Frequency-comb-based absolute frequency measurements in the mid-infrared with a difference-frequency spectrometer

We demonstrate the possibility of extending the well-established metrological performance of optical frequency-comb synthesizers to the mid-IR region by phase locking the pump and signal lasers of a difference-frequency source to two near-IR teeth of an optical comb. An uncertainty of 800 Hz (1.1 x 10(-11)) in the absolute frequencies of CO2 transitions near 4.2 microm has been measured by cavity-enhanced saturated-absorption spectroscopy. Prospects for the creation of a new dense set of high-quality molecular frequency standards in the IR are discussed.     

Noise characteristics of a high-power ytterbium-doped fibre amplifier at 1083 nm

Experimental results are reported for the noise characteristics of an Yb-doped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narrow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum output power of the amplifier is 1.2 W with a gain larger than 30 dB. An increase of the intensity-noise spectral density relative to the signal, by approximately 6.5 dB, is introduced by the amplification process, due to signal-amplified spontaneous-emission (ASE) beat noise. A remarkable increase of the noise level with decreasing frequency is observed below ≈35 kHz, probably due to technical noise of the amplifier pump diodes. The spectral broadening due to amplifier phase noise was measured to be less than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kHz-linewidth diode laser at 1083 nm is therefore expected to be in the same range. Received: 5 October 1999 / Revised version: 2 December 1999 / Published online: 24 March 2000     

Wide-bandwidth frequency locking of a 1083-nm extended-cavity DBR diode laser to a high-finesse Fabry–Pérot resonator

Received: 28 July 1997/Revised version: 27 November 1997     

THE MECHANISM OF THE 9,10-DIBROMOANTHRACENE MEDIATED TRIPLET-SINGLET ENERGY TRANSFER IN THE TETRAMETHYL-1,2-DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*

Abstract— The ternary chemiluminescent system consisting of tetramethyl-dioxetane (TMD), 9 ,10-dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (³K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines-cence involves triplet-singlet (TS) energy transfer from ³K to DBA, followed by singlet-singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of k^TS_K.DBA= (1.4 ± 0.4) ± 10⁹M^-1s^-1 and an efficiency of ø^TS_K.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. k^SS_DBARU= 1.5 ± 10¹⁰ M^-1 and (2.2 ± 0.2) ± 10¹⁰M^-1s^-1, respectively.     

Precision frequency measurement of visible intercombination lines of strontium

We report the direct frequency measurement of the visible 5s(2) 1S0-5s5p 3P1 intercombination line of strontium that is considered a possible candidate for a future optical-frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb generator referenced to the SI second through a global positioning system signal. The 88Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88Sr-86Sr isotope shift to be 163 817.4 (0.2) kHz.     

High-sensitivity spectroscopy of CO2 around 4.25 μm with difference-frequency radiation

We demonstrate the possibility to perform very high-sensitivity spectroscopy of CO₂ around 4.25 μm wavelength, by use of a difference-frequency radiation source and a White-type multipass absorption cell. Several methods for fringing noise reduction were successfully adopted. In particular, a novel technique to reduce fringes by choosing proper values of the frequency modulation amplitude is described in detail. Pressure-broadening measurements of high-J rovibrational transitions are presented. Achievable laboratory and field sensitivity limits are discussed.     

Frequency-comb-referenced mid-IR sources for next-generation environmental sensors

We report on recent development of IR spectrometers based on non-linear optical generation and quantum-cascade lasers. Frequency stabilization and referencing to optical frequency-comb synthesizers is described. Their characteristics for spectroscopic as well as metrological applications are pointed out. The potential of the combination of mid-IR sources with enhancement cavities for high-resolution and sensitive measurements of gas spectra is illustrated. Finally, we describe wave-front engineering of long wavelength beams for spatial control and imaging applications.