He-Ne Probe Laser Research Articles

Trace gas detection by laser intracavity photothermal spectroscopy

A novel laser intracavity photothermal detector is described. In this scheme, sample absorption of the pump laser power takes place within the cavity of a probe He-Ne laser causing modulation in the gain and in turn the output power. Comparison of this intracavity detector with two other photothermal techniques, namely, phase fluctuation optical heterodyne spectroscopy and thermal beam deflection, is made in terms of practicality and sensitivity. For in situ measurements, sensitivity of 0.5 x 10(-7) cm(-1) for a probe length of 3 cm has been achieved.

Thermal effects in a Nd:glass laser rod pumped in a double circular close-coupled cavity

Thermal effects produced in a Hoya LSG-91H Nd:glass laser rod pumped uncooled in a close-coupled double circular chamber, at high input powers, were evaluated in the single shot and repetitively pulsed modes by passing a He-Ne laser probe beam through the rod and observing the changes in the beam intensity. When pumped with a 200 μs, 100 J flashlamp pulse, it was observed that the thermal effects lasted for about 2-2.5 s at the center of the rod and 0.2-0.5 s at the rod edges. The minimum induced focal length of the laser rod was -57.3 cm in the single shot mode and -54.9 cm in the repetitively pulsed mode. In the repetitively pulsed mode, in addition to the lens effect, a prism effect was also observed, which increased in strength with increase in input energy. These lens and prism effects were found to be dependent on the energy deposition profile in the laser rod and on its thermal properties.

Photodisplacement microscopy using a semiconductor laser

A photodisplacement microscope has been realised, using a modulated semiconductor laser as the heating source and a phase sensitive HeNe laser probe for detection. Experimental results indicate that the instrument can have a wide range of applicability, including problems in nondestructive examination.

Optical inhomogeneities in a Lamberton-and-Pearson-type CO2laser

A simple optical technique for the detection of shock waves in a pulsed discharge is described. The technique uses an apertured photomultiplier and He-Ne probe laser to obtain data on the passage of a shock front across the pulsed discharge. This method has been applied to a study of shock wave propagation in a TEA CO2 laser discharge.

Spatial and temporal behaviour of electron temperatures in laser sparks in nitrogen, argon and helium

Spatially resolved recordings of the plasma emission in a narrow spectral band and the absorption of an He-Ne laser probe beam have been used to deduce the electron temperature and estimate the density in sparks produced by a Q-switched Nd laser in nitrogen, argon and helium at pressures from 0.5 to 4.5 atm. A uniform temperature decay with time constants of several hundred nanoseconds is observed in nitrogen and argon in the range of 5-1 eV, whereas in helium a secondary heat wave emerges from the initial breakdown zone approximately=150 ns after breakdown. The temperatures obtained are in good agreement with published spectroscopic measurements under similar conditions.

Direct comparison of thermal and magnetic profiles in ``Curie point'' writing on MnGaGe films

Measurements have been made of both the real-time temperature profile and the steady-state magnetization profile achieved in a film of MnGaGe as a result of ``Curie point'' writing with a GaAs laser pulse. A HeNe laser probe having a half-power diameter of 1 μ was used to measure both profiles. Temperature was measured during and after application of the heat pulse by relating the time-dependent transmission change of the heated area of the film to the temperature-calibrated shift of the absorption edge of MnGaGe. Magnetization information was obtained by measuring the Faraday rotation within the written area after the film had cooled to ambient. A comparison of the two profiles indicates that (a) magnetization reversal occurs at temperatures well below the Curie point, even in the absence of an external bias field, and (b) the critical temperature required for reversal increases with an increase in the size of the heated area. Both results can be explained qualitatively by local demagnetization effects.

On the nature of oriented optical damage in polymethylmethacrylate

The role of SBS-generated hypersonic phonons in the formation of laser-induced oriented optical damage in polymethylmethacrylate was investigated by means of the Bragg diffraction of a probing He-Ne laser beam. No evidence whatsoever of SBS-generated phonons was found during damage formation.