Iodine-stabilized He-Ne Laser Research Articles

Powerful iodine stabilized He-Ne laser as wavelength reference

In order to meet the requirement of high output power of the laser monochromatic light source in the precision measurement, a high-power iodine stabilized He-Ne laser system with a fully enclosed, integrated structure was developed. The principle of saturation spectral detection, the method of absorption peak recognition and locking and the frequency stability of iodine stabilized laser were studied. Firstly, the basic principle of detecting saturation absorption spectrum of iodine molecular using the three harmonic method was introduced, and its mechanism of eliminating the power background was analyzed. Then, the stability of the integrated resonant cavity in the iodine stabilized laser was demonstrated, and the effects of axial expansion and lateral asymmetric deformation on the output power were discussed in detail. After that, the correspondence between the profile of laser output power and the iodine molecular saturation absorption peaks was presented, the feasibility of using the secondary harmonic signal to achieve absorption peak recognition was introduced, and the long-term locking ability of high-stability resonant cavity was demonstrated. Finally, the wavelength stability and reproducibility of high-power iodine stabilized He-Ne laser were analyzed. The experimental results showed that the standard deviation for the frequency jitter of high-power iodine stabilized He-Ne laser was 33 kHz, the stability at 1 000 s and the reproducibility in three months were 4.1×10−13 and 3.3 kHz (7.0×10−12), respectively. Its absolute frequency was 3.0 kHz lower than the recommended value by the International Committee for Weights and Measures (CIPM).

Influence of Intracavity Power on Frequency Characteristics of Iodine-Stabilized He-Ne Laser

Influence of Intracavity Power on Frequency Characteristics of Iodine-Stabilized He-Ne Laser

Beat frequency measurement of the stabilized He-Ne laser 633 nm calibration in SNSU-BSN

In the metrology area, typical stabilized lasers are used as length primary standard. KIM-1, i.e. the iodine stabilized He-Ne laser in National Measurement Standards Laboratory-National Standardization Agency of Indonesia (SNSU-BSN) has been traceable to SI through CCL-K11 inter-laboratory comparison. The result was suitable for KIM-1 to be used as the length primary standard in SNSU-BSN. Beat frequency measurement has been applied in the optical frequency and wavelength calibration system for stabilized He-Ne laser 633 nm using KIM-1 as a reference standard. In the calibration replica, a dual-frequency mode (Agilent 5519B) took a role as DUT laser, which emits a pair of beams with a central wavelength of 632.991 354 nm in the vacuum with frequency difference 3.4 to 4.0 MHz and ±0.02 ppm stability for a typical lifetime. As a measurement result, the beat frequencies of the 1st and 2nd polarized beam of Agilent 5519B against KIM-1 are (121.33±0.06) MHz and (118.59±0.06) MHz.

Characterization and applications of auto-locked vacuum-sealed diode lasers for precision metrology.

We demonstrate the performance characteristics of a new class of vacuum-sealed, autolocking diode laser systems and their applications to precision metrology. The laser is based on adaptations of a design that uses optical feedback from an interference filter and it includes a vacuum-sealed cavity, an interchangeable base-plate, and an autolocking digital controller. A change of the base-plate allows operation at desired wavelengths in the visible and near infrared spectral range, whereas the autolocking ability allows the laser to be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We characterize the frequency stability of this laser system based on the Allan deviation (ADEV) of the beat note and of the lock signal. We find that the ADEV floor of 2 × 10-12 and short-term linewidth of ∼200 kHz are strongly influenced by current noise and vacuum sealing. Reducing the current noise and cavity pressure decreases the ADEV floor and increases the averaging time at which the floor occurs, which is a signature of long-term stability. We also show that evacuating the cavity to ∼1 Torr reduces the range of the correction signal of the feedback loop by approximately one order of magnitude, thereby increasing the lock range of the controller. The long-term stability allows the laser to be incorporated into a commercial gravimeter for accurate measurements of gravitational acceleration at the level of a few parts-per-billion, which are comparable to values obtained with an iodine-stabilized He-Ne laser. The autolocking and pattern-matching features of the controller allow the laser to be tuned and stabilized with respect to a temperature tunable transmission spectrum of a fiber-Bragg grating. This capability may be suitable for the development of a differential absorption LIDAR transmitter that can generate data at both on-line and off-line lock points using a single laser.

