Harmonic Generation In Nonlinear Crystals Research Articles

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

Approximate Technique for Solution of the Problem of Second Harmonic Generation in Nonlinear Crystals: Part 1

A technique is suggested for an approximate solution of the set of equations responsible for second harmonic generation in nonlinear uniaxial crystals. The algorithm of this technique is reduced to numerical calculation of a triple integral. The study consists of two parts. In the first part, two approximations are considered, which allow a reduction of nearly two orders of magnitude in the computation time of double integrals over the transverse coordinates. In the second part, we discuss an approximate technique for estimating the power of interacting waves, which also allows a further reduction in the computation time by an order of magnitude by reducing minimum number of required steps in the recurrence process. The test results show that the use of these approximations can decrease the accuracy of the solution of the nonlinear problem but can keep the errors acceptably low.

Approximate Technique for Solving the Problem of Second Harmonic Generation in Nonlinear Crystals: Part 2

Approximate Technique for Solving the Problem of Second Harmonic Generation in Nonlinear Crystals: Part 2

Approximate technique for solution of the problem on second harmonic generation in nonlinear crystals. Part 2

Approximate technique for solution of the problem on second harmonic generation in nonlinear crystals. Part 2

Approximate technique for solution of the problem on second harmonic generation in nonlinear crystals. Part 1

Approximate technique for solution of the problem on second harmonic generation in nonlinear crystals. Part 1

Some problems of optimum focusing in the process of second harmonic generation in nonlinear crystals. Part 2. Results of numerical calculations

The problem of the second harmonic generation (SHG) of monochromatic spatially coherent paraxial radiation in homogeneous uniaxial quadratically nonlinear crystals upon focusing of a beam into a crystal by two crossed cylindrical lenses with different focal lengths is considered theoretically. Parameters of optimum focusing are determined as functions of the main radiation power. This part of the paper presents main results of numerical calculations. It is shown that, with an increase in the main radiation power, parameters of optimum focusing vary insignificantly at first. Then, beginning from a certain power depending on the initial conditions of the problem, the SHG efficiency maximum becomes attainable with increasingly weaker focusing. The efficiency maximum monotonically increases and probably tends to 100% with an infinite increase in the power.

Some problems of optimum focusing in the process of second harmonic generation in nonlinear crystals. Part 1. Mathematical apparatus

The problem of the second harmonic generation (SHG) of monochromatic spatially coherent paraxial radiation in homogeneous uniaxial quadratically nonlinear crystals upon focusing of a beam into a crystal by two crossed cylindrical lenses with different focal lengths is considered theoretically. The aim of the investigations was to determine optimum focusing parameters as functions of the main radiation power. The first part of this paper presents a mathematical apparatus necessary for carrying out the planned investigations. A variant of transforming a system of nonlinear wave equations to a form more convenient for further use is proposed. Some important particular cases admitting simpler solutions are considered. An asymptotically exact analytical solution of the SHG problem is presented.

Role of the longitudinal piston error in a tiled-grating compressor in second and high-order harmonic generation

In this work, we study the limitations for overcoming the longitudinal piston error in a femtosecond tiled-grating compressor using nonlinear measurements like second harmonic generation. In particular, we observe the influence of this error when developing high-power laser experiments such as high-order harmonic generation. The generation of nonlinear processes with femtosecond pulses compressed in tiled-grating systems is studied. Special attention is paid to the role of the longitudinal piston error which is the most difficult to overcome in the compressor alignment. A complex spatio-temporal structure is expected to appear due to that misalignment. Both second harmonic generation in nonlinear crystals and high-order harmonic generation in gases are studied and a strong dependence with piston error is found, thus leading to a sub-micron modulation in the generated signal. In particular, the high sensitivity of the high-order harmonics to the longitudinal position allows one to use this processes for the accurate alignment of the compressor to few tens of nanometers.

Measuring pulse-front tilt in ultrashort pulse laser beams without ambiguity of its sign using single-shot tilted pulse-front autocorrelator

The measurement of pulse-front tilt (PFT) in ultrashort pulse laser beams, without ambiguity of its sign, has been carried out using an in-house built single-shot tilted pulse-front autocorrelator (TPFAC) based on second harmonic generation in non-linear crystal. The experiment is carried out for the beam propagation through a single prism and a pair of prisms. Expressions of PFT angle have been derived to account for beam size, beam propagation effects and for arbitrary incidence of the laser beam. The measured PFT angles were found in accordance with theoretically calculated values. The calculated sensitivity of TPFAC is found to be larger than that offered by the other techniques.

Ultra-fast fibre laser systems based on SESAM technology: new horizons and applications

A promising route to manufacturing portable (sub-)picosecond fibre lasers is to use a semiconductor saturable absorber mirror (SESAM). With SESAMs, the mode-locked regime can be achieved for different values of cavity dispersion for a broad spectrum ranging from 0.8 to 1.6 μm. The fibre lasers, characterized by a high efficiency and reliability and a small footprint, are very attractive for applications traditionally occupied by solid-state lasers. The broad fluorescence spectrum makes different fibre gain media attractive for tuneable and ultra-short-pulse sources. In this paper, we discuss recent advances in ultra-fast fibre lasers. We study the fundamental properties and technical challenges of mode-locked fibre lasers operating in the 0.9–1.6 μm range, and the methods to achieve high peak-powers from all-fibre devices. The key component is the SESAM, notably, a dilute nitride SESAM. The SESAM supplies a strong mechanism for picosecond pulse generation that is entirely self-starting for a wide range of cavity dispersion and ensures stability against Q-switched mode-locking. In particular, compact mode-locked lasers stabilized by near-resonant SESAMs can be realized in a short fibre cavity free from any dispersion compensator. An appropriate dispersion delay line at the output of the master source may be used for pulse clean-up. The high-quality pulses obtained can then be compressed using traditional methods, when the pulse first undergoes spectral enrichment via self-phase modulation in an auxiliary fibre and then gets compressed in a grating pair. The fibre laser is capable of efficient wavelength conversion via second harmonic generation in non-linear crystals. Using a periodically poled LiNbO3 crystal for frequency doubling, we produce sub-100 fs pulses at 0.8 μm with a 50% conversion efficiency.

