Roman L. Shubochkin

Selective laser excitation and inhomogeneous band broadening of Nd3+ ions in disordered CaF2-YF3 crystals

We have investigated the structure of inhomogeneously broadened absorption and fluorescence bands of Nd 3+ ions in disordered yttrofluorite crystals by selective laser excitation at T = 77 K. Measurements of the Stark splittings of 4 I 9/2 multiplet for two groups of optical centers were obtained and indicate a linear change of Stark level energies for the two groups of centers as the excitation frequency was changed. The dispersion of the Stark splittings displays a weak correlation of energies between the resonant transition and nonresonant ones for both center groups. Finally, an analysis of the spectra of nonresonant laser excitation at several fluorescence lines for the two groups of centers has also allowed us to observe energy levels in the high lying 4 G 5/2 , 2 G 7/2 multiplets.

Pulsed actively modelocked pulsed laser based on Nd3+ -doped disordered garnet and LiF:F2 crystal

It is well known that Neodymium glasses are widely used as active media in powerful picosecond laser systems. However, low thermal conductivity of glasses with broad bands of absorption and luminescence limits their use in pulsed lasers with high repetition rate. At the same time, disordered crystals having broad inhomogeneous bands of active ions and combining properties of both glasses and crystals may be reckoned as active media for ultrashort pulse lasers with high repetition rate. It has been shown recently that Calcium-Niobium-Gallium disordered garnet crystals doped with Nd3+ ions (CNGG:Nd3+) with broad inhomogeneous spectrum of amplification are prospective active media for the laser generation of powerful ultrashort pulses1 . In ref. 1 a passively mode-locked (PML) with a saturable dye absorber CNGG:Nd3+ laser generated trains of 7 ps pulses at a repetition rate of 0.3 Hz. To eliminate a liquid absorber and get an all solid state laser configuration one can mode-lock a laser actively with a crystalline modulator. But while the active mode-locking (AHL) technique may lead to the generation of high stable and reproducible laser pulses with a high repetition rate, its main drawback in comparison with the PML is relatively large pulse duration, in particular, at lamp pumping. Nevertheless, the use of a highly efficient LiNb03 acousto-optic modulator (AOMJ 2 •3 in a glass laser has led to the generation of pulses with duration of 13 ps 4 , so the operation of a laser on disordered crystals doped with Nd 3+ ions actively mode-locked with the AOM is a matter of considerable interest. It is known also that LiF crystals with F 2 color centers are successfully employed for passive Q-switching6 and the application of these crystals as passive Qswitchers to AHL lasers may give sufficient rise to pulse peak power. The aim of this work is to investigate the operation of actively mode-locked with LiNb03 AOM laser on a Calcium-Lithium-Niobium-Gallium disordered garnet crystal doped with Nd3+ ions (CLNGG:Nd3+) and a LiF:F2 passive Q-switch.

Polarization phase nonreciprocity in all-fiber single-mode ring interferometers

A polarization model is used to experimentally study polarization phase nonreciprocity in all-fiber ring interferometers. The possibility of measuring the extinction ratios of fiber polarizers by means of fiber optic ring interferometers is demonstrated. The maximum extinction ratio values obtained are 84 and 86 dB.

Nonreciprocal phase bias in a fiber gyro with imperfect spatial mode filters

Nonreciprocal phase biases were experimentally investigated in a single-mode fiber-optic Sagnac type gyro with nonsingle-mode spatial filters. A good correlation between the nonreciprocal phase biases in the fiber-optic ring interferometer and the intensities of the higher order core modes and cladding modes in the fibers used as spatial filters was obtained. A new experimental method for determination of the optimum spectral range between the source wavelength in the gyro and the effective cutoff wavelength of the single-mode spatial filter was proposed.