{'fraction_non_alphanumeric': 0.036308623298033284, 'fraction_numerical': 0.029500756429652043, 'mean_word_length': 5.240566037735849, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Passively mode-locked semiconductor laser for coherent population trapping in 87Rb

Recent growing interest in miniature atomic frequency references and precision magnetometers has motivated investigations of coherent population trapping (CPT) and its use in such applications [1]. System designs based on picosecond mode-locked lasers have been previously reported for generating the CPT effect, using Ti:Sapphire lasers passively mode-locked at a submultiple of the hyperfine splitting 87Rb levels [2], or laser diodes modulated electrically [3] or with an external electro-optic modulator [4] at the 87Rb splitting frequency. In this work we investigate a novel approach for achieving CPT in 87Rb vapour cells. We use a 795nm semiconductor laser passively mode-locked [5] at the 87Rb standard frequency (∼6.834GHz). This approach eliminates the need for any RF driving circuit, allowing a more compact, integrable and easy to drive implementation of CPT in 87Rb. For this purpose we have fabricated 5.678mm long lasers with 3µm wide and 1.2µm deep ridge waveguides, with a 150µm long saturable absorber (SA) at one facet. The laser material used is a 793nm GaAs/AlxGa1−xAs single quantum well (QW) graded-index separate confinement heterostructure (GRINSCH), with an epitaxial design similar to the one reported in [6].