FEATURE ULTRAFAST LASERS
Time-resolved microscopy images of live tissue taken at sub-mllimetre depths g
industrial femtosecond hybrid fibre laser was featured at Laser World of Photonics in Munich. When coupled with the company’s Spirit-OPA and Spirit-NOPA, the system delivers a high-energy tuneable laser output across the visible and infrared spectrum for three-photon deep-tissue bio-imaging and ultrafast spectroscopy applications.
The fastest of flashes Ultrafast lasers provide numerous advantages over conventional imaging tools in microscopy applications, specifically time-resolved microscopy, which involves taking multiple high-resolution pictures of a sample one after the other in quick succession. ‘A normal camera’s ability to take a series of pictures quickly is limited by the mechanical speed of its rotating shutter, whereas ultrafast lasers feature no moving parts,’ explained by Dr Tim Paasch- Colberg, director of marketing for Toptica Photonics, whose ultrafast lasers are often used for time-resolved microscopy. ‘They can therefore achieve much faster imaging rates…as most of them operate at 20-80 million pulses per second, so in principle many images can be taken each second.’ Achieving such speeds enables the study of processes on very fast time scale, for example the chemical processes occurring in live biological samples. In principle there are two main
wavelengths used in time-resolved microscopy according to Paasch-Colberg, 780nm and 1,050nm, as between them they can be used to study a broad variety of samples. Toptica Photonics offers both of these wavelengths in its FemtoFiber
46 Electro Optics December 2017/January 2018
ultra product line, which was released only recently, at repetition rates of 80MHz and pulse widths of <150fs and <120fs respectively. ‘Many ultrafast microscopy techniques
also require a lot of power, and these two machines are at around the highest powers currently available at these wavelengths – up to 500mW for 780nm and up to 5W at 1,050nm,’ Paasch-Colberg said. According to Paasch-Colberg, a key
feature sought after by researchers using ultrafast lasers is the ability to operate them hands-free without difficulty, having them act simply as another tool in their experiment. Manufactures therefore design ultrafast lasers to work completely maintenance-free and operate as a compact box that can be turned on when needed. This small footprint and simple functionality therefore makes them easy to integrate into a wide range of equipment setups.
Probing the surface Lithuanian manufacturer Ekspla considers itself a specialist in picosecond lasers, for which it targets applications involving non- linear phenomena, such as sum frequency generation (SFG) vibrational spectroscopy, a highly sensitive technique used to analyse surfaces. The process uses two beams, one in the visible and one in the mid-IR region, that spatially and temporally overlap at the surface of a material. An output beam is then generated at a frequency equal to the sum of the two input beam frequencies, leaving the surface to be picked up by a detector. ‘We develop special devices for this application,’ said Dr Zenonas Kuprionis,
commercial director at Ekspla. ‘A single laser is used to produce both beams. One beam is going directly from the laser, and the same laser is used to pump an optical parametric amplifier. Both beams are precisely synchronised. In this particular application the visible beam is used to convert information coded in the absorption of the IR beam to the spectral range in which photon detectors are the most sensitive.’
The picosecond laser provided by Ekspla
for SFG vibrational spectroscopy is its PL2230 series, a diode-pumped high energy picosecond Nd:YAG laser offering 20-80ps 35mJ pulses at a 50-100Hz repetition
“A key feature sought after by researchers using ultrafast lasers is the ability to operate them hands-free without difficulty”
rate. The firm also produces its PG501 optical parametric amplifier for use in SFG vibrational spectroscopy, in addition to complete SFG spectrometer systems. According to Kuprionis, one of the most important laser features for non- linear surface spectroscopy applications is the spectrum linewidth of the tuneable linewidth sources used. Ekspla is therefore trying to make this as narrow as possible in order to distinguish the different vibrational features of live tissue samples. ‘To achieve a narrow spectrum line from
OPAs you need to be very careful with the pumping laser line,’ said Kuprionis, who
@electrooptics |
www.electrooptics.com
Toptica Photonics
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