All-fiber Femtosecond Laser Research Articles

W-type normal dispersion thulium-doped fiber-based high-energy all-fiber femtosecond laser at 1.7 µm.

We propose a parabolic W-type thulium-doped fiber for the 1.7 µm high-energy femtosecond pulsed laser. Despite its attractive normal dispersion, the fiber offers high gain in 1.7 µm region thanks to its distributed short-pass filtering effect. With a proper dispersion management in an all-fiber chirped pulse amplification (CPA) scheme, we demonstrate so far the highest pulse energy of 128.0 nJ in a stable pulse of 174 fs in the 1.7-1.8 µm region, which marks above an order of magnitude improvement in pulse energy while exhibiting the shortest pulse duration among fiber-based CPA works at 1.7 µm. Hence, we provide a pathway to an energy scalable and efficient femtosecond laser at 1.7 µm via a compact and elegant all-fiber solution.

Single-Cavity Three-Color All-Fiber Femtosecond Laser

In this letter, the design and characterization of an all-fiber femtosecond laser is reported that generates three wavelengths at 1030 nm, 1550 nm, and 1900 nm from a single cavity. The cavity is based on Er-doped fiber and it is mode-locked by a fiber coupled saturable absorber mirror. We take advantage of fiber optics nonlinearity to generate 1030 nm and 1900 nm wavelengths which can be amplified using well-known Yb-doped and Tm-doped amplifiers. The third output of the laser can be optimized to generate femtosecond pulses at a wide range of central wavelength from 1700 nm to 2000 nm. Since all three outputs of the laser are being generated from the same cavity, they can be easily synchronized to be used in various pump and probe applications. This approach reduces the size, power consumption and cost of the laser compared to three individual mode-locked cavities. The laser can be packaged in a 20 cm × 20 cm × 20 cm form factor.

Single-cavity dual-wavelength all-fiber femtosecond laser for multimodal multiphoton microscopy.

A single-cavity dual-wavelength all-fiber femtosecond laser is designed to generate 1030 nm wavelength for high resolution multiphoton imaging and 1700 nm wavelength for long penetration depth imaging. Considering two-photon and three-photon microscopy (2PM and 3PM), the proposed laser provides the single-photon wavelength equivalent to 343 nm, 515 nm, 566 nm and 850 nm, that can be employed to excite a wide variety of intrinsic fluorophores, dyes, and fluorescent proteins. Generating two excitation wavelengths from a single laser reduces the footprint and cost significantly compared to having two separate lasers. Furthermore, an all-reflective microscope is designed to eliminate the chromatic aberration while employing two excitation wavelengths. The compact all-fiber alignment-free laser design makes the overall size of the microscope appropriate for clinical applications.

All-fiber femtosecond laser providing 9 nJ, 50 MHz pulses at 1650 nm for three-photon microscopy

The spectral window lying between 1.6 and 1.7 μm is interesting for in-depth multiphoton microscopy of intact tissues due to reduced scattering and absorption in this wavelength range. However, wide adoption of this excitation range will rely on the availability of robust and cost-effective high peak power pulsed lasers operating at these wavelengths. In this communication, we report on a monolithically integrated high repetition rate (50 MHz) all-fiber femtosecond laser based on a soliton self-frequency shift providing 9 nJ, 75 fs pulses at 1650 nm. We illustrate its potential for biological microscopy by recording three-photon-excited fluorescence and third-harmonic generation images of mouse nervous tissue and developing Drosophila embryos labeled with a red fluorescent protein.

High-repetition-rate all-fiber femtosecond laser with an optical integrated component.

We demonstrate a high-repetition-rate all-fiber soliton pulse laser mode-locked by the nonlinear polarization rotation technique. The laser cavity is effectively shortened by incorporating an optical integrated component possessing the hybrid functions of a polarization-dependent isolator, a wavelength-division multiplexer, and an output coupler. Resultant output soliton pulses have a fundamental repetition rate of 384MHz, a 3-dB spectral bandwidth of 25.2nm, and a dechirped pulse duration of 115fs. By using an external power amplification and pulse recompression system, the average output power of the laser is boosted to 207mW. The amplified pulses have a 2.33-ps duration, which is recompressed to 340fs. Numerical simulations reproduce the generation of high-repetition-rate soliton pulses in the fiber laser. Such a simple and low-cost high-repetition-rate fiber laser is a potential laser source for various practical applications.

Mid-infrared supercontinuum generation spanning 1.8 octaves using step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 µm.

A nearly two-octave wide coherent mid-infrared supercontinuum is demonstrated in a dispersion-engineered step-index indium fluoride fiber pumped near 2 µm. The pump source is an all-fiber femtosecond laser with 100 fs pulse width, 570 mW average power and 50 MHz repetition rate. The supercontinuum spectrum spans from 1.25 µm to 4.6 µm. Numerical modelling of the supercontinuum spectra show good agreement with the measurements. The coherence of the supercontinuum is calculated using a numerical model and shows a high degree of coherence across the generated bandwidth allowing it to be used for frequency comb applications.

Development of a compact hardware/software package for noninvasive diagnostics of skin diseases in the THz frequency range

The key elements of a mobile hardware/software package for noninvasive diagnostics of skin diseases in the THz frequency range have been designed, produced, and approved in model experiments. These elements are a compact THz oscillator based on an all-fiber femtosecond laser system and a unit for recovering electrodynamic characteristics of layered objects from scattered THz radiation spectra. Generation of 250-fs optical pulses at a wavelength of 1.03 µm with energy of 0.3 µJ and a repetition frequency of 1MHz is demonstrated and the efficiency of optical-THz conversion is found to be 5×10−6. The proposed algorithm is constructed based on an iterative procedure and can be used for dispersive and absorbing media. It has higher operating speed in comparison with the algorithms for solving inverse problems, which are based on functional minimization methods.

High-power source of THz radiation based on orientation-patterned GaAs pumped by a fiber laser

We demonstrate a new source of frequency-tunable THz wave packets based on parametric down-conversion process in orientation-patterned GaAs (OP-GaAs) that produces muW-level THz average powers at the repetition rate of 100 MHz. The OP-GaAs crystal is pumped by a compact all-fiber femtosecond laser operating at the wavelength of 2 mum. Such combination of fiber laser and OP-GaAs technologies promises a practical source of THz radiation which should be suitable for many applications including imaging and spectroscopy.