All-fiberized 1840-nm femtosecond thulium fiber laser for label-free nonlinear microscopy

High-power, frequency-doubled all-polarization-maintaining fiber laser system at 925 nm

We demonstrate a high-power 925-nm pulsed laser system based on a frequency-doubled, all-polarization-maintaining (PM) fiber laser source operating at 1.8 µm. The seed is a figure-9 mode-locked oscillator, which incorporates a nonlinear amplifying loop mirror. After power scaling and pulse compression, the 1.8-µm laser source can provide femtosecond pulses with a repetition rate of 31.3 MHz and an output power of 2.24 W. Through frequency doubling in a nonlinear crystal, the 925-nm laser delivers a pulse duration of 503 fs and an output power of 818 mW, which is the highest power provided by all-PM fiber laser systems at this wavelength, as far as we know. Furthermore, this 925-nm all-PM fiber laser is employed as the excitation light source for two-photon microscopy (TPM) and second-harmonic generation (SHG) microscopy.

Acoustic bright solitons propagation in bubbly liquids

We study the propagation rules of acoustic bright solitons in bubble-containing media, as well as the strong anti-interference ability of acoustic solitons; and the effects of nonlinearity, dispersion, and dissipation on the dynamic properties of acoustic solitons are also analyzed. Based on the bubble-liquid mixture model, a lossy nonlinear Schrödinger equation is obtained. The analytical expression of the enveloped bright-acoustic solitons in the bubbly liquids is derived, which can accurately capture the propagation law of the acoustic bright solitons in the physical system, even if there is viscous loss in the medium. The dissipation-induced dynamics of acoustic solitons is studied through analytical and numerical methods, and the balancing effects of nonlinearity and dispersion in the propagation of bright solitons are analyzed. Furthermore, the particle nature and dynamic stability of bright-acoustic solitons in bubble-containing media are emphasized through fully elastic collisions between solitons moving in the same and opposite directions. This process obeys the energy and momentum conservation laws. After the collision, solitons can maintain their original amplitude, speed, and shape and continue to propagate undisturbed.

Broadband thulium fiber amplifier for spectral region located beyond the L-band

We present the development of a pair of silica-based thulium-doped fiber amplifiers working together in a broad spectral range from 1.65 µm to 2.02 µm. For the one optimized for shorter wavelengths, we designed and prepared optical fiber with a depressed cladding. We show the performance of the amplifiers achieving small-signal gain of at least 10 dB over 350 nm range from 1670 nm to 2020 nm, maximum gain of 40.7 dB with a noise figure as low as 6.45 dB and an optical signal-to-noise ratio of up to 50 dB. To the best of our knowledge, it is the first time that thulium fiber amplifiers of straightforward design without using redundant spectral filters operating efficiently in such a wide spectral region are demonstrated.

High-sensitivity and high-speed measurements of ultrashort pulses as short as 74 fs at 1.9 µm using a GRENOUILLE device

Ultrashort laser pulse sources in the wavelength range of 1.8 to 2 µm have many potential applications including medicine, materials processing, and sensing. In the use of such lasers, a crucial task is to measure their pulse's temporal intensity and phase. Such measurement devices are most useful when they are simple to build and operate and also have high speed and high sensitivity. The GRENOUILLE measurement device with few components, no moving parts, sensitivity of hundreds of picojoules, and measurement speed of hundreds of milliseconds, is commonly used to solve this problem at other wavelengths. In this paper, the measurement of ultrashort pulses by a GRENOUILLE device, developed using a silicon matrix sensor, for pulses in the wavelength range of 1.8 to 2 µm has been demonstrated. It is shown that ultrashort pulses with durations of 74 to 900 fs and a maximum spectral FWHM of 85 nm can be measured with this device. The recently developed ultra-reliable RANA approach was used for pulse retrieval from the measured traces. The device's performance was validated by comparing its measurements with those obtained by the robust FROG technique.