Compact ultrafast semiconductor disk laser: targeting GFP based nonlinear applications in living organisms

Abstract

We present a portable ultrafast Semiconductor Disk Laser (SDL) (or vertical extended cavity surface emitting laser—VECSELs), to be used for nonlinear microscopy. The SDL is modelocked using a quantum-dot semiconductor saturable absorber mirror (SESAM), delivering an average output power of 287 mW, with 1.5 ps pulses at 500 MHz and a central wavelength of 965 nm. Specifically, despite the fact of having long pulses and high repetition rates, we demonstrate the potential of this laser for Two-Photon Excited Fluorescence (TPEF) imaging of in vivo Caenorhabditis elegans (C. elegans) expressing Green Fluorescent Protein (GFP) in a set of neuronal processes and cell bodies. Efficient TPEF imaging is achieved due to the fact that this wavelength matches the peak of the two-photon action cross section of this widely used fluorescent marker. The SDL extended versatility is shown by presenting Second Harmonic Generation images of pharynx, uterus, body wall muscles and its potential to be used to excite other different commercial dyes. Importantly this non-expensive, turn-key, compact laser system could be used as a platform to develop portable nonlinear bio-imaging devices.

Low repetition rate SESAM modelocked VECSEL using an extendable active multipass-cavity approach

“…First experiments with a SESAM modelocked VECSEL on living organisms were reported in 2011 [27]. High quality multi-photon images were obtained with a SESAM modelocked VECSEL operating at 500 MHz pulse repetition rate with 287 mW average output power and a pulse duration of 1.5 ps corresponding to a peak power of 400 W. Recently, peak powers in the Kilowatt-level were reported, e.g.…”

High peak-power picosecond pulse generation at 126 µm using a quantum-dot-based external-cavity mode-locked laser and tapered optical amplifier

“…These were placed in water solution, sandwiched between two cover glasses. This sample can be excited using ~625 nm if a linear excitation scheme is considered; however, in our case the two-photon action cross-section of Crimson dye at 1260 nm is ~16 GM [27] -under this condition a few Watts of peak power together with the laser repetition rate would enable the production of nonlinear images of such a sample [4]. The available peak power at the sample plane was ~ 3-4 W at the operating wavelength (1.26 μm) of the MOPA system (the microscope objective measured transmission was ~28%).…”

“…If these conditions are met, such excitation sources could potentially replace the expensive and bulky solid-state ultrafast laser sources. In order to be able to make relative comparisons between the applicability of laser sources for NLM applications, a figure-ofmerit (FOM) can be defined as a function of their average power, pulse duration, and repetition rate [4]. The FOM is defined as the product of the average power and the peak power (Pavg × Ppeak), which can be recast into the equation: Pavg 2 / (frep · Δτ), where frep and Δτ are the repetition rate and the pulse duration, respectively.…”

“…These laser diode systems typically involved two or more stages of amplification (based on semiconductor and/or fiber amplifiers), as well as extra-cavity dispersion compensation schemes. Very recently, NLM imaging has been demonstrated with a compact, picosecond, vertical external-cavity surface-emitting laser emitting at 965 nm [4]. This device was able to efficiently produce TPEF images of several fluorescent markers including green fluorescent protein, as the laser's emission wavelength virtually matched the maximum two-photon action cross section of this protein.…”

Two-photon fluorescence imaging with 30 fs laser system tunable around 1 micron

“…Finally, we demonstrate the developed laser system potential for nonlinear microscopy [18] by obtaining high-signal-to-noise ratio (SNR) two-photon excitation fluorescence (TPEF) images of a mouse intestine section labeled with different dyes. This laser system enables both multimodal microscopy and nanosurgery and should have advantages in wavelength and peak power over the typically used laser systems [5].…”