We have developed a transportable laboratory sample of a photonic microwave oscillator (PMO) based on an optical frequency standard (He–Ne/CH4 laser, λ = 3.39 μm) and an optical frequency divider (femtosecond Er-doped fiber laser, λ = 1.55 μm). The radiation spectrum of the oscillator is a comb of frequencies in the range from 1 to 10 GHz. A relative Allan deviation is demonstrated to be less than 1 × 10–14 at averaging times of 1–1000 s for spectrum components with frequencies of 1.0 and 9.2 GHz. The choice of frequencies is determined by the prospect of using the designed PMO as a master oscillator in Cs/Rb fountain-type time and frequency standards. At averaging times from 1 to 200 s, the resulting frequency instability is lower than that of commercial hydrogen masers. The spectral power density of phase noise for the specified frequencies at offsets of less than 100 Hz from the carrier frequency is significantly lower than that of the best electronic and optoelectronic oscillators. The designed oscillator seems useful for problems of fundamental time and frequency metrology, development and phase calibration of precision microwave equipment, coherent radar detection, monitoring, and communications, as well as in cases requiring relatively long (10–2–103 s) accumulation of a weak signal in the region of small carrier frequency offsets and/or synchronization holding of distributed sources.

The results on intensity noise and repetition frequency stability measurements for a passively mode-locked Cr:ZnSe laser pumped by a thulium-doped fiber laser at a wavelength of 1.94 pm are presented. The stability parameters and intensity noise are compared for three different generation regimes of the Cr:ZnSe laser. The laser operated at a repetition rate of 129.5 MHz and a central wavelength of 2.45 pm.

The results on intensity noise and repetition frequency stability measurements for a passive mode-locked Cr:ZnSe laser pumped by a thulium-doped fiber laser at a wavelength of 1.94 µm are presented. The stability parameters and intensity noise are compared for three different generation regimes of the Cr:ZnSe laser. The laser operated at a repetition rate of 129.5 MHz and a central wavelength of 2.45 µm.

A radio-optical synthesiser intended for operation in a radio-frequency master oscillator with an optical lie-Ne/CH4 frequency standard (lambda = 3.39 mu m) is developed on the basis of a femtosecond erbium-doped fibre laser. The synthesiser generates equidistant harmonics in the frequency range of 1-10 GHz with stability determined by the optical frequency standard. A stable supercontinuum spectrum is formed in the range around 1.06 mu m, which provides stable 24-hour operation of the synthesiser and is important for practical applications in off-laboratory conditions. A direct comparison of the output frequencies of two synthesisers shows that the up-grade of the fibre laser and detection system of femtosecond pulses results in the synthesiser intrinsic instability of 5 x 10(-15) at the averaging time of 1 s. Such a value is by an order of magnitude less than that obtained in our earlier works.

We have demonstrated a microwave master oscillator operating on optical principles and based on a He – Ne/CH4 optical frequency standard (λ = 3.39 μm) and femtosecond fibre laser system ( λ = 1.54 μm). The output signal spectrum of the oscillator has the form of an equidistant frequency comb in the range 60 MHz to 10 GHz with a 60-MHz step. Comparison of the frequencies of two master oscillators shows that the short-term output frequency instability for the comb components in the range 0.8 – 1.5 GHz is under 1 × 10−14 at an averaging time of 1 s. We have tested microwave signals from the oscillator using apparatus in the reference facility at the State Time and Frequency Service, All-Russia Research Institute of Physical and Radio Engineering Measurements. A signal at a nominal frequency of 100 MHz synthesised from one comb component was compared to signals from two hydrogen masers with enhanced short-term stability in the reference facility. The short-term frequency stability of the synthesised signal has been shown to be twice better than the stability of the masers and to be limited by the intrinsic instability of the commercial synthesiser of a 100-MHz nominal frequency. Our experiments confirm that the proposed microwave optical master oscillator is potentially attractive for use in systems with increased requirements for short-term frequency stability, in particular in time and frequency fountain references.

