Laser Frequency Measurements Research Articles

Measurement of far-infrared laser frequencies generated by optically pumped N2H4 and N2D4

A three-laser heterodyne system has been used to measure the frequencies of four previously observed far-infrared laser emissions generated by optically pumping either hydrazine (N2H4) or its fully deuterated isotope (N2D4) with a continuous-wave carbon dioxide laser. These newly measured frequencies have fractional uncertainties of ± 2 × 10−7 and correspond to laser wavelengths ranging from 63.9 to 158.4 μm. This work represents the first measurement of a N2D4 laser frequency.

Stabilized frequency comb with a self-referenced femtosecond Cr:forsterite laser

A frequency comb is generated with a Cr:forsterite femtosecond laser, spectrally broadened through a highly nonlinear optical fiber to span from 1.0 to 2.2 ,m, and stabilized using the f-to-2f self-referencing technique. The repetition rate and the carrier-envelope offset frequency are stabilized to a hydrogen maser, calibrated by a cesium atomic fountain clock. Simultaneous frequency measurement of a 657-nm cw laser by use of the stabilized frequency combs from this Cr:forsterite system and a Ti:sapphire laser agree at the 10(-13) level. The frequency noise of the comb components is observed at 1064, 1314, and 1550 nm by comparing the measured beat frequencies between cw lasers and the supercontinuum frequency combs.

Measurement of far-infrared laser frequencies from optically pumped CHD/sub 2/OH

A three-laser heterodyne system was used to frequency measure 11 previously observed optically pumped far-infrared (FIR) laser emissions of CHD/sub 2/OH. These newly measured frequencies have fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/ and correspond to laser wavelengths ranging from 47.8 to 238.0 /spl mu/m. The pump laser offset frequency was measured for 15 CHD/sub 2/OH FIR laser emissions.

Frequency measurement of acetylene-stabilized lasers using a femtosecond optical comb without carrier-envelope offset frequency control

We have established a frequency measurement system for frequency-stabilized lasers operating in telecommunication wavelength bands, by using a femtosecond optical comb without the need for carrier envelope offset frequency control. This system has been used to measure the frequency of an acetylene-stabilized laser operating at 1542 nm for a period of over 10 hours. The frequency stability of the acetylene-stabilized laser is estimated to be 3x10-12 for a 10-s averaging time, improving toward 1x10-13 after 10000 s. We have measured three acetylene-stabilized lasers, including one commercially available laser, and confirmed that the frequency values are in good agreement (a frequency scatter of 2.1 kHz) with previously measured results reported by different institutes. In addition to the P(16) line of acetylene at 1542 nm, we measured the absolute frequencies of the P(24) line at 1547 nm, the P(1) line at 1534 nm, and the R(5) line at 1530 nm with a view to improving the accuracy of the acetylene frequency atlas. The acetylene-stabilized laser serves as an important optical frequency standard for telecommunication applications.

Coherent multiwave heterodyne frequency measurement of a far-infared laser by means of a femtosecond laser comb

We demonstrate the possibility of using a femtosecond laser to measure with high accuracy the frequency of a far-infrared (FIR) monochromatic source, such as an optically pumped molecular laser, by generating in a suitable mixer a signal in the radio-frequency region at the frequency difference between n steps of a femtosecond comb and the FIR source. All the couples of modes lying a distance of n steps from one another contribute coherently to the heterodyne signal. The technique has been tested up to 670 GHz.

Absolute frequency measurement of an acetylene-stabilized laser at 1542 nm.

The absolute frequency of an acetylene-stabilized laser at 1542 nm is measured at its second harmonic (771 nm) by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. Frequency stability and reproducibility of the acetylene-stabilized laser are evaluated by the femtosecond comb with a H maser as a frequency reference. The absolute frequency of a laser diode stabilized on the P(16) transition of 13C2H2 is determined to be 194 369 569 383.6(1.3) kHz. The acetylene-stabilized laser serves as an important optical frequency standard for telecommunication applications.

Laser frequency measurements and spectroscopic assignments of optically pumped 13CH3OH

A three-laser heterodyne system was used to measure the frequencies of twelve optically pumped laser emissions from 13CH3OH in the far-infrared (FIR) region. These emissions, ranging from 54 to 142 μm, are reported with fractional uncertainties up to ±2×10-7 along with their polarization relative to the CO2 pump. Using the 9P32 and 10R14 CO2 lines, complete spectroscopic assignments for two laser systems were confirmed.

