Photoacoustic absorption spectrometer for highly transparent dielectrics with parts-per-million sensitivity

Abstract

A sensitive photoacoustic absorption spectrometer for highly transparent solids has been built and tested. As the light source an optical parametrical oscillator pumped by a nanosecond pulse laser with 10 Hz repetition rate is employed, covering the complete wavelength range from 407 to 2600 nm. A second-harmonic-generation unit extends the range of accessible wavelengths down to 212 nm. A lead-zirconate-titanate piezo transducer, directly coupled to the sample, detects the photoacoustically generated sound waves. Absorption spectra of lithium triborate, lithium niobate, and alpha barium borate crystals with absorption coefficients down to 10(-5) cm(-1) are presented.

Photon momentum transfer at water/air interfaces under total internal reflection

“…In this Letter, we investigate the perturbation induced by an unfocused laser pulse in the water/air interface using photoacoustic detection. Photoacoustic waves (PAs) generated by transient volume changes can be detected with high sensitivity using ultrasonic transducers [20][21][22][23][24]. This enables the measurement of the displacement of the surface molecules (inwards or outwards relative to the medium) either as a result of (inward or outward) pressure at the surface or of thermoelastic changes.…”

Green-induced blue absorption in MgO-doped lithium niobate crystals

“…LiNbO 3 crystals are also utilized for optical modulators and filters [4]. For many applications, the wide transmission window, from 350 to 4200 nm wavelength, and the high transparency, α ≈ 10 −3 cm −1 at 1 μm [5], are of relevance.…”

“…% MgO (MgCLN) suppresses light-induced absorption in the infrared regime [6], increases the transparency for some wavelengths [5], and avoids the undesired photorefraction, i.e., optical damage [10].…”

Observation of a different birefringence order at optical and THz frequencies in LBO crystal

“…−5 cm −1 [3,4]. It has the highest surface damage threshold for laser radiation amongst all known nonlinear crystals, which is even higher than that of UV-grade fused silica [5].…”

“…LBO has the advantages of very high optical damage threshold, very low opti-155 cal losses in the visible, absence of multiphoton absorption, and good thermal, thermo-optical and mechanical properties [1,3,4,5,9,10], all of which make it an attractive crystal for nonlinear generation of THz radiation.…”