Two microwave reference oscillators based on a He-Ne/CH 4 optical frequency standard (λ = 3.39 μm) and femtosecond Er fiber laser (λ = 1.55 μm) optical-to-microwave frequency divider were created. The measurements have demonstrated short term frequency instability (Allan deviation) of the output microwave signal at 1.5 GHz at the level of 1×10 -14 (τ = 1 s). Interrogative oscillator with such stability is attractive for application in Cs and Rb atomic fountains.

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 mu m produced a broadband output of 200 mW at 2.6 mu m with an incident power slope efficiency of 6.4%.

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 low repetition rate deviation in the averaging time interval 1-1·10 3 s, a low relative intensity noise -125 dBc/Hz, 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.

We have developed a low-noise optical-to-microwave frequency divider based on a femtosecond erbium fibre laser. The source of an optical signal was a He - Ne/CH4 frequency standard. Comparison of two frequency dividers showed that the relative instability of output microwave signals, introduced by the dividers, is 10(-14) - 10(-16) for the averaging time tau = 1 - 100 s. The instability obtained corresponds to the requirements imposed on interrogative oscillators for time and frequency standards based on Cs or Rb atomic fountains.

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 mu m produced a broadband output of 280 mW at 2.6 mu m 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 mu m with a resolution of 10 nm and an output power up to 55 mW.

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.

Solid-state cw Cr2+ : ZnSe laser has been used for Doppler-free spectroscopy of lines of the vibrational — rotational v1 + v4 band of methane. Saturated-dispersion resonances on the components of the R(2) line near λ = 2.36 mm are revealed. The parameters of the saturated-dispersion resonance obtained upon cooling intracavity methane cell to a temperature of 77 K confirmed good prospects of developing an optical master oscillator with a high (10-15 - 10-16) short-term frequency stability based on a Cr2+ : ZnSe/CH4 laser.

The mid-IR cw tunable solid state Cr2+:ZnSe laser with spectral density of intrinsic frequency noise less than 30 mHz/Hz(1/2) was created. The laser was applied for sub-Doppler spectroscopy of (v(1)+v(4)) vibrational-rotational band of methane and narrow resonances of saturated dispersion at lambda = 2.36 mu m were demonstrated for the first time. Characteristics of resonances and low frequency noise of the laser pave the way to a short-term frequency stability at the level of 10(-15)-10(-16).

An optically pumped cw laser on a Cr2+:ZnSe crystal with a tunable (in the range of 2.3-2.6 mu m) wavelength, operating with generation of two axial modes, has been developed. It is shown that the minimum laser frequency-noise spectral density does not exceed 0.03 Hz Hz(-1/2). Application of this laser in problems of Doppler and Doppler-free spectroscopy makes it possible to detect spectral absorption lines of gases with sensitivities of 5 x 10(-12) and 2 x 10(-10) cm(-1), respectively (averaging time tau = 1 s). Having stabilised this laser with respect to the Doppler-free resonances of saturated dispersion of methane molecule, one can obtain a short-term frequency stability of 10(-15)-10(-16) (tau = 1 s).

Continuous tuning of the lasing wavelength from 2350 to 3450 nm in the cw Cr 2+ :CdSe laser is demonstrated. It is shown that the laser efficiently operates at a wavelength of 3.28 µ m, 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.

An optical clock based on an Er 3+ fiber femtosecond laser and a two-mode He–Ne/CH 4 optical frequency standard ( λ =3.39 μm) is realized. Difference-frequency generation is used to down convert the 1.5-μm frequency comb of the Er 3+ femtosecond laser to the 3.4-μm range. The generated infrared comb overlaps with the He–Ne/CH 4 laser wavelength and does not depend on the carrier–envelope offset frequency of the 1.5-μm comb. In this way a direct phase-coherent connection between the optical frequency of the He–Ne/CH 4 standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock is measured against a commercial hydrogen maser. The measured relative instability is 1×10 −12 at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift of the He–Ne/CH 4 optical standard is dominant.