Iodine-stabilized He-Ne Laser Research Articles

Accuracy comparison of absolute optical frequency measurement between harmonic-generation synthesis and a frequency-division femtosecond comb

Using an iodine-stabilized He-Ne laser as a transfer oscillator, we compare absolute measurements of the optical frequency from a traditional frequency synthesis chain based on harmonic generation and from the frequency division technique of an ultrawide bandwidth femtosecond frequency comb. The agreement between these two measurements, both linked to the Cs standard, is 220+/-770 Hz, yielding a measurement accuracy of 1.6x10(-12). We report 473 612 353 604.8+/-1.2 kHz as a preliminary updated value of the absolute frequency of the " f" component for the He-Ne laser international standard at 633 nm.

Cancellation of laser dither modulation from optical frequency standards

We demonstrate the removal of the dither modulation from an iodine-stabilized He-Ne laser by using a frequency-modulated acousto-optic modulator and feed-forward techniques. This procedure reduces the linewidth of the beat between this laser and a flywheel He-Ne laser from 6 MHz to 8 kHz, the undithered beat linewidth being ~7 kHz. Dither suppression greatly reduces counter errors during beat measurements from stroboscopic effects between the counter's gate and the frequency of the dither modulation and increases the utility of the already formidable array of dithered laser frequency standards by making locking to them an easier task.

Iodine-stabilized He-Ne laser pumped by transverse rf-discharge

Iodine-stabilized He-Ne laser pumped by transverse rf-discharge

A 633 nm iodine-stabilized diode-laser frequency standard

An extended-cavity diode laser has been stabilized to hyperfine components of the 6-3, P(33) transition of the B-X system of 127I2 at 633 nm, and its performance evaluated by comparison with an iodine-stabilized He-Ne laser. The Allan standard deviation follows a slope of 3.8 × 10-11 τ-1/2, reaching a minimum of 1.7 × 10-12 at 500 s, and the reproducibility of the diode laser locked to component b21 has been determined to be 7 kHz (standard uncertainty) corresponding to a fractional uncertainty of 1.5 × 10-11. In addition, the influence of modulation depth, iodine pressure and axial power density on laser frequency has been investigated. Complete hyperfine interval sets and absolute frequency determinations of component b21 are presented for modulation depths of 2 MHz and 6 MHz.

A compact iodine-stabilized HeNe laser and crossover resonances at 543 nm

We have constructed a compact iodine-stabilized 543 nm HeNe laser using the third-harmonic locking technique. From the signal-to-noise ratio, the noise-limited-stability would be better than 1×10 −12 for integration time >1 s. Moreover, several crossover resonances of R(12) 26–0 line are investigated and identified. Two crossover resonances are found adjacent to the hyperfine component a 9, the recommended wavelength standard. Instead, we suggest the hyperfine component b 10 of R(106) 28–0 line as the wavelength standard for the absence of neighboring main lines or crossover resonances.

Iodine-stabilized extended-cavity diode lasers at λ ≈ 633 nm: result of an international comparison

A comparison of three 127I2-stabilized extended-cavity diode lasers has been carried out between the Danish Institute of Fundamental Metrology (DFM) and the Bureau International des Poids et Mesures (BIPM). Two of the lasers are stabilized using intra-cavity saturation spectroscopy, the third one using extra-cavity saturation spectroscopy. All lasers are locked using the third harmonic detection technique on different hyperfine components of the P(33)6-3 transition. The range of frequency differences measured during the four days of the comparison was from -340 kHz to 150 kHz. The large fluctuations are due to the poor repeatability of the extended-cavity diode lasers with intra-cavity absorption cells (ECL4 and BIREL1-1). The frequency stability and repeatability of the diode laser (ECL1) using an external absorption cell is roughly one order of magnitude lower in performance than the He-Ne lasers. Using an iodine-stabilized He-Ne laser (DK3) as reference and the recommended values given in the practical realization of the definition of the metre, we found a mean offset from the expected frequency difference between ECL1 and DK3 of -12 kHz and a standard uncertainty of 10 kHz.

Wavelength measurements of three iodine lines between 780 nm and 795 nm

The vacuum wavelengths of hyperfine components of three different rovibronic transitions of the B 0u+ - X 1Eg+ spectrum of molecular 127I2 in the near-infrared were determined with a relative standard uncertainty of δλ/λ = 1.3 × 10-10. The measurements were performed by interferometric wavelength comparison using as standards an iodine-stabilized He-Ne laser at 633 nm and a dye laser stabilized to the intercombination line of Ca at 657 nm. The vacuum wavelengths of hyperfine component a10 of the R(96) lines of both the (0-14) and (0-15) bands and the component a of the P(166) line of the (0-14) band were determined to be 781.488 441 03(10) nm, 793.527 910 44(10) nm and 790.109 812 76(10) nm, respectively.

