Name: stimulated stokes and antistokes raman scattering in microspherical whispering gallery mode resonators
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Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi
Ente Cassa di Risparmio di Firenze (No. 2014.0770A2202.8861)

1. Realizzazione di Ultrahigh fattore di qualità microsfere <ol><li> Striscia circa 1-2 cm di fibra di silice standard di monomodale (SMF) al largo delle sue rivestimento acrilico utilizzando una spogliarellista ottica. </li><li> Pulire la parte messa a nudo con acetone e fendere esso. </li><li> Introdurre la punta spaccati in un braccio di una giuntatrice a fusione e produrre una serie di scariche ad arco elettrico utilizzando il controller splicer. Selezionare &quot;operazione manuale&quot; dal menu di controllo splicer, impostare i valori per il livello di potenza ad arco e arco della durata di 60 e 800 msec, rispettivamente; selezionare &quot;arco&quot; e spingere il fondo &quot;+&quot;. </li><li> Una volta che una sfera sta prendendo forma, smettere di ruotare la fibra di 90 ° e ripetere il punto 1.3. </li><li> Ripetere passaggio 1.3 almeno 4 volte per ottenere una microsfera di circa 160 micron. Ripetere 16 volte per ottenere una microsfera di circa 260 micron. Nota: Le scariche elettriche arco produrrà l&#39;alta temperatura di fusione necessaria per fondere il vetro di silice. il surface tensione trarrà uno sferoide dalla punta della fibra addolcito; le dimensioni delle sfere è direttamente proporzionale al numero di colpi d&#39;arco, saturando ad un diametro di circa 350 micron, come si può vedere in Figura 1 19. La rotazione assicura una forma sferica del risonatore. </li></ol> 2. Disegno di una fibra Tapered Nota: è necessario anche La fibra rastremata per l&#39;accoppiamento luce nelle microrisonatori. La dimensione della microsfera determinerà la vita del cono. Per diametri sfera maggiore di 125 micron, il diametro del cono può essere di circa 3-4 um. Per più piccoli, il diametro del cono dovrebbe essere più piccolo, dire 1-2 micron. Per mantenere le perdite a livello basso e di avere solo una modalità nella sezione rastremata (quello fondamentale), la rastremazione deve essere adiabatica (transizione graduale dalle spessore diametro sottile). La lunghezza totale tipica della sezione rastremata adiabatica è di circa 2 cm. Figure 2 mostra il dispositivo fatto in casa per tirare la fibra e la figura 3A mostra una microphoto di una tipica zona di vita. <ol><li> Striscia 3-4 cm di una fibra di silice normale monomodale (SMF) off suo rivestimento acrilico utilizzando un estrattore ottica, e collegare la fibra termina ad un laser (input) e un misuratore di potenza (output). Assicurarsi che la zona spogliato è circa a metà della fibra, non ad una estremità. Utilizzare un terminatore fibra nuda per essere in grado di collegare la fibra termina al misuratore laser e di potenza. Posizionare il laser e il misuratore di potenza sulla parte superiore del banco di lavoro. </li><li> Posizionare la fibra spogliato all&#39;interno di un cilindro corto allumina, e le estremità della fibra rivestiti in due fasi di traduzione che azionano simultaneamente durante il processo di trazione. </li><li> Riscaldare il cilindro allumina (che agisce come un forno) da una fiamma di ossigeno-butano fino ad una temperatura prossima ad un punto di fusione di silice (circa 2.100 ° C). </li><li> Dedurre la adiabaticity del cono dal observation della trasmissione di una luce laser operante a 635 nm. Verificare che in uscita un punto circolare omogenea è conservata mentre assottiglia, indicando che si verifica alcuna modalità scrambling. Smettere di tirare e ritirarsi fiamma quando la potenza trasmessa ferma oscillante, ed è costante nel tempo. </li><li> Incollare la fibra rastremata in un vetrino da microscopio sagomato a forma di U per accogliere il cono (vedere