A frequency tunable external-cavity diode laser (ECDL) using a narrow bandwidth (∼0.3 nm) interference filter has been developed for resonance ionization spectroscopy of strontium (Sr) with high isotopic selectivity. Improved wavelength and single mode stabilities of this interference-filter-type ECDL (IF-ECDL) over a commonly used (also home-made) Littrow-type ECDL were theoretically expected and experimentally confirmed by both a wavelength meter and a home-made Fabry-Perot interferometer. The measured spectral profile of the dominant isotope 88Sr using our IF-ECDL in the 689.4 nm intercombination transition shows that the Lorentzian component (∼1.3 MHz) of the spectrum width is consistent with the obtained fringe width of the interferometer. High 90Sr isotopic selectivity of ∼104 with respect to 88Sr is expected in this transition, which indicates that even if the manufacturing accuracy is not comparable to commercial Littrow-type ECDLs, our compact IF-ECDL having sufficient wavelength stability is a promising laser source for background-free analysis of radioactive 90Sr in marine samples.
There are difficulties to analyze 90 Sr from the sample in the field due to less abundant (x10-9) than other strontium isotopes. Therefore, it requires developing the detecting system with high selectivity of isotopes. To present >10 7 selectivity of strontium isotopes detection, 689.44 nm (Γ= ~7.5 kHz; 5s 2 1 S 0-5s5p 3 P 1 o) is applied to do multi-step resonance ionization mass spectrometry. Here, we develop interference filtered external cavity diode laser system to enhance isotope selectivity of strontium with multi-step resonance ionization at 5s 2 1 S 0-5s5p 3 P 1 o-5s4d 3 D 2 .
We investigated a promising three-step resonance ionization scheme of strontium (Sr) 5s21S0 ⟶ 5s5p 3P1° ⟶ 5s5d 3D2 ⟶ 4dnp (or 4dnf, n = 39) using the first-step intercombination transition for the enhancement of isotope selectivity. The power broadening observed in the 2nd transition indicates that laser power of less than 0.2 mW is sufficient for saturating this transition. Isotope separation can be successfully expected with application of the 3rd transition due to the narrow width of the 4dnp (or 4dnf, n = 39) autoionization level, paving the way for analysis of trace 90Sr in environmental applications.
We have proposed and developed an apparatus combining isotope-selective resonance ionization and high sensitivity ion trap techniques for the spectroscopic analysis of radioactive strontium 90 Sr. Using a JRIA 90 Sr standard solution sample, 90 Sr + ion crystals were successfully observed. The applied voltage condition in the ion trap was optimized for strong radial confinement of Sr + ions, which improves trapping stability during frequency scanning.
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