Lecture 9: Spectroscopic Applications

Question 1

grating most efficient when

Answer 1

diffracted order emerges from the grating as if by direct reflection

Question 2

solution for grating efficiency

Answer 2

created tilted faces or a BLAZE in the grating

direct majority of light into order of interest

Question 3

direct of specular reflection off the face of each groove - direction

Answer 3

a relative to facet normal

determined by blaze angle gamma

can be varied independent of diffraction angle

Question 4

select blaze angle so that

Answer 4

specular reflection coincides with angle of diffraction

Question 5

blazed grating - envelope shifted so that diffracted intensity

Answer 5

peaks around required order

energy directed away from the useless 0th order

orders other than desired order are strongly suppressed

Question 6

littrow configuration - special case

Answer 6

incident beam normal to face of facet

specular reflection retro-reflected

Question 7

littrow configuration

Answer 7

same lens used for both incident and reflected beam

auto-collimating - collimated on input and output to grating

sight tilt in grating displaces spectrum from entrance slit

Question 8

spectroscopic application

Answer 8

exoplanetary detection

Question 9

echelle grating

Answer 9

typically 20-200 lines per mm
optimised for high orer
blazed for maximum efficiency in range m=10-100
large blaze angle

Question 10

echelle spectrograph pros

Answer 10

very wide spectral coverage achieved
very high resolution
employed in detection of exoplanets