Figura 3B). Utilizzare un vetrino da microscopio delle dimensioni 76x26x1.2 mm. </li></ol> 3. Realizzazione di piccole microsfere Nota: Le piccole microsfere con diametro di sotto delle dimensioni di una fibra normale rivestito richiedono precedente rastremazione della fibra. Il diametro minimo ottenuto con questo metodo è di circa 25 micron. <ol><li> Seguendo la sezione 2, disegnare una fibra rastremata, tirando fino a che non si rompe. </li><li> Seguire tutte le fasi della sezione 1 (fabbricazione di microsfere UHQ), ma nella fase 1.3, modificare i valori in splicer controller come segue: potere ad arco 20, durata dell&#39;arco 1.200 msec. </li></ol> 4. Giunto luce nella microsfera Nota: Usiamo il cono di luce paio nella microsfera e misurare le risonanze del microrisonatore. <ol><li> 4.1. Preparare un supporto / alluminio PVC a forma di T con un canale nel mezzo. Fissare la deriva in fibra residua del microsfere con un pezzo di magia adesivo o un nastro adesivo di carta nel supporto. Fissare il supporto con due viti in una fase di traduzione con attuatori piezoelettrici e una risoluzione di posizionamento di 20 nm. </li><li> Fissare la rastremazione incollato al vetrino in un&#39;altra fase di traduzione con il piano scorrevole disposto perpendicolarmente allo stelo fibra microsfere. Splice le estremità del cono di cavi in ​​fibra terminati. Collegare un&#39;estremità al diodo laser sintonizzabile e l&#39;altra ad un rivelatore fotodiodo InGaAs. </li><li> Utilizzare un tubo microscopio con lunga distanza di lavoro (&gt; 20 mm) per control il divario tra il cono e microsfere. Per monitorare il sistema in altro luogo direzione a specchio a 45 ° rispetto alla direzione di tubo in modo che la posizione del cono rispetto all&#39;equatore della microsfera può essere controllato. <ol><li> Posizionare l&#39;equatore della microsfera a contatto con la fibra rastremata. </li></ol></li><li> Accendere il laser e controllare lo spettro di trasmissione del sistema di microsfere-cono in un oscilloscopio. <ol><li> Tune il laser CW operante a 1.550 nm fino all&#39;apparizione di risonanze. Le risonanze possono essere identificati come Lorentzian forma tuffi nello spettro. </li></ol></li><li> Misurare la larghezza di riga di risonanza (larghezza massima della metà del tuffo a forma Lorentziano). Calcolare il fattore Q come la frequenza della pompa divisa per la larghezza di riga di risonanza. </li><li> Ridurre / aumentare la distanza tra la sfera e il cono, cambiando sia in larghezza e profondità di risonanza per aumentare / diminuire l&#39;efficienza di accoppiamento. </li></ol><pclass = &quot;jove_title&quot;&gt; 5. Stimolata Raman Scattering <ol><li> Inserire un amplificatore in fibra drogata con Erbio (EDFA) tra il laser CW operante a 1.550 nm e l&#39;attenuatore. L&#39;EDFA funziona nella gamma di lunghezze d&#39;onda di 1,530-1,570 nm. Nota: Questo aumenterà la potenza del laser, raggiungendo una potenza di uscita massima di 2 effetti non lineari W. bisogno di potenze di ingresso elevate figura 4 mostra uno schizzo del set-up sperimentale.. </li><li> Collegare una estremità del cono con cavi in ​​fibra terminati a uno splitter 3 dBm. Collegare una delle fibre in uscita splitter per l&#39;analizzatore di spettro ottico e l&#39;altra ad un fotorilevatore che è collegato all&#39;oscilloscopio. </li><li> Tune il laser da alta a basse frequenze fino a risonanza con una deriva termica paragonabile alla lunghezza d&#39;onda velocità di scansione del laser è trovato. Una volta raggiunta la termica autobloccante 20 un allargamento della risonanza può essere visto sul oscilloscopio. </li><li> Controllare la potenza trasmessa attraverso il conoin un analizzatore di spettro ottico. Aumentare la potenza fino a visualizzare la linea laser Raman. Esso viene intonata dalla lunghezza d&#39;onda della pompa a circa 13,5 THz. </li></ol>

