Influence of Edge Effects on Laser-Induced Surface Displacement of Opaque Materials by Photothermal Interferometry

We demonstrate the influence of edge effects on the photothermal-induced phase shift measured by a homodyne quadrature laser interferometer and compare the experiments with rigorous theoretical descriptions of thermoelastic surface displacement of metals. The finite geometry of the samples is crucial in determining how the temperature is distributed across the material and how this affects the interferometer phase shift measurements. The optical path change due to the surface thermoelastic deformation and thermal lens in the surrounding air is decoded from the interferometric signal using analytical and numerical tools. The boundary/edge effects are found to be relevant to properly describe the interferometric signals. The tools developed in this study provide a framework for the study of finite size effects in heat transport in opaque materials and are applicable to describe not only the phase shift sensed by the interferometer but also to contribute to the photothermal-based technologies employing similar detection mechanisms

Vpliv robnih učinkov na lasersko induciran pomik površine neprozornih materialov s fototermalno interferometrijo

We demonstrate the influence of edge effects on the photothermal-induced phase shift measured by a homodyne quadrature laser interferometer and compare the experiments with rigorous theoretical descriptions of thermoelastic surface displacement of metals. The finite geometry of the samples is crucial in determining how the temperature is distributed across the material and how this affects the interferometer phase shift measurements. The optical path change due to the surface thermoelastic deformation and thermal lens in the surrounding air is decoded from the interferometric signal using analytical and numerical tools. The boundary/edge effects are found to be relevant to properly describe the interferometric signals. The tools developed in this study provide a framework for the study of finite size effects in heat transport in opaque materials and are applicable to describe not only the phase shift sensed by the interferometer but also to contribute to the photothermal-based technologies employing similar detection mechanisms.Prikažemo vpliv robnih učinkov na fototermalno inducirani fazni premik, ki ga merimo s homodinskim kvadraturnim laserskim interferometrom in poskuse primerjamo z eksaktnimi teoretičnimi opisi termoelastičnih površinskih premikov kovin. Končna geometrija vzorcev je ključnega pomena pri določanju, kako se temperatura porazdeli po materialu in kako to vpliva na merjenje faznega premika interferometra. Razliko optične poti zaradi površinske termoelastične deformacije in termalne leče v okoliškem zraku dekodiramo iz interferometričnega signala s pomočjo analitičnih in numeričnih orodij. Mejni/robni učinki so pomembni za pravilen opis interferometričnih signalov. Orodja, razvita v tej študiji, nudijo okvir za preučevanje učinkov zaradi končnih dimenzij pri prenosu toplote v neprozornih materialih in niso uporabna le za opisovanje faznega premika, ki ga zazna interferometer, temveč prispevajo tudi k fototermalnim tehnologijam, ki uporabljajo podobne mehanizme zaznavanja

Vloga elektrostrikcije pri tvorbi akustičnih valov z optičnimi silami v vodi

We present semi-analytical solutions describing the spatiotemporal distributions of temperature and pressure inside low-absorbing dielectrics excited by tightly focused laser beams. These solutions are compared to measurements in water associated with variations of the local refractive index due to acoustic waves generated by electrostriction, heat deposition, and the Kerr effect at different temperatures. The experimental results exhibited an excellent agreement with the modeling predictions, with electrostriction being the dominant transient effect in the acoustic wave generation. Measurements at show that the thermoelastic contribution to the optical signal is significantly reduced due to the low thermal expansion coefficient of water at this temperature.Predstavljamo pol-analitične rešitve, ki opisujejo prostorsko-časovne porazdelitve temperature in tlaka znotraj dielektrikov z nizko absorpcijo, ki jih vzbujamo s tesno fokusirani laserski žarki. Te rešitve primerjamo pri različnih temperaturah z meritvami v vodi, ki so povezane s spremembami lokalnega lomnega količnika kot posledica preleta akustičnih valov, ki nastanejo z elektrostrikcijo in z odlaganjem toplote ter s Kerrovim učinkom. Eksperimentalni rezultati so pokazali odlično skladnost z napovedmi modeliranja, pri čemer je bila elektrostrikcija prevladujoč prehodni učinek pri ustvarjanju akustičnih valov. Meritve pri 4,0 °C kažejo, da je termoelastični prispevek k optičnemu signalu znatno oslabljen zaradi nizkega toplotnega razteznega koeficienta vode pri tej temperaturi

Razkritje sevalnih sil na površini in v notranjosti dielektrične tekočine

Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies, further playing a paramount role in a host of nanotechnology applications. Nonetheless, the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density. Here, we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid. From the optical convoluted signal, we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density. It is shown, for the first time, that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects. Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces, thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.Natančen nadzor interakcij med svetlobo in snovjo je ključnega pomena za številne metodologije optičnih manipulacij in karakterizacij materialov. Poleg tega igra zelo pomembno vlogo tudi v številnih nanotehnoloških aplikacijah. Kljub temu pa je potrebno temeljne vidike interakcij med elektromagnetnim poljem in snovjo še nedvoumno določiti v smislu gostote gibalne količine elektromagnetnega polja. Za zaznavanje sevalnih sil na površini in v notranjosti dielektrične tekočine smo uporabili tesno fokusirane laserske bliske. Iz zapletenega optičnega signala smo z uporabo teoretične interpretacije, ki temelji na gostoti mikroskopske Ampèrove sile, ločili toplotne in nelinearne optične učinke od sevalnih sil. Prvič je prikazano, da časovno odvisna porazdelitev tlaka znotraj tekočine izvira pretežno iz elektrostrikcijskih učinkov. Naši rezultati osvetljujejo prispevek optičnih sil k površinskim pomikom, opaženih na dielektrični meji zrak-voda, s čimer osvetljujejo dolgoletno polemiko o osnovni definiciji gostote gibalne količine elektromagnetnega polja v snovi