We report on a novel type of laser in which a semiconductor optical amplifier (SOA) receives frequency-selective feedback from a glass-waveguide circuit. The laser we present here is based on InP for operation in the 1.55 μm wavelength range. The Si3N4/SiO2 glass waveguide circuit comprises two sequential high-Q ring resonators. Adiabatic tapering is used for maximizing the feedback. The laser shows single-frequency oscillation with a record-narrow spectral linewidth of 24 kHz at an output power of 5.7 mW. The hybrid laser can be tuned over a broad range of 46.8 nm (1531 nm to 1577.8 nm). Such InP-glass hybrid lasers can be of great interest in dense wavelength division multiplexing (DWDM) and as phase reference in optical beam-forming networks (OBFN). The type of laser demonstrated here is also of general importance because it may be applied over a huge wavelength range including the visible, limited only by the transparency of glass (400 nm to 2.35 μm).
Juequan Chen, Eric Louis, Fred Bijkerk, Chris Lee, Herbert Wormeester, Reinhard Kunze, Hagen Schmidt, Dieter Schneider, Roel Moors, Willem van Schaik, Monika Lubomska
Carbon contamination layers, deposited on extreme ultraviolet (EUV) multilayer mirrors during illumination were
characterized ex situ using spectroscopic ellipsometry (SE), laser generated surface acoustic waves (LG-SAW), and by
their EUV reflectance loss. We show SE is more sensitive to the deposition of carbon layers than the EUV reflectance
loss, even in the presence of the highly heterogeneous structure of the multilayer. SE has better overall sensitivity, with a
detection limit of 0.2 nm, while LG-SAW has an approximate detection limit < 5 nm.
We report a singly resonant optical parametric oscillator (SRO) based on a ZnGeP2 crystal directly-pumped by
a lamp-pumped Q-switched CrTmHo:YAG laser. The IR wavelength was tuneable from 4.7 μm to 7.8 μm via
crystal angle tuning. A maximum optical to optical efficiency of 56% was obtained from pump (2.09 μm) to
total IR at a pump energy of 6.5 mJ. The corresponding idler energy was 1.45 mJ. The SRO was measured to
have a slope efficiency of 64% and a threshold of 1 mJ. The spatial beam quality of the idler, characterized by
the M2 parameter, was 1.38 when the SRO was pumped at 2.5 times threshold. These results show that ZnGeP2
OPOs directly pumped by a CrTmHo:YAG laser can be operated efficiently, while maintaining good IR beam
quality. The wide tuning range and a high pulse energy makes this SRO particularly suitable for spectroscopic
applications, and, tests in the field medical application, e.g., for cutting of soft tissue during surgery or corneal
corrections.
We generate mid-infrared pulsed light tunable between 5.6 &mgr;m and 6.6 &mgr;m using an optical parametric oscillator
(OPO) directly pumped by a Cr,Tm,Ho:YAG, Q-switched laser operating at 2.1 &mgr;m. The Holmium laser uses a
RTP Q-switch to produce pulses shorter than 100 ns and energies of up to 42 mJ in a single spatial transverse
mode at a repetition rate of 5 Hz. To our knowledge this is the first report on a lamp pumped Cr,Tm,Ho:YAG
laser using a RTP crystal as an electro-optical Q-switch.
The OPO is based on a ZnGeP2 (ZGP) crystal cut for type I phase matching. The singly resonant OPO
(SRO) uses a linear cavity consisting of two plane mirrors to minimize the required pump flux to reach threshold.
The SRO has a threshold of 2.4 mJ, a maximum idler pulse energy of 3.1 mJ, and is tunable from 5.6 to
6.6 &mgr;m. Operation in this wavelength range, combined with wide tuning and a high pulse energy makes this
SRO particularly suitable for tests in the field medical application, e.g., for cutting of soft tissue during surgery
or corneal corrections.
Frequency modulation (FM) techniques are well known methods for improving signal-to-noise ratios in laser
spectroscopy. Such techniques have proven particularly effective with diode lasers due to the ease with which they can
be frequency modulated via their injection current. Although singly-resonant optical parametric oscillators (OPOs) are
flexible, powerful and widely-tunable sources for mid-infrared laser spectroscopy, the utilization of FM techniques with
OPOs suffers from the inconvenience of requiring an external mid-IR modulator. As a consequence, FM techniques have
not been implemented with such devices. In this paper we describe the implementation of wavelength-modulation
spectroscopy (WMS) and frequency-modulation spectroscopy (FMS) using a singly-resonant OPO pumped by a fiber-amplified
diode laser. The OPO was capable of producing output powers of up to 1W in the 3.15-3.8 &mgr;m range with
continuous tuning over >100GHz on millisecond timescales. Frequency modulation, via injection current, of the diode
laser transferred directly to the OPO's idler output, allowing mid-IR FM to be achieved without external modulation
devices. WMS and FMS spectra of methane were then recorded, clearly demonstrating that this approach provides a
means of implementing these important techniques with powerful, widely tunable, mid-IR sources while retaining the
simple, flexible modulation properties of diode lasers.
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