A Novel Approach of Sensitive Infrared Signal Detection for Space Applications

Develop an innovative frequency up-conversion device that will efficiently convert the infrared signals into visible/near-infrared signals to enable detection of infrared signals with high sensitivity, high dynamic range, fast response, and low noise background.

We propose an innovative approach to overcome the infrared signal detection difficulties.  In this investigation, a Periodical Poled MgO Lithium Niobate (PPMgOLN) based frequency up-conversion devices will be developed to efficiently convert the infrared signals into visible/near-infrared signals which can be sensitively detected by well-developed superior silicon avalanche photodiodes (Si-APD). This innovative device will allow detect infrared signals with high sensitivity, high dynamic range, fast response, and low noise background.
        The principle of up-conversion device is based on non-linear interaction btween two optical beams.  When a strong pump beam  and a weak probe beam interact in a suitable nonlinear crystal, a signal at third frequency is generated under the condition of energy and momentum conservation. For example, interaction between a pump beam at 1.06µm and weak infrared 2.05µm beam in the PPMgOLN crystal can generate photons at 0.7µm wavelength. The number of probe photons is much smaller than that pump photons because the probe beam is usually very weak. Only a small portion of pump photons have the chance to mix with probe photons to generate photons at sum frequency of the pump and probe beam. Therefore, the circulating power in the crystal is constant because of the negligible pump depletion. In theory, every infrared probe photons can be converted into visible/near infrared photons
   An intra-cavity pumped up-conversion device is designed to demonstrate the frequency up conversion capbility. One periodically poled PPMgOLN is used in this study.  A CW 808 nm diode laser is used to pump a Nd:YAG rod inside the cavity to generate the 1064 nm pump beam. The leakage of 1064 nm light is used to monitor the circulating intra-cavity pump power. A two-micron DFB laser was also aligned through the PPMgOLN to simulate the weak probe beam.  CaF2 dispersion prisms and laser line filters were used to separate the generated 700 nm photons from the photons at other wavelengths for accurate visible signal measurement.
    The up-converted photons can be measured with Silicon Single Photon Avalanche Photodiode detector to take advantages of its high quantum efficiency and low dark current. Thus, extremely weak infrared signal can be measured with unprecedented sensitivity and accuracy.