Watt-level gigahertz femtosecond fiber laser system at 920 nm

Abstract

We demonstrate a watt-level femtosecond fiber laser system at 0.9 µm with a repetition rate of >1 GHz, which is the highest value reported so far for a fundamental mode-locked fiber laser. The fiber laser system is seeded by a fundamental mode-locked fiber laser constructed with a home-made highly Nd3+-doped fiber. After external amplification and pulse compression, an output power of 1.75 W and a pulse duration of 309 fs are obtained. This compact fiber laser system is expected to be a promising laser source for biological applications, particularly two-photon excitation microscopy.

All-polarization-maintaining Nd-doped ultrafast fiber laser oscillator at 929 nm mode-locked via a 3x3 nonlinear amplifying loop mirror

“…When using Nd-doped fibers, particular attention has to be paid to filter out the dominant four-level transition at 1064 nm and efficiently emit light via the three-level transition in the 920 nm band [16]. For that purpose, one can use specially designed double-clad W-shaped Nd-doped fibers, which can sufficiently suppress the emission at 1064 nm [17][18][19][20][21]. Despite the availability of specialty fibers, most systems utilize free-space spectral filtering [22][23][24][25][26].…”

Coordination engineering in Nd3+-doped silica glass for improving repetition rate of 920-nm ultrashort-pulse fiber laser

“…Taking Nd3+-doped multicomponent fibers and silica fibers as gain media, ultrafast fiber lasers ranging from 905 to 932 nm have been previously studied using different passive mode-locking techniques, including nonlinear amplification loop mirrors, 21 – 23 nonlinear polarization rotation, 24 , 25 and semiconductor saturable absorber mirrors (SESAMs) 26 , 27 . In particular, due to high rare-earth (RE) ions’ solubility, these Nd3+-doped multicomponent fibers enable gigahertz repetition rate 920 nm ultrashort pulses 26 …”

“…In particular, due to high rare-earth (RE) ions’ solubility, these Nd3+-doped multicomponent fibers enable gigahertz repetition rate 920 nm ultrashort pulses 26 – 28 Nevertheless, owing to the inherent difference in glass softening temperature and thermal expansion coefficient, the low-loss and high-strength fusion splicing between multicomponent fibers and silica fibers has been an obstacle to their commercialization 29 . Furthermore, the low damage threshold of multicomponents is another concern for their long-term running.…”

“…However, in terms of Nd3+-doped silica fibers, two issues have been limiting the performance improvement of 920 nm ultrashort pulses; taking the pulse repetition rate as an example, it is still well below 100 MHz 21 – 25 —much lower than that of these multicomponent fibers, 26 – 28 which hardly meets the requirement of TPM imaging speed increase, as higher repetition rates are required to shorten the pixel dwell time via dense two-photon excitation 27 . The first issue, generally regarded as the most challenging one, is the competitive 1.06-μm amplified spontaneous emission (ASE) of the four-level transition (F43/2→I411/2), which originates from the same upper laser level (F43/2) as the 920 nm but with a stronger intensity 30 , 31 .…”

“…Taking Nd 3þ -doped multicomponent fibers and silica fibers as gain media, ultrafast fiber lasers ranging from 905 to 932 nm have been previously studied using different passive modelocking techniques, including nonlinear amplification loop mirrors, [21][22][23] nonlinear polarization rotation, 24,25 and semiconductor saturable absorber mirrors (SESAMs). 26,27 In particular, due to high rare-earth (RE) ions' solubility, these Nd 3þ -doped multicomponent fibers enable gigahertz repetition rate 920 nm ultrashort pulses. [26][27][28] Nevertheless, owing to the inherent difference in glass softening temperature and thermal expansion coefficient, the low-loss and high-strength fusion splicing between multicomponent fibers and silica fibers has been an obstacle to their commercialization.…”