Frequency stabilization of an internal mirror HeNe laser at 543.5 nm to I2-Saturated absorptions

An internal mirror green HeNe (GRENE) laser at 543.5 nm has been frequency stabilized to I₂-Doppler free absorption signals with a frequency stability of few parts in 10¹⁰. The saturated absorption signals were detected using doubly-differential saturated absorption which eliminates the Doppler background and allows first-derivative locking methods. Two absorption lines R(12)26-0 and R(106)28-0 of ¹²⁷I² were investigated and the hyperfine structure was resolved. Random polarization flips of the GRENE were suppressed by applying a transverse magnetic field to the laser tube near the anode.Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-3300 Braunschweig, Fed. Rep. Germany     

611.8 nm single-mode He-Ne laser

The conditions for optimum 611.8 nm laser operation are obtained and a convenient method for indicating 3.39 µm suppression is proposed. Single longitudinal mode 611.8 nm generation is obtained using higher gas-mixture pressure and application of an axial magnetic field. Several milliwatt monomode output power and 0.75 multimode-to-monomode power conversion coefficients are obtained without an internal iodine cell. A comparison of the experimental results with a single-mode laser theory is given.     

Performance of internal-mirror frequency-stabilized He-Ne lasers emitting green,yellow or orange light

A comprehensive control system has been developed for the stabilization of internalmirror He-Ne lasers to their power envelopes. It is designed particularly for use with lasers emitting at 552, 505, or 490 THz (543, 594, 612 nm). The aim has been to combine convenience in routine operation with good day-to-day resettability and minimal frequency drift during a day. The lasers are observed to emit in up to four modes simultaneously and their tuning behaviour is highly alignment-sensitive. They also tend to flip between modes having orthogonal linear planes of polarization. Reliable control of polarization and mode frequency are possible using permanent magnets and active length control through thermal expansion. The stabilized single-frequency outputs have frequency drifts of about 2×10^–8 per year, and powers of between 150 W and 850 W.     

A technique for frequency stabilization of an internal mirror He-Ne laser

A technique for frequency stabilization of an internal mirror He-Ne laser using phase sensitive detection without cavity length modulation is suggested. The orthogonally plane polarized modes are separated and then convered into two photoelectric signals using two photodetectors. The photoelectric signals are switched alternately so as to generate a square wave, whose amplitude is proportional to the intensity difference between the two orthogonal polarizations. A lock-in amplifier is used to detect this square wave, with the switching frequency as reference. The phase detected signal is used for thermal stabilization of the laser. The frequency stability of 5 × 10⁻⁹ was obtained with an integration time of 1 s.     

Discharge pumped C1F laser at 285 nm

This paper reports on experiments carried out in order to improve the performance of the TEA discharge pumped C1F uv laser at 285 nm. Factors which influence the gas degradation with increasing operating time, resulting in a decrease of laser output power, were investigated, aiming at a better understanding of the relevant mechanisms. By optimizing several parameters, laser pulse energies beyond 25 mJ were obtained in a high-pressure discharge laser chamber. C1F lasing has also been demonstrated in a commercially available multigas TEA laser system.As a byproduct of our C1F experiments, laser action on the correspondingDA transition of Cl₂ at 258 nm has also been achieved for the first time in a discharge laser chamber.     

Polarization properties of multimode internal mirror He-Ne lasers

The polarization behaviour of internal mirror multimode He-Ne lasers oscillating at 632.8 nm has been experimentally studied. It has been found that phase anisotropy of the cavity plays a dominant role in determining this behavior and fixing polarization configuration of the modes.     

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.     

Laser investigations at 269 nm for XeF(D-X) in Ne crystals

From line narrowing in amplified spontaneous emission at the D-X transition (269nm) of XeF in solid Ne a gain coefficient of 3.4 cm^–1 has been derived and ground-state losses of 2.8 cm^–1 have been determined by variation of the absorption length. A dielectric laser cavity has been optimized with the reflectivities R₁=100% and R₂=70% for 1 cm long crystals; laser action has been achieved.     

Threshold and saturation properties of a solid-state XeF (C-A) excimer laser

A dielectric laser cavity of 1 cm length has been optimized for high gain (7 cm^–1) operation which is achieved in XeF doped Ar crystals. Mode structures on the C-A spectral distribution around 540 nm and far field transverse mode patterns are reported. Photchemical gain burning is observed in the spectral mode structures. The dependence of the laser threshold on pump energy, pumped length and on cavity losses is studied. XeF densities of 7×10¹⁷ cm^–3 and distributed losses of 1.2 cm^–1 are derived. The measured quantum efficiency of 14% and the saturation behaviour are consistently described. Losses by transient aborption and two photon absorption are discussed.     

Spatio-temporal coupling of laser fluctuations — Observations on a laser with internal frequency conversion

The amplitude of standing wave solid state lasers with frequency conversion inside the resonator can become unstable. We investigated the amplitude fluctuations of an end-pumped Nd:YAG-laser at low pump rates (below 160% threshold pump power) and also above. Detecting the individual mode instabilities separately and comparing them with a theoretical laser model, we can trace the origin of the mechanism leading to the observed fluctuations. At certain well defined discrete pump levels above 160% threshold the instabilities disappear. These stable emission states are associated with particular nonconventional mode patterns, some of them exhibiting a helical phase structure. Based on experimental observations and computer simulations of pump induced resonator aberrations we describe a mechanism for the emergence of the peculiar transversal modes and laser fluctuations.     

