Polarization properties and frequency stabilization of an internal mirror He-Ne laser emitting at 543.5 nm wavelength

Frequency stabilization to the gain profile of an internal mirror He–Ne laser emitting at 543.5 nm wavelength is described. The dependence of the power and polarization on frequency was investigated for multi-mode and two-mode operation. The emitted laser modes are linearly polarized. Two orthogonal eigenpolarizations fixed to the laser tube were observed. Spontaneous switching between these polarizations occurred when the laser frequency was scanning through the gain profile. In two-mode operation, these polarization flips have been suppressed by applying a weak magnetic field transversal to the gas discharge. Under such operation conditions the frequencies of the laser could be stabilized to the gain profile by controlling the power difference of the two modes to zero. The fractional frequency reproducibility is in the region of f/f3×10^–8.     

Self-phase locking in lasers with homogeneously broadened emission lines

It is shown by numerical analysis based on Lamb's equations of motion, that standing-wave lasers with purely homogeneously broadened emission lines exhibit regular multimode oscillations. Specifically, modes lying far from the line centre are quenched due to mode competition, and the amplitudes of the oscillating modes approach steady-state values. The stabilization of the amplitudes is normally accompanied, or followed, by an evolution of the phases towards a phase-locked regime, where the relative phases _n = 2 _n – _{n + 1} – _{n – 1} [ _n phase in then ^th mode, defined by (6)] attain either the value 0 or ± . The build-up times for the relative phases are found to vary over a wide range.     

Investigation on amplitude and frequency noise of injection-locked diode-pumped Nd:YAG lasers

Amplitude and frequency stability of an injection-locked diode-pumped miniature Nd:YAG ring laser were measured. The mechanism of amplitude-noise transfer to the injection-locked slave laser was experimentally investigated and consequences for the injection locking of solid-state lasers operating at high output powers are discussed.     

Q-switched Nd lasers pumped directly into the F3/2 emitting level

The influence of the direct pumping into the ⁴F_3/2 emitting level on the output characteristics of continuous-wave (CW) pumped, passively or actively (acoustooptic, AO) Q-switched Nd lasers is discussed. In case of passive Q-switching by Cr⁴⁺:YAG saturable absorber (SA) crystal, the change of pumping wavelength from 0.81 μm into the highly-absorbing ⁴F_5/2 level to 0.88 μm into the ⁴F_3/2 level of Nd does not modify the energy of the Q-switch pulse, but increases the pulse repetition rate and the laser average power for the same absorbed pump power. This is demonstrated with 0.81 and 0.88 μm CW laser diode-pumped Nd:YAG and Nd-vanadate lasers with average output power in the watt-level range at 1.06 μm. The effect is explained by the control of passive Q-switching by the intracavity photon flux that is influenced by the pump wavelength and by the initial transmission of the SA crystal. On the other hand, it is discussed and experimentally proved that due to the possibility to control externally the frequency of switching, in case of the AO Q-switched Nd laser the change of the pump wavelength from 0.81 to 0.88 μm increases the pulse energy for a fixed frequency, leading to a corresponding increase of the average laser power.     

Small-signal gain of Free Electron Laser in a resonator Gaussian mode

We present an analytical expression for the small-signal gain of a Free Electron Laser (FEL) in the presence of a Gaussian mode. To describe the electron beam evolution we use the one-dimensional (1-d) Vlasov equation. Our perturbation result, valid for small values of the parameterq (length of the undulatorL divided by the Rayleigh rangeZ _R), can be extrapolated to values ofq4÷5.     

Investigation of polarisation effects in injection locked lasers

Received: 14 June 1996/Revised version: 6 November 1996     

High-power,line-tunable14NH3 and15NH3 lasers

A high-power, line-tunable NH₃ laser pumped by a TEA CO₂ laser has been developed for application to laser isotope separation of tritium. Laser lines from¹⁵NH₃ are newly observed in a range from 11.24 to 13.23 m. The performance of an¹⁵NH₃ laser is compared to that of an¹⁴NH₃ laser.     

Theory of passively mode-locked cw dye lasers

The circulation of an ultrashort light pulse in a continuously pumped modelocked dye laser with a linear cavity configuration containing the active dye, the saturable absorber and a bandwidth-limiting elements is treated. The steady-state condition that the pulse shape reproduces after each cavity round-trip leads to a nonlinear integro-differential equation for this pulse shape. An approximate method for the solution of this equation not limited to the case of low laser gain and small pulse energies is given. The stable single pulse region and characteristic pulse parameters, as energy, duration, intensity and asymmetry, are considered in dependence on the laser parameters.     

Output power enhancement of the 632.8 nm monomode He-Ne/I2-laser

For the He-Ne/I₂-laser, a stable monomode operation has been realized when the tube pressure exceeds a certain level. An output power of more than 1 mW has been obtained at the 632.8 nm laser transition. Within the monomode tuning range of the laser, the d, e, f, g, and h, i, j iodine hyperfine components of the R(127) line of the 11–5 band of the B ³ II ⁺ _0u–X ¹⁺ _0g electronic transition have been observed. The mode selection method used makes it possible to increase the contrast of the iodine hyperfine components.     

