Femtosecond Er-doped fiber laser source tunable from 872 to 1075 nm for two-photon vision studies in humans

Abstract

We report the development of a widely-tunable femtosecond fiber laser system and its application for two-photon vision studies. The source is based on an Er-doped fiber laser with spectral shift up to 2150 nm, followed by a second harmonic generation module to generate a frequency-doubled beam tunable from 872 to 1075 nm. The source delivers sub-230 fs pulses with nearly-constant duration over the entire tuning range, with output powers between 0.68–1.24 mW, which corresponds to a pulse energy of 13.2–24.1 pJ. Such pulse energy is sufficient for employing a system for measurements of two-photon scotopic spectral sensitivity of two-photon vision in humans. The laser parameters allow for very efficient and safe two-photon stimulation of the human visual system, as proved by a good separation between one- and two-photon thresholds for wavelengths below 950 nm, which we have confirmed for 3 healthy subjects.

High-power Raman soliton generation tunable from 1.76 to 1.84 µm in all-fiber polarization-maintaining erbium-doped amplifier

“…The other popular technique to obtain ultrashort pulses at 1700 nm excitation window is Raman soliton lasers taking advantage of the soliton self-frequency shift (SSFS) [10][11][12][13][14][15][16][17][18]. The soliton pulses propagating in optical fibers are affected by stimulated Raman scattering (SRS), causing energy to continuously transfer from the shorter wavelength to the longer wavelength, resulting in the SSFS.…”

“…In 2018, B. Li et al demonstrated a soliton generation tunable in 1.58-2.52 µm wavelength range with 14 mW output power by employing a compact fiber source to pump a 2 m long large-mode-area silica fiber [15]. In 2022, D. Stachowiak et al demonstrated a 1742 to 2136 nm wavelength tunable femtosecond pulse laser source with available output power of 120 mW based on an anomalous-dispersion highly nonlinear fiber pumped by a 1.5 µm fiber laser [17]. However, these broadband tunable femtosecond laser sources have not obtained Raman solitons with high output power.…”

Methods of determining the contrast sensitivity function for two-photon vision

“…The investigations of the two-photon vision phenomenon are driven by the need of a better understanding and finding more potential applications of the phenomenon. The following aspects of the effect have been investigated so far: the influence of the laser pulse train parameters for visual threshold [12][13][14], the visual threshold changes in the function of wavelength [15,16], the visual acuity for the two-photon vision [18] and the pupil response to an infrared stimulus [17]. The explored phenomenon applications are mainly focused on microperimetry [13,[19][20][21][22].…”

High-Power Raman Soliton Generation at 1.7 μm in All-Fiber Polarization-Maintaining Erbium-Doped Amplifier

“…The other popular technique to obtain ultrashort pulses at 1.7 µm is Raman soliton lasers taking advantage of the soliton self-frequency shift (SSFS). [10][11][12][13][14][15][16][17][18][19] When propagating in optical fibers, soliton pulses are affected by stimulated Raman scattering (SRS), causing energy to continuously transfer from the shorter wavelength to the longer wavelength, resulting in SSFS. In fact, the current method to obtain the 1.7 µm high-power femtosecond fiber laser using for MPM is through SSFS in largemode-area (LMA) passive fiber.…”