[en] A femtosecond fluorescence up-conversion instrument has been developed at Molecular Photochemistry Section, Radiation and Photochemistry Division, BARC, during the Xth plan program. This state-of-the-art instrument has been built around a mode-locked Ti:sapphire laser oscillator having a pulse width of 50 fs and operated at a frequency of 80 MHz. In the present setup the Ti:sapphire laser oscillator is pumped at 532 nm by 5 W diode pumped solid state laser (DPSS). The fundamental laser light of Ti:sapphire laser oscillator is converted to its second and/or third harmonic by using suitable BBO crystals and these higher harmonics are used accordingly to excite the experimental samples. The fluorescence from the sample is mixed with the residual fundamental laser light (gate pulse) of the Ti:sapphire laser in a nonlinear medium of 0.5 mm type-1 BBO crystal. The sum-frequency light produced in up-conversion crystal is detected by a combination of suitable band-pass filter, monochromator and time-gated photon counting device. An optical delay line including a computer controlled translational stage with step size of 0.1 μm is used to introduce and scan the time delay between the excitation and the gate pulses. In the present instrument, samples in various forms (solution, thin films and gas) can be investigated with minor adjustments of the optics at the sample position. The typical instrument response function measured is about 180 fs (FWHM). In this report, we briefly discuss various aspects of the instrument, including the basic principle of time-resolved fluorescence measurements using sum-frequency generation, setting up of the up-conversion laboratory and the technical design and selection criteria for various laser systems, optical components, detection systems, etc. We also present some of our research works on ultrafast chemical processes using this instrument. Presently, the instrument is working very satisfactorily and is being used extensively to investigate the dynamics and mechanism of various ultrafast processes of having contemporary research interests in chemical sciences. (author)