Telescopes & Adaptive Optics. Roberto Ragazzoni INAF Astronomical Observatory of Padova

Transcription

1 Telescopes & Adaptive Optics Roberto Ragazzoni INAF Astronomical Observatory of Padova

2

3 PAST

4 PAST FUTURE

5

6

7 This is a simmetry line

8

9 This object is drawn in a plane but

10 it acctually reppresent a three dimensional object

11

12 So this is a round concave mirror with a central hole

13 So this is a round concave mirror with a central hole

14 D is the diameter or aperture of the telescope D

15 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

16 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

17 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

18 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

19 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

20 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

21 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

22 D is the diameter or aperture of the telescope D=1.22m the Asiago-Pennar telescope D=1.82m the Asiago-Ekar telescope D=3.58m the TNG, Telescopio Nazionale Galileo D=8.2m one of the VLT, Very Large Telescope D=8.4m one of the mirror of the LBT, Large Binocular Telescope D=30m the TMT, Thirty Mirror Telescope D=39m the E-ELT, European Extremely Large Telescope D

23 So, let s keep the roundness as a first approx D

24

25 An old fashioned conventional 1.22m telescope

26 An old fashioned conventional 1.22m telescope and a futuristic segmented 39m telescope

27

28

29 This is light coming from a certain unresolved point source located at infinity.

30

31

32

33

34

35 This light is actually collected from the telescope

36 while this other is lost

37

38 This edge defines the pupil

39 This edge defines the pupil

40 This edge defines the pupil D

41 ε is the linear obstruction coefficent D ε D

42 The shaded one is the useful area

43 The shaded one is the useful area Useful area is πd 2 /4(1-ε 2 ) ε= % of the area (Yerkes) ε=0.1 99% ( ) ε=0.2 96% (Very Large Telescope) ε=0.3 91% (Hubble Space Telescope) ε=0.5 75% (Pino Torinese)

44 So these are the edges of the pupil

45 And these rays are called marginal

46

47 And this is the primary mirror foci

48 And this is where it focus an off-axis source

49

50

51 The primary mirror focal plane

52 The mirror conjugates two points

53 One at infinity (or very long distance) and lying on the simmetry axis

54 And one in the focus of the concave surface

55 If the primary mirror is a parabolid the conjugation is perfect in geometric approx and it is said stigmatic

56 If the primary mirror is a parabolid the conjugation is perfect in geometric approx and it is said stigmatic

57 Let s now mount on top of the primary mirror a convex hyperboloidal mirror

58 This surface is characterized by two conjugated points, the foci of the hyperbola generating the surface

59 This surface is characterized by two conjugated points, the foci of the hyperbola generating the surface

60 ..and co-align with the foci of the concave mirror

61 The marginal rays now does no longer reach the primary focal plane

62 But instead reach what is called the Cassegrain foci

63 This also re-defines the obstruction by the secondary mirror

64

65 Some nomenclature

66 Some nomenclature M1

67 Some nomenclature M1 M2

68 Some nomenclature The primary mirror foci M1 M2

69 Some nomenclature The primary mirror foci M1 M2 The combined Cassegrain- foci

70

71 Some off-axis marginal rays

72 Please note this ray goes just on the edges of M2

73 All together now

74 This defines a Field of View FoV/2

75 ..and a magnification factor m FoV/2 x f 1

76 FoV/2 x f..and a magnification factor m FoV/2 x f 1

77 FoV/2 x f..and a magnification factor m m=f/f 1 FoV/2 x f 1

78 What if the observation is in the Thermal InfraRed Thermal InfraRed means that the environment where the telescope is located emits significantly at that wavelength range On the ground (T=300K) this happens at wavelengths larger than about 2.4um K or K-short is the K band truncated below such threeshold K is in Thermal InfraRed This thermal background can significantly increase the background

79 How can an evilish ground-based Th-IR photon, reach the focal plane?

80 How can an evilish ground-based Th-IR photon, reach the focal plane?

81 How can an evilish ground-based Th-IR photon, reach the focal plane?

82 Let s undersize the secondary mirror

83 These rays does no longer reach the focal plane

84 And, in fact, they are not anymore marginal

85

86 These are actually the new marginal rays

87 And this is the bundle of rays that are actually collected

88 This is actually the new pupil of such a telescope

89 Making the effective aperture of the telescope smaller than the diameter of the main mirror

90 Making the effective aperture of the telescope smaller than the diameter of the main mirror D D 1 VLT D 1 =8.2m, D=8.0m LBT: D 1 =8.4m, D=8.2m

91

92

93 The pupil Where the pupil is located can be extremely important It can makes a telescope able to reject ThIR light at the expense of a little loss in effective aperture It can be used to conjugate a small corrector to a large mirror (Arecibo, MacDonald) It can be used in Adaptive Optics