Accurate Stabilization of a 3 mW Single-Mode Output He-Ne Laser by Intermittent Frequency Offset Locking to an Iodine Stabilized He-Ne Laser

A high-power, unmodulated frequency standard laser light with low running cost is a powerful tool for industrial measurement involving laser calibration and interferometry in length and shape. To obtain such a laser light, we developed an intermittent frequency offset locked laser (IFOL laser). This laser system, composed of an iodine stabilized He-Ne laser (I2SL) and a high-powered symmetric three-mode He-Ne laser (HP-3ML, optical output=5 mW), provides two stabilization operational modes: (1) independent mode (I-mode) and (2) slave mode (S-mode). Utilizing the frequency pulling effect, HP-3ML is stabilized at the condition of symmetric three-mode oscillation, and a 3 mW single-mode light with frequency instability of 10-12 is obtained (I-mode). When the optical frequency deviates from the allowed limit during I-mode, HP-3ML is temporarily offset-locked to I2SL (S-mode) with frequency resettability of 10-10 and frequency instability of 10-12. After completion of the drift reset in S-mode, HP-3ML is stabilized in I-mode again, and then I2SL is turned off. In a typical case of allowed drift in ±1 MHz, repetitive operation of I-mode for 10 days and S-mode for 5 min was satisfactory. Such an intermittent operation reduces the working time of I2SL dramatically, resulting in low running cost that enables long-term use in industrial measurement.

Iodine-stabilized extended cavity diode laser at λ=633 nm

An extended cavity diode laser at 633 nm has been frequency stabilized to I/sub 2/-Doppler-free absorption signals of the P(33)6-3 transition using a third-harmonic detection technique. The frequency was measured by the beat-frequency technique with an iodine-stabilized He-Ne laser as reference. A minimum value for the two-probe relative standard uncertainty of 1/spl times/ 10/sup -11/ (5 kHz) is reached after 100 s. We also report measurements of the hyperfine splittings of the P(33)6-3 transition and laser frequency dependence on modulation amplitude and iodine pressure.

Precision frequency measurement of the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of Sr/sup +/ with a 674-nm diode laser locked to an ultrastable cavity

We have measured the frequency of the 5s /sup 2/S/sub 1/2/-4d /sup 2/D/sub 5/2/ clock transition of a single Sr ion confined in a Paul trap. A diode laser locked to an ultrastable Fabry-Perot (F-P) cavity was used to probe the transition with a resolution of 3.5 kHz. The absolute frequency was determined from heterodyne measurements referenced to an iodine stabilized HeNe laser and a CO/sub 2/ laser yielding a value for the S-D transition of (444 779 043 963/spl plusmn/30) kHz. This work could lead to the development of a new optical frequency standard at 674 nm.

Frequency shifts of iodine stabilized He-Ne lasers at higher harmonic order stabilization

The frequency shifts of an /sup 127/I/sub 2/ stabilized He-Ne laser at 633 nm have been measured at the third, fifth, and seventh harmonic stabilization using a digital signal processing lock-in amplifier. The observed frequency shifts confirmed the previous theoretical prediction that the laser frequency depends on the harmonic order of stabilization. The lower effects of modulation amplitude shift, power shift, and iodine pressure shift at the fifth harmonic stabilization indicate a potential improvement of the frequency reproducibility of the laser standard. A model is suggested to describe the power shifts of the laser. The mechanism explains the lower power shift of some lasers when they are operated at relatively high intracavity power.

Frequency comparison of iodine-stabilized He-Ne lasers at 633 nm from the IMGC and the IFA-IFTAR

The results of an international comparison between the He-Ne lasers stabilized to 127I2 at 633 nm of the IMGC (Istituto di Metrologia "G. Colonnetti", Turin, Italy) and the IFA-IFTAR (Institute of Atomic Physics-IFTAR, Department of Lasers, Bucharest, Romania) are reported. The mean frequency difference, considering the hyperfine structure components d, e, f and g of the R(127) 11-5 transition, was Δν = νRO.2 - νIMGCA4/5 = 3,8 kHz, standard uncertainty u = 5,7 kHz, or Δν/ν0 = 0,8 × 10-11, standard uncertainty u = 1,2 × 10-11. The frequency stability, expressed as the relative Allan standard deviation of the beat note between the two lasers, resulted 3,7 × 10-12 for a 100 s sampling time.

Intermittent frequency offset lock of a symmetric three-mode stabilized He-Ne laser to an iodine stabilized He-Ne laser

Intermittent frequency offset lock of a symmetric three-mode stabilized He-Ne laser to an iodine stabilized He-Ne laser

Intermittent frequency offset lock of a symmetric three-mode stabilized He-Ne laser to an iodine stabilized He-Ne laser

There is a need for an intense, unmodulated single-frequency stabilized laser light that guarantees absolute optical frequency in a rapid laser calibration or an ultra-high resolution interferometer. To obtain such a light, we developed a new laser system that uses an intermittent frequency offset lock of a symmetric three-mode stabilized He-Ne laser to an iodine stabilized He-Ne laser. The proposed laser system provides two operational modes: (1) independent and (2) slave mode. In the independent mode, frequency of the three-mode laser is stabilized via control of frequency difference between two intermode beats. The resultant output is a single longitudinal mode light of maximum intensity that locates at the top of the gain curve. Frequency instability of 8X10-12 (at a sampling time of 100 s) which is better than conventional stabilized lasers is attained in the independent mode. Slow optical frequency drift during the independent mode is periodically corrected by the offset lock to the iodine stabilized laser (slave mode), resulting in accurate reset of the frequency drift. After reset of the frequency deviation, the three-mode laser is again operated in the independent mode. Due to such intermittent offset lock, duty factor of the iodine stabilized laser was reduced to a few % of continuous operation.

