Active Frequency Stabilization Research Articles

Active frequency stabilization of an ultra-high Q whispering-gallery-mode microresonator

We report on active frequency stabilization of a whispering-gallery-mode microresonator with an ultra-high quality factor exceeding 2×108 to an atomic transition using the Pound–Drever–Hall technique. The critically coupled resonator is stabilized to 5.4% of its linewidth, or 206 kHz. Thermal bistability and mode-splitting are also observed and have a significant effect on the error signal.

Frequency-stabilized Nd:YVO4 thin-disk laser

We have developed a Nd:YVO4 thin-disk laser at 914 nm with single-frequency operation and active frequency stabilization to a low-finesse reference cavity. The spectral density of laser frequency noise is analysed by means of noise measurements at the error point of the frequency control loop. To address the 31S0→33P1 magnesium intercombination line at 457 nm, we use an external frequency doubling stage based on periodically poled KTiOPO4 for the generation of more than 150-mW output power at 457 nm. Optical beat signal measurements at 457 nm with a frequency-stable dye laser show a short-time line width of the thin-disk laser of less than 100 kHz.

Reference Signal Synthesized from a Cryogenic Sapphire Oscillator Improved by Power Control Servo

Improvements in the frequency stability of a reference signal synthesized from a cryogenic sapphire oscillator (CSO) have been realized. This has been achieved by a power control servo with active Pound frequency stabilization in the loop oscillator based on a high Q-factor cryogenic sapphire resonator with a loaded Q-factor of 5 ×108 at 10.812 GHz and operating at a temperature of 6 K. The reference signal of 100 MHz was synthesized from the 10.812 GHz oscillation frequency. When compared with a 100 MHz hydrogen maser signal, the 100 MHz reference exhibited a fractional frequency stability of 5.6 ×10-15 at an integration time of 510 s, which is approximately two times better than that without power servo control.

Active and passive frequency stabilization for a Q-switched Z-fold radio-frequency-excited waveguide CO_2 laser with two channels

We report on passive offset frequency stability in free-running applications and active offset frequency stability achieved by use of a frequency-locking technique for a Q-switched Z-fold rf-excited waveguide CO2 laser with two channels. The laser structure of common electrodes and two channels has the advantage of compensating for the frequency variation caused by variations in temperature, cavity length, gas refractive index, and mechanical vibrations, so its offset frequency stability is higher than that of two separate lasers. In the experiments, the offset frequency shift was less than 6 MHz for 3 min in free-running mode. The technique of active offset frequency locking by counting was also introduced. The beat frequency shifting value was smaller than +/- 0.5 MHz in the long-term.

Active laser frequency stabilization and resolution enhancement of interferometers for the measurement of gravitational waves in space

Laser frequency stabilization is notably one of the major challenges on the way to a space-borne gravitational wave observatory. The proposed Laser Interferometer Space Antenna (LISA) is presently under development in an ESA, NASA collaboration. We present a novel method for active laser stabilization and phase noise suppression in such a gravitational wave detector. The proposed approach is a further evolution of the "arm locking" method, which in essence consists of using an interferometer arm as an optical cavity, exploiting the extreme long-run stability of the cavity size in the frequency band of interest. We extend this method by using the natural interferometer arm length differences and existing interferometer signals as additional information sources for the reconstruction and active suppression of the quasi-periodic laser frequency noise, enhancing the resolution power of space-borne gravitational wave detectors.

Digital control of an iodine stabilized He–Ne laser by using a personal computer and a simple electronic system

An electronic system used for active control and optical frequency stabilization of a He–Ne laser is described. It is based on digital acquisition and signal processing, using minimum of analog electronics, and a personal computer (PC). Main functions of the system: phase sensitive detection, automatic control, and user interface, are performed in software. Simultaneous frequency and iodine cell temperature stabilization algorithm is described. Electronic system is compact (occupies only desktop PC case), inexpensive (commercial, of-the-shelf, components are mostly used), and can be easily upgraded and reprogrammed (new stabilization algorithms can be implemented). It is now a part of the primary length standard of Yugoslavia.