<ol>
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The authors declare that they have no competing financial interests. D.F. is a PhD student at the University of Parma.

Le microsfere sono oscillatori non lineari compatti ed efficienti e sono molto facili da realizzare e gestire. fibre conici possono essere utilizzati per l&#39;accoppiamento e l&#39;estrazione della luce / dal risonatore. Resonance contrasto fino al 95% e fattori Q di circa 3 x 10 8 possono essere ottenuti. Il principale limite di queste tecniche di fabbricazione è la produzione di massa e di integrazione. Pulizia delle fibre è fondamentale per entrambe le microsfere e conicità...

Whispering risonatori modalità galleria (WGMR) mostrano due proprietà uniche, una lunga durata e volume fotone modalità di piccole dimensioni che consentono la riduzione della soglia di fenomeni non lineari 1-3. Whispering modalità galleria sono i modi ottici che si limitano all&#39;interfaccia aria dielettrico per riflessione interna totale. Il volume modalità piccola è dovuta alla elevata confinamento spaziale che il confinamento temporale è correlata al fattore di qualità Q della cavità. WGMR può avere diverse geometrie e ci sono diverse tecniche di fabbricazione adatti per l&#39;ottenimento di elevati risonatori Q 4-6 cavità Tensione superficiale come ad esempio microsfere di silice mostra vicino rugosità scala atomica, che si traduce in fattori di alta qualità. Entrambi i tipi di confinamento riducono significativamente la soglia per effetti non lineari dovuti al forte accumulo di energia all&#39;interno del WGMR. Permette anche Continuous Wave (CW) ottica non lineare. WGMR può essere descritto utilizzando esimoe numeri quantici n, l, m ed il loro stato di polarizzazione, di una forte analogia con l&#39;atomo di idrogeno 7. La simmetria sferica permette la separazione in senso radiale e dipendenze angolari. La soluzione radiale è data da funzioni di Bessel, quelli angolari dalle armoniche sferiche 8. Vetro di silice è centrosimmetriche e, di conseguenza, secondo i fenomeni di ordine legate alla Χ (2) le interazioni sono vietati. Alla superficie della microsfera, l&#39;inversione di simmetria è rotta e Χ (2) fenomeni può osservare 1. Tuttavia, le condizioni di accordo di fase per la generazione di frequenza secondo ordine sono più problematiche rispetto all&#39;equivalente in terza generazione di frequenza dell&#39;ordine, soprattutto perché le lunghezze d&#39;onda coinvolte sono molto diverse e il ruolo della dispersione può essere molto importante. Il secondo ordine interazioni sono estremamente deboli. Le scale di potenza generati con Q 3, mentre per un Third ordine interazione scale potenza generata con Q 4. 9 Per questo motivo, il focus di questo lavoro è terzo ordine suscettibilità non lineare ottico Χ (3) interazioni, come stimolata Raman Scattering (SRS) e stimolato Antistokes Raman Scattering (SARS) , essendo la SARS l&#39;interazione meno esplorati 10,11. Chang 12 e Campillo 13 pionieri degli studi di fenomeni non lineari utilizzando gocce di materiali altamente non lineari come WGMR ma il laser pompa è stata pulsava invece di CW. Microsfere di silice 14,10 e microtoroids 15 apposite piattaforme più stabili e robusti rispetto alle micro-goccioline, guadagnando gran parte dell&#39;attenzione negli ultimi decenni. In particolare, microsfere di silice sono molto facili da fabbricare e maneggiare. SRS è un processo di guadagno puro che può essere realizzato facilmente in WGMR silice 14,15, dal raggiungimento di una soglia è sufficiente. In questo caso, l&#39;elevato circulating intensità all&#39;interno WGMR garantisce Raman lasing, ma per oscillazioni parametriche non è sufficiente. In questi casi, oscillazioni efficienti richiedono fase e corrispondente modalità, l&#39;energia e la legge di conservazione del momento e una buona sovrapposizione spaziale di tutti i modi di risonanza da soddisfare 16-18. Questo è il caso per la SARS e FWM in generale.

<table><tbody><tr><td>Optical Fiber</td><td>Corning</td><td>SMF28</td><td></td></tr><tr><td>Fiber coating stripper</td><td>Thorlabs</td><td>T06S13</td><td>Available from other vendors as well</td></tr><tr><td>Fiber cleaver</td><td>Fitel</td><td>S325A</td><td>Available from other vendors as well</td></tr><tr><td>Fusion splicer</td><td>Furakawa</td><td>S177A-1R</td><td>Available from other vendors as well</td></tr><tr><td>Butane and Oxygen Gas</td><td>n/a</td><td></td><td>any vendor</td></tr><tr><td>Microscope tube</td><td>Navitar</td><td>Zoom 6000</td><td>Modular Kit</td></tr><tr><td>CCD camera</td><td>n/a</td><td>N/A</td><td>any will fit</td></tr><tr><td>Monitor</td><td>n/a</td><td>N/A</td><td>any monitor is valid</td></tr><tr><td>3-Axis Stage</td><td>PI Instruments, Thorlabs, Melles</td><td></td><td></td></tr><tr><td>Assorted posts and mounts</td><td>Thorlabs</td><td></td><td>Available from other vendors as well</td></tr><tr><td>Polarization control</td><td>Thorlabs</td><td>FPC030</td><td>Available from other vendors as well</td></tr><tr><td>Attenuator</td><td>Throlabs</td><td>VOA50</td><td></td></tr><tr><td>Photodiode</td><td>Thorlabs</td><td>PDA400</td><td>discontinued, replaced by PDA10CS-EC</td></tr><tr><td>Oscilloscope</td><td>Tektronix</td><td>DPO7104</td><td></td></tr><tr><td>Optical spectrum analyzer</td><td>Ando</td><td>AQ6317B</td><td></td></tr><tr><td>Erbium Doped Fiber Amplifier</td><td>IPG Photonics</td><td>EAD-2K-C</td><td></td></tr><tr><td>Tunable Laser</td><td>Yenista</td><td>TUNICS</td><td></td></tr></tbody></table>

