Influence of various gases on single bubble sonoluminescence

Influence of various gases on the intensity of single bubble sonoluminescence has been studied. The gases used were air, oxygen, nitrogen, argon and helium. Among these oxygen gave the brightest intensity with nitrogen giving the least. K e y w o r d s . Sonoluminescence; bubble dynamics PACS Nos 78.60; 43.25; 42.50 Single bubble sonoluminescence (SBSL) [1, 2] is the phenomenon of light emission from a single bubble driven into extreme nonlinear motion by an acoustic field. The light emitting bubble could be a source of picosecond flashes [2] if the SBSL intensity can be enhanced sutficiently. Towards this end we have investigated the influence of various gases on the intensity of SBSL. The apparatus used presently has been briefly described by Arakeri [3]. It basically consists of a 500 cc boiling flask driven into one of its resonant modes by a piezoelectric drive. A photomultiplier tube (RCA 4526) with a S-20 spectral response and a rise time of about 2 ns is used to measure SBSL intensity. The average of single pulse outputs of the PMT was recorded on a fast digital storage oscilloscope (Tekhind 2230) operated in repetitive sampling mode. The typical record obtained on the oscilloscope was presented earlier [3]. The area under the curve is directly related to the integrated charge output of the PMT and as described by Barber [4], this information can be used to obtain the number of photons emitted per flash. The present system was calibrated to give SBSL intensity in terms of the total number of photons emitted per flash. The maximum values attainable for each experimental condition are presented here. With the exception of one series of tests, the others used distilled water as the liquid medium. The steps in the preparation of samples with various dissolved gases were to repeatedly degas the liquid to a low gas content value and expose it to the particular gas under study. The gas content was monitored with a Van Slyke apparatus. This repeated degassing and exposure was done to ensure that most (if not all) of the air which was originally present was driven out. It was previously reported [3] that in air/water system, the SBSL intensity is strongly dependent on the extent of dissolved air content. Further studies indicated that the behaviour is more complex than suggested by the single set of experiments. Some additional results are presented in Figure 1. The behaviour in argon/water system is similar to that in air/water system at lower gas content (~) values. However, at higher ct, the SBSL intensity in argon/water system seems to reach a constant value. Thus, near saturation conditions the light intensity with argon is higher than that with air. This has been the finding with sonoluminescence (SL) from multi-bubble