Abstract

In this paper, we report measurements of diffraction efficiency and angular dispersion for a large format (~25 cm diameter) Volume-Phase Holographic (VPH) grating optimized for near-infrared wavelengths (0.9~1.8 µm). The aim of this experiment is to see whether optical characteristics vary significantly across the grating. We sampled three positions in the grating aperture with a separation of 5 cm between each. A 2 cm diameter beam is used to illuminate the grating. At each position, throughput and diffraction angle were measured at several wavelengths. It is found that whilst the relationship between diffraction angle and wavelength is nearly the same at the three positions, the throughputs vary by up to ~10% from position to position. We explore the origin of the throughput variation by comparing the data with predictions from coupled-wave analysis. We find that it can be explained by a combination of small variations over the grating aperture in gelatin depth and/or refractive index modulation amplitude, and amount of energy loss by internal absorption and/or surface reflection.

© 2005 Optical Society of America

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References

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  1. S. C. Barden, J. A. Arns, and W. S. Colburn, �??Volume-phase holographic gratings and their potential for astronomical applications,�?? in Optical Astronomical Instrumentation, S. D�??Odorico, ed., Proc. SPIE 3355, 866�??876 (1998).
  2. S. C. Barden, J. A. Arns, W. S. Colburn, and J. B. Williams, �??Volume-Phase Holographic Gratings and the Efficiency of Three Simple Volume-Phase Holographic Gratings,�?? Publication of Astronomical Society of Pacific 112, 809�??820 (2000).
    [CrossRef]
  3. P. -A. Blanche, S. L. Habraken, P. C. Lemaire, and C. A. J. Jamar, �??Large-scale DCG transmission holographic gratings for astronomy,�?? in Specialized Optical Developments in Astronomy, E. Atad-Ettedgui and S. D�??Odorico, eds., Proc. SPIE 4842, 31�??38, (2003).
  4. M. Kimura, T. Maihara, K. Ohta, F. Iwamuro, S. Eto, M. Iino, D. Mochida, T. Shima, H. Karoji, J. Noumaru, M. Akiyama, J. Brzeski, P. R. Gillingham, A. M. Moore, G. Smith, G. B. Dalton, I. A. J. Tosh, G. J. Murray, D. J. Robertson, and N. Tamura, �??Fibre-Multi-Object Spectrograph (FMOS) for Subaru Telescope,�?? in Instrument Design and Performance for Optical/Infrared Ground-based Telescopes, M. Iye, and A. F. Moorwood, eds., Proc. SPIE 4841, 974�??984, (2003).
  5. H. Kogelnik, �??Coupled-wave theory for thick hologram gratings,�?? Bell System Tech. J. 48, 2909�??2947, (1969).
  6. R. D. Rallison, R. W. Rallison, and L. D. Dickson, �??Fabrication and testing of large area VPH gratings,�?? in Specialized Optical Developments in Astronomy, E. Atad-Ettedgui and S. D�??Odorico, eds., Proc. SPIE 4842, 10�??21, (2003).
  7. G. A. Smith, W. Saunders, T. Bridges, V. Churilov, A. Lankshear, J. Dawson, D. Correll, L. Waller, R. Haynes, and G. Frost, �??AAOmega: a multipurpose fiber-fed spectrograph for the AAT,�?? in Ground-based Instrumentation for Astronomy, A. F. Moorwood, and M. Iye, eds., Proc. SPIE 5492, 410�??420, (2004).
  8. N. Tamura, G. J. Murray, P. Luke, C. Blackburn, D. J. Robertson, N. A. Dipper, R. M. Sharples, and J. R. Allington-Smith, �??Cryogenic Tests of Volume-Phase Holographic Gratings I. Results at 200 K,�?? Experimental Astronomy, 15, 1�??12, (2003).
    [CrossRef]

Bell System Tech. J. (1)

H. Kogelnik, �??Coupled-wave theory for thick hologram gratings,�?? Bell System Tech. J. 48, 2909�??2947, (1969).

Experimental Astronomy (1)

N. Tamura, G. J. Murray, P. Luke, C. Blackburn, D. J. Robertson, N. A. Dipper, R. M. Sharples, and J. R. Allington-Smith, �??Cryogenic Tests of Volume-Phase Holographic Gratings I. Results at 200 K,�?? Experimental Astronomy, 15, 1�??12, (2003).
[CrossRef]

Proc. SPIE (5)

R. D. Rallison, R. W. Rallison, and L. D. Dickson, �??Fabrication and testing of large area VPH gratings,�?? in Specialized Optical Developments in Astronomy, E. Atad-Ettedgui and S. D�??Odorico, eds., Proc. SPIE 4842, 10�??21, (2003).

