Femtosecond laser-induced damage threshold (LIDT) measurements for different optical components are well studied for a set of laser pulse repetition rates spanning the range between 1 Hz and 1 kHz. Recent years saw the advent of high-repetition-rate femtosecond systems with relatively high pulse energy. Therefore investigation of LIDT in the MHz region is essential. We performed several comparative femtosecond LIDT measurements on typically used ultrafast optical elements with different Ti:Sapphire laser systems having substantially different pulse repetition rates (a 1 kHz regenerative amplifier and a 4.3 MHz long-cavity oscillator) and found a substantially lower MHz LIDT threshhold.
Recent theoretical and experimental studies indicated that at certain conditions surface plasmon oscillations (SPOs) may
show non-classical properties. In this study we present the results of our measurements on spatial distribution and photon
statistics of the light emitted by surface plasmon oscillations. Both visible and near infrared lasers have been used for
generation of surface plasmons. The experiments were performed in the Kretschmann geometry using both gold and
silver layers at several laser pumping powers. We used different type of photo detectors in the photon counting regime to
measure the statistical properties of the light generated by surface plasmons. The photon statistics have been measured
by different methods. Time interval statistics, photon-number distribution and correlation function of the generated light
were determined and compared to those of the exciting laser. Correlations between statistical properties of the light
emitted by decaying surface plasmons and the exciting laser source have been studied.
We have developed our pervious experimental setup using correlated photon pairs (to the calibration of photo detectors) to realize a controllable photon source. For the generation of such photon pairs we use the non-linear process of parametric down conversion. When a photon of the pump beam is incident to a nonlinear crystal with phase matching condition, a pair of photons (signal and idler) is created at the same time with certain probability. We detect the photons in the signal beam with a single photon counting module (SPCM), while delaying those in the idler beam. Recently we have developed a fast electronic unit to control an optical shutter (a Pockels cell) placed to the optical output of the idler beam. When we detect a signal photon with the controlling electronic unit we are also able to open or close the fast optical shutter. Thus we can control which idler photons can propagate through the Pockels cell. So with this photon source we are able to program the number of photons in a certain time window. This controllable photon source that is able to generate a known number of photons with specified wavelength, direction, and polarization could be useful for applications in high-accuracy optical characterisation of photometric devices at the ultra-low intensities. This light source can also serve as a standard in testing of optical image intensifiers, night vision devices, and in the accurate measurement of spectral distribution of transmission and absorption in optical materials.
Taking advantage of our previous experimental results and calculations that establish a new approach to the calibration of photo detectors using correlated photon pairs, we developed an experimental setup with a fast electronic control unit for the direct measurement of photon statistics. The most convenient source for generating such correlated photon pairs is a nonlinear optical process of spontaneous parametric down conversion (SPDC). When a photon of the pump beam is incident to a nonlinear crystal with phase matching condition, a pair of photons (signal and idler) is created at the same time. The photons are detected in the signal beam, and a controllable shutter is placed in the idler beam. When a detection event is made in the signal beam the fast optical shutter opens for a certain (pre-programmed) time. While the opening time of the shutter is adjustable with good time resolution, the time interval between the photons in the idler beam can be scanned, so the photon statistics can be determined.
Laser particle spectrometry is one of the leading measurement technologies engaged in environmental monitoring, measuring the aerosol contamination of the air inside and outside of urban regions. It has a number of benefits against other methods - e.g. the possibility of real time, in situ measurement with high time resolution. These features make the light scattering based measurement methods superior to others in a mobile environmental laboratory. Our previously developed instruments are based on laser light scattering collected from different angular regions (90°, forward and backward directions) and a special illumination system increase the sensitivity and the resolution of the sizing. A collection of the developed optical instruments and other devices based on different methods were installed into a mobile environmental laboratory for monitoring atmospheric aerosols, which allows the comparison of the results obtained from different measurement methods. This laboratory has been used in 3 measurement campaigns where measurements were performed in 6 different locations.
We designed a special light source generating a pre-determined number of photons taking advantage of our previous experimental results and calculations that establish a new approach to the calibration of photodetectors and determination of the absolute value of quantum efficiency of photon-counting photomultipliers using a single detector and entangled-photon pairs. This source is capable of generating a known number of photons of specified wavelength, in specified direction, and polarization for high-accuracy optical measurements (optical metrology) at the ultra-low intensities. The design and the modeling have been performed taking into account the main time characteristics of electronics, efficiency of detectors, parameters of the signal, losses, etc. The data evaluation system has been designed and tested; the assembly of the experimental set-up has been performed. Main parts of the optical and electronic system (generation of photon pairs, detectors, Pockels cells, etc.) have been tested. Such light source can be successfully applied in different areas of optical metrology, especially in photometry.