Experimental investigation of the power shift of iodine-stabilized He-Ne lasers at 633 nm

A group of six iodine absorption cells has been tested in the cavity of an iodine-stabilized He-Ne laser for the investigation of the power-shift coefficient of the laser. It was found that the experimental method used for the power variation may significantly affect the laser frequency and the power-shift coefficient. The experimentally determined power-shift coefficient of the laser can be different for the different iodine absorption cells while other conditions are not changed. A weak correlation between the power-shift coefficient and the iodine-cell polarization extinction ratio is observed. Careful selection of iodine absorption cells and proper adjustment of the laser power are important to meet the specification of the power-shift coefficient given by the Comité International des Poids et Mesures (CIPM) for a reproducible 127I2-stabilized He-Ne laser.

An intermittent frequency offset lock of a transverse Zeeman laser to an iodine stabilized He-Ne laser

A single-mode frequency stabilized laser with modulation-free and moderate power is desired as a light source for an ultra-high resolution interferometer system and/or a rapid laser calibration system. For this purpose, we developed a new stabilized laser system that utilizes intermittent control of a 2 mW transverse Zeeman stabilized He-Ne laser (Zeeman laser) with an iodine stabilized He-Ne laser (I2 stabilized laser). Because of the intermittent control, working time of the I2 stabilized laser is reduced. The Zeeman laser has two operational modes: independent and slave mode. In the independent mode, the Zeeman laser is stabilized through control of Zeeman beat frequency. Temperature dependent drift of the oscillation frequency during the independent mode is periodically corrected by the slave operation utilizing frequency offset locking to the I2 stabilized laser. Frequency instability of the Zeeman laser in independent and slave modes is 7.7X10-11 and 2.0X10-11, respectively, at the sampling time of 100 s.

On the nth harmonic locking of the iodine stabilized He-Ne laser

The frequency shift of the iodine stabilized He-Ne laser when using the third or other higher order harmonic locking for frequency stabilization is studied in this report. Computer simulations reveal that there is a fundamental frequency shift combined with the modulation amplitude shift due to the third harmonic locking as long as the line profile is asymmetric. This shift is substantially reduced if stabilization on the fifth or other higher order harmonic is applied. The simulation results explain the frequency shifts of 23 and 35 kHz observed by Balling et al. when the stabilization was changed from the third harmonic to the fifth harmonic. The frequency separations of 127I 2 hyperfine components can be more reliably determined with the higher order harmonic locking. It is further suggested that a specification of the range of the modulation shift coefficients is necessary to improve the reproducibility of 127I 2 stabilized He-Ne lasers.

International comparison of stabilized He-Ne lasers by the saturated absorption of 127I2 at λ ≈ 633 nm involving the CEM (Spain), the IPQ (Portugal) and the BIPM

The results of an international comparison of iodine-stabilized He-Ne lasers at λ ≈ 633 nm, made by beat-frequency techniques, between the CEM (Spain), the IPQ (Portugal) and the BIPM are presented. Four lasers took part in the ten-day period of measurements, and were compared once or twice a day. The frequency differences between the lasers were all less than 6 kHz and the highest standard uncertainty of the mean of the frequency differences between two lasers was 7 kHz. These results lie inside the standard uncertainty given in the mise en pratique of the definition of the metre. Parameters which affect the frequency of the lasers, such as modulation width, iodine pressure and laser power, were also investigated.

Accurate frequency control of an internal-mirror He–Ne laser by means of a radiation-heating system

Radiation heating enables fast temperature control. I applied radiation heating to the oscillation frequency control of an internal-mirror He-Ne laser. The laser system has a fast frequency response, and its oscillation frequency is offset-locked in an iodine-stabilized He-Ne laser by a phase-lock loop circuit. The frequency discrepancy σ between the master and the slave lasers is less than 10(-13) with a 100-s gate time.

Determination of the xenon 6s[3/2]_2–6s′[1/2]_0 clock frequency by interferometric wavelength measurements

We have determined the wave number of the optical two-photon clock transition 6s[3/2](2)-6s'[1/2](0) in xenon by interferometrically comparing the wavelengths of the 6s[3/2](2)-6p'[1/2](1) (lambda = 450 nm) and 6s'[(1/2)] (0)-6p'([1/2]) (lambda = 764 nm) transitions with an iodine-stabilized 633-nm He-Ne laser. These measurements determine the frequency of the two-photon transition [4564.610902(13) cm(-1) for (132)Xe] to better than 1 MHz and provide precise values for the isotope shifts and the hyperfine structures of these transitions.