Stimulated Raman scattering microscopy by Nyquist modulation of a two-branch ultrafast fiber source

Abstract

A highly stable setup for stimulated Raman scattering (SRS) microscopy is presented. It is based on a two-branch femtosecond Er:fiber laser operating at a 40 MHz repetition rate. One of the outputs is directly modulated at the Nyquist frequency with an integrated electro-optic modulator (EOM). This compact source combines a jitter-free pulse synchronization with a broad tunability and allows for shot-noise limited SRS detection. The performance of the SRS microscope is illustrated with measurements on samples from material science and cell biology.

Broadband Coherent Raman Scattering Microscopy

“…The complexity of such laser systems has motivated an intense research effort aimed at drastically reducing footprint and price while increasing reliability, mostly through fiber‐format architectures. One class of systems is based on femtosecond Er:fiber oscillators at 1550 nm, seeding a pair of Erbium‐doped fiber amplifiers (EDFAs), one of them followed by a highly nonlinear fiber (HNF) for the generation of an octave‐spanning continuum from ≈1000 to ≈2200 nm: this enables the synthesis, via frequency doubling and spectral compression of the two pulse trains in a thick SHG crystal, of picosecond fixed frequency pump pulses at ≈775 nm and of tunable picosecond Stokes pulses in the 850–1080 nm range . This configuration has been recently upgraded by boosting the power of the Stokes arm via Yb:fiber or Tm:fiber amplification.…”

Stimulated Raman Scattering Microscopy with an All-Optical Modulator

“…It allows the separation of information-carrying signals from background noise, which often increases the signal-tonoise ratio by orders of magnitude. In the commonly used optical homodyne and heterodyne detection setups [2,3] probing is preferably performed at the Nyquist frequency (modulation at half the sampling frequency) to eliminate noise and favor short acquisition times [4,5]. Conventional electrically driven devices, such as acousto-optic modulators (AOMs) or electro-optic modulators (EOMs), are limited in modulation frequency and optical damage threshold, and require radio-frequency power electronics for driving.…”

Robust and rapidly tunable light source for SRS/CARS microscopy with low-intensity noise

“…Although avoiding the aforementioned complexity, fiber lasers possess high-relative intensity noise in the MHz regime [18][19][20] due to amplified spontaneous emission in the rather long gain region of the fiber. Balanced detection is typically used to overcome this issue, at the cost of significant complication of the detection system to handle spatially variable transmission of scattering specimens.…”