stimulated stokes and antistokes raman scattering in microspherical whispering gallery mode resonators

microsfere dielettrici possono limitare luce e suono per un periodo di tempo attraverso il fattore sussurra di alta qualità modalità galleria (WGM). microsfere di vetro può essere pensato come riserva di energia, con una grande varietà di applicazioni: sorgenti laser compatto, sensori biochimici altamente sensibili e fenomeni non lineari. Un protocollo per la fabbricazione di entrambe le microsfere e sistema di accoppiamento è dato. Gli accoppiatori qui descritti sono fibre conici. Generazione efficiente di fenomeni non lineari relativi alla suscettibilità non lineare ottico terzo ordine Χ (3) interazioni in microsfere di silice triplamente risonanti è presentato in questo articolo. Le interazioni qui riportati sono: stimolata Raman Scattering (SRS), e quattro processi wave mixing composto stimolata Anti-Stokes Raman Scattering (SARS). Una prova del fenomeno cavità avanzata è data dalla mancanza di correlazione fra la pompa, di segnale e folle: un modo di risonanza deve esistere per ottenere la coppiadi segnale e di folle. Nel caso di oscillazioni hyperparametric (quattro onde e stimolato anti-Stokes Raman scattering), le modalità devono soddisfare la conservazione dell&#39;energia e del momento e, ultimo ma non meno importante, avere una buona sovrapposizione spaziale.

I fattori Q delle microsfere fabbricati seguendo il protocollo di cui sopra è superiore a 10 8 (Figura 5) per grandi diametri (&gt; 200 micron) e superiore a 10 6 per piccoli diametri (&lt;50 micron). Resonance contrasto superiore a 95% (vicino a accoppiamento critico) può essere facilmente osservato. Per le alte intensità di circolazione, i seguenti effetti non lineari nella regione infrarossa può essere osservato: stimolate Raman (SRS), cascat...

Watch this Scientific Journal Video about Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators at JoVE.com

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Stimolata Stokes e Antistokes Raman Scattering in Microspherical Whispering Gallery modalità risonatori

Generazione efficiente di fenomeni non lineari relativi alla suscettibilità non lineare ottico terzo ordine Χ (3) interazioni in microsfere di silice triplamente risonanti è presentato in questo articolo. Le interazioni qui riportati sono: stimolata Raman Scattering (SRS), e quattro processi wave mixing composto stimolata Anti-Stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...

stimulated-stokes-antistokes-raman-scattering-microspherical

Universidad de Cartagena UDEC

Research

JoVE Journal

Engineering

11.2K Views.  Enrico Fermi Center.  Generazione efficiente di fenomeni non lineari relativi alla suscettibilità non lineare ottico terzo ordine Χ (3) interazioni in microsfere di silice triplamente risonanti è presentato in questo articolo. Le interazioni qui riportati sono: stimolata Raman Scattering (SRS), e quattro processi wave mixing composto stimolata Anti-Stokes Raman Scattering (SARS). 

