Low-finesse Etalon Research Articles

Laser wavelength metrology with low-finesse etalons and Bayer filters

We present a wavelength meter with picometer-scale resolution based on etaloning effects of inexpensive glass slides and the built-in color filters of a consumer grade CMOS camera. After calibrating the device to a commercial meter, we tested the device's calibration stability using two tunable visible lasers for a period of over 16 days. The wavelength error over that entire period has a standard deviation of 5.29 parts per million (ppm) about a most probable error of 0.90 ppm. Within 24 hours of calibration, this improves to 0.04 ppm with a standard deviation of 3.94 ppm.

Optimization Procedures using Effect of Etalon Finesse and Driving Term on Optical Bistability

In this work, analytical study for simulating a Fabry-Perot bistable etalon (F-P cavity) filled with a dispersive optimized nonlinear optical material (Kerr type) such as semiconductors Indium Antimonide (InSb). Because of a trade off between the etalon finesse values and driving terms, an optimization procedures have been done on the InSb etalon/CO laser parameters, using critical switching irradiance (Ic) via simulation systems of optimization procedures of optical cavity. in order to achieve the minimum switching power and faster switching time, the optimization parameters of the finesse values and driving terms on optical bistability and switching dynamics must be studied.
 In addition, for different values of a cavity finesse (for example, F = 25 and 2.37) the switching intensity takes low values with a high finesse etalon compared to a high switching intensity with a low finesse etalon. So, the minimum switching power for a low finesse etalon is ⁓0.785mW, and is about 0.0785mW for a high finesse etalon. The driving term peak of a high finesse etalon becomes higher and the slowing down region becomes less, leading to a fast switching as compared with a slow switching in a low finesse etalon. So that, the minimum switching time was about 300ns for a low finesse etalon, and about 150ns for a high finesse etalon.

Self-mixing interference effects in tunable diode laser absorption spectroscopy

We report the effects of self-mixing interference on gas detection using tunable diode laser spectroscopy. For very weak feedback, the laser diode output intensity gains a sinusoidal modulation analogous to that caused by low finesse etalons in the optical path. Our experiments show that self-mixing interference can arise from both specular reflections (e.g. cell windows) and diffuse reflections (e.g. Spectralon™ and retroreflective tape), potentially in a wider range of circumstances than etalon-induced interference. The form and magnitude of the modulation is shown to agree with theory. We have quantified the effect of these spurious signals on methane detection using wavelength modulation spectroscopy and discuss the implications for real gas detectors.

Transmission of active and passive optical reference signals over a 16 channel, 534.4 km WDM optical fibre network

Active and passive optical frequency reference signals have been transmitted over a 534.4 km optical fibre network carrying live traffic and an equivalent fibre test-bed. The active references comprised an optical-transition locked fibre-laser and a fibre-grating locked distributed feedback (DFB) laser. A low-finesse etalon and molecular absorptions in an acetylene gas cell were used as passive references. No degradation of the reference wavelength was observed down to the 10 -8 level and in a self-heterodyne experiment; the upper limits for line-broadening and frequency shift of the transmitted signal are 2 x 10 -9 , limited by the DFB characteristics. Amplified spontaneous emission (ASE) noise and interference signals were observed for active references. The passive reference signals were also degraded by the ASE noise. The technical and logistical issues associated with using a long-distance point-to-point all-optical link for frequency metrology have been discussed.

Continuous-wave pump-enhanced optical parametric oscillator with ring resonator for wide and continuous tuning of single-frequency radiation

We demonstrate a PPLN based pump-enhanced, singly-resonant optical parametric oscillator configured in a traveling wave geometry and pumped by a Ti:sapphire laser. The inclusion of a low finesse etalon within the OPO cavity stabilizes the signal frequency, and rotation of the etalon allows this frequency to be systematically hopped from axial mode to nearest neighbor axial mode over the entire free spectral range of the etalon (83GHz). Tuning of the pump frequency allows the signal frequency to be smoothly tuned over a cavity free spectral range. More than 35mW of single frequency idler power was generated in the spectral range 2800-3000nm for 600mW pump power. The superiority of traveling wave over standing wave geometries in these regards is discussed.

Evaluation of multiple beam interference effects in infrared gas spectroscopy

Spectral interference resulting from the tendency of infrared windows to act as low-finesse etalons is evaluated for various infrared materials. The effect's temperature dependence and implications to concentration measurements is demonstrated by modelling the etalon's influence on the absorption band. It is shown that semiconductor and zinc chalcogenide windows exhibit a very strong temperature sensitivity, with lower refractive index windows, such as fluorides, having a lesser but still significant sensitivity which can lead to spurious results. Elimination of any spectral distortion or changes in concentration due to etalon effects requires the windows to be wedged with a minimum angle of approximately 1.0-0.7 mrad depending on the window material.