Second optical harmonic generation in nonlinear crystals with a disordered domain structure

A theory describing the second harmonic generation in nonlinear-optical crystals with random domains is developed. The theory takes into account the fluctuations of both the phase mismatch and the nonlinear coupling coefficient of the interacting waves. It is shown that, in such crystals, the maximal efficiency of fundamental-to-second harmonic conversion is low, and the dependence of the average intensity of the second harmonic on the fundamental intensity differs considerably from a square law.

Atomic absorption spectroscopy with tunable semiconductor diode lasers

In atomic absorption spectroscopy (AAS) the replacement of hollow cathode lamps by compact, inexpensive and easy to operate semiconductor diode lasers offers the possibility of multi-element analysis, background correction, extension of the dynamic range and internal standardization. Today, already 60% of all elements which are determined by conventional AAS can be measured if the fundamental wavelengths of commercially available diode lasers and the wavelengths obtained by second harmonic generation in non-linear crystals are taken into account

Diode Laser—Pumped Solid-State Lasers

Diode laser-pumped solid-state lasers are efficient, compact, all solid-state sources of coherent optical radiation. Major advances in solid-state laser technology have historically been preceded by advances in pumping technology. The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers. The latest advance in pumping technology is the diode laser. Diode laser-pumped neodymium lasers have operated at greater than 10 percent electrical to optical efficiency in a single spatial mode and with linewidths of less than 10 kilohertz. The high spectral power brightness of these lasers has allowed frequency extension by harmonic generation in nonlinear crystals, which has led to green and blue sources of coherent radiation. Diode laser pumping has also been used with ions other than neodymium to produce wavelengths from 946 to 2010 nanometers. In addition, Q-switched operation with kilowatt peak powers and mode-locked operation with 10-picosecond pulse widths have been demonstrated. Progress in diode lasers and diode laser arrays promises all solid-state lasers in which the flash lamp is replaced by diode lasers for average power levels in excess of tens of watts and at a price that is competitive with flash lamp-pumped laser systems. Power levels exceeding 1 kilowatt appear possible within the next 5 years. Potential applications of diode laser-pumped solid-state lasers include coherent radar, global sensing from satellites, medical uses, micromachining, and miniature visible sources for digital optical storage.

Duration of the second harmonic of quasisingle-mode laser radiation under conditions of strong energy exchange

A direct numerical solution of reduced equations is used to study theoretically second harmonic generation in nonlinear crystals in the case of strong energy exchange. An allowance is made for the aperture effects and for diffraction. It is shown that transformation of single-mode radiation in crystals with critical phase matching is not very inferior in respect of the conversion efficiency to that in crystals with 90° phase matching, and that displacement of an extraordinary wave relative to an ordinary one prevents the reverse energy conversion. It is shown that in the case of a strong energy exchange in crystals with critical phase matching the efficiency of second harmonic generation decreases strongly even in the presence of slight spatial distortions in a transverse cross section of the fundamental-frequency beam.

Thermal Lensing Spectroscopy With Picosecond Pulse Trains and aNew Dual Beam Configuration

In this communication, we wish to report on the use of synchronously mode-locked picosecond lasers in a pump-probe configuration for TL spectroscopy. The peak power for these picosecond lasers is very high and, of course, the fundamental of the dye laser (red beam) can be efficiently (~10%) doubled in frequency (U.V. beam) by second harmonic generation in nonlinear crystals. We use this generated U.V. beam as a probe to monitor the very weak absorption of the red beam. An arrangement [4] of the beams involving different waist positions for the pump and probe is used. This arrangement results in an enhancement of sensitivity (at least a factor of three to seven). Also, a different dependence of the signal on the cell position compared to the single beam method is obtained. Finally, we have obtained the Δν = 5 CH-stretching overtone absorption spectrum of liquid toluene with this method (see Figure 1). Suggestions are made regarding new applications of this picosecond pulse thermal lensing technique.

Spectral phase-matching properties for second harmonic generation in nonlinear crystals

The spectral phase-matching bandwidths in LiIO3, LiNbO3, CDA, and KDP (type I and type II) for second harmonic generation (SHG) at 1.06 μm have been accurately measured using a tunable line-narrowed Nd : glass laser. The present results disagree with previously published data. Mechanisms such as sum-frequency generation which could contribute to the discrepancy are discussed and demonstrated in a 90° phase-matched deuterated CDA crystal.

Powerful dye laser oscillator-amplifier system for high resolution and coherent pulse spectroscopy

A peak power output of 100 kW in the visible at a linewidth as low as 60 MHz has been generated by using a cw dye laser oscillator followed by three single pass dye amplifier stages (or one double pass stage and one single pass stage), pumped by a single 1 MW nitrogen laser. The very high output power obtained in this laser system may be used to produce coherent ultraviolet pulses by sum or second harmonic generation in non-linear crystals or by third order mixing in atomic vapor.