Video: Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Rejection of Fluorescence Background in Resonance and Spontaneous Raman Microspectroscopy

Raman spectroscopy is often plagued by a strong fluorescent background, particularly for biological samples. If a sample is excited with a train of ultrafast pulses, a system that can temporally separate spectrally overlapping signals on a picosecond timescale can isolate promptly arriving Raman scattered light from late-arriving fluorescence light. Here we discuss the construction and operation of a complex nonlinear optical system that uses all-optical switching in the form of a low-power optical Kerr gate to isolate Raman and fluorescence signals. A single 808 nm laser with 2.4 W of average power and 80 MHz repetition rate is split, with approximately 200 mW of 808 nm light being converted to &lt; 5 mW of 404 nm light sent to the sample to excite Raman scattering. The remaining unconverted 808 nm light is then sent to a nonlinear medium where it acts as the pump for the all-optical shutter. The shutter opens and closes in 800 fs with a peak efficiency of approximately 5%. Using this system we are able to successfully separate Raman and fluorescence signals at an 80 MHz repetition rate using pulse energies and average powers that remain biologically safe. Because the system has no spare capacity in terms of optical power, we detail several design and alignment considerations that aid in maximizing the throughput of the system. We also discuss our protocol for obtaining the spatial and temporal overlap of the signal and pump beams within the Kerr medium, as well as a detailed protocol for spectral acquisition. Finally, we report a few representative results of Raman spectra obtained in the presence of strong fluorescence using our time-gating system.

We discuss the construction and operation of a complex nonlinear optical
system that uses ultrafast all-optical switching to isolate Raman from fluorescence
signals. Using this system we are able to successfully separate Raman and fluorescence
signals utilizing pulse energies and average powers that remain biologically safe.

Rifiuto di fluorescenza di fondo in risonanza e spontanea microspettroscopia Raman

Raman spectroscopy is often plagued by a strong fluorescent background, particularly for biological samples. If a sample is excited with a train of ...

Ricerca

Bioingegneria

Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field Sensors

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The optical modes are frequently referred to as "whispering gallery modes" (WGM) or "morphology dependent resonances" (MDR) and exhibit high optical quality factors. Some proposed applications of micro-cavity optical resonators are in spectroscopy1, micro-cavity laser technology2, optical communications3-6 as well as sensor technology. The WGM-based sensor applications include those in biology7, trace gas detection8, and impurity detection in liquids9. Mechanical sensors based on microsphere resonators have also been proposed, including those for force10,11, pressure12, acceleration13 and wall shear stress14. In the present, we demonstrate a WGM-based electric field sensor, which builds on our previous studies15,16. A candidate application of this sensor is in the detection of neuronal action potential.
The electric field sensor is based on polymeric multi-layered dielectric microspheres. The external electric field induces surface and body forces on the spheres (electrostriction effect) leading to elastic deformation. This change in the morphology of the spheres, leads to shifts in the WGM. The electric field-induced WGM shifts are interrogated by exciting the optical modes of the spheres by laser light. Light from a distributed feedback (DFB) laser (nominal wavelength of ~ 1.3 &mu;m) is side-coupled into the microspheres using a tapered section of a single mode optical fiber. The base material of the spheres is polydimethylsiloxane (PDMS). Three microsphere geometries are used: (1) PDMS sphere with a 60:1 volumetric ratio of base-to-curing agent mixture, (2) multi layer sphere with 60:1 PDMS core, in order to increase the dielectric constant of the sphere, a middle layer of 60:1 PDMS that is mixed with varying amounts (2% to 10% by volume) of barium titanate and an outer layer of 60:1 PDMS and (3) solid silica sphere coated with a thin layer of uncured PDMS base. In each type of sensor, laser light from the tapered fiber is coupled into the outermost layer that provides high optical quality factor WGM (Q ~ 106). The microspheres are poled for several hours at electric fields of ~ 1 MV/m to increase their sensitivity to electric field.

A high-sensitivity photonic micro sensor was developed for electric field detection. The sensor exploits the optical modes of a dielectric sphere. Changes in the external electric field perturb the sphere morphology leading to shifts in its optical modes. The electric field strength is measured by monitoring these optical shifts.

Sviluppo di Whispering Galleria polimerici modalità micro-ottici sensori di campo elettrico

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The ...

Ingegneria

Microwave Photonics Systems Based on Whispering-gallery-mode Resonators

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

The customized techniques developed in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators are presented. The protocols to obtain and characterize these resonators are detailed, and an explanation of some of their applications in microwave photonics is given.

Microonde Photonics sistemi basati su risonatori-galleria-mode Whispering

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Fabbricazione e la sperimentazione di microfluidici optomechanical Oscillatori

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

The paper describes a method for producing extreme nanowires by melt infiltration into carbon nanotubes and how 1D systems may be characterized and investigated using Resonance Raman Spectroscopy to determine vibrational and optical excitation energies.

Risonanza Spettroscopia Raman di estrema nanofili e altri sistemi 1D

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the ...