Synchronisation of the radiation frequencyof diode lasers with the mode frequencyof a highly stable femtosecond Ti:sapphire laser

The phase locking of diode lasers to the frequencycomponent (mode) of the output radiation of a highly stablefemtosecond Ti:sapphire laser, resulting in the amplificationof the mode power by several orders of magnitude, is reported. The possibilities of using femtosecond lasers for creationof a new generation of miniature optical clocks and forsynthesis and measurements of absolute laser frequencies arediscussed.

Optical clockworks and the measurement of laser frequencies with a mode-locked frequency comb

Femtosecond laser-frequency comb techniques are vastly simplifying the measurement and synthesis of optical frequencies. A single mode-locked femtosecond laser, with its spectrum broadened by self-phase modulation in a microstructured or tapered nonlinear fiber, can produce millions of sharp laser lines in a precise evenly spaced grid spanning much of the visible and near-infrared spectrum. The absolute frequency of each line is determined by two observable radio-frequency signals. The pulse repetition rate gives the spacing of the comb lines and the rate at which the phase of the lightwave slips, relative to the intensity envelope from pulse to pulse determines the offset frequency by which each line is displaced from a precise integral multiple of the repetition frequency. This offset frequency can be measured most easily if the comb spans more than an optical octave so that one can observe a radio frequency beat note between the second harmonic of the infrared comb lines with the corresponding comb lines at the blue end. Such an optical-frequency synthesizer makes optical oscillations readily countable and provides the long-awaited compact optical clockwork for an all-optical clock.

Absolute frequency measurement of the iodine-stabilized He-Ne laser at 633 nm

The absolute frequency of an iodine-stabilized He-Ne laser at 633 nm stabilized on the i (or a13) component of the 11-5 R(127) hyperfine transition of the 127I2 molecule is measured using a femtosecond optical comb generator and an iodine-stabilized Nd:YAG laser standard at 1064 nm. We link the measured absolute frequency to the current internationally adopted value via frequency intercomparison between JILA and the Bureau International des Poids et Mesures (BIPM), leading to the determination of the absolute frequency of the BIPM-4 standard laser. The resulting absolute frequency fi(BIPM) of the BIPM-4 standard laser is fi(BIPM)=473612214711.9±2.0 kHz, which is 6.9 kHz higher than the value adopted by the Comite International des Poids et Mesures (CIPM) in 1997.

Sub-systems for optical frequency measurements: application to the 282-nm /sup 199/Hg/sup +/ transition and the 657-nm Ca line

We are developing laser frequency measurement technologies that should allow us to construct an optical frequency synthesis system capable of measuring optical frequencies with a precision limited by the atomic frequency standards. The system will be used to interconnect and compare new advanced optical-frequency references (such as Ca, Hg(+ ), and others) and eventually to connect these references to the Cs primary frequency standard. The approach we are taking is to subdivide optical frequency intervals into smaller and smaller pieces until we are able to use standard electronic-frequency-measurement technology to measure the smallest interval.

Optically Pumped Far-Infrared Laser Lines in Hydrazine, Methanol, Heavy Water, and Ammonia: New Laser Lines and Frequency Measurements,

A far-infrared laser cavity designed to favor short-wavelength laser lines was used to generate optically-pumped far-infrared laser radiation. New far-infrared laser lines were discovered in hydrazine, heavy water, ammonia, and several short-wavelength lines previously discovered in methanol were observed. Wavelength, frequency, and relative intensity measurements were performed on laser lines in the wavelength range 42.4 to 253.7 μm. Each far-infrared frequency measurement was obtained by mixing the far-infrared radiation with radiation from two reference CO2 lasers and from a microwave synthesizer in a metal-insulator-metal diode. The pump laser was a high-Q Fabry Perot resonator oscillating on 275 grating-selected laser lines including regular, sequence, and hot band lines.

Optically Pumped FIR Laser Lines from CH3OH: New Laser Lines, Frequency Measurements, and Assignments

We report the identification and characterization of eight new FIR laser lines from methanol (CH3OH) in the range 48.4 to 453.7 μm pumped by sequence and hot bands of a cw CO2laser. Frequency measurements for most of the new FIR laser lines and from previously reported ones were obtained in the range 0.6–6.8 THz with a one-sigma reproducibility of two parts in 107. We propose an assignment of energy levels for two of the new laser lines and for five pumped by 10R(46) previously reported. The high frequency lines with absorption centers outside of the tuning range of the CO2laser pump showed doublets. These were used to evaluate the offsets of the CO2absorption transitions.

