High-finesse Etalon Research Articles

High stability in near-infrared spectroscopy: part 1, adapting clock techniques to optical feedback

Optical feedback is an efficient way to narrow and stabilise semi-conductor lasers. As a step forward for ultra-stable, yet highly tunable sources, we developed a new prototype of a three-mirror V-shaped optical cavity (VCOF). It is made of a precisely machined Zerodur spacer, that holds 3 optical contacted mirrors forming a high finesse V-shaped cavity. This arrangement allows the resonant light to be sent back to the seeding laser, triggering a drastic narrowing of the emission linewidth well below the cavity mode width without the need for high-bandwidth active electronic lock of the laser on the cavity. Low expansion material and precise temperature control of the reference cavity leads to a source with Hz level frequency drift and 70 Hz-level emission linewidth at 215 THz. We discuss the benefits of this new prototype compared to its predecessor for high-sensitivity cavity ring down spectroscopy (CRDS). To serve this purpose, the frequency stabilised laser was characterised on short, mid and long time scales, using a high finesse etalon, a self referenced optical frequency comb and a long term saturated CRDS absorption Lamb dip measurement on water.

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.

Electro-Optic Tuning of a Monolithically Integrated Widely Tuneable InP Laser With Free-Running and Stabilized Operation

We report on the free-running and frequency stabilized operation of a ring resonator-tuned full-band tuneable laser. The laser is a monolithically integrated semiconductor ring laser tuneable over 34 nm, from 1522–1556 nm, fabricated using a commercially-available, InP-based, active-passive foundry technology. The mode selection is implemented using the Vernier effect by reverse-biasing voltage-controlled electro-optically tuned ring resonators. The laser exhibits a typical intrinsic linewidth of 110 kHz over the C-band and a side-mode suppression ratio (SMSR) exceeding 50 dB. The linewidth over the tuning range does not significantly vary, showing that the tuning mechanism does not cause linewidth broadening. The power dissipated in the tuning elements is 1.4 mW per ring. Using the same reverse bias voltage-controlled electro-optic tuning, we also demonstrate the locking of the laser to a high-finesse etalon using Poun–Drever–Hall frequency locking. Our implementation requires a single control loop because of the reverse bias tuning. All deployed tuning effects in the phase modulators have the same sign therefore resulting in a flatter frequency dependent phase response compared to current injection feedback. The control loop has a bandwidth of 500 kHz and a control range of 2.9 GHz. We report 1 kHz level linewidth for millisecond observation times for the stabilized laser.

Complete single-shot measurement of arbitrary nanosecond laser pulses in time

For essentially all applications, laser pulses must avoid variations in their intensity and phase within a pulse and from pulse to pulse. Currently available devices work very well for both long (>10ns) and short (<100ps) pulses. But intermediate (~ns) pulses remain difficult to measure and, not surprisingly, are the least stable. Here we describe a simple, elegant, complete, all-optical, single-shot device that measures ~ns pulses and that does not require a reference pulse or assumptions about the pulse shape. It simultaneously achieves a very high spectral resolution of <1pm and a very large delay range of ~10ns (several meters of light travel). It accomplishes both goals using high-efficiency, high-finesse etalons: one to generate high angular dispersion for a high-resolution spectrometer, and another to tilt the pulse front by ~89.9° without distorting it in time. Using this device, we completely measure microchip and fiber-amplifier pulses.

Harmonically mode-locked semiconductor-based lasers as high repetition rate ultralow noise pulse train and optical frequency comb sources

Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low noise applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low noise rf sources as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb sources with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb source is created, referenced to the intracavity etalon.

Thermal noise and radiation pressure in MEMS Fabry-Perot tunable filters and lasers

In this paper, we examine thermal noise and radiation-pressure effects in MEMS tunable Fabry-Perot etalons. We show that thermal noise causes a jitter in the center wavelength in very high finesse etalons. In turn, the jitter causes an effective increase in the time-averaged filter bandwidth. Radiation pressure is of little consequence in conventional Fabry-Perot etalons, but it can give rise to nonlinearities and hysteresis in the tuning response of high-finesse MEMS filters. We develop models of noise and optical nonlinearities and compare the models with a series of measurements on commercial tunable high-finesse MEMS Fabry-Perot etalons.

Long-Range, Resonant Vibrational Energy Exchange in Polyatomic Molecules: The Fundamental Acetylenic CH Stretching Spectrum of CH3Si(C.tplbond.CH)3

published in Advance ACS Abstracts, May 1, 1994. 0022-3654/94/2098-5614~04.50/0 of 1000, indicating that the molecule is in the extreme local mode limit. However, in the fundamental region there is littledifference between the symmetrized local mode and the normal mode wave functions, although they suggest different dynamics since they represent qualitatively different classical motions. In the local mode model, it is natural to interpret the splitting between equivalent bonds dynamically, as the time it takes for the excitation, initially localized on one bond, to transfer to one of the other symmetrically equivalent bonds. To better understand theobserved splitting in CH3Si(C=LH)j, we also examine the splitting of the symmetric and antisymmetric CH modes in diacetylene. For this molecule, the splitting is known from experiment and the force field from ab initio calculations. This allows us to separate out different contributions to the splitting, which is not possible for CH3Si(C=CH)3 at this time. Experimental Section Triethynylmethylsilane was prepared from CH3SiC13 [Aldrich] and H C s C M g C l [Aldrich] in tetrahydrofuran according to the procedures outlined in ref 7. The final product was 77% pure by lH NMR. The impurity, THF, caused no complications in the recording of the spectrum since its infrared absorptions occur a t a different frequency than the compound of interest. The spectrometer, which was described in detail earlier,ja consists of a continuously scanning continuous wave 3.0-pm color center laser [Burleigh] and a molecular beam machine with bolometer detection. Helium gas passed, a t various backing pressures, over a room-temperature liquid sample of CH3Si(CECH)~. The gas line leading into the machine was at 90 OC and the 50 pm diameter nozzle a t 120 OC. Above 50 psi He backing pressures, severe clustering was observed as a negative signal from the bolometer. This is caused by predissociating species leaving the molecular beam path upon absorption of radiation. Only slight clustering occurred at 30 psi of He, and the spectrum taken at this pressure was used for the analysis. We used two high-finesse etalons (7.5 GHz and 150 MHz free spectral range) to monitor and linearize the laser frequency. The instrumental line width of our spectrometer is approximately 8 MHz, due to slightly nonorthogonal crossings of the laser with the molecular beam. An absorption spectrum of acetylene in a gas cell was recorded along with the bolometer signal and was combined with published frequencies8 to establish an absolute frequency calibration of the spectrum.

Efficient, single-axial mode oscillation of a beta barium borate optical parametric oscillator pumped by an excimer laser

Intracavity etalons have been used to obtain single axial mode oscillation of a beta barium borate optical parametric oscillator pumped at 308 nm by a XeCl excimer laser. Two high finesse etalons were sufficient to select a single axial mode of the resonant signal wave over a tuning range 400–560 nm with the increase in oscillation threshold due to etalon insertion being kept below 1.5 times. Addition of a grating enabled single axial mode oscillation to be maintained out to degeneracy (616 nm).