Optical Wavelength Meter Calibration Using Iodine Stabilized He-Ne Laser by Direct Measurement Method

Non-stabilized He-Ne lasers are widely used in calibration laboratories and industries. Wavelength calibration is a requirement to know the real wavelength of a non-stabilized He-Ne laser and its deviation. More importantly, calibration process creates a traceability link from the calibrated device to the primary standard of length measurement. One major wavelength calibration method for non-stabilized He-Ne lasers is using direct measurement method which requires a wavelength meter. The wavelength meter has to be calibrated first using a stabilizedHe-Ne laser prior to its use. The recommended radiation power of the stabilized laser in RCM-LIPI, IodineStabilized He-Ne Laser (KIM-1), is (50 ± 25) μW. Here, we examine the calibration process of the high precision wavelength meter with a measurement range of -25 dBm to +10 dBmor equals to 3.16 μW to 10 mW for a wavelength measurement range of 600 nm to 1650 nm. Several uncertainty evaluations for measurement were applied to assess the wavelength meter's performance. The results show that the wavelength meter produces a wavelength reading that is still within the desired band of measurement, thus making it a valid measurement instrument to calibrate the wavelength of non-stabilized He-Ne lasers with 10-3 nm of resolution. The wavelength meter's measurement capability can also be traced back to the length main standard, Iodine Stabilized He-Ne Laser (KIM-1).

Frequency stabilization of internal-mirror He–Ne lasers by air cooling

Instead of the traditional heating method, the cavity length of an internal-mirror He-Ne laser is controlled by air cooling which is implemented by a mini cooling fan. The responsive property of the cooling fan and the thermal expansion of the internal-mirror laser tube are investigated. According to these investigations, a controlling system is designed to drive the cooling fan controlling the cavity length of the laser. Then the frequency is stabilized by comparing the light intensities of two operating longitudinal modes. The results of beating with an iodine stabilized He-Ne laser show that a relative uncertainty (Δf/f-) of 4.3×10(-9) in 5 months, a frequency fluctuation of <1.4 MHz, and an Allan deviation of 6×10(-11) (τ=10,000 s) in 20 h are obtained.

Measurement of Long-Term Dimensional Stability of Glass Ceramics Using a High-Precision Line Scale Calibration System

Length measurement was conducted for two years on glass ceramics, Zerodur®and Clearceram®, which have a low coefficient of thermal expansion, and on synthetic quartz. Commercially available glass ceramics were used for evaluating long-term stability, or secular change. Synthetic quartz ensured longterm length measurement stability. Two line scales of 300 mm length made of each material for a total of six line scales were simultaneously manufactured and measured to evaluate dimensional stability variation of the materials over time. Measurements were conducted with a line scale calibration systemdeveloped by Nikon. The calibration system is a onedimensional laser interferometer, featuring reduced Abbe’s errors, laser interferometer paths in a vacuum and real-time wavelength calibration of laser frequency using a 633 nm iodine-stabilized He-Ne laser. Long-term quartz stability was 4.3 nm and 5.4 nm (2σ). The yearly stability coefficients of the two glassceramic scales were -0.22 and -0.23 parts per million per year (ppm/yr) for Zerodur and -0.16 and -0.16 ppm/yr for Clearceram. No significant difference in stability between the two scales was observed for Zerodur or Clearceram.