Frequency-stabilized diode-pumped Nd:YAG laser of high power

We describe a frequency-stabilized diode-pumped Nd:YAG laser of high power whose single-mode operation is obtained by suppressing the spatial hole burning through the twisted-mode technique. Active frequency stabilization is achieved by fringe side locking the laser beam to a reference Fabry-Perot cavity. Output power up to 800 mW in single-transverse and -longitudinal mode operation with a linewidth of less than 20 kHz is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power stabilized cryogenic sapphire oscillator

Microwave oscillators of exceptional short-term stability have been realized from cryogenic sapphire resonators with loaded Q factors in excess of 10/sup 9/ at 11.9 GHz and 6 K. This has been achieved by a power stabilized loop oscillator with active Pound frequency stabilization. These oscillators have exhibited a fractional frequency stability of 3-4/spl times/10/sup -15/ for integration times from 0.3 to 100 s. The relative drift of these two oscillators over one day is a few times 10/sup -13/. To reduce the long-term drift, which is principally due to excessive room temperature sensitivity, we have added cryogenic sensors for the power and frequency stabilization servos to one of these oscillators. We have also implemented a servo to reduce the room temperature sensitivity of our phase modulators. Testing of this oscillator against a Shanghai Observatory H-maser has shown an Allan deviation of 4/spl times/10/sup -15/ from 600 to 2000 s. >

Longitudinal mode separation tuning in 633 nm helium-neon lasers using induced cavity birefringence

The theory of laser cavity birefringence induced by insertion of two quarter-wave plates into the cavity is developed to show how the intermode frequency of a two-mode laser can be tuned through a free spectral range by relative rotation of the plates. Birefringence is demonstrated in a helium-neon laser at 633 nm using an open cavity having a tube with anti-reflection coated windows. The lock-in between modes when the intermodal frequency approaches zero was investigated and found to be smallest when the tube was placed between the plates which were aligned with axes parallel. Active frequency stabilization at a frequency separation of 50 MHz was demonstrated using the mode-balancing technique.

Squeezing by second-harmonic generation in a monolithic resonator

We have measured the intensity fluctuations of the second-harmonic mode generated in a MgO:LiNbO3 external monolithic cavity pumped by a Nd:YAG laser. The cavity has mirror coatings for both the fundamental and the second-harmonic mode. We scan the cavity using the electro-optic effect of the crystal and observe that the second-harmonic beam of 2 mW exhibits a quantum noise reduction of 40(±5)%. In addition, we report on the active frequency stabilization of the monolithic device used in our squeezing experiments. Several fast tuning parameters such as the electro-optic effect, the photo-elastic effect, and the laser frequency have been investigated. With these tuning parameters the monolithic resonator can be locked on double-resonance at the phase-matching temperature, which is a prerequisit for observing squeezing in a cw-regime.

Frequency stabilization of a diode-laser-pumped microchip Nd:YAG laser at 13 μm

We report the active frequency stabilization of a diode-pumped microchip Nd:YAG laser using a frequency-modulation sideband locking technique. The novel aspect of this scheme is that the piezo-mounted output coupler acts as both the frequency modulator and the frequency-correcting element. When the laser is locked to a reference cavity of 300-MHz free spectral range and 5-MHz linewidth, the laser frequency stability is found to be 88 kHz relative to the cavity.

Performance of the acousto-optical spectral line receivers at the metsahovi 14 m radio telescope

The spectral line receiving system at the 13.7 m radio telescope at the Metsahovi Radio Research Station is described. A cooled low noise Schottky mixer receiver in 72–115 GHz range is employed. The back end system comprises three acousto-optical spectrometers (AOS) with bandwidths of 11 MHz, 100 MHz and 600 MHz, of which only the 11 MHz AOS has been described previously in a refereed article. Active frequency stabilization has been realized for the spectrometers, and is described here in detail for the first time. A description of the receiver and back end system and the results of performance measurements are given. As a result of active stabilization an excellent frequency stability has been achieved, amounting to ±0.005, ±0.003 and ±0.01 in units of resolution bandwidth for the 11, 100 and 600 MHz AOS, respectively. Special measures have been taken to eliminate background light and prevent interference fringe patterns. Tests of the noise performance of the three AOS show that cycle times of >250 s are achieved.

