Jes Henningsen

Saturated absorption in acetylene and hydrogen cyanide in hollow-core photonic bandgap fibers

Saturated absorption is studied in overtone transitions of C2H2 and H13CN molecules confined in the hollow core of a photonic bandgap fiber. The dynamics of filling and venting the fiber is markedly different for the two molecules owing to the presence of a permanent dipole moment in one of them. Saturation is observed for input power down to 10 mW, and well resolved Lamb dips limited by transit time broadening across the 10 ?m core diameter are observed with a counter-propagating probe beam.

Dynamics of gas flow in hollow core photonic bandgap fibers

The dynamics of gas flow in a hollow core photonic bandgap fiber is studied over four decades of pressure covering free molecular flow as well as hydrodynamic flow. Expressions are derived that allow for determination of the pressure inside the fiber as a function of time and position in the limits of Knudsen number Kn>>1 and Kn<<1. The expressions, which are validated by using absorption lines of acetylene as probes of the pressure inside the fiber, provide a straightforward way of predicting the temporal response for gas sensors of any fiber geometry.

Sensitive measurement of adsorption dynamics with nonresonant gas phase photoacoustics

A nonresonant photoacoustic cell, excited by 10-micros CO(2) laser pulses, is compared with conventional resonant cells excited with modulated cw radiation. By combining high sensitivity with small volume and small surface area, the nonresonant cell shows superior performance in measurements of time-dependent concentrations. The potential of the cell is illustrated by measurements of the time evolution of adsorption and desorption of ammonia molecules from surfaces of quartz and stainless steel.

Photoacoustic spectroscopy of O3 with a 450-MHz tunable waveguide CO2 laser

Abstract Photoacoustic absorption signatures have been obtained for ozone in 450-MHz tuning windows of a waveguide CO 2 laser. Out of 42 observed absorption lines, 31 are assigned to the ν 1 and the ν 3 bands, and 7 to various hot bands of 16 O 16 O 16 O. Two lines are assigned to the ν 3 band of the isotopomers 16 O 16 O 18 O and 16 O 18 O 16 O, which were present in their natural abundance. Precise collision broadening measurements are reported for two lines of the 16 O 16 O 16 O ν 3 band.

Photoacoustic spectroscopy of C 2 H 4 with a tunable waveguide CO 2 laser

A photoacoustic gas spectrometer using a wave-guide CO(2), laser, tunable over 500-MHz windows in 70 lines, is described. The spectrometer is used for mapping Doppler-limited spectral signatures of ethylene and for measuring pressure-broadening rates for collisions with N(2), Ar, and He. A total of 41 observed transitions are assigned to the nu(7), nu(10), and nu(4) bands of normal ethylene and to the nu(7) band of the (13)C(12)CH(4) isotopomer.

DFB fiber lasers as optical wavelength standards in the 1.5 /spl mu/m region

A single-mode distributed feedback (DFB) fiber laser has been frequency locked to a CO/sub 2/ absorption line at 1578.665 nm to demonstrate its potential as a wavelength standard. A frequency stability of 10/sup -8/ (/spl ap/2 MHz) was achieved on a time scale of minutes. A mechanical lead screw provided coarse wavelength tuning, white wavelength modulation and fast frequency corrections were applied by straining the fiber laser with piezoelectric transducers. With a suitable choice of absorption line, such a system may serve as an absolute frequency reference for dense wavelength-division multiplexing grids in telecommunication.

Intraline tunable CO2 waveguide lasers and applications in high resolution spectroscopy

Abstract Although early publications on the CO 2 waveguide laser reported tuning ranges close to and exceeding 1 GHz in individual laser lines, this potential has not been widely exploited for spectroscopy. In this paper we outline the difficulties which have hampered spectroscopic applications, and we point out their theoretical background and the avenues for solution. Following this, we review the work that has been done, including fundamental as well as applied spectroscopic work.

Absolute frequency measurement of the R(12) 26-0 and R(106) 28-0 transitions in /sup 127/I/sub 2/ at /spl lambda/=543 nm

A direct phase coherent determination of the absolute frequency of the a15 component in the R(12) 26-0 and b10 component in the R(106) 28-0 transitions in 127I2 at 543 nm has been made at the International Bureau of Weights and Measures. Lasers from the Czech Metrology Institute (Czech Republic), the National Institute of Metrology (China), the Centro Nacional de Metrologia (Mexico), the Standards, Productivity and Innovation Board (Singapore), the Centre for Metrology and Accreditation (Finland), the Danish Institute of Fundamental Metrology (Denmark), the National Physical Laboratory (U.K.), and the International Bureau of Weights and Measures took part. The mean frequency values found are f(a15)=551579856480.4 kHz, uc=4.8 kHz and f(b10)=551580162397.1 kHz, uc=4.6 kHz for the current group of lasers, where uc is the combined standard uncertainty. This constitutes a 30-fold improvement in accuracy for this radiation, which is recommended for the realization of the definition of the meter. If only lasers equipped with an iodine cell temperature control are considered, the group of lasers shows a dispersion of 7 kHz. This value is indicative of the level of reproducibility that can be expected at present for this type of standard

Molecular transitions as medium-precision wavelength standards for optical communication

Molecular vibration-rotation transitions in overtone or combination bands are well suited as absolute wavelength standards throughout the wavelength range used for optical communication. In this paper, we describe two different implementations. In the first, radiation from a superluminescent diode is sent through a cell containing H/sup 13/CN. This provides the spectrum with a characteristic signature from absorption in the 2/spl nu//sub 3/ overtone band, and allows for calibration in the 1530-1560 nm range. In the second implementation, radiation from a distributed feedback (DFB) fiber laser is locked to a Doppler broadened absorption line at 1548.8193 nm in the /spl nu//sub 1/+/spl nu//sub 3/ combination band of /sup 13/C/sub 2/H/sub 2/. The resulting standard has a relative Allan deviation of less than 10/sup -8/ beyond 100 s of integration time, and the signal can be disseminated through optical networks without degradation in stability. A novel feature of the fiber laser is all thermal control of the wavelength through resistive heating of a thin-film gold coating.

Wavelength modulation of fibre lasers - : a direct comparison with semiconductor DFB lasers and extended cavity lasers

A strain modulated fibre laser is compared with a DFB laser and an extended cavity laser by studying absorption lines in CO2 at 1578.665 nm and 1572.992 nm in second harmonic spectroscopy.