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Watt-level ultrafast 1.75 μm laser system based on thulium-doped core and terbium-doped cladding fluoride fibers

Dina Grace Banguilan, Yuto Iye, Kazuhiko Ogawa, Eiji Kajikawa, Takao Fuji

TL;DR

The paper introduces a watt-level ultrafast laser at $1.75$–$1.76\,\mu$m based on a Tm:Tb:ZBLAN fiber system. A Raman-shift seed from a silica/Er-doped fiber seed is amplified through a three-stage all-Tm:Tb:ZBLAN chain, with ASE suppression achieved by Tb-doped cladding. Dispersion management combines a tunable CFBG stretcher with a Treacy compressor, achieving $217$ fs pulses and ~$0.7$ W after compression at high pump powers. The work presents a compact, all-fiber solution for bright SWIR ultrafast pulses, with potential for three-photon and multiphoton imaging in biological tissue.

Abstract

We report watt-level femtosecond pulses in the 1.75 $μ$m region using a thulium-doped core, terbium-doped cladding fluoride (Tm:Tb:ZBLAN) fiber laser system. The seed pulse is generated through stimulated Raman scattering in a silica fiber pumped by an erbium-doped fiber laser. The soliton is subsequently amplified through a multi-stage Tm:Tb:ZBLAN amplifier. The tunability of our chirped fiber Bragg grating stretcher, matched with a Treacy compressor, compresses the pulse to 217 fs. Our system generates ~250 nJ of single-pulse energy, with a corresponding average power of ~1 W at a 4 MHz repetition rate. The laser system is suitable for multiphoton microscopy.

Watt-level ultrafast 1.75 μm laser system based on thulium-doped core and terbium-doped cladding fluoride fibers

TL;DR

The paper introduces a watt-level ultrafast laser at –m based on a Tm:Tb:ZBLAN fiber system. A Raman-shift seed from a silica/Er-doped fiber seed is amplified through a three-stage all-Tm:Tb:ZBLAN chain, with ASE suppression achieved by Tb-doped cladding. Dispersion management combines a tunable CFBG stretcher with a Treacy compressor, achieving fs pulses and ~ W after compression at high pump powers. The work presents a compact, all-fiber solution for bright SWIR ultrafast pulses, with potential for three-photon and multiphoton imaging in biological tissue.

Abstract

We report watt-level femtosecond pulses in the 1.75 m region using a thulium-doped core, terbium-doped cladding fluoride (Tm:Tb:ZBLAN) fiber laser system. The seed pulse is generated through stimulated Raman scattering in a silica fiber pumped by an erbium-doped fiber laser. The soliton is subsequently amplified through a multi-stage Tm:Tb:ZBLAN amplifier. The tunability of our chirped fiber Bragg grating stretcher, matched with a Treacy compressor, compresses the pulse to 217 fs. Our system generates ~250 nJ of single-pulse energy, with a corresponding average power of ~1 W at a 4 MHz repetition rate. The laser system is suitable for multiphoton microscopy.

Paper Structure

This paper contains 4 sections, 5 figures.

Table of Contents

  1. Introduction
  2. Tm:Tb:ZBLAN laser system
  3. Pulse compression results
  4. Summary and conclusion

Figures (5)

  • Figure 1: (a) Schematic of the laser system. AOM: acousto-optic modulator, EDFA: Erbium-doped fiber amplifier, CFBG: chirped fiber Bragg grating, BPF: bandpass filter, and DM: dichroic mirror. (b) Energy level transitions of Tm$^{3+}$ and Tb$^{3+}$.
  • Figure 2: Output spectra of the Raman shift fiber with various pump powers for the EDFA. The pulse reflected by the CFBG is also shown.
  • Figure 3: (a) Output spectra of the first Tm:Tb:ZBLAN preamplifier at various pump powers. (b) Output spectra of the second Tm:Tb:ZBLAN preamplifier at several pump powers. (c) Power spectra and (d) slope efficiency of the final power amplifier at different pump powers. The ASE spectrum of the Tm:Tb:ZBLAN fiber at 9.75 W is also shown in (c) alongside the amplified spectrum.
  • Figure 4: Normalized SHG-FROG traces (top row) of the output pulses from the power amplifier, with their corresponding retrieved spectral profile and phases (bottom row), for pump powers of (a,e) 2.23 W, (b,f) 5.10 W, (c,g) 9.13 W, and (d,h) 9.75 W.
  • Figure 5: Pulse characterization result at a pump power of 9.75 W with CFBG fine-tuning. (a) The SHG-FROG trace of the compressed pulse by the grating pair. Retrieved pulse in (b) time and (c) frequency domain.