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Next Generation Light Sources for Imaging Fibre Lasers - Compact, Cost-Effective, Turnkey Solutions

Nov. 01, 2007
Fig. 1: The all-fibre MOPA (Master Oscillator Power Amplifier) – flexibility to meet the demands of a huge application space.
Fig. 1: The all-fibre MOPA (Master Oscillator Power Amplifier) – flexibility to meet the demands of ... more
Fig. 1: The all-fibre MOPA (Master Oscillator Power Amplifier) – flexibility to meet the demands of ... Fig. 2: The visible spectrum of the SC400 spatially dispersed through a transmission diffraction ... Fig. 3: Example high-spec. flow cytometry development platform showing up to 8 discrete laser lines ... Fig. 4: Image courtesy of the Laser Analytics Group, University of Cambridge, UK2-D Fluorescent ... John Clowes 

Next Generation Light Sources for Imaging Fibre Lasers - Compact, Cost-Effective, Turnkey Solutions. Lasers continue to be increasingly important components within biological imaging and analysis systems - from Argon-Ion and HeNe lasers used within flow cytometry and confocal microscopy, to femtosecond Ti: Sapphire and DPSS femtosecond sources in multi-photon microscopy. However, many commercial imaging systems are still limited in performance by the availability of suitable laser sources - both in the limited availability of wavelengths and in the size, cost and reliability of conventional laser technologies. Ultrafast fibre lasers offer turnkey, compact and reliable solutions for next generation biomedical imaging systems. Here we introduce the basic concept of the ultrafast fibre laser and describe some of the applications and benefits of this technology within biophotonics research and imaging systems.

Ultrafast fibre lasers, with their compact form, inherent reliability and low cost of ownership are becoming the laser of choice for many biomedical imaging applications, challenging the Ti:Sapphire laser within multi-photon excitation microscopy and diode, HeNe and Ar-Ion lasers within fluorescence imaging. The Master Oscillator, Power Amplifier (MOPA) architecture of Fianium's ultrafast fibre lasers provides simplicity and flexibility by design [fig. 1]. The MOPA comprises two independent modules - a low-power femtosecond or picosecond fibre laser followed by a high power diode-pumped fibre amplifier. By independently changing the parameters of the oscillator or the amplifier modules, one can achieve very different performance parameters from the laser, tailored to a given application. This approach has quickly enabled ultrafast fibre lasers to meet the growing demands of a wide range of applications.

The master oscillator is an all-fibre, passively modelocked laser which is both turnkey operated and self-starting without the need for any adjustment. The pulse repetition rates of the laser (from less than 1MHz to several hundred MHz) are ideally suited to quasi-cw laser applications and also for lifetime imaging applications. For applications within microscopy, ultrafast lasers are typically associated with multi-photon fluorescence microscopy, where femtosecond Ti:Sapphire lasers have been the historic laser of choice.

While not offering the broad wavelength tunability of the Ti:Sapphire, Fianium's FP1060-s femtosecond lasers do offer a low-cost, compact solution at discrete wavelengths from 980 nm to 1100 nm and offer potential for incorporation into any existing microscope system. Delivering average powers up to 5 Watts and with pulse durations shorter than 250 femtoseconds, the long wavelengths of the FP1060, extending beyond the tuning limits of most Ti:Sapphire sources, offer many benefits for Two Photon Fluorescence (TPF) and Second Harmonic Generation (SHG) microscopy [1, 2]. The FP1060 high power lasers from Fianium operate within the picosecond or femtosecond regime and can provide pulse energies from a few pico-joules to ten microJoules, particularly important for materials processing, both of devices and of tissues.

Extension of the FP1060 laser source from the near Infra Red to the visible and UV region of the spectrum, is achieved through nonlinear frequency conversion techniques including harmonic generation to 532 nm, 355 nm and 266 nm and in the generation of ultra broad band "supercontinuum" spectra - a phenomenon that will have a huge impact on next generation biomedical imaging systems. The supercontinuum fibre laser is based on a high power picosecond source (FP1060) and highly nonlinear photonic crystal fibre. The nonlinear interaction between the high intensity pulsed optical field within the tight confinement of a silica optical fibre waveguide, results in the generation of a continuous spectrum spanning from the visible (below 400 nm) extending in the IR to beyond 2 um. Fianium's SC400 and SC450 supercontinuum fibre lasers, utilising high pulse repetition rates in the MHz range, deliver high spectral brightness in the range of several milli-Watts per nm across the entire optical spectrum. Filtration of several nm of this spectrum can deliver tens of mW optical power at any wavelength required - a vast improvement over the discrete wavelengths offered by conventional diode and HeNe laser sources.

Furthermore, the repetition rates of the supercontinuum make them ideally suited to fluorescence imaging applications requiring either a quasi-continuous wave or a pulsed regime for time-resolved measurements. The remainder of this article focuses on examples of the use of Fianium SC400 and SC450 supercontinuum fibre lasers within fluorescence imaging.

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Keywords: Argon-Ion lasers biological imaging confocal microscopy femtosecond Fianium Flow Cytometry Fluorescence Imaging FP1060 HeNe lasers Imaging Fibre Lasers John Clowes laser source Light Sources multi-photon microscopy Ti: Sapphire Ti:Sapphire Laser Turnkey Solutions

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