Mikhail A. Gubin

Femtosecond Er3+ Fiber Laser for Application in an Optical Clock

The main elements needed for the realization of a compact femtosecond methane optical clock are developed and studied. A femtosecond laser system on an Er3+ fiber (λ = 1.55 μm) contains an oscillator, an amplifier, and a fiber with a relatively high nonlinearity in which the supercontinuum radiation is generated in the range 1–2 μm. In the supercontinuum spectrum, the fragments separated by an interval that is close to the methane-optical reference frequency (λ = 3.39 μm) exhibit an increase in intensity. The supercontinuum radiation is converted into the difference frequency in a nonlinear crystal to the range of the methane-reference frequency (λ = 3.3–3.5 μm), so that the frequency components of the transformed spectrum have sufficient intensities for the subsequent frequency-phase stabilization with respect to the methane reference. A system that stabilizes the pulse repetition rate of the femtosecond Er3+ laser is also employed. Thus, the repetition rate of the ultrashort pulses of the femtosecond fiber laser is locked to the methane reference. The pulse repetition rate is compared with the standard second. Thus, the scheme of an optical clock is realized.

Near-infrared saturation spectroscopy of cesium molecules using a diode laser

We study sub-Doppler saturation resonances at cesium molecular transitions in the absorption band B1Πu ← X1∑g+ near 780 nm by using a commercial diode laser. The saturation power is measured as low as 5.7 mW with the laser beam diameter of 0.1 cm. Optical saturation is associated with the optical pumping of molecular ground-state levels. The long relaxation time of ground-state levels could attract interest to electromagnetically induced transparency and quantum state memory in the molecular gas. We propose to use the molecular transitions as references for doubled-frequency sources in the communication band around 1550 nm.

Observation of electromagnetically induced transparency in cesium molecules

We have studied electromagnetically induced transparency (EIT) in diatomic cesium molecules in a vapor cell by using tunable diode lasers. We have observed a sub-natural Λ-resonance in absorption molecular band B1Πu − X1Σg+ at different cesium vapor pressures. The width of the EIT resonance shows a linear dependence on a cesium vapor pressure.We have studied electromagnetically induced transparency (EIT) in diatomic cesium molecules in a vapor cell by using tunable diode lasers. We have observed a sub-natural Lambda-resonance in an absorption molecular band at different cesium vapor pressures. The width of the EIT resonance shows a linear dependence on cesium vapor pressure. Narrow Lambda-resonances in molecules can be used as frequency references for femtosecond laser frequency combs.

Continuous-wave broadly tunable diode laser array-pumped mid-infrared Cr2+:CdSe laser

We demonstrate the operation of a room-temperature, solid-state, broadly tunable Cr-doped CdSe single-crystal continuous-wave laser. Longitudinal pumping with a continuous-wave diode laser array at 1.94 μm produced a broadband output of 280 mW at 2.6 μm with an incident power slope efficiency of 12%. With an intracavity Brewster-cut CaF2 prism, we tuned the Cr2+:CdSe laser from 2.45 to 3.06 μm with a resolution of 10 nm and an output power up to 55 mW.

Stable Similariton Generation in an All-Fiber Hybrid Mode-Locked Ring Laser for Frequency Metrology

Ultrashort pulse lasers constitute an important tool in the emerging field of optical frequency metrology and are enabling unprecedented measurement capabilities and new applications in a wide range of fields, including precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. We demonstrate the generation of stable 127-fs self-similar pulses at a central wavelength of 1560 nm with 7.14-mW average output power. Similariton lasers have a low repetition rate deviation in the averaging time interval 1-1·103 s, a low relative intensity noise -120 dBc/Hz (30 Hz to 10 kHz), a narrow single comb line width of 32 kHz, and high reliability. Thus, such lasers are highly promising for further development of the stabilized combs and open up a robust and substantially simplified route to synthesizing low-noise microwaves.

Testing of Cr:ZnSe Laser with Intracavity Methane Cell in 77-300 K Temperature Range

The mid-IR cw tunable solid state two-mode Cr²⁺:ZnSe laser with intracavity methane cryocell was developed. The laser was applied for sub-Doppler spectroscopy of (υ₁+υ4) vibrational-rotational band of methane and observation of narrow resonances of saturated dispersion at λ = 2.36 μm. The new technique of low pressure methane gas cooling was used instead of liquid nitrogen “jacket” design applied in our previous work. Parameters of saturated dispersion resonances were estimated in 77-300 K temperature range. The experiments confirmed that laser with the new “dry cooled” methane cell has prospectives for reaching a short-term frequency stability at the level of 10^-15-0^-16 and can be used as a compact device.

Tunable single-frequency CW Cr2+:CdSe laser

Continuous tuning of the lasing wavelength from 2350 to 3450 nm in the cw Cr2+:CdSe laser is demonstrated. It is shown that the laser efficiently operates at a wavelength of 3.28 µm, which is promising for the methane optical frequency standard. The single-frequency mode of the laser with a lasing linewidth not exceeding 60 MHz is implemented in this spectral range.

Tunable CW Solid-State Mid-IR Cr 2+ :CdSe Single Crystal Laser with Diode Laser Array Pumping

We demonstrate the first Cr2+:CdSe single crystal laser with diode laser array pumping. Laser efficiency of 12% with output power of 280 mW was obtained. Tunable CW operation was observed in 2450 - 3060 nm range.

Variable spectral filter based on optically saturated selective reflection

We have studied the selective reflection from glass-rubidium vapor interface at a large incidence angle in pump-probe experiment. The linear reflectivity can be more than 0.9 in a narrow spectral range (several GHz) at the blue side of the atomic resonance. The effect can be called the reduced total selective reflection. The reflectivity has been decreased two times due to the optical saturation. The obtained results can be used to develop a variable optical filter or optical switcher. Our estimations show that switching time can be less than the natural lifetime of the excited state. We suggested a multi-reflection scheme to increase the contrast of the variable spectral filter.

Diode array-pumped mid-infrared cw Cr2+:CdSe laser

The operation of a room-temperature, solid-state, Cr-doped CdSe continuous-wave laser is demonstrated. Longitudinal pumping with a continuous-wave diode laser array at 1.94 µm produced a broadband output of 200 mW at 2.6 µm with an incident power slope efficiency of 6.4%.