SPETTROMETRI di IMMAGINE

Questo significa che, accoppiato ad una telecamera matrice bianco\nero, l'immagine lineare viene trasformata in immagine spettrale. Questo sistema si basa su una tecnica unica e brevettata che è la prisma - reticolo - prisma.

Questo fa dell’Imspector il primo spettrometro d'immagine a visione diretta nel quale la luce viaggia direttamente attraverso l'asse ottico dello strumento.

Vi sono notevoli vantaggi dati da questa configurazione:

- Lo spettrometro si installa interponendolo tra il corpo della telecamera e l'ottica di un sistema già esistente senza bisogno di dover riconfigurare il sistema optomeccanico

- Produce un’ immagine di alta qualità senza distorsioni

- Non vi sono ottiche riflettive ed il sisstema è indipendente dalla polarizzazione

- Il sistema è molto robusto e compatto (L135 x W70 x 1160) mm ed è ideale per l'applicazione in ambiente industriale.

- Il sistema è molto facile da customizzare per specifici impieghi OEM nella regione 380-2400 nm

Principio di funzionamento ottico e note tecniche

PGP Operating Priciple

The basic operation of the direct-vision, dispersing PGP spectrograph is illustrated in figure at left. The PGP is composed of a specially designed volume type transmission plane grating made of dichromated gelatin (DCG) and cemented between two symmetrical or nearly symmetrical prisms. The grating is designed to operate under Bragg condition and the prism angles change accordingly. A collimated light beam is dispersed at the PGP so that the center wavelength passes axially through the grating and prisms. Shorter and longer wavelengths are dispersed symmetrically on both sides of the central wavelength. It is possible to add an optional filter inside the PGP to limit straylight, to cut off unwanted wavelength bands or to flatten the spectral response. (The spectral flattening property is extremely important with CCD detectors and common halogen light sources which typically lead to high difference between blue vs. red signal level)

Spectrograph Construction

A spectrograph based on the PGP element is composed of a narrow slit, a collimator lens, a PGP element and a focusing lens (see figure). Radiation entering the spectrograph through the slit is collimated by the first lens and refracted at the prism surface to the right incident angle of the holographic grating. The grating disperses the light according to the common grating equation. Spatial information on the entrance slit is transferred to the image plane at the axis parallel to the slit length direction. The spectrum is formed perpendicular to the optical axis with a good spectral linearity. The tubular direct vision (on-axis) construction leads to low geometrical aberrations both in spatial and spectral axis. The optical properties are further quaranteed by using very high quality triplet lenses that are specially designed for imaging purposes.

Stray Light Properties

Any tubular optic construction is sensitive to ghost images and straylight caused by reflections in optical surfaces. There is also a risk of straylight caused by transmitted unwanted orders of diffraction in the holographic grating. These have been taken into account by designing a special optics for the entrance slit and by using critically positioned baffles inside the tube. All the air/glass surfaces have multilayer coatings to reduce backward reflections. The tilted surfaces of the prisms also refract remaining forwarded reflections to blackened walls of the spectrograph tube.