Abstract
We demonstrate an efficient scheme to accelerate the self-similar pulse evolution and reduce the intensity noise of a free-running femtosecond fiber amplifier based on the pump wavelength optimization. Experiments and simulations indicate the enhanced tolerances of the pulse self-similar amplification to the seed signal power and pump wavelength fluctuations, with the optimum 915 nm pump wavelength. ∼20% increase in the compressed pulse quality and ∼31% reduction in the amplifier root-mean-square (RMS) relative intensity noise (RIN) (1.5 kHz to 5 MHz) have been observed, even with a more than 4 times higher pump laser diode (LD) RIN than the case of 976 nm. ∼50 fs transform-limited pulses are generated with the ∼0.03% amplifier RMS RIN. The proposed scheme can lower the requirements of low-noise self-similar femtosecond fiber amplifiers on the power stability of the seed oscillator and the thermal control of the pump LD, thus denoting potentials for the various satellite-based high-precision applications of femtosecond laser in space.
Highlights
High-quality femtosecond laser pulses with high power, short duration, and low noise have important applications in frontier scientific and space technology, such as optical frequency combs, coherent pulse synthesis, high-order harmonic generation, spacecraft networking, and formation flying [1,2,3]
At the same amplification gain of 20 dB, an optimal pump wavelength of 915 nm can result in a compressed pulse quality increase of about 20% and a root-mean-square (RMS) relative intensity noise (RIN) reduction of about 31% integrated from 1.5 kHz to 5 MHz, even though the pump laser diode (LD) RIN is more than 4 times higher
Spectrums of the negative-chirped pulse can be narrowed and smoothed by the interaction with self-phase modulation (SPM), and temporal durations can be compressed by the positive group velocity dispersion (GVD) [11, 12]. e amplifier is composed of an endpumped 2 m DC Yb fiber with a 20 μm core. e signal end of the amplifier is spliced to the single-mode fiber (SMF) pigtail in nonlinear pulse preshaper (1% fusion loss). e pump end of the amplifier is spliced to a combiner. e maximum output power of the LDs is 20W for both 976 nm and 915 nm. e compressor is conducted by a Littrow double-pass 600 lines/mm grating pair to ensure a ∼75% transmission
Summary
High-quality femtosecond laser pulses with high power, short duration, and low noise have important applications in frontier scientific and space technology, such as optical frequency combs, coherent pulse synthesis, high-order harmonic generation, spacecraft networking, and formation flying [1,2,3]. At the same amplification gain of 20 dB, an optimal pump wavelength of 915 nm can result in a compressed pulse quality increase of about 20% and a root-mean-square (RMS) relative intensity noise (RIN) reduction of about 31% integrated from 1.5 kHz to 5 MHz, even though the pump LD RIN is more than 4 times higher. With this approach, transformer limit (TL) pulses of ∼50 fs are generated after compression, and the RMS RIN of the amplifier is ∼0.03%. E result of the comparison shows that the appropriate pump wavelength of 915 nm ensures a smoother amplified spectrum and a smaller pulse base after compression, which indicates a more sufficient self-similar amplification. The efficient self-similar pulse evolution in this case attributes to the noise performance due to the inherent stability
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