Active frequency stabilization of a 1062-μm, Nd:GGG, diode-laser-pumped nonplanar ring oscillator to less than 3 Hz of relative linewidth

We present results on the frequency stabilization of two diode-laser-pumped ring lasers that are independently locked to the same high-finesse interferometer. We measure the relative frequency stability by locking the lasers one free spectral range apart and observing the heterodyne beat note. The resultant beat note width of 2.9 Hz is consistent with the theoretical system noise-limited linewidth and is approximately 20 times that expected for shot-noise-limited performance.

Computer control of frequency tunable CO 2 lasers

Application of active frequency stabilization and cavity scanning techniques, under computer control, to CO 2 lasers has been demonstrated. The methods avoid the need for passive stabilization and are appropriate for automated medium resolution spectroscopic systems including lidars. Procedures for self-adjustment of low pressure lasers and securing double mode laser outputs from high pressure lasers are described.

Single- and double-frequency cw dye laser with active frequency stabilization and electronic spectral scanning

A cw dye laser capable of generating both single- and double-frequency radiation with a high output power (P1W) was made and investigated. A simple system for active stabilization of the laser, was based on an external passive Fabry-Perot etalon with a drift in the lasing frequency of less than 3 MHz/h. Electronic discrete-continuous tuning in a range of 200 GHz was provided by using galvanometers to rotate intracavity Fabry–Perot etalons.

Diode-laser-pumped Nd:YAG laser injection seeding system

We have designed and tested a compact injection seeding system consisting of a diode-laser-pumped Nd:YAG master oscillator and a permanent-magnet Faraday isolator. With active resonator frequency stabilization, this system permits highly reliable single-axial-mode operation of a Q-switched Nd:YAG laser over a period of hours. The system is capable of injection seeding both stable and unstable resonator designs and is suitable for injection seeding commercial lasers with only minor modifications.

Active Stabilization of Crystal Oscillator FM Noise at UHF Using a Dielectric Resonator (Short Papers)

A low-noise 600-MHz crystal oscillator circuit is described. It uses a dielectric oscillator as the dispersive element of a discriminator in an active frequency stabilization loop which reduces the near-carrier FM noise. The innovation in the circuit is an essentially noiseless active carrier suppression loop, which allows maximum utilization of a low-noise RF amplifier to reduce the discriminator threshold (Delta f/sub rms/) to 2.5x10-5 Hz in a 1-Hz bandwidth. The FM noise 1 kHz from the carrier was reduced by 44 dB to this threshold, equivalent to a phase-noise spectral density of -152 dBc/Hz.

Gas-laser resonator stabilized by thermal compensation

A fast-response thermal compensation system was developed, by means of which the length of a gas-laser resonator could be stabilized to within 1/6 108 deg−1. The principal calculation formulas and the experimental results are reported. Recommendations are given on the fabrication of thermal compensators. The system considered can be used for lasers with passive or active frequency stabilization, and for passive optical resonators.

Active frequency stabilization of a 20 watt CO2laser with etalon wavelength selection

An active laser frequency stabilization scheme involving the use of an internally vibrated laser mirror has been successfully used to stabilize the output of a two-meter long, sealed-off CO 2 laser operating at powers greater than 20 watts. Long-term frequency variations in the laser were reduced from a free-running stability of about 4 parts in 107to a peak variation of 1 part in 108by this electronic technique. Heterodyne beat frequency measurements were used to obtain the data. The laser short-term stability was improved by hermetically sealing the region between the GaAs Brewster windows and the laser mirrors.

Frequency stabilization and noise suppression in the argon FM laser

We describe 1:108active frequency stabilization, 20-to 30-dB suppression of low-frequency noise, and suppression of axial-mode beats to 1100 MHz in an argon FNI laser at 5145 A.