Articles

the understanding of brain computations requires methods that read out neural activity on different spatial and temporal scales. Following signal propagation and integration across a neuron and recording the concerted activity of hundreds of neurons pose distinct challenges, and the design of imaging systems has been mostly focused on tackling one of the two operations. … Read more

Experimental studies of single molecule mechanics require high force sensitivity and low drift, which can be achieved with optical tweezers. We built an optical tweezer setup for force measurements in a two bead assay. A cw infrared laser beam is split by polarization and focused by a high numerical aperture objective to create two traps. … Read more

Two-photon scanning microscopy (TPSM) is a powerful tool for imaging deep inside living tissues with sub-cellular resolution. The temporal resolution of TPSM is however strongly limited by the galvanometric mirrors used to steer the laser beam. Fast physiological events can therefore only be followed by scanning repeatedly a single line within the field of view. … Read more

We present a new instrument, based on a low-frame-rate 8Hz CCD camera used in a heterodyne opticalmixing configuration, that can create wide-field laser Doppler maps. As an illustration, we show results obtained in a mouse brain, in vivo, showing the Doppler signature of blood flow. The instrument is based on a frequency-shifting digital holography scheme. … Read more

We present an instrument for performing correlation spectroscopy on single fluorescent particles while tracking their Brownian motion in three dimensions using real-time feedback. By tracking CdSe/ZnS quantum dots in water (diffusion coefficient 20 ím2/s), we make the first measurements of photon antibunching (at 10 ns) on single fluorophores free in solution and find fluorescence lifetime … Read more

two-photon calcium imaging of neuronal populations enables optical recording of spiking activity in living animals, but standard laser scanners are too slow to accurately determine spike times. here we report in vivo imaging in mouse neocortex with greatly improved temporal resolution using randomaccess scanning with acousto-optic deflectors. We obtained f luorescence measurements from 34–9 layer … Read more

We report on a Q-switched short-length fiber laser producing 100 W of average output power at 100 kHz repetition rate and pulse durations as short as 17 ns.Upto2mJof energy and sub-10-ns pulse duration are extracted at lower repetition rates. This performance is obtained by employing a rod-type ytterbium-doped photonic crystal fiber with a 70 m … Read more

A practical problem that arises when using acousto-optic modulators sAOMsd to scan the laser frequency is the dependence of the beam diffraction angle on the modulation frequency. Alignment problems with AOM-modulated laser beams can be effectively eliminated by using the AOM in the double-pass con®guration, which compensates for beam de¯ections. On a second pass through … Read more

A novel optical phase-shifting method based on a well-known acousto-optic interaction is proposed. By using a pair of acousto-optic modulators (AOMs) and properly aligning them, we construct an optical phase shifter that can directly control the phase of a collimated beam. The proposed phase shifter is insensitive to the polarization of the incident beam when … Read more

We have developed confocal multicolor single-molecule spectroscopy with optimized detection sensitivity on three spectrally distinct channels for the study of biomolecular interactions and FRET between more than two molecules. Using programmable acousto-optical devices as beamsplitter and excitation filter, we overcome some of the limitations of conventional multichroic beamsplitters and implement rapid alternation between three laser … Read more