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

Abstract

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.

Dual-color deep-tissue three-photon microscopy with a multiband infrared laser

“…This strategy has two key advantages: (i) when the laser is focused at a depth equivalent to several times the scattering mean free path inside the tissue, 3P excitation shows a greatly improved rejection of the out-of-focus fluorescence background 3 , 4 ; (ii) the wavelength windows at approximately 1300 and 1700 nm offer a better combination of tissue scattering and absorption properties compared to the 700–1100 nm wavelength range commonly used in two-photon-excited fluorescence (2PEF) microscopy 4 , enabling superior penetration. In addition, 1300 nm was found to be a nearly optimal wavelength for 3P excitation of green fluorescent protein (GFP) and derived calcium indicators 5 , and 1700 nm is appropriate for 3P excitation of widely used genetically encoded red probes, such as red fluorescent protein (RFP) and tdTomato 4 , 6 . Due to the weakness of 3P absorption cross-sections, however 7 , 8 , the pulsed excitation regime typically used for 2P microscopy (80 MHz, 100 fs, up to 2 nJ pulses at the sample surface) is not appropriate for 3P microscopy.…”

“…Optimized laser sources are required to develop such an imaging approach to its full potential 6 , 11 – 13 . In particular, as many potential applications require study of interactions between cells/tissue components labeled with different fluorophores, one important challenge is to develop laser sources that enable efficient two-color three-photon imaging.…”

Advanced multimodal laser imaging tool for urothelial carcinoma diagnosis (AMPLITUDE)

“…Other possible approaches to design fiber pulsed sources operating in the spectral region around 1.7 µm include Raman shifting the pulsed radiation emitted by an Er-fiber laser [17,23] and special Tm-doped active fibers in combination with optical elements suppressing amplification at 1.85 µm [24,25]. The all-fiber femtosecond Raman-based laser approach was notable for the shortest pulses (65 fs [17]) in this wavelength region so far.…”

Megawatt peak power tunable femtosecond source based on self-phase modulation enabled spectral selection

“…Compatible with fiber technology, use of nonlinear fiber-optic methods to generate wavelength widely tunable femtosecond pulses from an ultrafast fiber laser is of particular interest. The typical methods include soliton self-frequency shift [3][4][5][6][7][8][9][10][11][12][13][14], dispersive wave generation [15][16][17][18], and four-wave mixing [19][20][21].…”