Low background applications place the most stringent requirements on detector material, requiring the lowest possible dark currents, highest quantum efficiencies, negligible image persistence (image latency or “ghosts”), high operability, and good uniformity. Rockwell Scientific’s MWIR (λco=5μm) MBE HgCdTe/CdZnTe consistently meets these stringent requirements due to a number of growth techniques unavailable to other MWIR materials. The first part of this paper focuses on the advantages offered by MBE HgCdTe on CdZnTe detectors. The second part focuses on the functional capabilities of our most recent multiplexers, the HAWAII-1RG and HAWAII-2RG. Finally, the paper briefly concludes with a look at the future of SCA control with Rockwell Scientific’s new NGST ASIC for control and digitization of the HAWAII-RG series multiplexers.

The HAWAII-2 is an IR 20482 focal plane array (FPA) that is being developed for next-generation IR astronomy. It will supplant our HAWAII 10242 as the largest high- performance imaging array available for IR astronomy. As with our prior IR sensor, the flip-chip hybrid will consist of a low-capacitance HgCdTe detector array mated to a low- noise CMOS silicon multiplexer via indium interconnects. In order to accommodate reasonable telescope optics and fabrication of the large sophisticated readout using world- class submicron CMOS, the FPA has 18 micrometers pixel pitch. We anticipate > 5 percent yield of defect-free multiplexers using 0.8 micrometers CMOS. The HgCdTe detector arrays will be fabricated on large wafers including sapphire and silicon. Though the first FPAs will have 2.5 micrometers cut-off, the readout will be able to support longer wavelengths. Also reported are the latest 1024 X 1024 FPA results with 2.5 micrometers HgCdTe detectors.

We describe stimulus-response measurement techniques based on the photoconductive generation and sampling of picosecond electrical pulses for measuring the high frequency scattering parameters of high speed microwave devices. We compare these techniques with more conventional microwave diagnostic techniques.

Picosecond optoelectronics provides the capability to measure the frequency response of solidstate devices with much greater bandwidth than conventional techniques.1 Short electrical pulses are fed into device terminals, and the output is optoelectronically sampled to measure the device impulse response function. The Fourier transform of this data yields the frequency response curve. All elements of the scattering matrix (S matrix) can be obtained through the use of various combinations of device terminals as input and output ports. Thus all information obtained from conventional CW network analyzer techniques is available from the time-domain picosecond optoelectronic data, with excellent bandwidth capability and electronic simplicity. Here we present impulse response measurements of a submicron field effect transistor.

The optical excitation of FETs gives insight into the dynamical processes ocurring within the device and is also of interest for evaluating the FET as a high-speed optical detector. Excitation by ultrafast optical pulses yields information on the transport and trapping of carriers on a picosecond time scale, and offers an alternative to pulsing the device in the conventional electronic manner. Use of the FET as an optical detector is potentially interesting because, in contrast to the PIN diode, gain can be obtained, without the extra noise associated with avalanche devices.1 In addition, the output of a FET in an integrated circuit can be optically modulated, and in conjunction with electro-optic sampling this can be used for non-invasive diagnostics of fast GaAs ICs.2 We have studied the electrical response of a submicron-gate GaAs FET to optical excitation by picosecond laser pulses.

A new method of high-resolution multiphoton spectroscopy based on competition between ionization and stimulated-emission channels is described. It combines features of multiphoton photoionization with those of optical-optical double resonance. Results obtained for ${\mathrm{I}}_{2}$ demonstrate the method and identify intermediate states involved in multiphoton photoionization. The method offers the potential for extremely sensitive sub-Doppler spectroscopy of complex molecules.