RESUMO
Between a frequency comb mode and a continuous-wave (cw) laser, we demonstrate that a frequency-to-voltage converter can be used to transfer frequency instability in the 10-14 range for integration times τ between 0.25 and 2100 s. The technique is relevant when the optical beat between laser signals is weak and a high level of frequency stability is required both in the short term and long term, as in the case of laser cooling with very narrow transitions. The impressive stability transfer arises through the use of a synchronous voltage-to-frequency converter that relies on an external CMOS oscillator. Aided by an atomic reference to the frequency comb, the method grants long-term stability to the cw laser, superior to that achieved with most optical cavities.
RESUMO
We use integrated circuit-based frequency-to-voltage conversion of a frequency comb beat signal as the means for laser frequency stabilization that is suitable for narrow-line laser cooling. The method is compared to an atomic beam lock where the laser frequency instability for the new scheme shows an improvement of 2 orders of magnitude at sub-1 s and grants a lock-capture range that is approximately 30 times greater. We employ the locking method on a 1111.6 nm laser that is frequency doubled and used in a dual-wavelength magneto-optical trap for Yb171 atoms, producing atomic cloud temperatures of â¼20 µK.
RESUMO
With 199Hg atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is ~15 Hz. Here we lock an ultrastable laser to this ultranarrow 1S0-3P0 clock transition and achieve a fractional frequency instability of 5.4×10(-15)/âτ for τ ≤ 400 s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0×10(-17) s(-1) (-16.9 mHz s(-1) at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4×10(-16) per cavity.
RESUMO
We present an assessment of the (6s2) (1)S0 â (6s6p)(3)P0 clock transition frequency in 199Hg with an uncertainty reduction of nearly 3 orders of magnitude and demonstrate an atomic quality factor Q of â¼10(14). The 199Hg atoms are confined in a vertical lattice trap with light at the newly determined magic wavelength of 362.5697±0.0011 nm and at a lattice depth of 20E(R). The atoms are loaded from a single-stage magneto-optical trap with cooling light at 253.7 nm. The high Q factor is obtained with an 80 ms Rabi pulse at 265.6 nm. We find the frequency of the clock transition to be 1,128,575,290,808,162.0±6.4(syst)±0.3(stat) Hz (i.e., with fractional uncertainty=5.7×10(-15)). Neither an atom number nor second order Zeeman dependence has yet been detected. Only three laser wavelengths are used for the cooling, lattice trapping, probing, and detection.
RESUMO
We report on the Lamb-Dicke spectroscopy of the doubly forbidden (6s(2))(1)S(0)â(6s6p)(3)P(0) transition in (199)Hg atoms confined to a vertical 1D optical lattice. With lattice trapping of â²10(3) atoms and a 265.6 nm probe laser linked to the LNE-SYRTE primary frequency reference we have determined the center frequency of the transition for a range of lattice wavelengths and at two lattice trap depths. We find the Stark-free (magic) wavelength to be 362.53(0.21) nm-essential knowledge for future use of this line in a clock with anticipated 10(-18) range accuracy. We also present evidence of the laser excitation of a Wannier-Stark ladder of states in a lattice of well depth 10E(R).
RESUMO
Laser cooling and trapping of neutral mercury is performed in a single-stage (1)S(0)â(3)P(1) 3D magneto-optical trap. We give a detailed account of the atom cloud size and temperature for both bosonic ((200)Hg and (202)Hg) and fermionic ((199)Hg and (201)Hg) isotopes. The bosonic isotope temperatures are in close agreement with Doppler cooling theory, while temperatures obtained for the fermionic isotopes are lower, suggesting the presence of sub-Doppler cooling. A minimum temperature of 29±4 µK is achieved for (201)Hg.
RESUMO
Details for constructing an astronomical frequency comb suitable as a wavelength reference for échelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 microm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of approximately 8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested.
RESUMO
We demonstrate a fundamentally mode-locked fiber laser with a repetition frequency in excess of 2 GHz at a central wavelength of 1.535 mum. Co-doped ytterbium-erbium fiber provides the gain medium for the laser, affording high gain per unit length, while a semiconductor saturable absorber mirror (SAM) provides the pulse shaping mechanism in a standing wave cavity. Results are shown confirming cw mode-locking for 1 GHz and 2 GHz repetition frequency systems. The response of the frequency comb output to pump power variations is shown to follow a single pole response. The timing jitter of a 540MHz repetition-rate laser has been suppressed to below 100 fs through phase-lead compensated feedback to the pump power. Alternatively, a single comb line of a 850MHz repetition-rate laser has been phase-locked to a narrow linewidth cw laser with an in-loop phase jitter of 0.06 rad(2). The laser design is compatible with low-noise oscillator applications.
RESUMO
We investigate the comb linewidths of self-referenced, fiber-laser-based frequency combs by measuring the heterodyne beat signal between two independent frequency combs that are phase locked to a common cw optical reference. We demonstrate that the optical comb lines can exhibit instrument-limited, subhertz relative linewidths across the comb spectra from 1200 to 1720 nm with a residual integrated optical phase jitter of approximately 1 rad in a 60 mHz to 500 kHz bandwidth. The projected relative pulse timing jitter is approximately 1 fs. This performance approaches that of Ti:sapphire frequency combs.
RESUMO
Optical frequency combs generated by femtosecond fiber lasers typically exhibit significant frequency noise that causes broad optical linewidths, particularly in the comb wings and in the carrier-envelope offset frequency (f(ceo)) signal. We show these broad linewidths are mainly a result of white amplitude noise on the pump diode laser that leads to a breathing-like motion of the comb about a central fixed frequency. By a combination of passive noise reduction and active feedback using phase-lead compensation, this noise source is eliminated, thereby reducing the f(ceo) linewidth from 250 kHz to <1 Hz. The in-loop carrier-envelope offset phase jitter, integrated to 100 kHz, is 1.3 rad.
RESUMO
We demonstrate an optical frequency comb with fractional frequency instability of =2x10(-14) at measurement times near 1 s, when the 10th harmonic of the comb spacing is controlled by a liquid helium cooled microwave sapphire oscillator. The frequency instability of the comb is estimated by comparing it to a cavity-stabilized optical oscillator. The less conventional approach of synthesizing low-noise optical signals from a microwave source is relevant when a laboratory has microwave sources with frequency stability superior to their optical counterparts. We describe the influence of high frequency environmental noise and how it impacts the phase-stabilized frequency comb performance at integration times less than 1 s.
RESUMO
We have demonstrated two continuous-wave nonlinear processes: third-harmonic generation (THG) of 1064-nm radiation with a lithium triborate (LBO) crystal, and second-harmonic generation of 696-nm radiation in deuterated rubidium dihydrogen arsenate. With 34 mW of 1064-nm and 25 mW of 532-nm radiation incident upon the LBO crystal, as much as 60 nW of third-harmonic power has been produced. We present the characteristics that optimize the production of nonlinear power in this sum-frequency generation process. In the second experiment, 15 nW of radiation at 348 nm was produced with 9 mW of 696-nm incident radiation. Both processes will play an important role in the new generation of optical synthesis techniques.