Use Of Etalon Research Articles

Development of super luminescent diode based sensing technique for multiple-gas monitoring

A multiple-gas sensor based on absorption spectroscopy technique using a super luminescent diode source of 1.5 μm is proposed and realized for combustion applications. This technique allows CH4 and CO2 gas sensing in bio-gas plant to monitor the quality of the gas. In this study, a solid Fabry–Perot etalon with a free spectral range of 517 GHz is also used and the detection limit is improved, allowing measurement with lower resolution spectrum analyzer. The detection limit of 292 ppm for C2H2 (at 1,543.7 nm), 4,492 ppm for CH4 (at 1,525.92 nm) and 6.5 % for CO2 (at 1,572.68 nm) is attained for 2 m path length with the spectrum analyser of 0.02 nm resolution. With the use of etalon, nearly the same detection limit is attained for all the species at 1 nm resolution.

Spectral broadening in continuous-wave intracavity Raman lasers

Spectral broadening of the fundamental field in intracavity Raman lasers is investigated. The mechanism for the spectral broadening is discussed and the effect is compared in two lasers using Raman crystals with different Raman linewidths. The impact of the spectral broadening on the effective Raman gain is analyzed, and the use of etalons to limit the fundamental spectral width is explored. It was found that an improvement in output power could be obtained by using etalons to limit the fundamental spectrum to a single narrow peak.

Large-energy, narrow-bandwidth laser pulse at 1645 nm in a diode-pumped Er:YAG solid-state laser passively Q-switched by a monolayer graphene saturable absorber

Nonlinear transmission parameters of monolayer graphene at 1645 nm were obtained. Based on the monolayer graphene saturable absorber, a 1532 nm LD pumped 1645 nm passively Q-switched Er:YAG laser was demonstrated. Under the pump power of 20.8 W, a 1645 nm Q-switched pulse with FWHM of 0.13 nm (without the use of etalon) and energy of 13.5 μJ per pulse can be obtained. To the best of our knowledge, this is the highest pulse energy for graphene-based passively Q-switched Er:YAG laseroperating at 1645 nm, suggesting the potentials of graphene materials for high-energy solid-state laser applications.

Wavelength control of tunable dense wavelength-division multiplexing sources by use of a Fabry-Perot etalon and a semiconductor optoelectronic diode.

A high-resolution tunable-wavelength controller is achieved by use of an etalon for control of wavelength drift and a semiconductor optical diode (SOD) for channel recognition. The etalon provides a stable wavelength reference, and the SOD can detect mode-hopping and incomplete-tuning problems in tuning a laser. With the help of a Fabry-Perot etalon as a precise wavelength reference, the usual concern with the temperature stability of a SOD can be relaxed at least tenfold compared with wavelength control with a single SOD. We demonstrate the feasibility of monitoring tunable lasers by using a Fabry-Perot laser diode (FPLD) or a semiconductor optical amplifier (SOA). The induced voltage of the FPLD and that of the SOA are modeled with analytic expressions that can help to optimize the operation of a SOD sensor.

A method for screening adhesive materials for small displacements during environmental aging

This paper discusses the use of etalons fabricated from prepared glass slides to quantify the dimensional stability of two adhesive materials in damp environments. This technique facilitated the screening of adhesives for a kinematically demanding application. In addition to describing the etalon technique, additional data are provided on the performance of the device with the selected adhesives. One of the adhesives is simply identified as a cationic cured adhesive, while the other adhesive was Loctite 3615. A range of adhesive bond gaps from 50 to 500 μm was examined for the adhesive that showed the least displacement resulting from environmental aging. The results of this testing were applied to a kinematically sensitive device for verification of the adhesives use in this geometry.

Electrically induced transmissivity modulation in polymeric thin film Fabry-Perot etalons

We report the observation of electrically induced changes in transmissivity in Fabry-Perot devices consisting of spin-cast azo-dye/polymer films deposited between gold mirrors. In poled samples the observed modulation shows a linear dependence on the applied modulating voltage. The ratio of the transmissivity modulation observed using incident transverse magnetic polarization to that observed using transverse electric polarization is used to demonstrate that the electrooptic effect dominates the modulation. This is, to our knowledge, the first reported use of a polymeric thin film linear electrooptic material in a Fabry-Perot structure and demonstrates the use of etalons to enhance electrooptic effects in very thin films.

Single mode nitrogen pumped dye laser

A N 2-laser pumped, tunable dye laser has been operated in a stable single longitudinal cavity mode without the use of etalons, polarized pump sources or intracavity polarising elements. The all-reflective cavity employs a grazing incidence beam expansion grating and a Littrow tuning grating. The time averaged linewidth of 0.02 cm -1 (630 MHz) for 5 × 10 -3 M R6G dye was observed to be the same as the single shot linewidth, with an efficiency of 0.5%. A dye concentration of 10 -2 M R6G increased the single mode linewidth to the value predicted by a single pass model of the cavity and increased the efficiency to 1.5%. A Littrow grating can be used to replace the feedback mirror and enhance the output signal to noise ratio.

Main trends in the application of airphoto methods to geographical research in the U.S.S.R.: A review of publications, 1962–1964

Soviet geographers are presently working on research problems in the field of airphoto interpretation which apply to the development of interpretation methods and uses of aerial photography in various areas of the national economy. The main areas of investigation are the following: 1. (1) Analysis of landscape representation on aerial photographs and the development of airphotographic techniques and uses. 2. (2) Development of integrated survey methods and correlation of landscape types for special photo interpretation purposes. 3. (3) Setting up a system for photo interpretation through the use of etalons (sample photographs), compilation of descriptive keys, coding of photo interpretation material on punched cards. 4. (4) Working out quantitative methods for photo interpretation, and the statistical analysis of such information, and 5. (5) Promoting the use of airphoto interpretation techniques in fields of general and special research.

Observations in the wavelength range 1 to 3 mm

Measurements at these wavelengths are likely to give more information than those carried out at longer wavelengths since appreciable changes in the brightness temperature are found, not only throughout a lunation, but also during eclipse. The lunation measurements give 0·36 ± 0·05 for the ratio of thermal to electromagnetic attenuation coefficients at 1·5 mm wavelength. During total eclipse a drop of 30% in the mean disk brightness temperature at this wavelength has been measured. The two results taken together are not consistent with models of the lunar surface which suppose a thin dust layer of lower thermal conductivity but otherwise the same physical properties as the under­lying rock. Polarization and isothermal mapping measurements have been made with telescopes capable of resolving areas small compared with the total lunar disk. From these measure­ments an effective dielectric constant of about 2 has been deduced. These results together with measurements made at other wavelengths will be interpreted in terms of a rough model for the lunar surface. At present, in order to get more detailed information, there is a need for a greater wave­length and angular resolution. The use of etalons and large optical telescopes will be indicated.