Intercomparison of Northern European¹²⁷I₂- Stabilized He-Ne Lasers at λ = 633 nm

Abstract

An international comparison of 12712 He-Ne stabilized lasers, used as length standards, has been made. Five laboratories from Sweden, Denmark (two laboratories), Finland and Germany were represented. In addition, two lasers from the Bureau International des Poids et Mesures took part in order to relate the results to earlier comparisons. The reproducibility of the frequency mean of the four components d, e, f and g in the transition R(127)ll-5 in iodine 127 for the different lasers was found to be 15 kHz, taken as the standard deviation of the distribution of frequency among the group of ten lasers. Using laser BIPM4 as reference the frequency average of the group of lasers was +3,6 kHz, making this a good reference laser for the current ensemble. Measurements of frequency dependence on modulation amplitude, iodine pressure and, for some lasers, intracavity power are reported. The relative frequency partition of the four components d, e, f and g of each laser was also determined and shown to exhibit characteristics which are new for this type of stabilized laser.

Benchmarking the length measurement capabilities of the National Institute of Standards and Technology

“…International comparisons have demonstrated that iodine stabilized lasers usually agree well within the accepted 5 x 10' 11 uncertainty [5,6,7]. However, it must be noted that a small but significant number of iodine stabilized lasers exhibit larger errors, primarily due to either contaminated iodine cells or problems with the stabilization electronics, which must correctly identify the center of the iodine transition to very high accuracy.…”

Ultrastable metrology laser at 633 nm using an optical frequency comb

“…If the recommendations of mise en practique [25] are met a relative uncertainty of the He-Ne laser frequency of about 21·10 -12 is achievable. The user has to guarantee that the setup is operating under well-known operating conditions [11], because the emitted wavelength is closely connected with the purity [26], temperature and pressure of the mixture inside the iodine cell [27] and power-induced frequency shiftings [28]. An iodine-stabilized laser is additionally susceptible to the optical feedback of reflected light [1], which is hard to identify and to prevent [27].…”

“…An iodine-stabilized laser is additionally susceptible to the optical feedback of reflected light [1], which is hard to identify and to prevent [27]. Hence, the wavelength standard is supposed to be traced in periodical intervals back to another wavelength standard to verify its proper operation, for example by comparison with other iodine-stabilized lasers [28] or an optical frequency comb [29]. Derived from this, an iodine-stabilized He-Ne laser has two major drawbacks if its wavelength is used directly for interferometric measurements in the NPMM-200.…”

Iodine‐stabilized He‐Ne laser at λ=633 nm: design and international comparison

“…A regular verification of laser performance for reliable applications is made through international comparisons. 4,5 The main objective of such a comparison is to verify the performance of each participating laser as a frequency standard while operating properly under the specifications of the just-mentioned recommendation. Moreover, it is important to assess the sensitivity of the frequency of each laser to the factors known to cause changes of frequency.…”