Intermode Beat Research Articles

Axial mode locking in a cw YAG:Nd3+ring laser

The first results are reported of forced phase mode locking in a cw YAG:Nd3+ ring laser. The locking was produced by inserting an electrooptic LiNbO3 phase modulator in the resonator. The modulator varied the resonator perimeter at the intermode beat frequency. The time, spectral, and frequency characteristics of the laser were investigated in the phase mode locking regime. The width of the locking band was determined. In the phase locking regime the competition between the opposite waves was much weaker and there was also a reduction in the locking range when the ring laser was rotated. Moreover, spontaneous axial mode locking was observed in the absence of periodic variations of the resonator parameters.

Generation of ultrashort pulses in a negative-feedback laser

The results are given of theoretical and experimental investigations of stimulated emission from a modelocked negative-feedback solid-state (ruby) laser. Under certain conditions, governed by the delay time in the feedback circuit, the laser suffers from high-frequency instabilities in the form of sehvlocked intermode beats. These instabilities increase significantly the stringency of the requirements which have to be satisfied if negative feedback is to be used for amplitude stabilization.

Characteristics of three-mode self-locked helium-neon laser radiation

An experimental study was made of several dynamic characteristics of a three-mode helium-neon laser emitting at λ = 0.63 μ under self-mode-locked conditions. A study was made of the behavior of the intensities of the axial modes and of the total output power under 0 and π mode-locking regimes. This study was carried out both over the whole stimulated emission range and in the frequency intervals corresponding to self-locking. A comparative study was made of the concurrent features in the intensities of the intermodal beats and in the total radiation intensity; a correlation between them was established. A study was made of the behavior of the intermodal beat frequency under 0 and π mode-locking conditions throughout the mode-locked range.

Influence of gain saturation on the frequency pulling of the stimulated emission from linear ring He–Ne lasers

An investigation was made of the dependences of the intermodal beat frequency of a linear laser and of the difference frequency of a ring laser on the gain of the active medium and the losses in the resonator. These dependences made it possible to determine the reduction in the frequency pulling with increasing output power, relative to the total pulling. A determination of this reduction made it possible to compare the results of experiments carried out under different conditions. A comparison was made of the experimental results with the calculations.

Frequency self-stabilization of intermode beats in a gas laser

Frequency self-stabilization of intermode beats in a gas laser

INFLUENCE OF SELF-FOCUSING ON THE STABILITY OF STEADY-STATE LASER EMISSION

An investigation is made of the stability of steady-state laser emission in the case when the resonator contains a lens whose focal length is a function of the field amplitude. Fast perturbations (with characteristic frequencies of the order of the intermode beat frequency) are considered. The amount of nonlinear matter in the resonator needed to produce an instability is determined. Fast perturbations require much less nonlinear matter than the slow perturbations discussed earlier.

The engineering width of the spectral line of intermode beats of an He?Ne laser

The engineering width of the spectral line of intermode beats of an He?Ne laser

Pulse Velocity and Mode Pulling in a Laser with Equally Spaced Modes

Mode pulling and pulse velocity in an inhomogeneously broadened laser are examined starting from the assumption that the steady-state dispersion of the gain medium results in equally spaced modes. By summing the mode E-fields in the cavity it is found that the pulse velocity is less than that of light and equal to the classical group velocity dω/dk. The pulse shape is stable with time even in the presence of dispersion. The ratio of the intermode beat frequency to that of the empty cavity equals the ratio of the pulse velocity to that of light. Previous measurements on the He–He self-locked laser support these results.

Laser Mode Structure Experiments for Undergraduate Laboratories

Experiments dealing with laser mode structure are presented which are suitable for an upper division undergraduate laboratory. The theory of cavity modes is summarized. The mode structure of the radiation from a helium-neon laser is measured by using a photodiode detector and spectrum analyzer to detect intermode beating. Off-axial modes can be visually detected in the expanded laser beam and their presence correlated with signals displayed on the spectrum analyzer in agreement with the theory.