Thermal lens measurements of optical computation of the laser beam spot size

Abstract

A signal processor, which computes the second spatial moment or spot size of a laser beam In two dimensions by optical rather than electronic means, reduces the Impact of spatial noise on thermal lens measurements. The spot size determination Is sufficiently fast to allow time averaging by either transient recording or lock-in amplification; the ultimate speed of computation Is limited only by the transit time of light through the device. The thermal lens detection limits using the optical processor are A m,n = 1.1 X 10~7 for a 1 cm path length In CCI4 and a laser power of 80 mW. This method of spot size detection Is contrasted with photodiode array profiling of the laser beam, which is also used to illustrate the problems of spatial noise In thermal lens measurements.

Time-resolved photothermal and photoacoustic methods applied to photoinduced processes in solution

“…Using an approach based on the diffraction theory of Sheldon et al, 44 Carter and Harris successfully predicted absolute values of the thermal lens response. 46 In order to achieve accuracy, the aberrant nature of the photoinduced lens was taken into account.…”

Generalization of multivariate optical computations as a method for improving the speed and precision of spectroscopic analyses

“…This dot product can be calculated either explicitly by MDCs or implicitly MOCs. In previous applications of MOC, the ILS/LD model was either implicitly assumed or explicitly applied [1,[9][10][11][12].…”

“…For example, Caulfield and Mueller employed a linear variable filter for predictive classification of colored glasses [9]. In 1985, Jansen and Harris employed optical computations to calculate the two-dimensional second moment of a laser beam waste to determine focus diameter during thermal lens experiments [10]. More recently Lewis et al employed optical computations for edge finding in chemical images [11] and Prakash et al demonstrated the advantages of optical computations for multivariate calibration of rhodomine dye mixtures [1].…”

Time-resolved photothermal lens calorimetry for investigating mixed-order photoinitiated reaction kinetics in liquids

“…sample) and is centered on a mask having a radially-symmetric, parabolic transmittance profile; the intensity of radiation transmitted by this mask, collected with a plano-convex lens and focused onto a photomultiplier, is proportional to the second spatial moment of the probe beam intensity distribution. 35 Changes in the far-field area of the beam caused by the thermal lens are thus detected using information from the entire probe beam and not just the center intensity; this approach reduces the impact of spatial noise on the measurement and improves the precision of the signal by 1 order of magnitude over measuring the beamcenter intensity.…”