Passively Q-Switched KTA Cascaded Raman Laser with 234 and 671 cm−1 Shifts

A compact KTA cascaded Raman system driven by a passively Q-switched Nd:YAG/Cr4+:YAG laser at 1064 nm was demonstrated for the first time. The output spectra with different cavity lengths were measured. Two strong lines with similar intensity were achieved with a 9 cm length cavity. One is the first-Stokes at 1146.8 nm with a Raman shift of 671 cm−1, and the other is the Stokes at 1178.2 nm with mixed Raman shifts of 234 cm−1 and 671 cm−1. At the shorter cavity length of 5 cm, the output Stokes lines with high intensity were still at 1146.8 nm and 1178.2 nm, but the intensity of 1178.2 nm was higher than that of 1146.8 nm. The maximum average output power of 540 mW was obtained at the incident pump power of 10.5 W with the pulse repetition frequency of 14.5 kHz and the pulse width around 1.1 ns. This compact passively Q-switched KTA cascaded Raman laser can yield multi-Stokes waves, which enrich laser output spectra and hold potential applications for remote sensing and terahertz generation.

Three-dimensional capillary waves due to a submerged source with small surface tension

Steady and unsteady linearised flow past a submerged source are studied in the small-surface-tension limit, in the absence of gravitational effects. The free-surface capillary waves generated are exponentially small in the surface tension, and are determined using the theory of exponential asymptotics. In the steady problem, capillary waves are found to extend upstream from the source, switching on across curves on the free surface known as Stokes lines. Asymptotic predictions are compared with computational solutions for the position of the free surface. In the unsteady problem, transient effects cause the solution to display more complicated asymptotic behaviour, such as higher-order Stokes lines. The theory of exponential asymptotics is applied to show how the capillary waves evolve over time, and eventually tend to the steady solution.

Selective generation of individual Raman Stokes lines using dissipative soliton resonance pulses

Pumped by rectangular-shaped dissipative soliton resonance (DSR) pulses at 1030 nm, selective excitations of Raman Stokes lines of up to third order with extinction ratios of 8 dB and fifth order with extinction ratios of 4 dB are demonstrated experimentally. The rectangular DSR pulses are generated from a dual-amplifier ytterbium-doped figure-of-eight mode-locked laser constructed using all $10~\unicode[STIX]{x03BC}\text{m}$ -core-diameter large-mode-area fibers. By varying the two pump powers, the peak power of the output DSR pulses can be continuously tuned from 10 W to 100 W and from 30 W to 200 W, respectively, for two different lengths of the nonlinear amplifying loop mirror inside the cavity. High-frequency components are found to correspond to parts of the pulse in the trailing edge when two bandpass filters are used to separate the propagated pulse. Consequently, it provides an all-fiber technique to achieve selective excitation of the Raman shift by adjusting the peak power of the DSR pulse.

Effect of the Oscillating Electric Field Due to the Oscillating Electric Dipole on Raman Lines

Raman Effect is the measurement of the intensity and wavelength of the inelastically scattered radiation that falls on a molecule. The electric field of the incident radiation polarizes the molecule on which it falls and this leads to the creation of an oscillating dipole. The incident polarized laser light is inelastically scattered by the molecular sample. The scattered light contains modified wavelengths called the Stokes and anti-Stokes lines or wavelengths. The oscillating electric dipole, created by the incident radiation, creates an oscillating electric field around it. Since the oscillating electric field of the incident radiation creates an oscillating electric dipole that create an oscillating electric field around it, it was surmised that this oscillating electric field can affect the frequency of vibration or oscillation of the oscillating electric dipole that produces it. This novel effect will change the frequency (frequencies) of the scattered radiation resulting in Stokes and anti-Stokes lines with modified frequencies. This theoretical research and its importance can be understood like this. For instance, if there are two cells or molecules, side by side, in which one is a healthy cell and the other is cancerous, or two different types of molecules are sitting side by side, this types of scattering should be able to distinguish one from the other since the Stokes and anti-Stokes lines from the two molecules will not be identical. Thus, the incident radiation of angular frequency ω1 polarizes the charges of the molecule on which it falls and this leads to the creation of an oscillating dipole of frequency ω2. The oscillating dipole creates an oscillating electric field that can create additional frequency of the oscillating dipole that created it, and let this be ωD. Then the Raman lines can have frequencies (ω1+ω2+ωD), (ω1+ω2-ωD), (ω1-ω2+ωD), and (ω1-ω2-ωD). Depending on the relative magnitudes of ω2 and ωD, Raman lines will be designated as Stokes and Anti-Stokes lines. Due to the law of conservation of energy, ωD will be less than ω2 since an oscillating dipole cannot create field of frequency more than its own frequency. Hence the frequencies (ω1-ω2+ωD) and (ω1-ω2-ωD) correspond to Stokes lines, and frequencies. (ω1+ω2+ωD) and (ω1+ω2‑ωD) will correspond to Anti-Stokes lines. Calculations for Stokes and Anti-stokes lines have been done for some molecules, namely Ammonia compound (NH3), Nitrousoxide compound (N2O), Water (H2O), Sulphur dioxide compound (SO2), Ozone compound (O3). Calculations have also been done for compounds containing carbon, such as Dichloromethane compound (CH4Cl2), Formic acid compound (CH2O2), Methanol compound (CH4O), Benzene compound (C6H6), Propane compound (C3H8), and Carbonyl chloride compound (Cl2CO). The theory developed predicts new phenomena of getting Stokes and anti-Stokes lines with modified wavelengths which have not been observed experimentally as of to-day.