Absolute Gravity Measurement at KRISS

Acceleration due to gravity is essential in the field of measurement and calibration of mass related quantities such as force, pressure, hardness, and so on. Applications of gravity are becoming more important in mineral resource exploration, geography, environmental monitoring, etc. Most gravity measurements in Korea are being carried out by using a relative gravimeter. The reliability of the measurements made by using relative gravimeters should be calibrated periodically at different absolute gravity points. However, Korea Research Institute of Standards and Science (KRISS) had only one absolute gravity point measured by the Chinese National Metrology Institute in 1996, and the gravity value was not measured or evaluated again until 2007. KRISS established an absolute gravity standard facility using the free-fall gravimeter principle equipped with an iodine-stabilized He-Ne laser and a Rb clock for the first time in Korea in order to make a reliable gravity calibration chain. The Korean gravity standard is now traceable to fundamental SI units of Korean time and length standards. A gravity difference of approximately 22 μGal at the old absolute gravity site has been detected by precise measurements and evaluation. The absolute gravity points established in Korea can be used for reference data and for the calibration of relative gravimeters.

Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser.

We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [127I2 R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements.

Direct frequency counting with enhanced beat signal-to-noise ratio for absolute frequency measurement of a He-Ne/I_2 laser at 633 nm

We obtain a heterodyne beat signal between an iodine-stabilized He-Ne laser at 633 nm and a low power comb mode of an optical frequency synthesizer with an enhanced signal-to-noise ratio (SNR) up to approximately 35 dB. This is accomplished by the adoption of a fiber coupler and the reduction of the shot noise induced by adjacent comb modes. SNR is improved more than 15 dB compared with that of conventional methods. We measure the absolute frequency of the He-Ne laser mentioned above directly utilizing the enhanced SNR. A quantitative analysis of SNR and some information on experimental criteria for the correct frequency counting are given.

Digitalization of the Control System for the Iodine Stabilized He-Ne Laser

We have developed a digital control system for the iodine stabilized He-Ne laser. Adoption of the significant evolution in digital signal processing technique for the control system of the iodine stabilized He-Ne laser enables sophisticated software control, which cannot be easily achieved by analog design.

Optical amplifier for femtosecond frequency comb measurements near 633 nm

An optical amplifier operating at the 633-nm wavelength region is designed for absolute frequency measurements of iodine-stabilized He-Ne lasers with an optical femtosecond frequency comb generator. The same setup can also be used in other applications that require relatively high (15 mW) laser powers with good spectral characteristics. Radiation of a master laser is amplified by a microlens-coupled diode laser, which is injection locked to the frequency of the master laser. The amplifier can be reliably operated over several hours with very low phase noise. Optical amplification of more than 39 dB is demonstrated.

Optical frequency measurements with the global positioning system: tests with an iodine-stabilized He–Ne laser

Global positioning system- (GPS-) referenced optical frequency combs based on mode-locked lasers offer calibrations for length metrology traceable to international length standards through the SI second and the speed of light. The absolute frequency of an iodine-stabilized He-Ne laser [127I2 R(127) 11-5 f component] was measured with a femtosecond comb referenced to a multichannel GPS timing receiver. The expected performance and limitations of GPS-referenced comb measurements are discussed.

Broadband precision wavelength meter based on a stepping Fabry–Pérot interferometer

We have constructed a broadband apparatus for wavelength metrology capable of absolute accuracy at a level of better than 2 parts in 109. An evacuated plane-parallel Fabry–Pérot interferometer with continuously adjustable mirror separation is used to compare the wavelength of a single-frequency tunable laser with that of an iodine-stabilized HeNe laser used as a wavelength standard. This work details apparatus construction, a thorough investigation of systematic errors, and data analysis. The wavelengths of five Doppler-free Te2130 transitions in the region from 475.6 to 490.8 nm have been measured and are found to be in excellent agreement with previous measurements. In addition, the wavelengths of five previously unmeasured Te2130 transitions spanning the region from 424.9 to 462.3 nm have been determined for use as new reference wavelength standards.