Improvement of the wavelength tunability of etalon-type laser diodes and mode recognition and stabilization in diode laser spectrometers

A simple arrangement is presented for the improved wavelength tunability, mode recognition and stabilization of commercial single mode laser diodes. A glass plate with or without a partially reflective coating is mounted in front of the laser diode chip. The plate acts as the low-reflectivity mirror of an extended resonator and helps to select particular longitudinal modes within the gain profile even where laser action is not possible without the feedback. Mode selection is performed by piezoelectric tuning of the external cavity. Mode recognition is achieved by the measurement of the reflected intensity from a second very thin glass plate in the laser beam acting as a low-finesse etalon. The intensity pattern from the etalon is used for mode stabilization of the arrangement.

Time-resolved frequency chirp measurement using a silicon-wafer etalon

A new method for determination of time-resolved frequency chirp in modulated light sources of optical communication systems is presented. A thin silicon wafer acting as a low-finesse etalon was used as an optical frequency discriminator. The method provides a polarization-insensitive way to easily characterize the frequency chirp with high time-resolution.

Phase locking in an infrared short-pulse free-electron laser

The feasibility of the phase-locking procedure for the external selection of a single mode with reasonable power has been tested by simulation of the optical pulse evolution in a short-pulse free-electron laser using a model based on the self-consistent solution of the equations of motion for the electrons and the wave equation driven by single-particle currents. The simulations show that a high degree of coherence between successive pulses can be induced by a low-finesse etalon. Saturated operation in a greatly reduced number of modes, but with the same total power, is attained with a slight delay in the growth of the power as compared to the case without phase locking.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simulations of mode reduction with an intracavity etalon in an RF-Linac based FEL

Coherence between successive light pulses from an rf-linac based FEL can be induced by means of an intracavity interferometric element such as an etalon. This considerably reduces the number of active cavity modes and facilitates the selection of a single narrow line from the laser output. Computer simulations for the operation of an etalon in the FELIX design are shown. The model based on the wave equation driven by single particles has been applied in simulations using a small number (up to six) of initially independent pulses. The case with 40 separate pulses in the cavity is treated with a simpler model. The simulations show that a low-finesse etalon suffices to obtain a large degree of coherence between successive pulses. Saturated operation in a reduced number of modes, but with the same total power, is attained with a delay of a few microseconds.

Fast turnoff in optical switching of low-finesse GaAs etalons operating in reflection

Subnanosecond switch-off times have been found in nonlinear GaAs Fabry-Perot etalons operating in reflection. Both pump and probe beams had photon energies exceeding the bandgap energy in GaAs. A laser diode was used as pump source.

Mode control and high energy operation of a multiatmosphere TE CO 2 laser using a three-mirror resonator

High energy operation, without optical damage to the grating, of a narrow-aperture multiatmosphere continuously-tunable TE CO 2 laser using a simple three-mirror resonator is reported. Single-longitudinal-mode emission has been obtained by incorporating a low finesse etalon into the three-mirror resonator. An order of magnitude increase in single mode energy is reported.

Analytical description of a Fabry-Perot spectrometer 5: Optimization for minimum uncertainties in the determination of Doppler widths and shifts; corrigendum

Based on the statistical criterion of least uncertainty, it has been found that there exists an optimum combination of source and instrumental parameters, which lead to the most efficient use of a Fabry-Perot spectrometer in the measurement and determination of either line profile position or temperature. Results are given in order to optimize the design of a spectrometer and/or quantitatively deduce the uncertainties of determination from measurements. Comparisons between the present results, the luminosity-resolution product method, and the usual method to determine line positions show the present quantitative method to give the most efficient spectrometer and the best estimates of uncertainty. A useful result of this investigation shows that a low reflective finesse etalon provides the optimum spectrometer. The implicit relaxation of the surface quality of the flats and precision of etalon adjustment deduced from this result lead not only to simplified operation but to lower instrumental costs as well.

Analytical description of a Fabry-Perot spectrometer 5: Optimization for minimum uncertainties in the determination of Doppler widths and shifts

Based on the statistical criterion of least uncertainty, it has been found that there exists an optimum combination of source and instrumental parameters, which lead to the most efficient use of a Fabry-Perot spectrometer in the measurement and determination of either line profile position or temperature. Results are given in order to optimize the design of a spectrometer and/or quantitatively deduce the uncertainties of determination from measurements. Comparisons between the present results, the luminosity-resolution product method, and the usual method to determine line positions show the present quantitative method to give the most efficient spectrometer and the best estimates of uncertainty. A useful result of this investigation shows that a low reflective finesse etalon provides the optimum spectrometer. The implicit relaxation of the surface quality of the flats and precision of etalon adjustment deduced from this result lead not only to simplified operation but to lower instrumental costs as well.