Real-time gas sensing based on optical feedback in a terahertz quantum-cascade laser

We report on real-time gas sensing with a terahertz quantum-cascade laser (QCL). The method is solely based on the modulation of the external cavity length, exploiting the intermediate optical feedback regime. While the QCL is operated in continuous-wave mode, optical feedback results in a change of the QCL frequency as well as its terminal voltage. The first effect is exploited to tune the lasing frequency across a molecular absorption line. The second effect is used for the detection of the self-mixing signal. This allows for fast measurement times on the order of 10 ms per spectrum and for real-time measurements of gas concentrations with a rate of 100 Hz. This technique is demonstrated with a mixture of D2O and CH3OD in an absorption cell

Aphallia - report of two cases

Aphallia is an extremely rare congenital malformation of unknown cause. The incidence is reported in the literature to be 1 in 10-30 million live births. Almost 100 cases have been described to date. Aphallia is associated with other congenital malformations (in particular urogenital and gastrointestinal anomalies) in >50% of cases. The diagnosis is made clinically and shows the complete absence of the corpora cavernosa and the corpus spongiosum with a urethral opening along the perineal midline (most frequently ventral to the anus and in the ventral rectal wall). Two case reports from the authors' department: The first child was a male newborn (46,XY) with penis agenesis and additional bilateral intraabdominal testis, an anorectal malformation (ARM) with a rectovesical fistula, as well as left renal duplication and grade III vesico-ureteral reflux on the right side. The second child was a male newborn (46,XY) with aphallia without further urological or anorectal malformation. Only right inguinal hernia was present. In the first patient, several corrective surgeries were performed in the further course in view of the additional malformations. With regard to the aphallia, the various temporary treatment options (scrotal or parascrotal phalloplasty or penis prosthesis) were discussed with the parents. Masculinizing surgery by means of definitive phalloplasty was planned once the patient has reached puberty. Due to the technical demands of phallus reconstruction, feminization is still favored in some countries in the literature, which nowadays, however, cannot be justified medically or legally

Fast Spectral Terahertz Imaging through Frequency Tuning in a Quantum-Cascade Laser

Due to a variety of molecular rotational lines, spectroscopy in the terahertz (THz) spectral region is a powerful tool. It can be applied to detect and identify numerous chemical compounds in particular gases. Thus, it holds a large potential for a broad range of applications e.g. in astrophysics, medicine, and security. At present, THz imaging is realized with a variety of different techniques. However, relatively little work has been done regarding the combination of THz spectroscopy and imaging. In this contribution, we will present a QCL-based spectrometer that is capable of fast spectral imaging with a resolving power in the order of 10^6 and with high spatial resolution. The spectral information is obtained by tuning the frequency of the QCL. Frame rates of up to 3 Hz are realized by the combination of a fast scanning mirror (FSM) and a sensitive single-pixel Ge:Ga detector with a short response time

Real-time gas sensing based on optical feedback in a terahertz quantum-cascade laser

We report on real-time gas sensing with a terahertz quantum-cascade laser (QCL). The method is solely based on the modulation of the external cavity length, exploiting the intermediate optical feedback regime. While the QCL is operated in continuous-wave mode, optical feedback results in a change of the QCL frequency as well as its terminal voltage. The first effect is exploited to tune the lasing frequency across a molecular absorption line. The second effect is used for the detection of the self-mixing signal. This allows for fast measurement times on the order of 10 ms per spectrum and for real-time measurements of gas concentrations with a rate of 100 Hz. This technique is demonstrated with a mixture of D2O and CH3OD in an absorption cell

Spectral terahertz imaging based on a quantum-cascade laser and a fast scanning mirror

We demonstrate a transmission setup for fast THz spectral imaging based on a 3.4 THz continuous-wave multimode QCL, a fast scanning mirror (FSM), a gas cell, and a single pixel Ge:Ga detector. The THz radiation emitted by the QCL is focused on a THz transparent poly-4-fluorethylen (PTFE) tube located inside a gas cell that contains gaseous methanol. By rapid movement of the FSM, the beam is spirally scanned across the gas cell. The transmitted radiation is detected by the photoconductive Ge:Ga detector. At the same time, the QCL frequency is rapidly modulated by sweeping its current. The resulting field of view covers an elliptical area of 18.2x17.8 mm² dimension and is acquired within 1.5 s, including at least four spectra per pixel. Thus, we obtain information about the peak absorption and the line width. In addition to an imaging-only system which allows for fast screening of hidden objects, the present approach reveals the participating gases by spectral analysis. Furthermore, variations in the gas concentration can be recorded with a frame rate of up to 3 Hz since the measurement time can be further reduced by adjusting the field of view and the spectral range to the point of interest. This is demonstrated by using a tube with a hole of 0.2 mm diameter. During methanol injection, the inflowing gas is continuously imaged, and the leakage from the PTFE tube into the evacuated gas cell is observed. In addition to the relative absorption, the local pressure is mapped by exploiting the effect of pressure broadening. Both representations offer the unambiguous localization of the exiting gas. In summary, this system is a very promising approach for leakage detection and sensitive identification of hazardous substances