計測の信頼性の表現法 不確かさ レーザ波長測定における不確かさ

計測の信頼性の表現法 不確かさ レーザ波長測定における不確かさ

New Optically Pumped FIR Laser Lines and Frequency Measurements from CH3OD

This work reports the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH3OD in the range 42.6 μm to 207.2 μm. A highly efficient CO2 laser was used as the pump laser for an Optically-pumped Fabry-Perot FIR laser. The frequencies of most of the new lines were measured in the range 1.7 to 6.4 THz. Twenty-eight CO2 lines were used as pump lines; nineteen of these had frequencies lower than those previously used to pump CH3OD in a FIR laser. Sixteen of the new FIR lines had absorption transitions which belong to the OD bending vibrational mode.

New FIR Laser Lines and Frequency Measurements of CD 3 OD

The isotopomer of methanol, CD3OD, was optically pumped by a cw C02 laser resulting in 53 new far-infrared (FIR) laser lines. The wavelengths are in the range 42.9 pm to 189.9 pm with the majority below 100 pm. Ten different C02 lines were used for the first time to pump CD3OD yielding new FIR laser lines. Some of the COZ pump lines belong to the hot-bands and sequence-bands of C02 in the 10 pm region. The fiequency was measured for 40 FIR laser lines in the range 1.5 THz to 6.9 THz, 32 of which were new laser lines.

Frequency measurements of saturated-fluorescence-stabilized CO 2 laser lines: comparison with an OsO 4 -stabilized CO 2 laser standard

frequency grid, to test the performance of the saturated fluorescence method for CO2 laser frequency stabilization. The Allan variance for the saturated-fluorescence-stabilized CO2 laser reached 60 Hz for an integration time of 300 s. We also performed three absolute measurements of CO2 laser frequencies stabilized by the saturated fluorescence method, with a sub-kHz accuracy. We obtained a 1.7 kHz redshift of the CO2 saturated fluorescence lines, which we attribute essentially to pressure. This is in contradiction with the previous observation of a blueshift [K.L. SooHoo, C. Freed, J.E. Thomas, H.A. Haus: Phys. Rev. Lett. 53, 1437 (1984)]. Furthermore, significant deviations of the measured frequencies from the data of Maki et al. [A.G. Maki, C.-C. Chou, K. Evenson, L.R. Zink, J.T. Shy: J. Mol. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO2 frequency grid.

New far-infrared laser lines and frequency measurements of acetaldehyde and vinyl fluoride

Eight far-infrared laser lines have been obtained by optically pumping acetaldehyde (CH3CHO) and nine by pumping vinyl fluoride (CH2CHF) with a cw CO2 laser. The far-infrared laser structure used a metal-dielectric waveguide cavity. This is the first reported observation of four of the laser lines in acetaldehyde. In this work, we measure the frequency, optimum pressure of operation, relative intensity, relative polarization, and pump offset from CO2 laser-line center.

Laser Lines and Frequency Measurements of Fully Deuterated Isotopomers of Methanol

Fully deuterated isotopomers of methanol (12CD3OD and 13CD3OD) were optically pumped with a CO2 laser. Five new far-infrared laser lines were discovered in 12CD3OD and 25 in 13CD3OD in the range 43.697 to 719.426 μm. The frequencies of these new and some previously reported laser lines, the pump offset, the relative polarization, the relative intensity, and the optimum pressure of operation were measured.

High resolution spectroscopy of 13CH 3OH around the 10R(20) CO 2 laser emission: New FIR laser lines, frequency measurements and assignments

We investigated the IR absorption spectrum of 13CH 3OH around the frequency of the 10R(20) CO 2 laser line. We found two absorption lines which can be excited by 10R(20) and studied the FIR laser emissions excited by this pump line using a waveguide CO 2 laser of 300 MHz tunability. We report two new FIR laser lines of large offset, not previously observed due to their weakness and closeness to other stronger lines. We measured the frequencies of five FIR laser lines for the first time by an accurate heterodyne technique and present the complete assignments of the IR-FIR laser systems relative to this pump line. Furthermore we present new frequency values for two FIR laser lines whose frequencies had been previously wrongly measured.