Injection locking of ArF excimer lasers

Injection-locking characteristics of an ArF excimer oscillator-amplifier laser are described including the use of stable-unstable optical cavities. Output intensities of 1 MW cm^–2 have been produced with 3 mJ output energy, a spectral linewidth better than 5×10^–3 nm and an injection locking efficiency of 0.9.     

Operation of KrF and ArF tunable excimer lasers without Cassegrain optics

A commercial tunable excimer laser consists of an oscillator-amplifier combination. The oscillator produces high-quality light that is sent to the amplifier and is distributed throughout the amplifier cavity via Cassegrain optics. We describe here two alternative approaches, a single-pass configuration for use with KrF and a triple-pass configuration with ArF, both of which do away with the Cassegrain optics. In each approach, the beam energy is the same as with Cassegrain optics. For KrF, the changes provide better locking, a higher degree of linear polarization, and a better spatial beam homogeneity, but a poorer beam divergence. For ArF, there is also better beam homogeneity, but the locking efficiency and divergence are not as good as with Cassegrain optics.     

Spectral properties of diode-pumped non-planar monolithic Nd:YAG ring lasers

The coherence length of a single-frequency monolithic Nd:YAG ring laser is determined by using a highly unbalanced all-fiber Mach-Zehnder interferometer. A coherence length larger than 1500km and a 3 dB linewidth less than 60 Hz is estimated.Furthermore, an easy method to measure the temperature dependence on several laser parameters is described. This method is based on the laser emission in multiple axial modes, which is enforced by coherent optical feedback. A model explaining the multimode behaviour is presented.     

Spectral purity of pulsed dye lasers

High-spectral purity of pulsed dye lasers is required by many experiments. Unfortunately, the dye laser output is usually accompanied by a spectrally broadband background of spontaneous emission (ASE). We have carried out detailed studies of the ASE background using a dye laser operating with an oscillator, pre- and main amplifier.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Relaxation-oscillations in the C → A laser emission of XeF in Ar crystals

Transversely pumped 1 cm long crystals are operated in a plan-parallel cavity with dielectric mirrors of 100% and 30% reflectivity. Relaxation-oscillations in the laser emission at 540 nm with frequencies in the range of (1 to 1.8)·10⁹ s^–1 are observed. A square root dependence on pump rate is shown and an internal loss coefficient of 5.4 cm^–1 is derived.On leave from the Polish Academy of Sciences IF-FM, Fiszera 14, PL-80-952 Gdansk, Poland     

Preionization and discharge stability study of long optical pulse duration UV-preionized XeCl lasers

This paper presents a complete study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser. The detailed study was made possible using the technique of laser-induced preionization which utilizes the uv radiation from a KrF laser to preionize a second rare-gas halide laser. In addition to the preionization study, high spatial and temporal resolution framing camera photographs have been used to investigate the growth of discharge instabilities which can lead to the premature termination of the XeCl optical pulse. The roles played by HCl, Xe, the buffer gas as well as the discharge energy loading in the development of discharge instabilities have been determined experimentally.     

High-frequency discharge stability of waveguide He-Ne lasers

The paper deals with the small-signal behavior and the stability of discharges in narrow capillaries. A theory is presented, which assumes that the time constants of the particle balance and the wall sheath extension determine the small signal behavior of a positive column. The column admittance is used to analyze the stability of an electric circuit typical for a He−Ne waveguide laser discharge. Numerical evaluation shows qualitative agreement of the experimental and the theoretical stability diagrams.     

Interference of atom,and atomic spatial lattices in light fields

A scheme is proposed to observe interference of atoms by using a weakly coherent atomic beam scattered at two standing light waves. It is shown that atoms can transfer spatial coherence over rather large distances.     

CW injection phase locking in homogeneously broadened media II. Phase locking and tunability of CO2 waveguide lasers

Injection phase locking of a powerful CO₂ waveguide laser with a stable singlefrequency master oscillator is described. The locking range is experimentally investigated versus both injected signal frequency and slave cavity length. A locking tunability up to ±180 MHz from CO₂ 10P(20) line center has been achieved. Experimental results are in excellent agreement with the theoretical development exposed in the preceeding paper.     

A plasma effect in injection-mode selection of TEA CO2 lasers

We present experimental evidence obtained by a laser heterodyne technique for a chirp of about 10¹⁴ Hz/s in the cavity resonance during the pulse build-up time of a TEA CO₂ laser. The frequency sweep arises from the refractive-index contribution of the time-dependent electron density in the exciting discharge plasma. The phenomenon provides a mechanism, previously unexplained, for the extended and asymmetric mode selection zone in injection experiments.