3.13.2 Experimental instruments
Spectrometer(JJY-type),mercury lamp,Grating,prism,plane mirror.
The JJY-type spectrometer is the optical apparatus for disintegrating light and measuring angles.It is used to determine the physical parameters i.e.prism’s angle,index of refraction,grating constant,wavelength,spectrum and so on by measuring the angles in some optical experiments which are reflection,refraction,interference,diffraction and polarization of light.It is the basic component for many optical instruments,such as the spectrometer,spectrophotometer and monochromator,etc.Therefore,the spectrometer is one of the basic instruments in optical experiments.
The spectrometer is mainly composed of base,telescope,collimator,stage and dial,as shown in Figure 3.13.1.
(1)A cylindrical central vertical axis is fixed in the center of the base,which is called the main axis,around which the telescope and dial can rotate.
(2)The collimator is used to generate parallel beams,and it is composed of an achromatic objective lens,lens barrel and adjustable slit.The slit can be adjusted to range from 0 mm to 2 mm,and it can expand and rotate along the lens tube.The collimator is installed on the fixed column of the base,and the horizontal and high-low position of the collimator can be finely tuned by the bolt on the column,as shown in Figure 3.13.2.
(3)Abbe type autocollimator telescope is composed of Abbe type autocollimator eyepiece,achromatic objective lens and lens barrel,which is used to observe images and determine light direction,as shown in Figure 3.13.3.The telescope is installed on the rotating arm and can rotate around the main shaft.The height and horizontal position of the optical axis of the telescope can be adjusted finely by the screws on the arm.
Figure 3.13.1 The configuration of the spectrometer
1—Collimator’s slit equipment;2—Slit locking bolt;3—Collimator’s tube;4—Vernier disc brake bracket;
5—Stage;6—Stage adjustment bolt;7—Stage locking bolt;8—Telescope;9—Eyepiece tube’s locking bolt;
10—Abbe autocollimator eyepiece;11—Eyepiece visibility adjusting hand wheel;
12—Telescope’s angle adjustment bolt;13—Horizontal adjustment bolt of telescope optical axis;
14—Support arm;15—Telescope’Azimuth trimming screw;16—Telescope locking bolt;
17—Telescope’s rotating base and dial locking bolt;18—Telescope’s brake bracket;19—Base;
20—Telescope’s rotating base;21—Master dial;22—Vernier’s inner disk;23—Column;
24—Vernier disk’s fine-tuning bolt;25—Vernier disk’s locking bolt;26—Collimator’s horizontal adjustment bolt;
27—Collimator’s angle adjustment bolt;28—Slit’s width adjustment hand wheel(https://www.daowen.com)
Figure 3.13.2 Schematic diagram of collimator
Figure 3.13.3 Schematic diagram of autocollimating telescope
The focal length of the eyepiece can be adjusted through making the Abbe eyepiece move and rotate along the sleeve of the eyepiece.Similarly,the focal length of the objective lens can be adjusted through making the sleeve move or rotate along the lens barrel.There is a small hole with a small bulb beside it on the side of the eyepiece sleeve.The light emitted by the small bulb will illuminate the small green cross window on the reticent plate inside the eyepiece sleeve after a total reflection by a 45° prism,and spread outward along the telescope barrel.
(4)The stage is used to the place lens and other optical devices.It can rotate around the main shaft,and can also be raised or lowered.There are three leveling screws in the stage to make it perpendicular to the main shaft.
(5)The dial and the inner dial of the vernier can rotate around the main shaft,and each grid value is 0.5 degrees(30 minutes).Two angular vernier reading devices are symmetrically arranged in the direction of the dial diameter.During measuring,two reading values are read out through the magnifying glass,and then the average value is taken.In this way,the reading difference caused by the eccentricity between the dial and the main shaft can be eliminated.
The relative orientation of the telescope and the platform can be determined by the reading on the dial.There is a circle scale of 0°～360° on the main dial,which has the index value of 30′.In order to improve the precision of angle measurement,two verniers are set on the inner dial with a 180° interval.There are 30 divisions on the verniers,which are equivalent to 29 divisions on the main dial,and thus the division value is 1′.The reading method is the same as the principle of vernier caliper(called angle vernier here).When recording the measurement data,the readings of two verniers must be read simultaneously to eliminate the eccentricity between the scale center of the dial and the rotation axis of the instrument.There are specific aspects which should be considered to place the position of the vernier,i.e.the convenience of reading,the 0° line of the dial does not pass through the vernier reading during measuring,and its reading method is similar to that of the vernier caliper.The reading method is as follows:Taking the zero line of the angle vernier as the standard the degree value on the dial should be read,and the score value should be obtained from the line that just coincides with the scale on the vernier.If the zero line of the vernier is outside the half degree line,the reading value should be increased by 30′.
