The process of luminescence excitation of negatively charged NV centers in diamond is investigated by the up-conversion method with a femtosecond resolution. Our experimental technique allowed us to register that NV- center luminescence starts in the whole 600-800 nm spectral range in a time not exceeding 30 fs after excitation by the second harmonic of the femtosecond ytterbium laser. We have established that there is no time-dependent Stokes shift in the luminescence spectrum of the NV- center, which could be caused by relaxation of coherent phonon excitation. A theoretical model of NV- center describes the dynamics of the luminescence spectrum due to non-resonant Rabi oscillations of color center polarization and provides a quantitative agreement with experimental data. Thus, NV- center is a promising source of quantum light with ultrafast formation of luminescence.

Laser generation of NV‐centers in diamond with pulse energy up to 48 μJ and efficiency about 1% is performed. Also, we observe strong influence of low‐intensity short‐wavelength irradiation on pulse energy: in presence of this irradiation the pulse energy increased by factor up to 3.5. Additionally, we make an attempt to estimate theoretically our samples’ gain coefficient. GA. Laser generation with pulse energy up to 48 μJ and efficiency about 1% is performed using diamond, containing NV‐centers, as laser active element. Diamond crystal was pumped by 532 by 532 nm radiation. Also, strong influence of low‐intensity short‐wavelength irradiation on pulse energy is observed: in presence of this irradiation the pulse energy increased by factor up to 3.5.

We propose a new algorithm based on the Fourier transform with matched non-linear frequency modulation for processing femtosecond laser ranging data. The algorithm allows us to compensate for both the influence of the third-order dispersion in the fiber-based dispersive Fourier spectrometer and the influence of imbalanced second- and third-order dispersions in the interferometer. Computer simulations and experimental results show that the proposed algorithm significantly increases the accuracy of measuring the position of an object at larger displacements than the well-established non-linear time stretching.

Using numerical simulation methods, we study the features of the light field dynamics during filamentation under conditions of anomalous group velocity dispersion of mid-IR femtosecond pulses focused by an axicon into lithium and calcium fluoride crystals. The emergence of singularities with a wavefront discontinuity, which do not appear in a beam focused by a parabolic lens, is found. Wavefront discontinuities form near minima of the light field intensity. A strictly periodic change in spatial and energy parameters is demonstrated—the “breathing” of a light bullet formed in an axicon-focused beam as it propagates in a medium with material dispersion. A change in the oscillation period of the light bullet core with a change in the carrier wavelength is independent of the radiation focusing method and coincides with the results of analytical estimates that are calculated for a Gaussian wave packet focused by a parabolic lens with an undistorted harmonic carrier.

The spectrum transformation of a femtosecond wave packet during filamentation in fused silica under conditions of normal, zero, and anomalous group velocity dispersion has been investigated using numerical simulation methods. It has been shown that the generation of plasma, which induces phase modulation of the light field, leads to rapid anti-Stokes spectral broadening. It has been established that the short-wavelength shift of the broadband supercontinuum spectrum is significantly greater under anomalous group velocity dispersion compared to normal and zero dispersion. The influence of the wave packet energy on the dynamics of spectral broadening has been examined. Estimates of the numerical scheme have been obtained based on dispersion analysis of the broadband supercontinuum propagation process in the medium.

The photoluminescence spectra of two synthetic diamond samples containing 1-10 ppm NV centers and 100-200 ppm substitutional nitrogen were studied under optical pumping at 532, 560, and 575 nm. At pump intensities less than 0.5-1.0 MW/cm2, a vibronic photoluminescence band of NV- centers in the negative charge state was observed. With an increase in the pump intensity above 0.5-1.0 MW/cm2, a superluminescence band was observed on the long-wavelength shoulder of the phonon wing in the range 700-760 nm. The intensity of superluminescence band increased with increasing pump intensity. It is shown that the position of the superluminescence band with maxima in the range 715-720 nm is unchanged at all of optical pump wavelengths.

The generation dynamics of plasma and color centers in a LiF crystal under conditions of multipulse filamentation by mid-IR femtosecond laser radiation has been experimentally and numerically investigated. A model describing the dynamic competition between the excitonic and electron–hole channels during saturation of the concentration of color centers (CCs) in LiF under exposure to multipulse femtosecond radiation is developed. The competition between the excitonic and electron–hole channels of CC generation is physically interpreted.

Analytically, numerically and experimentally the effect of the material dispersion of the dielectric on the oscillation period of the electric field in a single cycle wave packet (a light bullet) is investigated. Wave packet oscillates due to periodic phase shift between the envelope of the pulse and its carrier wave. The influence of nonlinear shift of phase and group velocities on the analytical estimation of the oscillation period of a light bullet with a different carrier wavelength is considered. Keywords: group velocity, phase velocity, material dispersion, absolute phase shift, single-cycle wave packet, filamentation, light bullet.

For the first time, the formation of a mid-IR single-cycle light bullet during propagation of a femtosecond laser pulse with an arbitrary initial polarization ellipticity of the light field has been experimentally and numerically investigated. It is established that the polarization ellipticity determines the effect of the carrier-envelope phase on the nonlinear-optical interaction of the light bullet with the medium.

