Stimulated Raman scattering microscope with shot noise limited sensitivity using subharmonically synchronized laser pulses

Abstract

We propose and demonstrate the use of subharmonically synchronized laser pulses for low-noise lock-in detection in stimulated Raman scattering (SRS) microscopy. In the experiment, Yb-fiber laser pulses at a repetition rate of 38 MHz are successfully synchronized to Ti:sapphire laser pulses at a repetition rate of 76 MHz with a jitter of <8 fs by a two-photon detector and an intra-cavity electro-optic modulator. By using these pulses, high-frequency lock-in detection of SRS signal is accomplished without high-speed optical modulation. The noise level of the lock-in signal is found to be higher than the shot noise limit only by 1.6 dB. We also demonstrate high-contrast, 3D imaging of unlabeled living cells.

Multimodal Imaging of Living Cells with Multiplex Coherent Anti-stokes Raman Scattering (CARS), Third-order Sum Frequency Generation (TSFG) and Two-photon Excitation Fluorescence (TPEF) Using a Nanosecond White-light Laser Source

“…In general, CARS or Raman images at CH2 bend and stretch vibrational modes were widely used to detect lipid droplets inside the adipocytes. [34][35][36] In the case of fibroblasts, however, formation of lipid droplets depends on various conditions such as the composition of culture medium. In the present study, no droplet-like structure was observed in Fig.…”

Photothermal Microscopy for High Sensitivity and High Resolution Absorption Contrast Imaging of Biological Tissues

“…To implement high-sensitivity imaging in pump-probe microscopy, it is necessary to circumvent the intensity noise of the probe beam. In stimulated emission and stimulated Raman microscopy, the intensity of the pump beam is modulated at high frequency (>1 MHz) because the laser intensity noise of a solid state laser used for probing occurs primarily at low frequencies (from kilohertz to DC) in the form of 1/f noise [14,23,24]. However, in PT microscopy, the high-frequency modulation scheme reduces signal intensity because the time response of the PT signal is, in principle, determined by heat conductivity and is decreased by half at~1 MHz for a tightly focused laser beam [25][26][27][28].…”

Heterodyne detected nonlinear optical imaging in a lock‐in free manner

“…Although laser shot noise limit can be reached by MHz modulation in SRS microscopy [8][9][10]16], the signal to noise ratio (SNR) at low laser power is actually limited by the electronic noise of the LIA's input preamplifier. For an ideal voltage preamplifier the source of the electronic noise is the thermal Johnson-Nyquist noise of the input impedance,…”