A fully autonomous ozone, aerosol and nighttime water vapor lidar: a synergistic approach to profiling the atmosphere in the Canadian oil sands region

Lidar technology has been rapidly advancing over the past several decades. It can be used to measure a variety of atmospheric constituents at very high temporal and spatial resolutions. While the number of lidars continues to increase worldwide, there is generally a dependency on an operator, particularly for high-powered lidar systems. Environment and Climate Change Canada (ECCC) has recently developed a fully autonomous, mobile lidar system called AMOLITE (Autonomous Mobile Ozone Lidar Instrument for Tropospheric Experiments) to simultaneously measure the vertical profile of tropospheric ozone, aerosol and water vapor (nighttime only) from near the ground to altitudes reaching 10 to 15 km. This current system uses a dual-laser, dual-lidar design housed in a single climate-controlled trailer. Ozone profiles are measured by the differential absorption lidar (DIAL) technique using a single 1 m Raman cell filled with CO2. The DIAL wavelengths of 287 and 299 nm are generated as the second and third Stokes lines resulting from stimulated Raman scattering of the cell pumped using the fourth harmonic of a Nd:YAG laser (266 nm). The aerosol lidar transmits three wavelengths simultaneously (355, 532 and 1064 nm) employing a detector designed to measure the three backscatter channels, two nitrogen Raman channels (387 and 607 nm) and one cross-polarization channel at 355 nm. In addition, we added a water vapor channel arising from the Raman-shifted 355 nm output (407 nm) to provide nighttime water vapor profiles. AMOLITE participated in a validation experiment alongside four other ozone DIAL systems before being deployed to the ECCC Oski-ôtin ground site in the Alberta oil sands region in November 2016. Ozone was found to increase throughout the troposphere by as much as a factor of 2 from stratospheric intrusions. The dry stratospheric air within the intrusion was measured to be less than 0.2 g kg−1. A biomass burning event that impacted the region over an 8-day period produced lidar ratios of 35 to 65 sr at 355 nm and 40 to 100 sr at 532. Over the same period the Ångström exponent decreased from 1.56±0.2 to 1.35±0.2 in the 2–4 km smoke region.

A fully autonomous ozone, aerosol and night time water vapor LIDAR: a synergistic approach to profiling the atmosphere in the Canadian oil sands region

LIDAR technology has been rapidly advancing over the past several decades. It can be used to measure a variety of atmospheric constituents at very high temporal and spatial resolutions. While the number of LIDARs continues to increase worldwide, there is generally a dependency on an operator, particularly for high-powered LIDAR systems. Environment and Climate Change Canada (ECCC) has recently developed a fully autonomous, mobile LIDAR system called AMOLITE (Autonomous Mobile Ozone LIDAR Instrument for Tropospheric Experiments) to simultaneously measure the vertical profile of tropospheric ozone, aerosol and water vapor (night time only) from near ground to altitudes reaching ten to fifteen kilometers. This current system uses a dual laser, dual LIDAR design housed in a single climate-controlled trailer. Ozone profiles are measured by the DIfferential Absorption LIDAR (DIAL) technique using a single 1 m Raman cell filled with CO2. The DIAL wavelengths of 287 nm and 299 nm are generated as the second and third Stokes lines resulting from stimulated Raman scattering of the cell pumped using the fourth harmonic of a Nd:YAG laser (266 nm). The aerosol LIDAR transmits three wavelengths simultaneously (355 nm, 532 nm and 1064 nm) employing a detector designed to measure the three backscatter channels, two nitrogen Raman channels (387 nm and 607 nm), and one cross-polarization channel at 355 nm. In addition, we have added a water vapor channel arising from the Raman-shifted 355 nm output (407 nm) to provide nighttime water vapor profiles. AMOLITE participated in a validation experiment alongside four other ozone DIAL systems before being deployed to the ECCC Oski-ôtin ground site in the Alberta Oil Sands region in November 2016. Ozone was found to increase throughout the troposphere by as much as a factor of 2 from stratospheric intrusions. A biomass burning event that impacted the region over an eight-day period produced LIDAR ratios of 35 to 65 sr at 355 nm and 40 to 100 sr at 532. Over the same period the Angstrom exponent decreased from 1.56 ± 0.2 to 1.35 ± 0.2 between the 2 to 4 km smoke region. The advantage of nearly continuous measurements obtained over a 12-month period will be presented, highlighting the synergistic advantage of AMOLITE’s tri-LIDAR design.

Rigorous results in existence and selection of Saffman–Taylor fingers by kinetic undercooling

The selection of Saffman–Taylor fingers by surface tension has been extensively investigated. In this paper, we are concerned with the existence and selection of steadily translating symmetric finger solutions in a Hele–Shaw cell by small but non-zero kinetic undercooling (ε2). We rigorously conclude that for relative finger width λ near one half, symmetric finger solutions exist in the asymptotic limit of undercooling ε2 → 0 if the Stokes multiplier for a relatively simple non-linear differential equation is zero. This Stokes multiplier S depends on the parameter $\alpha \equiv \frac{2 \lambda -1}{(1-\lambda)}\epsilon^{-\frac{4}{3}}$ and earlier calculations have shown this to be zero for a discrete set of values of α. While this result is similar to that obtained previously for Saffman–Taylor fingers by surface tension, the analysis for the problem with kinetic undercooling exhibits a number of subtleties as pointed out by Chapman and King (2003, The selection of Saffman–Taylor fingers by kinetic undercooling, Journal of Engineering Mathematics, 46, 1–32). The main subtlety is the behaviour of the Stokes lines at the finger tip, where the analysis is complicated by non-analyticity of coefficients in the governing equation.