seed pulses is induced to suppress the gain narrowing effect. Then, the pulses can be amplified to 22.8 mJ with a spectrum of 16 nm (FWHM), which supports 368 fs pulse duration near 2 μm by simulation.
The optical system plays a significant role to cesium atomic fountain clocks, which manipulates and detects population of cesium atoms. This paper presents a compact optical system for cesium atomic fountain clocks. The optical system provides two beams with 32mW separately for cooling atoms and six beams of 12mW respectively for trapping atoms with the frequency tuning from 80MHz to 220MHz. The relative intensity noise of the detect laser beam reduces from 1.33×10<sup>-6</sup> Hz to 1.52×10<sup>-10</sup> Hz at 1Hz by the laser power stabilization system. The optical system operates continuously for 30 days with the fluctuation of optical power less than 3% approximately. And the frequency stability is 3×10<sup>-15</sup> at 1000s. The results show the optical system satisfies with the needs of our cesium atomic fountain clock developed and establishes the foundation for cesium atomic fountain continuous operation.