Life-sciences applications such as harmonic generation microscopy or multiphoton microscopy require specific light sources with femtosecond pulses in the near-infrared (NIR) wavelength range to enable high-end imaging with low phototoxicity. With the Soprano series, Cycle provides an ultrafast fiber-laser with selectable wavelengths of 1,350 and 1,700 nm. But what is the technology behind such a fiber laser?
Common approaches to produce femtosecond pulses in the NIR-range are solid state lasers or solid-state pumped optical parametric amplifiers (OPA). But since these are expensive and quite susceptible to environmental influences their application is limited to special laboratories.
A promising way to produce more stable ultrafast laser pulses in this light range is nonlinear wavelength conversion in optical fibers – which is at the heart of Cycle’s Soprano lasers. For this technology, a short dispersion-shifting optical fiber is used for self-phase modulation (SPM) of an ultrafast, all-fiber laser oscillator. The SPM-fiber considerably broadens the narrowband input spectrum in such way that isolated spectral lobes occur. In the resulting spectrum, the leftmost and rightmost lobes contain a major portion of the laser’s power. By tuning the fiber to the desired spectral shape and then selecting the lobes with optical bandpass filters, Cycle builds a laser with 100-fs pulses in the desired near-infrared wavelength. This process is called SPM-enabled spectral selection (SESS) and provides a robust ultrafast laser source for the specific requirements of next generation microscopy techniques.
Figure 1 — (left column) Filtered optical spectra from 20-nun PCF NL-1050-ZERO-2: their peak wavelength and average power are labeled in the figure. (right column) Measured autoconelation traces (red solid curves) and autocorrelation traces calculated from the transform-limited pulses allowed by the filtered spectra (black dotted curves). Retrieved from Vol. 24, No. 14 | 11 Jul 2016 | OPTICS EXPRESS 15328.