6^th International Conference on Photonics July 30-31, 2017 Milan, Italy

Statement of Problem: Modern best structural solutions of microwave photonic systems for instantaneous frequency measurement (IFM) are based on “frequency-amplitude” measurement conversion using fiber Bragg gratings. The main disadvantage of microwave photonic systems for IFM with FBG is the monotonicity of the conversion characteristic in the area near the central wavelength of grating, which reduces the resolution of conversion at “low” radio frequencies (0.04 – 4 GHz). Methodology & Theoretical Orientation: A new method for measuring the instantaneous frequency of the microwave signal, based on the transformation of the "frequency-amplitude" in the classical fiber Bragg grating with a Gaussian spectral outline is presented. Previously measuring frequency components of microwave signals are shifted additively in electrooptical Mach-Zehnder modulator at a frequency equal to half width of the grating spectral contour. Findings: Using of these operations allows the instantaneous frequency measurements with high resolution and accuracy in the "low" frequency range. The proposed method is characterized by a simple realization and thermal stability as compared to methods using Bragg grating with special spectral contours: linear triangular and with a phase -shift, which are used to remove small slope of "frequency-amplitude" transformation and the monotonicity of the grating spectral contour at this frequencies. Conclusion & Significance: We described the principles of microwave photonic instantaneous frequency measurement system based on “frequency-amplitude” transformation in FBG. We identified possible way to improve their metrological characteristics in terms of available frequency range and resolution of low frequency identification by means of additional frequency shifting. Therefore, the low frequencies are measured on linear slope of FBG with good resolution and accuracy.

Tomomasa Ohkubo has his expertise in development of solar-pumped laser and numerical analysis of laser processing. He has completed his PhD from Tokyo Institute of Technology. He is Senior Assistant Professor of Department of Mechanical Engineering at Tokyo University of Technology. He is also Senior Assistant Professor of Department of Media Science at Tokyo University of Technology.

We developed solar-pumped laser system with Fresnel lens and solar cavity. The output power of the laser system was 120 W and the collection efficiency was 30W/m2. To keep the global environment, we must develop renewable energy systems, which replaces energy system with fossil fuels. Solar-pumped laser is one of a promising new technology to utilize solar energy for our society. For example, laser space solar power systems (L-SSPS) is proposed by Japan Aerospace Exploration Agency. L-SSPS proposes transmission of collected solar energy in the space to the earth by solar-pumped laser. In addition, energy cycle using magnesium as energy career is proposed by Yabe et al. Solar-pumped laser is expected as an energy source of reduction of magnesium in this energy cycle. We designed 2 m x 2 m of Fresnel lens to realize high power concentration of solar energy. Nd:YAG single crystal or Cr:Nd:YAG ceramic was used as laser medium. Whole system is installed on a Sun tracking system to realize continuous lasing. Using these equipment, we developed several type of solar cavity to confine solar energy and make it absorbed by laser medium. 80 W of peak output was realized as shown in green line in Figure 1 by a solar cavity, which is cone-shaped inner mirror holding laser medium at that of the central axis. 80 W of stable laser output was realized as shown in red line in Figure 1 by solar cavity, which is combined cone-shaped solar cavity and compound parabolic mirror (CPC). Furthermore, 120 W of stable output was realized using cone-shaped cavity and glass tube filled with water surrounding the laser medium. We called this system as liquid light-guide lens (LLGL) because the water works not only as coolant but also as a refractive optics.

Ho Lee has research experience on the development of dermal drug delivery via miniaturized electro-osmotic pumps, to femto-second laser machining, to laser-scanning microscopy applications in dermatological studies. He completed his PhD in Mechanical Engineering from the University of Texas at Austin in 2003. He followed this with a Post-doctoral fellowship at the same university for a year, then another at Harvard Medical School for three years. Since 2006, he has been a Professor at Kyungpook National University in the Mechanical Engineering Department. During his tenure, he also spent an additional year on sabbatical at Harvard Medical School. Currently, he is an Associated Professor and Director of a research laboratory that specializes in bio-optical applications, laser machining and micro-welding, and, more recently, laser-based 3D printing.