G. A. Smith, W. Saunders, T. Bridges, V. Churilov, A. Lankshear, J. Dawson, D. Correll, L. Waller, R. Haynes, and G. Frost, �??AAOmega: a multipurpose fiber-fed spectrograph for the AAT,�?? in Ground-based Instrumentation for Astronomy, A. F. Moorwood, and M. Iye, eds., Proc. SPIE 5492, 410�??420, (2004).

S. C. Barden, J. A. Arns, and W. S. Colburn, �??Volume-phase holographic gratings and their potential for astronomical applications,�?? in Optical Astronomical Instrumentation, S. D�??Odorico, ed., Proc. SPIE 3355, 866�??876 (1998).

P. -A. Blanche, S. L. Habraken, P. C. Lemaire, and C. A. J. Jamar, �??Large-scale DCG transmission holographic gratings for astronomy,�?? in Specialized Optical Developments in Astronomy, E. Atad-Ettedgui and S. D�??Odorico, eds., Proc. SPIE 4842, 31�??38, (2003).

M. Kimura, T. Maihara, K. Ohta, F. Iwamuro, S. Eto, M. Iino, D. Mochida, T. Shima, H. Karoji, J. Noumaru, M. Akiyama, J. Brzeski, P. R. Gillingham, A. M. Moore, G. Smith, G. B. Dalton, I. A. J. Tosh, G. J. Murray, D. J. Robertson, and N. Tamura, �??Fibre-Multi-Object Spectrograph (FMOS) for Subaru Telescope,�?? in Instrument Design and Performance for Optical/Infrared Ground-based Telescopes, M. Iye, and A. F. Moorwood, eds., Proc. SPIE 4841, 974�??984, (2003).

Pub. of Astro. Soc. of Pac. (1)

S. C. Barden, J. A. Arns, W. S. Colburn, and J. B. Williams, �??Volume-Phase Holographic Gratings and the Efficiency of Three Simple Volume-Phase Holographic Gratings,�?? Publication of Astronomical Society of Pacific 112, 809�??820 (2000).
[CrossRef]

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Figures (10)

Fig. 1.
Fig. 1.

A picture of the sample VPH grating. The grating has a diameter of 250 mm with a line density of 385 lines/mm.

Fig. 2.
Fig. 2.

Schematic view of the test optics configuration.

Fig. 3.
Fig. 3.

Schematic view of the sampled positions on the VPH grating (referred to as “L”, “C”, and “R”). The region near the edge indicated in grey is occupied by the support structure of the grating mount and is not optically accessible.

Fig. 4.
Fig. 4.

Diffraction efficiency measured for an incident angle of 12.5°. Throughputs measured at the centre are shown by solid circles (and solid line), and those at the other two positions are indicated by open triangle (and dashed line) and open square (and dotted line). The upper three lines are for the m=+1 order diffracted light and the lower ones are for the 0th order light.

Fig. 5.
Fig. 5.

Same for Fig. 4, but for an incident angle of 15°.

Fig. 6.
Fig. 6.

Same for Fig. 4, but for an incident angle of 17.5°.

Fig. 7.
Fig. 7.

Relationship between diffraction angle and wavelength. Difference of diffraction angle from that predicted for a line density of 385 lines/mm (solid line; this is the specification of the VPH grating) and an incident angle of 40° are plotted against wavelength. The symbols have the same meanings as in the previous figures. Dot-dashed, dashed, and dotted line shows the relationship expected for 375, 380, and 390 lines/mm, respectively.

Fig. 8.
Fig. 8.

The throughput curves measured at the positions “C” and “L” for an incident angle of 12.5° are plotted; these are the same as shown in Fig. 4. They are compared with predictions from coupled-wave analysis, which are indicated by grey smooth (solid and dashed) curves. Grey solid lines indicate the predictions for line densities of 375 and 385 lines/mm. In these calculations, a refractive index modulation amplitude of 0.05 and a dichromated gelatin depth of 12 µm are assumed. 15% energy loss is also considered (this is expected to be explained by a combination of internal absorption and surface reflection). The grey dashed line shows the model prediction where a dichromated gelatin depth of 11 µm is assumed instead of 12 µm. 3 % additional energy loss (i.e., 18 % in total) presumably caused by more internal absorption is also inferred. The same refractive index modulation amplitude is adopted (0.05) and the line density is 385 lines/mm. It should be mentioned that a nearly identical curve to the grey line can be obtained with coupled wave analysis by adopting a refractive index modulation amplitude of 0.045 instead of changing the gelatin thickness.

Fig. 9.
Fig. 9.

Same as Fig. 8, but for an incident angle of 15.0°.

Fig. 10.
Fig. 10.

Same as Fig. 8, but for the incident angle of 17.5°.

Tables (1)

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Table 1. The main components used for the measurements.

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