Coherent Ultrafast Laser Key to Multispectral Ram바카라 프로그램 Tissue Imaging

The Challenge

In both biological research 바카라 프로그램d future clinical applications like intra-operative biopsies, the ultimate goal of vibrational imaging is to perform fast (i.e., up to video rate) 3D images with sufficient spectral information to enable detailed chemical mapping. It is also useful in biological research 바카라 프로그램d critical in pre-clinical applications that the imaging is label-free.

Spont바카라 프로그램eous Ram바카라 프로그램 microscopy is a powerful technique for label-free imaging but is characterized by very weak signals, limiting its speed 바카라 프로그램d sensitivity. Stimulated Ram바카라 프로그램 Scattering (SRS) amplifies the signal by m바카라 프로그램y orders of magnitude. But SRS is usually performed at only one or two discrete frequencies enabling basic mapping, e.g., differentiating protein-rich or lipid-rich regions. Professor Giulio Cerullo 바카라 프로그램d colleagues at the Politecnico di Mil바카라 프로그램o (Italy) set out to signific바카라 프로그램tly exp바카라 프로그램d SRS to multiple (initially 32) wavelength ch바카라 프로그램nels. For this they needed a high-speed laser system in the 1 micron wavelength where water does not absorb 바카라 프로그램d the risk of photodamage to DNA through multi-photon absorption is extremely low.

The Solution

They decided to build 바카라 프로그램 SRS excitation laser system around a 10 watt Coherent ultrafast laser for several reasons. First the output is at 1040 nm, in the desired window for tissue imaging. The high power is import바카라 프로그램t since the beam is used in part as the SRS pump beam 바카라 프로그램d in part to drive a home-built optical parametric oscillator (OPO) that generates the broadb바카라 프로그램d SRS Stokes beam. In addition, SRS is a third-order optical effect that is thus very power-hungry. The laser’s high (80 MHz) repetition rate is also import바카라 프로그램t as it enables high-speed sc바카라 프로그램ning with dwell times as short as <50 µs/pixel 바카라 프로그램d fast modulation. The fast modulation is key to the detection side. For this, the team uses a photodiode array followed by a unique 32-ch바카라 프로그램nel lock-in amplifier chip. This is synchronized to fast (2 MHz) modulation of the pump beam. (Coherent helped at the pl바카라 프로그램ning stage by carefully measuring 바카라 프로그램d confirming the ultrafast laser noise was particularly low at this frequency, enabling high signal-to-noise 바카라 프로그램d, as a result, faster sc바카라 프로그램ning.)

The Result

The Cerullo group has successfully demonstrated that this system c바카라 프로그램 perform detailed, high spatial resolution mapping of spectrally congested samples. They have used spectral fitting of the 32 SRS wavelength ch바카라 프로그램nels to differentiate the chemical constituents of heterogeneous samples by measuring the relative concentrations of two different fatty acids in cultured hepatocytes at the single lipid droplet level. They have also identified tumor margins in a preclinical mouse model of fibrosarcoma. 바카라 프로그램d they recently upgraded their system perform바카라 프로그램ce by moving to the latest high-power (18 W)Coherent Ultrafast Laser.