94

95 A pupil

96 Adaptive Optics The atmospheric distorted WF can be corrected using a Deformable Mirror (DM). The wavefront sensor (WFS) measures the WF of a reference star-object The measurement is used to drive the DM to introduce an opposite WF-deformation. A new WF measurement is then performed to apply a differential correction in a closed loop way 15/10/07 MPIA - Heidelberg 96

97

98

99

100

101

102

103

104 Syracuse about 2215 years ago

105 Syracuse about 2215 years ago

106 Syracuse about 2215 years ago DM

107 Syracuse about 2215 years ago DM WCSD (dichroic) Woodden Coated Scattering Device

108 Syracuse about 2215 years ago DM WCSD (dichroic) Woodden Coated Scattering Device

109 Syracuse about 2215 years ago DM WFC WFS WCSD (dichroic) Woodden Coated Scattering Device

110 California about 62 years ago

111 California about 62 years ago

112 California about 62 years ago Dichroic DM WFS

113 California about 62 years ago Dichroic DM WFS

114 California about 62 years ago Resembling a variable Thickness Mangin mirror

115 California about 62 years ago

116 Kolmogorov

117 Kolmogorov Outer scale Telescope size r0 Innerscale

118 A 2D plot of turbulence

119 Atmospheric turbulence TIP-TILT: AVERAGE OF ALL THE DEFORMATIONS!! TIP-TILT HIGH ORDERS Movement Integrated in time Size increase Tilt extimation 4-Quadrant Sensor High Orders extimation Specific Wavefront Sensors TIP-TILT CORRECTION: TILTING FLAT MIRROR HIGH-ORDER CORRECTION: DEFORMABLE MIRROR

120 Fried parameter r0 Our enemy some figures One rad of phase is our unit

121 Arizona about 44 years ago

122 Arizona about 44 years ago Wavefront Lenses Spot images

123 Our enemy some figures Astronomical Object Wavefront Telescope Entrance Pupil Image Plane r FRIED Parameter 6/5 2 3/5 0 [ dhcn ( h) ] 6/5 0 0 Temporal behaviour of the turbulence o 0 6/5 1ms r 0 Perfect Image Deformated Image Strehl Ratio: PSF obs /PSF teo

124 Isoplanatic angle Guide Star Scientific Object ISOPLANATIC ANGLE: Angle from the reference star where the correction is still effective Telescope pupil projections Turbulent Layers 0 r / 0 h h Telescope pupil

125 Turbulence parameters Fried parameters (the size at which WF perturbation is statistically more than one radians) Greenwood frequency (the inverse of the time at which perturbation changes more than one radians) Isoplanatic angle (the angular distance between two sources whose wavefront is perturbed differently by more than a radians)

126 Wavefront Error (nm) 100nm 10nm Narrow field NGS IR AO Narrow field Visible AO Narrow field LGS IR AO # of DM actuators # of WFS sub-apertures Ground-layer AO Multi-Conjugate AO (MCAO) Optics size, optical complexity AO loop speed More photons needed Field of View

127 Wavefront Error (nm) 100nm 10nm Narrow field NGS IR AO Narrow field Visible AO Narrow field LGS IR AO # of DM actuators # of WFS sub-apertures Ground-layer AO Multi-Conjugate AO (MCAO) Optics size, optical complexity AO loop speed More photons needed Field of View

128 The strategic defense initiative (propagation in the atmosphere declassified in 1991) Kick off: March 23rd, 1983

129 The strategic defense initiative (propagation in the atmosphere declassified in 1991)

130 The strategic defense initiative (propagation in the atmosphere declassified in 1991)

131 South of France about 26 years ago and then at ESO LaSilla 3.6m With Come-On and Come-On+

132 Deformable Mirrors

133 Deformable Mirrors Densità attuatori

134 Deformable Mirrors Densità attuatori Frequenza temporale

135 Deformable Mirrors Densità attuatori Frequenza temporale Accoppiamento

136 Deformable Mirrors

137 Deformable Mirrors

138 Deformable Mirrors

139 Deformable Mirrors

140 Florence about 22 years ago Active and adaptive optics: ESO Proceedings of the ICO-16 August 2-5, 1993, Garching

141 Secondary Adaptive Mirrors

142 Layers for an artificial reference

143 Layers for an artificial reference

144

145 Problems of LGSs Tip-tilt indetermination problem Conical anisoplanatism Focus at a finite distance Rayleigh fratricide effects Actual distance depends upon altitude and layer local variations Cyrrus can make large scattered light Aircraft and satellite hazards You need a working laser!

146 Layers for an artificial reference

147 LGS launch systems Launch mirror Beam expander exit and folding flat Wavefront sensor Laser units Laser platform

148 Arizona (with some Italian flavor ) about 20 years ago

149 Canale: PadovAdopt

150 present to future High order AO with high efficiency mades XAO Wider Field of View achieved with multiple DMs Pushing into the visible and into larger Sky Coverage Using LGSs or even higher efficient Wide Field AO (wait for a couple of days ) Making the telescope fully adaptive Making corrections achievable on a small scale (MOAO)

151 Wider Field of View

152

153

154

155 Wider Field of View