Effect of frequency modulation amplitude on Iodine stabilized He-Ne Laser, at λ ≈ 633nm

Effect of frequency modulation amplitude on Iodine stabilized He-Ne Laser, at λ ≈ 633nm

A new method to determine the absolute mode number of a mode-locked femtosecond-laser comb used for absolute optical frequency measurements

The generation of optical frequency combs, directly referenced to the SI second, can be used to make measurements of optical frequencies. This provides a supreme method for the realization of the meter. However, an approximate knowledge of the frequency of the radiation is normally needed for such measurements in order to determine the integral order of the comb component used. Such information is usually obtained by prior wavelength measurements of the radiation under study. This paper demonstrates a new method to determine the absolute mode number in optical frequency measurements using mode-locked femtosecond lasers, thus eliminating the need for complementary wavelength measurements. Measurements of the frequency of an iodine-stabilized He-Ne laser at /spl lambda/=633 nm and a Nd:YAG laser at /spl lambda/=532nm are given as examples.

Interferometric determination of the diameter of a silicon sphere using a direct optical frequency tuning system

A new interferometer with a direct optical frequency tuning system using a phase-lock loop (PLL) offset locking has been developed to accurately measure the volumes of 1-kg single crystal silicon spheres. Three lasers are used in this system. The first one is an iodine-stabilized He-Ne laser, which is used as a reference laser. The second one is an offset-locked He-Ne laser whose optical frequency is offset-locked to the reference laser. The third one is an external cavity diode laser whose optical frequency is offset-locked to the offset-locked He-Ne laser by a PLL circuit. By changing the offset frequency between the diode laser and the offset-locked He-Ne laser, the optical frequency of the diode laser can be tuned continuously over a frequency range of 19 GHz and stabilized at a desired frequency with an uncertainty of 900 kHz within an integration time of 1/30 s. Accurate optical frequency changes in the diode laser produced by this system have been used to measure the sphere diameter by phase-shifting interferometry. Outlines of the interferometer and the frequency tuning system are presented. Preliminary results of the diameter measurement for a silicon sphere are also presented.

The bipm laser standards at 633 nm and 532 nm simultaneously linked to the si second using a femtosecond laser in an optical clock configuration

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.

Portable frequency standard at 633 nm with compact external-cavity diode laser

A portable (32 cm × 13 cm × 6 cm) laser frequency standard has been constructed by frequency-stabilizing a miniaturized external-cavity diode laser to the Doppler-free spectrum of iodine. Compact structure is achieved using a novel transmission grating. The laser has excellent noise properties, which leads to a high signal-to-noise ratio (SNR) of detection and allows direct observation of the inverse Lamb dips. The frequency stability matches that of iodine-stabilized He-Ne lasers at 633 nm; the relative frequency stability (square root of the Allan variance) follows a slope of 7.9 × 10−12τ−1/2 (10 s < τ < 4000 s). The best stability, 1 × 10−13 (47 Hz), is reached at an integration time of τ = 4000 s. The observed day-to-day repeatability (1σ) is 4 × 10−12 (1.6 kHz). Extensive measurements were made to evaluate the dependence of the laser frequency on the various operational parameters.

Absolute frequency measurement of the iodine-stabilized He-Ne laser at 633 nm

The absolute frequency of an iodine-stabilized He-Ne laser at 633 nm stabilized on the i (or a13) component of the 11-5 R(127) hyperfine transition of the 127I2 molecule is measured using a femtosecond optical comb generator and an iodine-stabilized Nd:YAG laser standard at 1064 nm. We link the measured absolute frequency to the current internationally adopted value via frequency intercomparison between JILA and the Bureau International des Poids et Mesures (BIPM), leading to the determination of the absolute frequency of the BIPM-4 standard laser. The resulting absolute frequency fi(BIPM) of the BIPM-4 standard laser is fi(BIPM)=473612214711.9±2.0 kHz, which is 6.9 kHz higher than the value adopted by the Comite International des Poids et Mesures (CIPM) in 1997.