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     

Laser and fluorescence properties of dye-doped sol-gel silica from 400 nm to 800 nm

Lasing and fluorescence properties of ten dyes covering the spectral range from 400 nm to 800 nm were studied in a silica matrix prepared by the sol-gel technique. The dye-doped sol-gel silica samples fluoresced strongly under laser excitation. Many of the samples were also induced to superradiate. In comparison to dyes in alcohol solvents, significant red-shifting was observed in the sol-gel silica fluorescence spectra. Plausible causes of the red-shift are discussed.     

Performance of a ten-liter electron avalanche-discharge XeCl laser device

This paper describes the laser performance of an X-ray preionized ten-liter volume, electron-avalanche discharge XeCl system, operated at dc charging voltages of up to 70 kV both with and without X-ray preionization. An output energy of more than 11J uniformly distributed over a (7×10) cm² spot size was achieved using a multichannel spark-gap as the main discharge switch. The discharge was also successfully operated in the switchless mode, yielding a 4.8 J output energy and a 0.9% efficiency. The time-resolved gain measurements provided information on the laser discharge evolution.ENEA GuestENEA Guest on leave from the Shanghai Institute of Optics and Fine Mechanics, the Chinese Academy of Sciences, Shanghai, China     

Spectral properties of a Tm:Ho:YAG laser in active mirror configuration

3+ :Ho³⁺:YAG laser is operated in active mirror configuration. This laser is characterised by a rather thin crystal (3 mm thickness in our experiment) and a very short resonator (about 3.2 mm). Therefore this laser is well suited for operation in a single longitudinal mode. Single-frequency operation is demonstrated with and without an intracavity etalon. It is further shown that single-frequency emission is reached with a stable cw emission. With a slight detuning of the outcoupling mirror, spiking can be achieved, resulting in an emission on different lines. The assignment of the observed laser lines to the known transitions between Stark sublevels of the ⁵I₇ and the ⁵I₈ level is discussed and compared with predictions in the literature. Received: 2 December 1997     

Gain dynamics of XeF and subpicosecond pulse generation at 351 nm

Subpicosecond pulse amplification at the 351 nm line of XeF is reported. The study of the gain dynamics of XeF with subpicosecond (subnanosecond) pulses resulted in 0.2 mJ/cm² (0.8 mJ/cm²) for the saturation energy density and 0.18 cm^–1 (0.21 cm^–1) for the small-signal-gain coefficient. In XeF a gain recovery of 78±4% with a 79±18 ps time constant is found.     

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.     

Short-term frequency stabilization of diode-laser-pumped Nd:YAG lasers using double-pendulum suspended cavities

We describe the improvement of short-term frequency stability of diode-laser-pumped Nd:YAG lasers. To improve the vibrational isolation of reference cavities, the reference cavities were suspended by a double pendulum with magnetic damping. The frequency noise was reduced to lower than 1 Hz/Hz at Fourier frequencies higher than 5 Hz and the minimum noise of 7 × 10^–3 Hz/Hz was recorded. The minimum root Allan variance was about 10^–14 for the sampling time of 0.01 s. Heating of the reference cavity by absorbed laser power caused the thermal drift of cavity resonance frequencies. It resulted in the laser linewidth in the range of 30–50 Hz.     

Gain and saturation measurements in a discharge excited F2 laser using an oscillator amplifier configuration

The small-signal gain coefficient and the saturation intensity of a F₂ pulsed discharge molecular laser at 157 nm have been measured using two discharge devices in an oscillator-amplifier configuration. The small signal gain coefficient was measured to be 5.2±0.4% cm^–1 at 3 atm total pressure and 1.5 cm electrode spacing and 4.1±0.4% cm^–1 at 2 atm total pressure and 2 cm electrode spacing while the values of the saturation intensity were 5 MW/cm² and 4.6 MW/cm², respectively.     

All-Solid-State Nd:YAG Laser Operating at 1064nm and 1319nm under 885nm Thermally Boosted Pumping

We report a high-effciency Nd：YAG laser operating at 1064 nm and 1319nm, respectively, thermally boosted pumped by an all-solid-state Q-switched Ti：sapphire laser at 885 nm. The maximum outputs of 825.4 m W and 459.4mW, at 1064nm and 1319nm respectively, are obtained in a 8-ram-thick 1.1 at.% Nd：YAG crystal with 2.1 W of incident pump power at 885nm, leading to a high slope efficiency with respect to the absorbed pump power of 68.5% and 42.0%. Comparative results obtained by the traditional pumping at 808nm are presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power at 1064nm under the 885nm pumping are 12.2% higher and 7.3% lower than those of 808rim pumping. At 1319nm, the slope efficiency and the threshold with respect to the absorbed pump power under 885nm pumping are 9.9% higher and 3.5% lower than those of 808 nm pumping. The heat generation operating at 1064 nm and 1319 nm is reduced by 19.8% and 11.1%, respectively.