S.N. Bagayev

Absolute frequency measurement of the In + clock transition with a mode-locked laser

The absolute frequency of the In(+) 5s(2) (1)S(0)5s5p (3)P(0) clock transition at 237 nm was measured with an accuracy of 1.8 parts in 10(13). Using a phase-coherent frequency chain, we compared the (1)S(0)(3)P(0) transition with a methane-stabilized HeNe laser at 3.39 microm, which was calibrated against an atomic cesium fountain clock. A frequency gap of 37 THz at the fourth harmonic of the HeNe standard was bridged by a frequency comb generated by a mode-locked femtosecond laser. The frequency of the In(+) clock transition was found to be 1,267,402,452,899.92 (0.23) kHz, the accuracy being limited by the uncertainty of the HeNe laser reference. This result represents an improvement in accuracy of more than 2 orders of magnitude over previous measurements of the line and now stands as what is to our knowledge the most accurate measurement of an optical transition in a single ion.s.

Frequency Comparison and Absolute Frequency Measurement of I2-stabilized Lasers at 532 nm

We present a frequency comparison and an absolute frequency measurement of two independent I2-stabilized frequency-doubled Nd:YAG lasers at 532 nm, one set up at the Institute of Laser Physics, No vosibirsk, Russia, the other at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. The absolute frequency of the I2-stabilized lasers was determined using a CH4-stabilized He-Ne laser as a reference. This laser had been calibrated prior to the measurement by an atomic cesium fountain clock. The frequency chain linking phase-coherently the two frequencies made use of the frequency comb of a Kerr-lens mode-locked Ti:sapphire femtosecond laser where the comb mode separation was controlled by a local cesium atomic clock. A new value for the R(56)32-0:a10 component, recommended by the Comite International des Poids et Mesures (CIPM) for the realization of the metre [1], was obtained with reduced uncertainty. Absolute frequencies of the R(56)32-0 and P(54)32-0 iodine absorp tion lines together with the hyperfine line separations were measured.

Monoclinic Tungstates KDy(WO 4) 2 and KLu(WO 4) 2 - New χ( 3)-Active Crystals for Laser Raman Shifters

Efficient high-order Stokes and anti-Stokes generation in the visible and near infrared (NIR) in monoclinic KDy(WO4)2 and KLu(WO4)2 1aser host crystals by stimulated Raman scattering (SRS) and Raman-induced four-wave mixing (RFWM) were observed at 300 K for the first time in the single-pass geometry under picosecond excitation. All scattering components were identified and connected with the SRS-active vibration modes of these tungstates.

Tunable single-frequency diode-pumped Nd:YAG ring laser at 1064/532 nm for optical frequency standard applications

We demonstrate a simple design for an infrared/green tunable unidirectional traveling-wave Nd:YAG laser consisting of only two intracavity components: a Nd:YAG gain medium and a KTP doubling crystal. The spectral linewidth of less than 10 kHz, and a widely tunable (∼400 GHz) green output up to 250 mW make this laser convenient for spectroscopy and frequency stabilization. We also demonstrate the results of long-term frequency stability of our laser stabilized onto the hyperfine luminescent peaks of molecular iodine.

Absolute frequency measurement of the 115In+ 5S2 1S0-5S5p 3P0 transition

Abstract We have measured the absolute frequency of the 115 In+ 5s 2 1 S0–5s5p 3 P0 clock transition at 236.5 nm with an accuracy of 3.3 parts in 1011. For this measurement, a frequency synthesis chain was used which links the indium clock transition to a methane-stabilized He–Ne laser at 3.39 μm and a Nd:YAG laser at 1064 nm whose second harmonic was locked to a hyperfine component in molecular iodine. A frequency gap in the chain of 1.43 THz at 850 nm was bridged with the help of an optical frequency comb generator. The frequency of the 115 In+ clock transition was determined to 1 267 402 452 914 (41) kHz, where the accuracy is limited by the uncertainty of the iodine reference. This measurement represents an improvement of more than three orders of magnitude in accuracy compared to previous measurements of the line.

Femtosecond continuously tunable second harmonic generation over the entire-visible range in orthorhombic acentric Gd2(MoO4)3 crystals

Second harmonic generation over the entire visible range in Nd3+ doped and undoped Gd2(MoO4)3 crystals under ultrashort hypercontinuum pumping is presented. The continuous tuning ranges from 487 to 790 nm in a single crystal.

Coherent combining of femtosecond pulses parametrically amplified in BBO crystals.

We report on the first experimental realization of coherent combining of parametrically amplified femtosecond pulses. The proposed and implemented two-loop active stabilization system allows us to achieve 110 as relative timing jitter between combined pulses, which is necessary for efficient coherent beam combining. In each channel of the two-channel laser setup, pulses were parametrically amplified in β-BaB2O4 (BBO) crystals to 50 μJ energy, compressed to 49 fs duration, and then coherently combined with efficiency as high as 97%. Currently, it is the shortest duration of amplified pulses for which coherent combining is demonstrated.

Tunable single-frequency diode-pumped Nd:YAG ring laser at 946 nm

A simple design for a quasi-three-level diode-pumped tunable unidirectional traveling-wave Nd:YAG laser operating at 946 nm is demonstrated using a cavity consisting of two intracavity components, a Nd:YAG gain medium, and a KTP crystal. 280 GHz of tuning up to 160 mW of single-frequency output has been obtained by inserting a temperature controlled birefringent filter into the cavity.

Coherent combining of multimillijoule parametric-amplified femtosecond pulses

We report on the first experimental realization of the coherent combining of multimillijoule parametric-amplified femtosecond pulses. An original two-channel laser system based on parametric amplification in β-BaB2O4 and LiB3O5 crystals was created. High-contrast laser pulses, with up to 100 mJ of energy and with a pulse duration of 23 fs, were generated in both channels. An original setup for active timing-jitter stabilization was developed. It allowed reduction of the relative timing jitter of the amplified pulses to 40 as, which enabled coherent combining with an efficiency as high as 95%. At the present time, this work demonstrates coherent combining of femtosecond pulses with both the highest energy and the shortest pulse duration.

Orthorhombic (LiNbGeO5): efficient stimulated Raman scattering and tunable near-infrared laser emission from chromium doping

Abstract The structural, optical, spectroscopic, and laser properties of pure and chromium-doped lithium–niobium germanate (LiNbGeO 5 ) single crystals are discussed in this paper. Efficient stimulated Raman scattering (SRS), investigated with the one-micron fundamental and second harmonic wave of a picosecond Nd 3+ :Y 3 Al 5 O 12 laser, reveals the potential of this new cubic non-linear susceptible ( χ (3) ) optical material for realizing effective solid state Raman shifters. The data are analyzed and compared with spectroscopic data from spontaneous Raman scattering. Pulsed tunable laser action of chromium-doped LiNbGeO 5 crystals was demonstrated in the spectral range between 1.3 and 1.52 μ m at cryogenic temperature and around 1.4 μ m at room temperature. Due to its excellent crystalline and optical properties, LiNbGeO 5 is a promising material for tunable near-infrared lasers with integrated frequency converters.