The ability to observe fast biological phenomena such as turbulent cell flow and rapid micro-vasculature responses has been of increasing interest in rheological studies. Two-photon laser scanning microscopy is an asset to these studies as it enables deep tissue optical sectioning and good spatial resolution in various in vivo animal models. As such, we developed a high-speed laser scanning two-photon microscope capable of acquiring 512 x 512 pixel images at up to 90 fps (frames per second) or 512 x 256 pixels at up to 180 fps. The high scan rate of the fast-axis was implemented via a rapidly rotating polygonal scanning mirror with 128 facets. The slow-axis was scanned using a high-speed galvanometer. Image acquisition was achieved using a custom-built photo-multiplier tube amplifier with a broad frequency band. Verification of the developed two-photon microscope's acquisition speed was established by imaging a fluorescent resolution target being moved at a variety of constant speeds. Evaluation of the frame acquisition speeds were done by comparing successive frames. Finally, the system's applicability to biological studies was qualitatively demonstrated by observing the slight movements in a sedated mouse due to its heartbeats.

Andrei Kotkov has his expertise in Laser Physics. He received his MS degree from the Moscow Physical-Technical Institute (State University) in 1982 and his PhD degree from the P N Lebedev Physical Institute (LPI) in 2001. He is Associate Professor focusing on Laser Physics at the LPI.

Because of its extremely broad spectrum, CO laser is a very attractive object for enriching and expanding spectrum of laser systems applying such a laser into short- and long-wavelength region of mid-IR. By frequency conversion of their radiation in nonlinear optical crystals their spectrum was expanded down to ~2.5 µm and up to ~17 m]. Up to now CO laser could emit hundreds of ro-vibrational lines within wavelength region from ~4.7 m for the lowest vibrational transition 1→0 up to ~8.2 m for high vibrational transition 37→36. The objective of our study is to understand which physical processes result in limitation of long-wavelength border for a CO laser spectrum and what the longest wavelength is. The CO laser emitting on the extra-high ever observed vibrational transitions up to 39→38 with wavelength of 8.7 m was for the first time launched. It should be noted that multi-quantum vibration-to-vibration VV exchange does play an important role in molecular kinetics on high vibrational levels of CO molecule. Population redistribution among the high vibrational levels is very important for development of a first-overtone (V+2→V) CO laser. Factors limiting the longest CO laser wavelength are discussed. The longest CO laser wavelength was experimentally demonstrated to be limited by asymmetric two-to-one quantum VV exchange between CO molecules in nitrogen-free gas mixture. In nitrogen-containing gas mixtures the longest wavelength is limited by inter-molecular asymmetric two-to-one quantum VV exchange between carbon monoxide and nitrogen molecules. Expansion of CO laser spectrum to longer wavelengths gives an opportunity to fill in a spectral gap between 8 and 9 m, and thereby to increase an opportunity of IR laser spectroscopy for environmental monitoring and other applications connected with propagation of laser radiation through the atmosphere.

Andrey Kozlov graduated from National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) in 2002 in specialty Solid State Physics. Since 2001, he works in the research group "Molecular Gas Lasers", Gas Lasers Laboratory in P N Lebedev Physical Institute of the Russian Academy of Sciences. He has published over 60 scientific papers with his participation, including a patent of the Russian Federation. He took part in creation of compact laser with a slab RF discharge excitation and cryogenic cooling of the active medium, operating both on fundamental and first overtone bands of CO molecule. Nowadays, he participates in a parametric study of this laser, as well as in researches of capabilities of frequency conversion of CO laser radiation in nonlinear crystals.

Slab CO laser with radio frequency (RF) pulse-periodic pumping and cryogenically cooled electrodes was launched in Q-switch mode. V-type optical scheme with two passes through the active medium was used. Q-switch mode was realized by rotating mirror. RF discharge parameters, composition and pressure of the laser gas mixture were optimized to increase the laser output pulse peak power. Laser pulse parameters were studied depending on the time delay between RF pumping pulse and Q-switching moment. The influence of output coupler transparency and RF pumping parameters on CO laser output spectrum was defined. Consequently, laser pulses with a repetition rate of 100 Hz, pulse duration of 0.65 s (FWHM) and maximum peak power up to 3.5 kW, which is significantly higher (about two orders of magnitude) than the peak power of the same CO laser operating in the free-running mode at similar pumping conditions, were obtained. Laser spectra consisted of ~90 lines in wavelength range from 4.9 to 6.7 m. The obtained CO laser pulses were used for the second harmonics and sum frequency generation in a nonlinear crystal ZnGeP2. Conversion efficiency was determined depending on radiation incidence angles and position of crystal relative to the focal plane of the focusing lens. Maximal value of external conversion efficiency was ~3%, which corresponding to internal conversion efficiency ~6%. The spectrum of converted radiation under these conditions consisted of ~200 spectral lines in wavelength range from 2.5 to 3.3 m.