Methane (CH4) is a greenhouse gas which directly influences climate changes on the planet. One of the sources of methane emissions in the atmosphere during human agricultural activities is the decay of animal manure and organic components of agricultural effluents. Therefore, remote control and measurement of the concentrations of agricultural products (mainly methane), which are essentially an anthropogenic factor of the impact on the atmosphere, is important. Here, we consider a possibility of creating a mobile laser absorption complex for methane monitoring at cites with agricultural effluents.
We demonstrate the development of broadband, infrared frequency combs tunable from 3 to 27 microns. The source is based on using a robust, few-cycle Er:fiber comb (10 fs pulse duration) to drive intra-pulse difference frequency generation within a quasi-phase-matched nonlinear medium (e.g. periodically poled lithium niobite or orientation patterned gallium phosphide). Since the down-converted light has a longer optical period, the electric field of this longer wave light can be directly sampled by the few-cycle Er:fiber pulse via electro-optic sampling (EOS), directly yielding spectroscopic information on the infrared light. Further, by implementing EOS in a dual frequency comb configuration, we can increase the spectroscopic acquisition speed to a rate of 50 Hz. This dual-comb EOS configuration enables a measurement bandwidth spanning 370 – 3300 cm^-1 with a resolution down to the 100 MHz (0.003 cm^-1) spacing of the infrared comb. Due to the brightness of this comb source and the broad acquisition bandwidth, we can perform high resolution and high sensitivity spectroscopy on chemically and biologically relevant compounds spanning the molecular fingerprint region, with an outlook towards fast acquisition, infrared frequency comb microscopy.
We report the development and initial results of two Terahertz imaging systems based on monochromatic sources at 0.2 and 2.52 THz. The first is based on a microwave oscillator, whose frequency is multiplied to 0.2 THz, used in conjunction with a zero-bias detector. The sample is scanned across the beam, and transmission images are obtained after processing. The second system allows real-time images, and consists of a methanol gas laser emitting at 119 microns (2.52 THz) and a commercial camera based on a microbolometer array. We describe the construction and performance of the methanol laser and a tunable CO2 laser, which emits 20 W at the 9P(36) pump line. Due to the high coherence of the laser, this system is particularly suited for diffraction and interference imaging. We have measured the absorption coefficients of a few samples assuming the Beer law.
In this work, we present results of broadband emissions ranging from 800 to 1500 nm
generated by using Photonic Crystal Fibres (PCFs) made from borosilicate glasses. The borosilicate
PCFs, fabricated by the Stack-and-Draw technique, consist of five hollow ring periods around the solid
core. The solid core is based on the lead-doped borosilicate glass. The PCFs with their external
diameters ranging from about 3.8 to 6 microns were excited with a commercial pulsed diode laser
(wavelength at 1065 nm, Power <100mW). The PCF length used to generate broadband emissions was
less than a meter. The Optical Attenuation of these PCFs was measured via the Cut-Back method and
their Dispersion Spectra were calculated by using the Finite Element Method (FEM) and the scanning
electronic microscope images. Finally, we believe that short borosilicate PCFs with lead-doped cores
(related to high non-linear properties) may be used in broadband emissions, supercontinuum
generations or other non-linear applications.
We describe a diode-laser-based system capable of generating >50 mW of single-frequency radiation near 425 nm. An alternative extended cavity diode laser injection seeds a semiconductor amplifier, whose output is frequency doubled by a nonlinear crystal placed in a power enhancement cavity. This system is particularly well suited for high-resolution spectroscopy in the blue region, and for laser cooling and trapping of calcium atoms.
Deceleration of an atomic beam of calcium was achieved by using the radiation of a frequency double diode laser at 845.2 nm. In order to enhance the violet beam generation the doubling crystal, KNbO3, is placed inside an external build-up cavity. The laser beam at 423 nm, counter- propagating with the atomic beam, is put into resonance with the 1S0 yields 1P1 transition of Ca. To keep the laser in resonance with the atomic transition during the cooling process, the Zeeman technique is used.
A standard grating-tuned extended-cavity diode laser is used for injection seeding of a tapered semiconductor laser/amplifier. With sufficient injection power the output of the amplifier takes on the spectral characteristics of the master laser. We have constructed master-oscillator power-amplifier systems that operator near 657 nm, 675 nm, 795 nm, and 850 nm. Although the characteristics vary from system to system, we have demonstrated output powers of greater than 700 mW in a single spatial mode, linewidths less than 1 kHz, coarse tuning greater than 20 nm, and continuous single-frequency scanning greater than 150 GHz. We discuss the spectroscopic applications of these high power, highly coherent, tunable diode lasers as applied to Ca, Hg+, I2, and two-photon transitions in Cs.
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