Marin N. Nenchev

Interference wedge properties relevant to laser applications: transmission and reflection of restricted light beams

The optical properties of the interference wedge are analysed for the case of restricted laser beam illumination. By further development of Brossels method, equations describing this case are derived and used to calculate the reflected and transmitted beam profiles for typical intracavity laser beam diameters (0.2–0.6 mm) for Gaussian and uniform intensity distributions. In particular, the experimentally observed formation of bright fringes outside the beam impact area at resonant wavelengths is explained. some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.

Improved passive self-injection locking method for spectral control of dye and Ti:Al2O3 lasers using two-step pulse pumping

Abstract An improved passive self-injection locking (PSIL) method for the spectral control of dye and Ti:Al 2 O 3 lasers using two-step pulse laser pumping is reported (theoretically, experimentally). By this pump technique, the typical unwanted free lasing which occurs in the non-selective cavity at high pump level is reduced by a few orders of magnitude compared with the standard PSIL application. This combined approach ensures high purity tunable emission at laser efficiency nearly equal to the maximum obtained in an optimized non-selective cavity and avoids optical damage problems. This makes the PSIL method competitive or preferable to other frequently used spectrally selective methods. Analysis and experimental check for two-wavelength lasers are included.

A novel technique for a narrow line selection and wideband tuning of Ti:Al2O3 and dye lasers

We have developed a novel simple technique for a wide gain laser narrow line selection and tuning using classical interferometric selectors (Fabry–Perot interferometer, interference wedge). Its most important advantage is that selection and tuning need only one thick interferometer instead of a combination of a thin (5 μm) and a thick (∼100 μm) one as in the conventional approach. This makes tuning much simpler without having to synchronize two tuning elements and the system as a whole essentially cheaper. The computer simulation and the experimental test have shown that the proposed technique is highly competitive compared with traditional interferometers with thicknesses of 30–70 μm. It assures a spectral resolution of less than ∼0.01 nm and tuning in the wide region (≥100 nm), in particular, it completely covers the spectrum of the dye solution and that of the Ti:Al2O3 crystal. Besides enlarging the tuning region, the linewidth is narrowed and the spectral purity of emission is increased. Using a quali...

Reflection and transmission of the unequal mirrors interference wedge

Some interesting features of the interference wedge of thickness 5–200 μm are found which characterize its reflection and transmission when it is constructed of unequal-reflectivity mirrors. The analysis of the wedges behaviour is made using equations derived by us for restricted laser beam illumination on the assumption of truncated Gaussian amplitude distribution and uniform phase distribution. It is shown that at resonant wavelengths the unequal-reflectivity mirrors interference wedge has a property of optical asymmetry in reflection for both contraincidences and that the earlier-reported phenomenon of spectrally controlled resurgence of light outside the nonresonantly reflected beam increases drastically to reach at resonance 60–70% of the reflected power. We ascertained that the wedge spectral selectivity is a function of the product of the reflectivities of its mirrors. Keeping one of them fixed and increasing the other, a higher wedge transmission may be obtained, but for a constant value of their product a maximum in transmission is achieved at equal reflectivities. Some of the dependences obtained have been checked experimentally.

Increase of the free-spectral range by composing a structure from wavelength tunable wedged interferometers

We have studied a structure composed from two wavelength tunable wedged interferometers and proved its potential for providing an increased free spectral range in comparison to a conventional interferential wedge. The interferential wedges with optical thickness from several micrometers to several hundred micrometers and apex angles of the order of tens microradians have been used. We have computed transmission for a monochromatic light beam with arbitrary wavefront using the angular spectrum approach for interferential wedges with different optical thicknesses and apex angles. We have conducted experiments with several stacks formed from different two wedges. Thus, we have confirmed selection of a single transmission resonance within the impact area of a large diameter beam instead of occurrence of multiple transmission peaks observed for a single interferential wedge. The stack enables wavelength tuning for a small diameter multi-wavelength beam in an increased spectral range at keeping high spectral resolution if the structure is formed by a thin and a thick interferential wedges. The experiments have shown that the selected transmission peak is narrowed spatially and spectrally at the expense of lower transmission, which is 50-60% of transmission provided by the used interferential wedges.