In the context of the NV− diamond laser creation (Savvin and Dormidonov in Nat. Commun. 12:7118, 2021), an urgent task is to determine the characteristics of diamonds that can affect laser generation. This work is aimed at investigating the mechanisms of the creation of superluminescence in diamond under the action of optical pumping by the second harmonic of the Nd:YAG laser (λ = 532 nm). It was found that when the HPHT diamond is irradiated by 532 nm radiation with an intensity above ~ 2.0 MW/cm2, a nonlinear intensity increasing in the spectral region 700–750 nm is manifested against the background of the spontaneous photoluminescence spectrum, which, with a further pumping intensity increase turns into a pronounced peak of superluminescence with a maximum of about 718 nm. An increase in the pumping intensity from 2.7 to 46 MW/cm2 widened this peak at half-maximum from 13 to 19 nm. At high levels of pumping intensity, nonlinear pumping radiation absorption and accumulation of NV centers in the excited state were detected. The position of the photoluminescence band was calculated depending on different values of the population inversion density of the color centers, taking into account the diamond's own absorption spectrum. The calculation results are close to the experimental data.

A nanosecond diode-pumped Nd:YAG laser with pulse repetition rate up to 1 kHz without liquid cooling of the of the active media has been demonstrated. The laser provided the following parameters: pulse width 8 ns (FWHM), pulse energy 10 mJ at 1064 nm and up to 4 mJ at 532 nm.

A light bullet (LB) is a wave packet of a few optical cycles that is extremely compressed in space and time, which is formed in the bulk transparent dielectric during femtosecond filamentation under anomalous group velocity dispersion. We demonstrate for the first time that the carrier-envelope phase shift during propagation of a near single-cycle LB causes synchronous oscillations of the spatial, temporal and energy parameters of its core with the period decreasing with increasing carrier wavelength. When analyzing the structure of color centers and induced plasma channels in fluorides, it was experimentally found that LB parameter oscillations lead to a periodic change in the nonlinear optical interaction with the dielectric.

A theoretical and experimental study of the formation and dynamics of a single-cycle mid-infrared wave packet during filamentation under anomalous group velocity dispersion condition is carried out.

Analytically, numerically and experimentally the effect of the material dispersion of the dielectric on the oscillation period of the electric field in a single cycle wave packet (a light bullet) is investigated. Wave packet oscillates due to periodic phase shift between the envelope of the pulse and its carrier wave. The influence of nonlinear shift of phase and group velocities on the analytical estimation of the oscillation period of a light bullet with a different carrier wavelength is considered.

We use time-resolved spectral probing to study the dynamics of transformation of the optical properties of a nonlinear medium during formation and propagation of an extremely compressed mid-IR femtosecond wave packet in calcium fluoride. Broadening, attenuation and distortion of the probe pulse spectrum have been experimentally observed varying the delay time of the probe pulse relative to the pump. By solving the unidirectional pulse propagation equation that describes propagation and filamentation of a pump pulse in a calcium fluoride crystal we determine temporal changes of the refractive index and absorption coefficient induced by an extremely compressed wave packet. A mechanism of the observed broadening and breakup of the probe pulse spectrum is proposed.

A method based on recording of the light-field amplitude of the pulse in the spatial structure of induced plasma channels or tracks of color centers in a transparent dielectric is proposed to determine the duration and phase of intense mid-infrared single-cycle femtosecond pulses. The track structure is recorded and detected in a single interaction of the studied pulse with the medium in which it is nonlinearly compressed. The modulation depth of the track profile is uniquely related to the number of oscillations of the light field under the envelope of the propagating pulse, which allows determining the pulse duration. The estimated duration of the mid-infrared light bullet in LiF is less than 10 fs. The duration of the laser bullet determined by the proposed method is compared with autocorrelation and cross-correlation measurements.

A light bullet is an extremely compressed in space and time wave packet of a few optical cycles, which is formed in the bulk transparent dielectric during femtosecond filamentation under anomalous group velocity dispersion. The effect of a carrier-envelope phase on the dynamics of the light bullet was demonstrated for the first time. The carrier-envelope phase change during a light bullet propagation causes synchronous oscillations of its spatial, temporal and energy parameters with the period decreasing with increasing carrier wavelength. The oscillation period of parameters of a near-single cycle light bullet with broadband frequency-angular spectrum can be described by an analytical estimate written for a Gaussian pulse with a harmonic carrier wave. When analyzing the structure of color centers and induced plasma channels in fluorides, it was experimentally found that light bullet parameters oscillations lead to a periodic change in its nonlinear optical interaction with the dielectric.

The formation of a single-cycle light bullet during the propagation of a mid-infrared femtosecond laser pulse with an arbitrary initial ellipticity of the light field polarization in lithium fluoride is studied for the first time experimentally and numerically. It is found that the ellipticity of polarization determines the effect of the absolute phase of the carrier frequency on the nonlinear optical interaction of the light bullet with the medium. The transition from the linear to circular polarization is accompanied by the disappearance of modulation of the density of color centers induced in lithium fluoride by the single-cycle light bullet. This occurs because the magnitude of the light field strength in the case of circular polarization always coincides with the maximum of the pulse envelope and the effect of “breathing” of the light bullet in the isotropic medium is fundamentally absent.

The state of research of the light bullets (LB) formation in the process of femtosecond laser pulse filamentation is presented. LB is a near single-cycle wave packet that is formed in the result of the light field self-organization in a nonlinear dispersive medium under matched spatiotemporal radiation self-compression in the regime of anomalous group-velocity dispersion (GVD). The formation of each LB is accompanied by the generation of a discrete portion of supercontinuum (SC) in the anti-Stokes region. LB is a short-lived robust object with parameters determined by fundamental properties of the medium and the laser pulse central wavelength.