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with &lt;10 MHz spectral-resolution and &lt;35 MHz Brillouin-shift measurement precision at &lt;100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

We describe the construction of a rapid continuous-wave-stimulated-Brillouin-scattering (CW-SBS) spectrometer. The spectrometer employs single-frequency diode-lasers and an atomic vapor notch-filter to acquire transmission spectra of turbid/non-turbid samples with high spectral-resolution at speeds up to 100-fold faster than those of existing CW-SBS spectrometers. This improvement enables high-speed Brillouin material analysis.

Ad alta velocità continuo-fluttui stimolato Brillouin Scattering spettrometro per analisi materiali

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

Fabbricazione di microsfere di polimeri per risonatore ottico e applicazioni laser

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Implementation of a Nonlinear Microscope Based on Stimulated Raman Scattering

Stimulated Raman scattering (SRS) microscopy uses near-infrared excitation light; therefore, it shares many multi-photon microscopic imaging properties. SRS imaging modality can be obtained using commercial laser-scanning microscopes by equipping with a non-descanned forward detector with proper bandpass filters and lock-in amplifier (LIA) detection scheme. A schematic layout of a typical SRS microscope includes the following: two pulsed laser beams, (i.e., the pump and probe directed in a scanning microscope), which must be overlapped in both space and time at the image plane, then focused by a microscope objective into the sample through two scanning mirrors (SMs), which raster the focal spot across an x-y plane. After interaction with the sample, transmitted output pulses are collected by an upper objective and measured by a forward detection system inserted in an inverted microscope. Pump pulses are removed by a stack of optical filters, whereas the probe pulses that are the result of the SRS process occurring in the focal volume of the specimen are measured by a photodiode (PD). The readout of the PD is demodulated by the LIA to extract the modulation depth. A two-dimensional (2D) image is obtained by synchronizing the forward detection unit with the microscope scanning unit. In this paper, the implementation of an SRS microscope is described and successfully demonstrated, as well as the reporting of label-free images of polystyrene beads with diameters of 3 &#181;m. It is worth noting that SRS microscopes are not commercially available, so in order to take advantage of these characteristics, the homemade construction is the only option. Since SRS microscopy is becoming popular in many fields, it is believed that this careful description of the SRS microscope implementation can be very useful for the scientific community.

In this manuscript, the implementation of a stimulated Raman scattering (SRS) microscope, obtained by the integration of an SRS experimental set-up with a laser scanning microscope, is described. The SRS microscope is based on two femtosecond (fs) laser sources, a Ti-Sapphire (Ti:Sa) and synchronized optical parametric oscillator (OPO).

Implementazione di un microscopio non lineare basato sullo scattering Raman stimolato

Stimulated Raman scattering (SRS) microscopy uses near-infrared excitation light; therefore, it shares many multi-photon microscopic imaging properties. ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional .

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...

Chimica

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy is a nonlinear optical technique for label-free chemical imaging. This analytical tool delivers chemical maps at high speed, and high spatial resolution of thin samples by directly interrogating their molecular vibrations. In its standard implementation, SRS microscopy is narrowband and forms images with only a single vibrational frequency at a time. However, this approach not only hinders the chemical specificity of SRS but also neglects the wealth of information encoded within vibrational spectra. 
These limitations can be overcome by broadband SRS, an implementation capable of extracting a vibrational spectrum per pixel of the image in parallel. This delivers hyperspectral data that, when coupled with chemometric analysis, maximizes the amount of information retrieved from the specimen. Thus, broadband SRS improves the chemical specificity of the system, allowing the quantitative determination of the concentration of the different constituents of a sample. Here, we report a protocol for chemical imaging with broadband SRS microscopy, based on a home-built SRS microscope operating with a custom differential multichannel-lock-in amplifier detection. It discusses the sample preparation, alignment of the SRS apparatus, and chemometric analysis. By acquiring vibrational Raman spectra, the protocol illustrates how to identify different chemical species within a mixture, determining their relative concentrations.

We present a protocol to acquire chemical images with broadband stimulated Raman scattering (SRS) microscopy. Based on an SRS microscope that operates with differential multichannel-lock-in detection, the protocol describes the sample preparation, adjustment of the SRS apparatus, and chemometrics to disentangle different constituents of chemically heterogeneous samples.

Imaging chimico multiplex basato sulla microscopia a dispersione Raman stimolata a banda larga

Stimulated Raman scattering (SRS) microscopy is a nonlinear optical technique for label-free chemical imaging. This analytical tool delivers chemical maps ...