DEVELOPMENT OF ORIGINAL OPTICAL AND QUANTUM ELECTRONICS DEVICES FOR APPLICATIONS IN COMMUNICATIONS, METROLOGY AND SCIENCES

The goal of the report is to present the development – principles, theories and computer simulations, experiments and practical realizations, of original and competitive methods, elements and devices for quantum electronics, optical communications, metrology, remote sensing and sciences: multi-channel WDM system with independent tuning of each input/output, multi-wavelength laser with independent control of each wavelength, lasers with emission, spectrally fixed at reference atomic absorption line, injection-locking laser system for high (~10-10) and linear amplification of low-power (~ μW, nW) modulated laser light, optical analogue of the transistor action – optical transistor, system for remote (up to kilometres) measurement of small (mm) translational elongation – shrinking of objects, new solution of tunable sub-nanosecond lasers and lasers with rectangular nanosecond (~1 ns) pulse emission, including controlled duration and tunable wavelength. The basic element of the devices developed is stable and compact interference wedged structures in new composite solution with very narrow transmission (≤ 0.01 nm) in relatively large spectral range (≥1 nm). The laser active media used are solid-state, semiconductor and dye.

Gaussian beam reflection from Fizeau interferential wedge

The goal of the present paper is to develop a procedure for calculation of the fringe pattern in reflection for Fizeau interferntial wedge considering both positive and negative incidence at which the incident light beam undergoes multiple reflections within the wedge in direction of increasing or decreasing wedge thickness respectively. High-reflectivity coatings wedges with apex angle of 5 - 100 μrad and thickness of 5 - 500 μm are considered. To avoid the drawbacks of the plane-wave approximation and to calculate the interference pattern for a limited beam illumination at any distance from the wedge, we proposed a plane-wave expansion approach. We analyzed the wedge interaction with a Gaussian beam as a beam structure of particular importance in laser technique. In addition, an analytical solution of the involved integrals was obtained for the Gaussian intensity distribution. It was shown that both contra-incidences of the light beam could be described by the same mathematical expressions, i.e. the reflected fringe pattern at positive incidence could be considered as prolongation of the reflected pattern at negative incidence at some distance from the wedge. Experimental verification is also provided.

Two-wavelength generation in a Ti:Al2O3 laser controlled by injection from a coupled two-wavelength laser: comparison with a simple amplification

In this paper we report a comparative study the amplification and spectral tuning characteristics of an injection seeded Ti:Sapphire laser and multipass (4 passages) amplifiers. We show the advantages of injection seeding method to amplify input pulses of low energy levels (nJ and sub nJ). In the multi-passages amplifiers the wave competition for the two wavelength amplification is low. For high level (mJ) pulses the both systems are comparable, but in the injection locking amplifier the temporal pulse shape distortion is essentially high. The energy and power amplification levels are compared both with the change of the output width. For the reported two new multi-passages schemes we are study the dependence of the characteristics on the input polarization.

Effective coupling of a laser oscillator-amplifier system with an unequal mirror interference wedge

Combining optical asymmetry in reflection of a unequal mirrors interference wedge with its focusing property at negative incidence, we propose effective separation of a laser oscillator from a highly excited amplifier in a tunable laser oscillator-amplifier system, i.e. solution of the problem with removal of the background radiation self- injection.

Near-maximum-efficiency two-wavelength Ti:Al2O3 laser using a novel combined PSIL-dual-pulse pumping spectral control

We demonstrate how a pulsed two-wavelength tunable Ti:Al2O3 laser can operate at near maximum efficiency, obtained in an optimized non-selective cavity. To achieve this efficiency we solve the intrinsic of the Passive Self- Injection Locking (PSIL) method problem of non-controlled free lasing at high pump level by combining the PSIL control with an appropriate dual-pulse pumping. Laser efficiency is increased and the background emission is limited to less than 1 percent in a region ten times larger compared with the standard PSIL control. From analysis we have found optimum conditions and show the advantages of this combined technique. The proposed approach is compared with spectral control of a Ti:Al2O3 laser, realized by injection from a coupled two-wavelength dye laser.